EPA-660/3-75-004
 FEBRUARY 1975
                                  Ecological Research Series
Phytoplankton  Composition and
Abundance in  Lake Ontario During  IFYGL
                                  National Environmental Research Center
                                    Office of Research and Development
                                   U.S. Environmental Protection Agency
                                          Corvallis, Oregon 97330

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                      RESEARCH REPORTING SERIES


Research reports of the Office of Research and Development,
U.S. Environmental Protection Agency, have been grouped into
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          1.   Environmental Health Effects Research
          2.   Environmental Protection Technology
          3.   Ecological Research
          4.   Environmental Monitoring
          5.   Socioeconomic Environmental Studies

This report has been assigned to the ECOLOGICAL RESEARCH STUDIES
series.  This series describes research on the effects of pollution
on humans, plant and animal species, and materials.  Problems
are assessed for their long- and short-term influences.  Investigations
include formation, transport, and pathway studies to determine
the fate of pollutants and their effects.  This work provides
the technical basis for setting standards to minimize undesirable
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                                         EPA-660/3-75-004
                                         FEBRUARY  1975
        PHYTOPLANKTON COMPOSITION AND
   ABUNDANCE IN LAKE ONTARIO DURING IFYGL
                     By

E. F. Stoermer, M. M. Bowman, J.  C.  Kingston
             and A. L. Schaedel
        Great Lakes Research Division
         The University of Michigan
          Ann Arbor, Michigan 48105
             Grant No.  R-800605
         Program Element No.  1 BA026
           ROAP/Task No. 21AKP/007
               Project Officer

              Nelson A. Thomas
    National Environmental Research Center
            Grosse lie Laboratory
         Grosse lie,  Michigan 48138
    NATIONAL ENVIRONMENTAL RESEARCH CENTER
     OFFICE OF RESEARCH AND DEVELOPMENT
    U.S. ENVIRONMENTAL PROTECTION AGENCY
           CORVALLIS, OREGON 97330

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                               ABSTRACT
Based on samples collected during the International Field Year for the
Great Lakes, the phytoplankton assemblage of Lake Ontario is dominated
by taxa indicative of degraded water quality, including many potentially
nuisance producing species.  Many taxa characteristic of the offshore
waters of the upper Great Lakes are either absent from the flora or very
rare.  Compared to the upper lakes, the flora of Lake Ontario undergoes
extreme seasonal succession, with diatoms predominating during the winter
and early spring,  green algae becoming abundant during the summer, and
blue-green algae showing a distinct fall peak.  Various species of micro-
flagellates are a relatively important element of the flora during all
seasons.  Succession during the spring bloom appears to be controlled
by the thermal bar, and our data suggest control by depletion of essen-
tial nutrients following stratification.  Striking differences were
apparent in samples collected on comparable dates in the spring of two
successive years.   These differences apparently result from exceptional
weather conditions which prevailed during the first sampling period.
The distribution of species particularly tolerant of disturbance appear-
ed to be controlled by both proximity to major population centers and
lake morphometry.   The abundance of halophilic species in most pro-
ductive areas suggests effects of conservative ion contamination as well
as nutrient enrichment.

This report was submitted in fulfillment of Grant No.  R802780 by  the
Great Lakes Research Division,  The University of Michigan,  under  the
primary sponsorship of the Environmental Protection Agency.   Work was
completed as of November 30,  1974.
                                 11

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                            CONTENTS


CONCLUSIONS AND RECOMMENDATIONS 	   1

INTRODUCTION 	   3

MATERIALS AND METHODS	9
   Particle Count Samples 	   9
   Phytoplankton Population Analysis 	   9
   Archival Plankton Collections 	  10
   Reference Chlorophyll Samples 	  10

RESULTS	13
   Chlorophyll Values at Master Stations 	  13
   Particle Count Data	17
      Areal distribution by size class	19
      Vertical distribution by size class 	  66
   Phytoplankton Data	114
      Areal distribution of total phytoplankton
        in near-surface waters 	   114
      Areal distribution of major groups in near-surface
        waters	120
      Diversity trends in near-surface waters 	  128
      Areal distribution of selected species 	 134
          Bacillariophyta 	 134
          Chlorophyta	236
          Cyanophyta	278
          Cryptophyta	317
          Pyrrophyta	317
          Microflagellates  	 328
      Vertical distribution of phytoplankton
        at master stations	339

 DISCUSSION  	   	363

REFERENCES	369
                               111

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                                   FIGURES
  1.   Primary  station  locations  	
  2.   Vertical distribution  of Chlorophyll a  at  master stations  .  .  .
  3.   Areal  distribution  of   5-10   urn particles	21
  4.   Areal  distribution  of  10-20   ym particles  	   30
  5.   Areal  distribution  of  20-40   ym particles  	   40
  6.   Areal  distribution  of  40-80   ym particles	49
  7.   Areal  distribution  of  80-150  ym particles  	   58
  8,   Vertical distribution  of   5-10  ym particles	67
  9.   Vertical distribution  of 10-20  ym and 20-40  ym particles   ...   83
 10.   Vertical distribution  of 40-80  ym and 80-150 ym  particles  ...   99
 11.   Areal  distribution  of  total cell counts	115
 12.   Seasonal average abundance of major phy topi ank. ton group
          cell counts	121
 13.   Areal  distribution  of  major phytoplankton  group  cell counts  .  .  122
 14.   Assemblage diversity (Shannon-Weaver index)   	  129
 15.   Distribution of  Asterionella  formosa 	  135
 16.   Distribution of  Cosoinodiscus subsalsa   	
 17.   Distribution of  Diatoma tenue var. elongation	
 18.   Distribution of  Fragilaria capucina	152
 19.   Distribution of  Fragilaria cipotonensis	158
 20.   Distribution of  Melosira islandica	
 21.   Distribution of  Nitzschia  bacata	
 22.   Distribution of  Nitzsahia  dissipata 	  175
 23.   Distribution of  Nitzschia  sp. (#2)	181
 24.   Distribution of  Stephanodiscus  alpinus	186
 25.   Distribution of  Stephccnodiscus  binderanus	192
 26.   Distribution of  Stephanodiscus  hantzschii	198
 27.   Distribution of  Stephanodiscus  minutus	203
 28.   Distribution of  Stephanodiscus  subtilis	209
 29.   Distribution of  Stephanodiscus  tennis	214
 30.   Distribution of  Suvirella  angusta 	  220
 31.   Distribution of  Synedra ostenfeldii	226
 32.   Distribution of  Tabellaria fenestrata	231
 33.   Distribution of  Arikistvodesmus  falcatus	237
 34.   Distribution of  Botvyococaus  bvaimii	243
 35.   Distribution of  Coelastrum mi-croporum	244
 36.   Distribution of  Gloeoystis planatoniea   	  249
 37.   Distribution of  Oocystis spp.	254
 38.   Distribution of  Pediastrum glanduiifevwn	259
 39.   Distribution of  Phacotus lenticulavis	261
 40.   Distribution of  Soenedesrms bicellularis	265
 41.   Distribution of Seenedesmus quadrieauda var.   longispina ....  271
 42.  Distribution of Saenedesmus quadricauda var.  quadrispina  •  • •  276
 43.   Distribution of Ulothrix spp.	279
 44.   Distribution of Anabaena flos-aquae 	  284
45.  Distribution of Anabaena variabilis 	  287
46.  Distribution of Anacystis cyanea  	  290
                                    iv

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47.  Distribution of Anaeystis •inoer'ta	296
48.  Distribution of Aphan-izomenon flos-aquae	301
49.  Distribution of Gomphosphaeria aponina  	 304
50.  Distribution of Gomphosphaeria lacustvis  	 305
51.  Distribution of Gomphosphaeria wiehurae 	 307
52.  Distribution of OsG-filatovLa Ivmnet'ioa	312
53.  Distribution of Cryptomonas erosa 	 318
54.  Distribution of Glenod-ini-um and Gymnodiniwn	323
55.  Distribution of Peridinium spp	329
56.  Distribution of microflagellates  	 334
57.  Vertical distribution of total phytoplankton cell
          counts at master stations  	 344
58.  Vertical distribution of diatoms at master stations 	 348
59.  Vertical distribution of green algae at master stations .... 352
60.  Vertical distribution of blue-green algae at master
          stations	356
61.  Vertical distribution of microflagellates at master
          stations	359
                                  v

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                           TABLES
1.   "Format for phytoplankton species
    Information	      _      7

2.   Format for particle count
    information	   g

3.  Example of label for archival samples 	 .....   8

4.  Correlations between fluorometrically determined
    chlorophyll a values and particle counts for all
    depths at master stations	18

 5.  Correlation coefficients for EPA spectrometrically
    determined chlorophyll  a values and:  (1)  fluoro-
    metrically determined  chlorophyll a values  (master
    stations only),  (2)  10-20  ym particle counts,  (3)
     20-40 ym particle  counts,  (4)  total cell counts	20

 6.   Correlation  between fluorometrically determined
     chlorophyll  a values and cell  counts  in total
     and by category at master stations	341

 7,   Correlation of particle counts in channels
     measured with cell counts as determined by
     visual identification for master stations 	  341
                                  vi

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                     CONCLUSIONS AND RECOMMENDATIONS


 1.  The phytoplankton flora of Lake Ontario is qualitatively and quan-
     titatively dissimilar from all but the most severely impacted re-
     gions of the upper Great Lakes.

          It would appear appropriate to develop separate predictive
          models for the lower (Erie and Ontario) and upper (Huron,
          Michigan and Superior) Great Lakes.
 2.  Our data suggest that there are considerable yearly differences in
     the abundance and composition of the phytoplankton assemblage in
     Lake Ontario, apparently related to weather conditions during the
     spring phytoplankton maximum.

          Data from IFYGL biology and chemistry projects should  be in-
          terpreted with caution,  especially as a basis for projections.
          Any further projects of this type should be designed to  pro-
          vide a multi-year data base.
 3.   Local effects of major population concentrations  are evident  in
     both the composition and abundance of  the  phytoplankton  flora, how-
     ever integrated,  lake-wide  effects appear  to be strongly controlled
     by morphometry.

          Predictive  models should  account  for  morphometric effects.


 4.   Although this project does  not provide direct evidence,  patterns of
     phytoplankton abundance and succession in  Lake Ontario are consis-
     tent with the hypothesis that  phosphorus is the primary  nutrient
     controlling productivity in the system.

          It  appears  that  limitation of  phosphorus loadings is an
          appropriate  first management  strategy.


5.  The  phytoplankton flora  of  most productive regions of Lake Ontario
    is dominated  by halophilic  species.

         Greater  emphasis  should be placed on reduction of conservative
         element  contamination,  as well as nutrient limitation.


6.  Lack of a sufficient historic data base restricts  interpretation  of
    present results in the context of  long-term trends within the  Lake
    Ontario system, except by analogy  to better studied comparable
    systems.

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          Effort should be made to develop such comparative data,  either
          by recovery and analysis of historic samples or by paleolimno-
          logic methods.
7.  The phytoplankton assemblage of Lake Ontario appears to be highly
    unstable, on both a seasonal and yearly basis.

          It is suggested that, due to this unstable food base, fisheries
          management practices successful in the upper Great Lakes may
          prove less productive if adopted in Lake Ontario.
    (Conclusions  regarding  particular  taxa  and  general  conditions  in Lake
    Ontario  are discussed in more  detail  in summary  section beginning on
    p.  363 following.)

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                             INTRODUCTION
This project was initiated as part of an integrated series of  investi-
gations of Lake Ontario under the general aegis of the International
Field Year for the Great Lakes.  The Field Year was conceived  primarily
as an attempt to construct a precise model of the hydrological character-
istics of Lake Ontario.  Since it was early recognized that the unique
bank of physical data generated would have great utility in constructing
a more general process model of the Lake Ontario ecosystem, the original
concept was modified to include biological and chemical measurements
appropriate to the construction of the more general model.  The general
plan has been published (IFYGL 1972) and need not be discussed here.
It is important to keep in mind, however, that the biological  and
chemical sampling effort was carried out largely within the constraints
of the original project concept.  It will be apparent also that the
original plan underwent evolutionary changes during the course of the
project, some of which were imposed by operational constraints in
sampling platform availability and operational capabilities.  Of
perhaps greater importance were modifications of the original  sampling
plan in response to the effects of a major meteorological "accident."
June 1972 was one of the coldest and wettest Junes on record in the
Lake Ontario basin.  Near the end of this extremely atypical month,
significant portions of the region were subjected to the fringe effects
of Tropical Storm Agnes (Atmospheric Environment Service 1972) which
resulted in record rainfalls at many stations within the Lake  Ontario
drainage basin. Since early results of several projects indicated
significant effects of these events, the originally conceived  sampling
plan was considerably extended to provide comparison between the spring
sampling periods in two successive years.

One of the primary objectives of the project was to obtain quasi-synoptic
coverage of the entire lake during successive time intervals represent-
ing periods of characteristic seasonal succession of biological popula-
tions within the lake.  Some emphasis was placed on the early spring
period, which has the highest seasonal standing crop of primary
producer organisms in most temperate lakes.

The 60 primary stations sampled are shown in Figure 1.  During May 1972,
sampling of these stations was only about 50% effective due to weather-
induced operational restrictions on the sampling platform utilized.
Sampling during 1973 was on a somewhat more restricted basis.   Nominally
40 of the 60 original stations were chosen, but operational problems
associated with severe winter weather resulted in the omission of a
limited number of stations on certain cruises.

In all cases arbitrarily specified depths were sampled.  Depths selected
were 1, 5, 10, 15, 20, 25, 30, 40, 50, 100, 150 and 200 m.  In cases
where depth at the station sampled did not permit a full 12-bottle
cast, sampling profile was truncated to the nearest specified depth and
an additional sample was taken about 5 m above bottom.  Depths sampled
are indicated in summary plots of vertical profile information following.

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                 LAKE   ONTARIO
                                                           «79-20m     «9S-18m
                                                                     «94-35m'
                              ©45-183m
                         *4O-175rrV44-174m
                                                                                 ,-444'
                                                                                   43'
FIG. 1.  Primary  station locations; master stations circled.

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Acquisition and interpretation of phytoplankton population information
suitable for use in a project of this size presents certain problems
which have never been completely solved.  Perhaps the most serious
difficulty is that identifications are not possible by other than manual
methods.  This means that analysis of samples, under the best of
conditions, proceeds quite slowly and is subject to human errors which
are difficult to control.  The problem is compounded in the present
instance by the fact that the phytoplankton of the Laurentian Great
Lakes is rather poorly known, and standard references covering the
taxonomic groups of greatest interest are not avialable.  It is thus
necessary, to a substantial degree, to treat with some rather fundamen-
tal taxonomic problems during the course of such an investigation.
Because of the strong seasonal succession of phytoplankton communities,
unique problems arise during each successive sampling during a year's
period.  This entire problem is further compounded by the diversity of
groups present and their basic biochemical differences.  Because of
these differences, no single preservation technique is completely
suitable for all organisms which may be encountered in any sample.  There
are many organisms present in the phytoplankton of Lake Ontario which
can only be identified with any degree of confidence in the living
condition.  When treating with the number of samples generated by the
IFYGL project, it is exceedingly difficult to treat every sample with
all methods necessary to assure the best treatment of every taxonomic
group which could conceivably be present in a given sample.  This is
especially true in the case of organisms which are best identified in
the brief time they remain viable after collection.  As a practical
matter it is usually necessary to make some compromise between the
amount of data coverage, in terms of samples taken, and data quality,
in terms of complete and confident identifications.

In this project we placed primary emphasis on development of information
regarding the abundance and distribution of particular populations.
Because of the necessity to process samples rapidly into a form where
they could be stored for considerable periods of time before final
analysis, we chose to prepare these samples as semi-permanent micro-
scope slides.

In order to extend the sample coverage, we also made a rapid automated
analysis of particles present in the waters sampled according to size
class.  While this measurement does not allow the identification of
particular populations or even, necessarily, the segregation of phyto-
plankton from other classes of particles occurring in the water, we
felt that comparison of trends in such measurements with population
information and gross biomass estimates developed by other projects
might serve to extend the usefulness of both types of observations.

Because of the current unsatisfactory state of taxonomic treatments of
Lake Ontario phytoplankton, we felt it highly desirable that one of the
outputs of IFYGL should be a coherent set of reference samples from the
lake which might serve as the basis for revisionary work on certain
groups by specialists.  Such archival samples are also highly desirable

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as a means  of  checking  results  of  the  project  and  to  provide a means of
extending observations  should this become desirable.   Such reference
samples also,  in a  sense,  serve to provide a standard  against which
future changes in the Lake Ontario ecosystem may be judged.

In this project we  also collected  and  analyzed a limited number of
chlorophyll samples from IFYGL  biology-chemistry master stations.  This
effort was  partially motivated  by  the  desire to be able to compare these
values, which  were  fluorometrically determined, with spectrometrically
determined  values from  these stations  by other projects.  These samples
were also used to inspect  correlations between this measure of standing
crop and the particle count and  population counts generated by this
project in  its initial  phases,  before  the more extensive set of
spectrometrically determined chlorophyll values developed by other
projects was available.

Summarization  of the information developed by this project presents
some problems.  Since the  information  is to be included in further
efforts to  develop a model of the Lake Ontario ecosystem,  it is
necessary to include the original semi-reduced data in an easily
available format.  This material is too extensive to be conveniently
reproduced  in  the standard report format.  In the interests of economy
and to reduce  errors of transcription,  we have submitted the semi-reduced
digital information on magnetic tape to the project officer together with
one complete hard-copy printout.  Printout format for the species count
information is shown in Table 1 and for the particle count information
in Table 2.   A summary listing of labels for archival samples has been
provided to the project officer, and an example of the label informa-
tion is given in Table 3.

Graphic summaries of this  information are presented in the results
section following.   The summaries include representations  of
abundance of particles by  size class for the seasons sampled,  of total
phytoplankton abundance, the abundance of most common major taxonomic
divisions,  and the distribution of some of the more important  or
interesting species  and genera.

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TABLE 1.   Format for  phytoplankton species information.
                  Lake Ontario  (IFYGL), Station 96-All Depths
                   year:   1973
                station:    96
               latitude:    43° 58.
number of cells counted:   1258

              diversity:     2.404
                                                  Julian day:   8D (21 flar)
                                                       depth:   n.1 m
                                                   longitude:   76° 40.H'
                                     volume of water scanned:    3.477 ml

                                                    evenness:    0.688
          division

Cyanophyta (blue-green algae)
Chlorophyta (green algae) . .
Bacillariophyta (diatoms) . .
Chrysophyta (ehrysophytes). .
Cryptophyta (cryptomonads). .
Pyrrophyta (dinof la gel l
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     TABLE 2.   Format for particle count
     information.
            LAKE ONTARIO PARTICLE COUNTS
                (PARTICLES/100 ML I

     CRUISE   7     JUNE 12 - JUNE 16t  1972

     STA DFP    PARTICLE SIZES {IN  MICRONS)
      *  (M)   5-10    10-20  20-40  40-80 80-150






1
2
2
2
3
3
3
3
5
5
5
1
5
10
15
20
25
30
1
5
10
1
5
10
12
1
5
10
97247
104374
95T36
97873
50819
44788
52286
98525
116173
117907
115860
115772
114153
87514
95381
84475
75784
23044
25281
23978
27320
19292
14890
11752
23623
24859
19870
24860
27945
25469
23368
38328
33454
24686
2053
1895
2249
2387
1194
780
530
3593
2646
1655
2122
2718
2431
2229
5031
4846
2985
98
82
135
123
36
40
60
144
172
228
225
20 J
169
187
193
382
147
8
3
14
7
7
3
10
11
10
21
23
17
12
13
10
35
10
TABLE 3.  Example  of  label for archival samples.
IFYGL Lake Ontario
500 ml raw water sample  thru GFC
filt. preserv. 6H20:  3 ETOH: 1 HCHO
Dr. Eugene Stoermer,  U.  of  Mich.
DATE:  1 NOV 72   STATION:  52
SAMPLE NO.: 1869  DEPTH:  1 m

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                         MATERIALS AND METHODS
All samples were collected by Niskin Bottle cast using a multiple bottle
rosette sampler.  In all cases discrete splits of the initial 5-liter
samples were taken by ship technical personnel and delivered to project
personnel for further processing.  Preservation and processing of
samples were initiated immediately, and all samples were preserved with-
in 1/2 hr of collection.  The only exceptions were discrete, small-volume
samples retained for immediate observation of living phytoplankton,
which were discarded without further processing after observations were
completed.
PARTICLE COUNT SAMPLES

Samples for particle count analysis were taken in 125 ml polypropylene
bottles pre-spiked with sufficient commercial formalin to give final
concentration of approximately 1%.  Early in the project some problems
were experienced with polymerization of the small volumes of formalin
used after prolonged storage, but this was corrected by reducing
storage time of spiked bottles to less than 10 days.  After collection
and preservation, samples were returned to the laboratory without
further treatment.

Samples were analyzed by passing 100 ml volumes through a HIAC optical
occlusion particle counter fitted with a 5-150 urn counting head.  Samples
were gently and uniformly agitated before analysis to assure uniform
suspension of particles.  Results of single, initial runs are reported
since it was discovered that results of multiple runs showed a reduc-
tion in readings in larger size channels and an increase in smaller
size channels, apparently resulting from mechanical disruption of the
larger phytoplankton colonies and detrital aggregates.  In all cases the
machine was adjusted to read in channels with nominal size of 5-10,
10-20, 20-40, 40-80, and 80-150 ym, according to manufacturer's
specifications.

Complete records of particle count results have been submitted to the
project officer on magnetic  tape.  Summary plots of this information
are given in the results section following.
 PHYTOPLANKTON POPULATION ANALYSIS

 Samples  for  phytoplankton  population analysis were taken as a 150 ml
 split  of the original  5-liter Niskin Bottle cast.  These subsamples were
 immediately  fixed with glutaraldehyde  (4% by volume) and stored in the
 dark at  approximately  4°C  for at least 4 hr  and not longer than 8 hr
 to  assure complete  fixation.  After fixation, sample bottles were gently
 agitated to  assure  resuspension of phytoplankton present and a 50 ml
 volume was withdrawn for  further processing.

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Material was  concentrated  by filtration onto  25 mm "AA" Millipore filters,
partially  dehydrated  through an ethanol series and embedded in beechwood
creosote.   Prepared filters  were mounted on 50 x 75 mm glass slides and
covered with  a  43 x 50 mm  #1 cover glass.  Preparations were allowed to
dry  for approximately two  weeks, during which time embedding medium lost
by volatilization was periodically replaced,  then the edges of the cover
glasses were  sealed with paraffin.

Material was  analyzed by visual counts  of phytoplankton cells present
using Leitz Ortholux  microscopes fitted with  fluorite oil immersion
objectives  giving approximately 1250X magnification and nominal Numerical
Aperture   of  1.32.  Population  estimates given are the average of two
10-mm radial  strips counted,  corrected  for volume.  Effective filtration
diameter in the filtration apparatus used is  20 mm.

Raw  counts were encoded in computer compatible format on punched cards.
Subsequent data sorting and manipulation were computerized.  Hard-copy
data summaries  in the format  shown in Table 1 are available for all
samples counted.  Summaries  include estimates of absolute frequency,
relative frequency, and error associated with these quantities.
Assemblage parameters calculated include estimates of diversity and
evenness as well as total  assemblage abundance and the contribution of
the  several major Divisions.

Summary information in the results section following is machine-plotted
from reduced data stored on magnetic tape.  Intermediate programs are
utilized to compile and call data of particular interest for plotting
routines or for further processing.
ARCHIVAL PLANKTON COLLECTIONS

Archival samples were taken as 500-ml subsamples of the original 5-liter
Niskin Bottle cast.  Subsamples were immediately filtered onto 47-mm
Watten "GFC" glass fiber filters, placed in 5-dram amber glass capsule
vials, and preserved in a mixture of 6 parts water of collection, 3
parts 95% ethanol, and 1 part commercial formalin.  Vials were then
sealed and temporarily labeled for return to the laboratory.  In the
laboratory, vials were inspected and additional preservative added
if needed, and then permanently labeled with computer-generated labels
of the type shown in Table 3.  Finally vial caps were sealed with paraf-
fin to assure against loss of preservative.
REFERENCE CHLOROPHYLL SAMPLES

Samples for chlorophyll analysis were taken as 250-ml splits of
original 5-1 Niskin Bottle casts at IFYGL master stations only.  Sub-
samples were immediately filtered onto 47-mm diameter HA Millipore
filters and placed in 5-dram amber glass capsule vials containing 10 ml
of 90% acetone, labeled and stored in the dark at approximately 0°C.
                                   10

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Samples were analyzed after return to the laboratory and usual storage/
extraction times were on the order of 6 days.  After return to the
laboratory, extracted samples were analyzed for chlorophyll a and
phaeopigments fluorometrically according to the methods of Strickland
and Parsons (1968).
                                  11

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                                RESULTS
CHLOROPHYLL VALUES AT MASTER STATIONS

The vertical distribution of chlorophyll a values in mg/m^ corrected for
phaeopigments at the master stations sampled in Lake Ontario is given
in Figure 2.  In May, mid-lake stations 24 and 75 showed relatively low
and uniform values throughout the water column.  At station 96, however,
values were extremely high (17 mg/m^ at 1 and 5 m) in the near-surface
water and significantly higher than the other stations at other depths.
In June, values were somewhat elevated at station 10, and a much larger
surface peak was present at station 24.  Stations 45 and 75, which both
fell within the "cold core" region during this sampling cruise, had
very low and vertically uniform chlorophyll a values.  Samples from
station 96 taken during this cruise were unfortunately lost due to a
laboratory accident.  In July, all master stations in the open lake
showed remarkably similar chlorophyll levels and patterns of vertical
stratification.  Peak values occurred at 10 m depth in all of them, and
significant decreases in chlorophyll concentration were noted both above
and below this depth.  At station 96, in the eastern end of the lake,
values were lower at all depths and fairly uniform down to 10 m.  There
was a very slight peak at 10 m, and values declined below that depth,
as they did at the other stations.  Corrected chlorophyll a values
were surprisingly low in August, particularly at stations 24 and 75.
Stations 10 and 45 showed slight peaks at 5 m depth, and values at
station 96 were also elevated and more uniform with depth.

In October, very low values were present at station 10.  Stations 24
and 45 had somewhat higher values and concentrations were fairly uniform
down to 100 m.  Surface values at station 75 were similar to those
found at the previous two stations, but declined below 20 m and became
very low below 30 m.  Chlorophyll values at station 96 were comparable
to the other stations sampled at the surface and remained at the same
levels at all depths sampled.  In November, no pronounced vertical
trends were evident at the stations sampled and values were quite low,
except at station 96 in the eastern end of the lake.  In February,
chlorophyll values were low and uniform at the open-lake stations
sampled.  No samples from station 96 were obtained during this cruise.
In March, values remained low and relatively uniform at the open-lake
stations, but were significantly elevated at station 96, in the
eastern end of the lake.  In April, values increased but remained
relatively constant with depth at the four open-lake stations.  Values
remained significantly higher, and  evidence of vertical stratification
was present at station 96.  In June, chlorophyll values increased
significantly in the upper part of  the water column, with peak values
occurring within the top 10 m at most of the stations.  Station 45
presented a somewhat anomolous case, with peak values occurring at 30 m.
                                    13

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              MflY  15-19,  1972
0 . .10 . W W _, 	 ,tfl 	 , 	 i«
0
*rt
& •
e
±80.
1—
200

•
» <
10


«
24


»
45


<
75
^ ~^ 17.7
17.2
I
•
96
              JUNE  12-16,  1972
        10
                  10
                           10
 ±50
   VI
  200
      10
45
                                    to
75
                                              to
96
              JULY  10-14,  1972
                           to
                                    to
                         45
         75
                                              to

         96
FIG. 2.  Vertical distribution of chlorophyll a at master
stations.
                       14

-------
 200
           RLJGUST  21-24,  1972
                 JO    __	tfl
  10
     10
75
          OCT 30  - NOV 3,  1972
                          to
                                   10
UJ
C
 200
          NOV 27 - DEC  1,  1972
           to
96
                                            to

•
10

^
2M

f

<
«45
J
/
•
75

>


. 96
        to
                 to
                          10
                                   to
                                            to
  so
  200
1
10
1
2^4
<
45
>
75
>
96
FIG. 2 continued.
                   15

-------

     10
           FEBRURRT 5-9,   1973
                         10
                  75
                                           10
                 96
  to
 ico
     10
           MRRCH  19-22,  1973
                10
           <>
24
                         to
                        —t—
                                  10
45
75
                                          10
96
HJ

O
     10
           RPRIL 24-28,  1973
   0    10        10
  0 |~	»	1—    1	1	-I—
           <>
      <>
24
45
75
               ?
96
FIG. 2 continued.
                      16

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  500
                JUNE  11-14,  1973
       10
                                 10
75
96
FIG. 2 continued.
PARTICLE COUNT DATA

Graphic representations of  the areal  distribution of particles in the
particular size classes measured in the  near-surface waters of Lake
Ontario are given in Figures 3-7.   Representations of verticle distri-
bution of particles in the same size  classes sampled on each  of  the
biology-chemistry cruises are given in Figures  8-10.

For the purposes of this project,  particle  count data are regarded as
relatively crude information,  but sufficiently  accurate to allow
reasonable interpretation of trends between points measured by more
accurate but more tedious methods.  Since there are obviously particles
other than living algae in  the seston of Lake Ontario,  it cannot be
expected that the particle  count technique  would give an acceptably
accurate estimation of the  abundance  of  phytoplankton on a direct basis.
Since particle count size classes are directly  related  to the volume
of particular particles sensed by the device, it might  be suspected
that a closer relationship  would be found between particle counts as
an estimate of phytoplankton abundance and  a measure of gross biomass,
such as chlorophyll, than to direct counts  of phytoplankton,  which con-
tain species of vastly different physical sizes and states of aggrega-
tion.  This supposition appears to be supported by the  results of our
study.  When compared with fluorometrically determined  chlorophyll
values from the master stations (Table 4),  reasonably close correlations
were found, particularly with the intermediate  size classes,  in  samples
from the first two cruises.  Although remaining significant statistical-
ly, correlation declined during the summer  months and tended  to  increase
in the fall.  No correlation was found in samples taken during Febru-
ary, but they increased again during  the early  spring sampling period.
Correlations for samples and cruises  on  comparable dates were not as
                                 17

-------
TABLE  4.   Correlations  between  fluorometrically determined chlorophyll a
values and particle  counts  for  all depths at master stations.
Month
                               P.C. Channel
              5-10
                10-20
20-40
40-80
80-150   5-150
R@.99
May
June
June*
July
August
October
November
February
March
April
April**
June
June***
.8670
.8684
.9114
.7893
.5994
.6940
.8317
.0067
.7434
.3159
.3305
.5647
.5952
.9467
.7806
.9297
.8638
.7006
.7328
.9298
-.3476
.9222
.5943
.7533
.7262
.8599
.9390
.2885
.8697
.6996
.6806
.6863
.9206
-.1164
.9621
.7294
.8843
.7964
.8060
.8042
.3640
.8584
.4977
.6505
.5586
.8704
-.1122
.8872
.2793
.6357
.8708
.8753
-.0318
.8092
.8130
.3749
.5145
.4259
.3779
-.2211
.1206
.0178
.1796
.7549
.7557
.9285
.8342
.9366
.8279
.6386
.7134
.8835
-.0695
.8294
.4930
.5514
.6471
.6986
.5256
.3843
.3887
.3575
.3477
.3575
-3932
.3801
.4182
.3477
.3509
.3646
.3683
**
***
Excluding 1 extreme outlier point apparently resulting from sedi-
ment contamination of P.C. sample (station 75, near-bottom sample,
221 m).
Excluding 1 extreme outlier point apparently resulting from contam-
ination of P.C. sample (station 45,  150 m sample).
Excluding outlier point apparently resulting from P.C. bottle con-
tamination (station 75, 1 m sample).
strong as they had been the previous year.

Correlations are strongly affected by the introduction of single nonrep-
resentative samples into the set considered.  In the results presented
(Table 4), we have recalculated certain values excluding data from
samples which were obviously contaminated with sediment.  While certain
other data points, particularly in the set from the October cruise,  are
regarded as suspicious, we have included all cases where source of con-
tamination could not be determined beyond reasonable doubt by inspection
of the sample.  It is apparent  that correlation could be improved
significantly by the adoption of arbitrary criteria for exclusion of
outliers.

The anomolous results obtained from the February samples are somewhat
confounding.  The most immediately plausible explanation would be a
systematic error in the chlorophyll results from this month.  We have
                                  18

-------
not been successful in detecting any such error.   We suspect that the
unsatisfactory result may arise from the fact that very low values for
particle counts and chlorophyll were present in samples from this cruise
and many of the algal populations present were in the larger size class,
resulting in relatively poor extraction of the chlorophyll present by
the method utilized. This factor also may produce a reduction in observed
correlations during the summer months when assemblages at most stations
were dominated by the larger green and blue-green algae.

Comparison of the particle count data with spectrometrically determined
chlorophyll values furnished by other projects is somewhat less encour-
aging (Table 5).  Although highly significant statistically except
during February, the correlations between results from the two methods
are not what might be expected from methods which purport to measure
the same quantity.  Correlations are particularly poor in results from
the summer cruises, and no correlation was found in the previously noted
anomolous February case.  Glooschenko et al. (1972) have noted particu-
larly high phaeopigraent fractions in Lake Ontario waters during the
summer months.  Although corrected chlorophyll a data were used in both
data sets discussed here, part of the apparent non-correspondence between
the two methods may result from inconsistencies in arriving at accurate
correction for phaeopigments.  The correlations between raw cell counts
of phytoplankton and spectrometrically determined chlorophyll values
are also very poor for the summer cruises.  A relatively high correla-
tion was found between raw cell counts and spectrometrically determined
chlorophyll a values in February, although correlations with other
parameters measured were extremely low.


Areal Distribution by Size Class

Data on the distribution of particles in the surface waters of Lake
Ontario are presented in Figures 3-7.  In addition to data gathered
as part of the principal project, we have included measurements made
under the auspices of a complementary project  (Intensive Study of
Lake-Wide Changes in Spring Phytoplankton and Certain Related Parameters,
supported by U.S. Department of Commerce NG-17-72) in the interests of
tracing the time course of early spring changes with the greatest
fidelity.  Cruises undertaken as part of the principal project are
designated as Main-Lake Biology-Chemistry (BC) and those undertaken as
part of the other project are designated as Spring Bloom (SB) cruises.

Samples taken on the first SB cruise showed relatively high densities
of 5-10 urn particles at stations in the Niagara and Toronto vicinities.
Over the rest of the lake, densities were moderate at most stations,
with pronounced low at several mid-lake stations and slightly elevated
at stations nearest shore (Fig. 3A).  Samples  taken on the second SB
cruise showed slightly reduced densities of particles in this size
class at stations near Niagara and Toronto, but increased levels at
stations nearest shore  in the rest of the lake, particularly along the
southern shore  (Fig, 3B).  Although the stations near Niagara and
                                  19

-------
TABLE  5.   Correlation  coefficients  for  EPA  spectrometrically determined
chlorophyll a values and:   (1)  fluororaetrically determined chlorophyll
a values  (master  stations only),  (2) 10-20  ym particle counts,  (3) 20-40
\im particle counts,  (4)  total cell  counts.
-

(1)
(2)
(3)
(4)
May
.8890
.7171
.5856
.6277
June
.9765
.5782
.4536
.5213
July
.8500
.7177
.6094
.3573
Aug.
.6949
.6194
.5291
-.1409
Oct.
.8930
.4724
.4703
.1644
Nov.
missing
missing
missing
missing
Feb.
.0206
.2930
.0195
.7740
March
.9027
.6474
.6610
.8628
April
.9643
.5410
.3941
.8837
June
.7103
.3863
.3335
.2835
Toronto were not sampled on the first BC cruise, samples taken at this
time showed continued increase in particle densities at nearshore sta-
tions along the southern shore (Fig. 3C).  Results from the third SB
cruise indicated that this trend continued, with increases beginning at
offshore stations in the southeastern part of the lake (Fig. 3D).  A
continued spread of relatively high particle densities in the 5-10 urn
size class was evident in the results from the fourth (Fig. 3E) and
fifth (Fig. 3F) SB cruises, particularly at stations in the eastern
and western ends of the lake.  By the time of the June 1972 BC cruise,
relatively high and uniform particle counts were found at all stations
sampled,  except for a group of offshore stations in the southern half
of the lake (Fig.  3G).  A similar situation was found on the sixth
(Fig. 3H) and seventh (Fig. 31) SB cruises, when particle densities
were relatively high and uniform except at station 45 which showed
strikingly low values at both sampling periods.  Particle densities
in this size range were fairly uniform in samples taken during July
(Fig. 3J) and August (Fig.  3K), although somewhat reduced values were
found at  stations in the Hamilton-Niagara vicinity during July and the
Oswego vicinity during August.  Stations sampled during the October BC
cruise showed markedly reduced and rather irregular 5-10 urn particle
densities (Fig. 3L).  By the time of the November 1972 BC cruise,
particle  densities were greatly reduced at all deep-water stations,
but remained high or tended to increase at stations near shore and in
the shallow northeastern basin (Fig. 3M).  Approximately the same
situation was evident during February 1973 (Fig. 3N), although slightly
increased particle densities were noted at a few offshore stations.   In
March (Fig. 3 0),  particle densities remained high at stations nearest
the southern shore but were consistently reduced at stations near the
north shore.  The same trend was visible during the April cruise
(Fig. 3P),  with a general reduction in average particle count values.
Similar to the previous year, by June 1973 particle count values had
become relatively uniform across the lake (Fig. 3Q) except for a couple
of strikingly low values at offshore stations and a pronounced high at
                                  20

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                           HflT  2-5,   1972
 TOROtnO
                                       ROCHESTER
                          MRT  10-12,  1972
 TOROKTO
                                        ROCHESTER
FIG. 3.  Areal distribution of 5-10 ym  particles.
                                                                     20COOO.OO
                                  21

-------
  TORONTO
                           MflT  15-19,  1972
\
\
                           ...A. -1   \
                                               T
                                                                  2cco:o.co
                                      ROCHESTER
                           MRT  24-25,   1972
  TORONTO
FIG.  3  continued.
                               22

-------
                         MflT 30 -  JUNE  2,1972
   TORONTO
                                         ROCHESTER
  TORONTO
                             JUNE 5-7,  1972
                                                                       200000.00
                                         ROCHESTER
FIG. 3 continued.
                                  23

-------
                          JUNE  12-16,  1972
  TORONTO
                                       ROCHES rea
                          JUNE  19-22.  1972
  TORONTO
                                      ROCHESTER
FIG.  3 continued.

-------
                          JUNE; 26-28,  1972
 TORONTO
                                         ROCHESTER
                            JULY  10-14.   1972
   TORONTO
        \
    \
fHULTON
         \
. — — •
s
\
\
y-
\
\
V
-A — '
\
\
^\.
\
\
\
_~- — -•
\
\
\

\
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\

              HfCHVl
              unit
\
\
\
\
\
*
\
\
\
V
\
\
\
-c
\
\
\
\ x
\
\>
^

-------
                         RUG  21-24,  1972
K
                                     ROCHESTLR
                       OCT 30 -  NOV  3,   1972
  TORONTO
   \
\
          *    \
\
        \
                   \
                                  \
                                                        €?.
                                                          \ -
                                                                  t7<
                                                               0 if
\
\
\ V
\
\ V
V
\

V x V

V " /
v v^7
\ J
^s?
s<2-QSUt.QZ

 FIG. 3 continued.
                                      ROCMcSTER
                                26

-------
                         NOV  27  -  DEC  1.   1972
  TORONTO
                                                                          200COO.OO
   TORONTO
MRML1IX
 N
 FIG.  3  continued
                              FEB  5-9,  1973
                                           ROCHESTER
                                                                           200000.00
                                       27

-------
                           MRR 19-22,  1973
   TORONTO
                                        ROCHESTEH
FIG. 3 continued.
                            RPR  24-28,  1973
   TOBOMTO
                     \
                                       ROCHESTER
                                   28

-------
                           JUNE  11-14,  1973
   TORONTO
                                         ROCHESTEB
 FIG.  3 continued.
station 12 near Niagara.

Samples from the first SB cruise (Fig.  4A)  showed relatively high den-
sities of 10-20 urn particles at stations near Niagara and Toronto and
at certain stations in the far eastern part of the lake.   Over the rest
of the lake there was a trend toward higher counts at stations nearer
shore, but values were appreciably less than in the Niagara area.  A
similar situation was found on the second SB cruise (Fig. 4B), although
counts at stations nearest shore in the main lake had increased
appreciably.  Samples from the first BC cruise (Fig. 4C)  showed de-
creased levels of 10-20 ym particles at nearshore stations along the
north shore, but levels remained high along the southern shore, partic-
ularly in the Mexico Bay region and in the northeastern basin.  Average
values decreased somewhat in samples from the third SB cruise (Fig. 4D)
and remained relatively stable in samples from the fourth SB cruise
(Fig. 4E) although relatively high values had begun to spread to
offshore stations.  This trend continued, on the basis of results from
the fifth SB cruise  (Fig. 4F), and by the time samples from the June
BC cruise were taken (Fig. 4G) significantly low values were found only
at a group of stations offshore in the southern half of the lake.  The
area of the lake having water with low particle densities apparently
continued to decrease, since such values were noted only at three sta-
tions sampled during the sixth SB cruise (Fig. 4H) and at a single
station sampled during the final SB cruise in late June  (Fig. 41).  In
                                      29

-------
                             MRT 2-5,  1972
            macaw
            Riven
                                        ROCHESTER
                           MRT  10-12,  1972
 TORONTO
                                       ROCHESTER
B
                                                                      eocoo.oo
FIG. 4.  Areal distribution  of  10-20 ym particles.
                                      30

-------
   TORONTO
NWILKM
                             MflT  15-19,  1972
                                                                       80000.00
                                         ROCHESTER
   TORONTO
                             MRY 24-25,  1972
                                         ROCHESTER
  FIG. k continued.
                                        31

-------
                         MRT 30 -  JUNE 2,1972
  TOftONTO
                                                                        80CCO.OO
                                         ROCHESTER
   TOROfTO
itfln/LH*
                              JUNE 5-7,  1972
                                          ROCHESTER
   FIG.  4 continued.
                                         32

-------
                        JUNE  12-16.  1972
TORONTO
                                                                   80000.00
                                      ROCHESTER
                         JUNE  19-22,  1972
 TORONTO
                                      ROCHESTER
 H
 FIG.  4 continued,
                                      33

-------
   TOflCNTO
HVULTCN
      \\
N   \
           mswmi
                        JUNE 26-28,  1972
                                  ROCHESTER
  TORONTO
                       JULY 10-14,  1972
          IHKX
                                 ROCHESTER
 FIG. 4 continued,
                                34

-------
                              RUG 21-24.  1972
   TORONTO
        \
            \
\   V    \
WXIL1CK
  K
         \
                  \
                   \


                   \
              »ircfnt\
              Mia
                                                                   \
                                              \
                                                                       \
                                                                 \
                                                                        \
\ v
\ .
v X X
X ^ - '

\

\
N.
\
^ ^
\ /X^t
\^S
^
^-/
BHEGO
                                            ROCHESTER
                                                                            80000.00
                                                                       \
    TOBOKTO
                           OCT  30  -  NOV 3,   1972
                                            ROCHESTER
  FIG.  A continued.
                                          35

-------
                      NOV  27  -  DEC  1,  1972
TORONTO
           HIKAVI
            RIVls
                                        ROCHESTER
M
                            FEB 5-9,  1973
  10ROWTO
                                          ROCHESTER
   FIG.  4 continued.
                                          36

-------
  TORONTO
WHIL1CN
                           MRR 19-22.  1973
                                                                         60000.00
                                          ROCHESTEfl
     IDflONlO
   IdHIUOH
                              RPR  24-28,   1973
     FIG.  4  continued.
                                             ROCHESTER
                                             37

-------
                             JUNE  11-14,  1973
    TORONTO
 IM1IUON
                                                                       eoooo.oo
                                         ROCHESTER
 FIG. 4 continued.
July  (Fig. 4J), 10-20 urn particle densities were relatively high  and uni-
form  at most stations sampled throughout the lake, although there was
some  tendency towards reduction in abundance at stations in the eastern
basin and near shore, which had highest values early in the season.
Particle count values in this channel remained relatively high and
uniform at all stations sampled during the August cruise (Fig. 4K),
although some minor but apparently systematic variations were present.
Average values were significantly lower in samples from the October
cruise (Fig. 4L) and quite irregular over the lake, although there was
some  tendency for higher values at stations nearest shore.  The latter
trend apparently continued, since samples from the November cruise
(Fig. 4M) showed significantly higher counts at stations nearest  shore
and in the far northeastern basin than in the open lake.  Counts  at
nearshore stations decreased somewhat in our February 1973 samples
(Fig. 4N), but substantial increases were noted at most stations  along
the southern shore in March (Fig. 4 0).  Values at these stations
decreased somewhat in April (Fig. 4P) but tended to increase slightly
at offshore stations and along the northern shore.  By June (Fig. 4Q),
relatively high levels were found at most stations across the lake,
but there appeared to be a definite south-to-north trend in abundance
with  highest values being found at nearshore stations in the Rochester
and Niagara vicinities.
                                      38

-------
Relatively low levels of 20-40 yiu particles were found at stations
sampled during the first SB cruise in early May (Fig. 5A) .  Highest
levels were noted at stations in the southwestern part of the lake,
near Niagara, and in the northeastern island area.  Approximately the
same situation was evident in samples collected during the second SB
cruise (Fig. 5B), but appreciably increased levels were found at stations
nearest shore,  Samples from the May BC cruise (Fig. 5C) showed consider-
ably increased levels at nearshore stations in the southern part of the
lake and in the northeastern Island area, but not at stations along the
north shore.  Maximum values noted on the previous cruise had declined
somewhat by the time samples were taken on the third SB cruise (Fig. 5D)
but remained relatively high in the eastern part of the lake.  This
pattern was changed by the time samples were taken on the fourth SB
cruise (Fig. 5E), and highest values were found at stations near Niagara.
A similar situation was found on the basis of samples from the fifth SB
cruise (Fig. 5F), although there was some tendency for higher values to
spread to stations farther from shore.  By the time of the June BC
cruise (Fig. 5G), highest values were found at a band of stations in
the north half of the lake and at stations along the southern shore,
with low values along the north shore and at offshore stations in the
southern half of the lake.  On the sixth SB cruise (Fig. 5H), lowest
values were found in the south central part of the lake, with relatively
higher densities in the north and east and particularly in the west end
of the lake.  Samples from the final SB cruise (Fig. 51) showed highest
values in the southwestern part of the lake and an apparent west-east
overall trend.  In July (Fig. 5J), average values were reduced and
densities more variable between stations, as they were in smaller size
ranges.  In August, average values increased somewhat (Fig. 5K) but
there was considerable variation between stations and no outstanding
regional patterns.  In October (Fig. 5L), particle densities in this
size class were reduced to low and rather uniform levels, but increased
at stations in the northeastern island area, and to a lesser extent at
nearshore stations throughout the lake (Fig. 5M) during November.  In
February (Fig. 5N), values were uniformly low except for a marked high
at station 14, near Niagara.  Our March samples showed increased values
at certain stations along the southern shore (Fig. 5 0), and by April
(Fig. 5P) this trend had spread to all nearshore stations and to stations
in the northeastern part of the lake.  Rather irregular values were
found in samples from the June 1973 cruise (Fig. 5Q), but there appeared
to be a north-south trend in abundance, as there was in the smaller
size ranges.

Samples from the first SB cruise (Fig. 6A) showed relatively high counts
of particles in the 40-80 ym channel at stations in the northeast and
southwest parts of the lake and at some stations in the north-central
region.  Results from the second SB cruise showed a slight increase at
stations nearest shore on both sides of the lake (Fig. 6B).  Conditions
were apparently similar during the time the samples from the May BC
cruise were taken  (Fig. 6C), with relatively high values at most
shallow stations.  Results from the third SB cruise (Fig. 6D) indicated
a slight decline, except at stations in the east and west ends of the
                                   39

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   10RON10
MIILTCN
   TORONTO
 B
                              MRT  2-5,  1972
                                          ROCHESTER
                             MRT  10-12,  1972
                                          ROCHESTER
                                                                        20000.00
 FIG. 5.  Areal  distribution of 20-40 ym  particles.
                                      40

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   TOROfTO
NMUM
                              MRY  15-19.   1972
                                                                        20000.00
                                          ROCHESTER
   TORONTO
                             MflT  24-25.  1972
D
 FIG.  5 continued,
                                          ROCHESTER
                                                                        20000.00
                                     41

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                        MRY 30 -  JUNE  2,1972
  TORONTO
                                                                      20000.00
                                        ROCHESTER
                            JUNE  5-7.  1972
  TOflOKTO
                                        ROCHESTER
FIG. 5 continued.
                                   42

-------
   TORONTO
                             JUNE  12-16.   1972
              HIVCD
                                           ROCHESTER
   TORONTO
                             JUNE  19-22.  1972
WMLTCN
 H
             NIAGAHI
              •HOI
                                          ROCHESTER
                                                                         20000.00
 FIG.  5 continued.
                                      43

-------
  TORONTO
                            JUNE 26-28.   1972
                                                                      20000.00
                                        ROCHESTER
  TORONTO
                           JULY  10-14.  1972
                                                                      20000.00
                                        ROCHESTER
FIG. 5 continued.

-------
                            flUG 21-24,  1972
  TORONTO
    \
                     \
                      \
                                            \
x * \
\
•* \.
1
\ \ X

X \
V
k \
v v
V
x V ^

\

N.
-^ 	 /
                                                                \
                                                                \
                                                                 \
\
                                                                      0 if
                                                                       \
     \
     ,20000.00
 K
             •ran
                                          ROCHESTER
   TORorno
NMUGM
                          OCT 30  - NOV  3,  1972
                                                                          20000.00
                                           ROCHESTER
  FIG. 5 continued.
                                      45

-------
       TORONTO
    M
               MVCX
                             NOV27 -  DEC 1.  1
972
                                         ROCHESTER
N
FIG.  5 continued,
                                  5-9.   1973
                                46

-------
   TORONTO
IWILTCH
 0
             \
              NHCHfWl
              MVCI
                             MRR 19-22,  1973
                      \
                                           fWCKESTER
20000.00
   TOBONTO
              dirt*
 FIG.  5 continued,
                             RPR 24-28.  1973
                            N.     >•
                       \
                                           ROCMESTEB
                                       47

-------
                          JUNE  11-m.  1973
  TORONTO
                                                                      20000.00
MMtltM
                                        ROCHESTER
 FIG. 5 continued.
lake, and the trend toward higher levels at these stations was evident
in the results from the fourth SB cruise (Fig.  6E).   Levels remained
relatively high in the west end of the lake at the time of the fifth
SB cruise (Fig. 6F), and increases were noted at some offshore stations.
The  same pattern evident in counts from the 20-40 urn channel appeared
 to be  present  in results from the June BC  cruise  (Fig. 6G), with  rela-
 tively high values along the south shore and in  the north central part
 of  the lake, and low counts along the north shore and  in the  south
 central region.  Relatively low counts  were present  at some offshore
 stations and a group of stations east of Niagara during the sixth SB
 sampling period (Fig. 6H), with relatively high counts at stations
 immediately west of Niagara.   During the final SB cruise (Fig. 61) there
 appeared to be a southwest to northeast trend in values, as there had
 been  in some  of the  smaller channels.  Samples from the  July BC  cruise
  (Fig.  6J)  showed  relatively high and uniform values except for low
 values at  a group of stations  in the south central part  of the lake and
  a  few stations near Toronto.   Values increased  appreciably at most
  stations  sampled  during August (Fig.  6K), but  declined  again in
  October (Fig. 6L).  In November (Fig.  6M), low values were found at most
  offshore stations but were uniformly higher  at stations nearest  shore
  and considerably higher at stations in the northeastern sector of the
  lake.  Only  isolated high counts with no particular pattern were found
  during February  1972  (Fig. 6N) and March 1973  (Fig. 60).  In April
                                         48

-------
   TORONTO
                                 MRT 2-5.  1972
                                                                          1000.00
                                          ROCHESTER
   TOROHTO
             MMGMV)
             B1VEH
                              MflT  10-12.  1972
                                          ROCHESTER
                                                                         1000.00
B
FIG. 6.  Areal distribution  of  40-80 urn particles.

-------
                             MflT  15-19.  1972
   TORONTO
                           \     \   X
             wscsrw
              DJVQ1
                             MRT  214-25.  1972
   TOROhfTO
                                        ROCHESTER
D
FIG. 6 continued.
                                    50

-------
                       MflY 30 -  JUNE 2.1972
  TOBONTO
            MUSI
                                       HOCHESTW
   TORONTO
                            JUNE  5-7,  1972
WMIUCN
              • IVDI
FIG. 6 continued
                                    51

-------
                            JUNE  12-16.  1972
    TORONTO
                                        ROCHESTER
                           JUNE  19-22,   1972
   TORONTO
H
FIG. 6 continued.
                                        ROCHESTER
                                      52

-------
                            JUNE 26-28.  1972
    TOROKTO
 IH1IL1CH
              WdCSfB
              BIYOI
                                         ROCHESTER
                            JULY  10-14.  1972
    TORONTO
FIG. 6 continued.
                                        53

-------
      TORONTO
                    \
   MtrllLTCX
   \   x
1   \   \
                     \
                 wucwal
                 HIVES
                                 RUG  21-24.   1972
\
\
\ A
x \
\
\
\
\
\
\
\
\
\
V
                                              ROCHESTER
 \
\
 K
     TOBOKTO
                KIVOI
                            OCT  30  -  NOV 3.   1972
                        \
                                             ROCHESTEB
FIG.  6  continued.
                                          54

-------
   TORONTO
M
    TORONTO
                          NOV  27  -  DEC  1.  1972
                                          ROCHESTER
                              FEB  5-9,   1973
 N
 FIG. 6 continued.
                                           BOCHESTCT
                                                                         1000.00
                                          55

-------
                            MflR  19-22.  1973
   TORONTO
                                        ROCHESTER
   70BON70
             Mivtn
                           RPR 24-28.  1973
                                        ROCHESTER
FIG. 6 continued.
                                       56

-------
                            JUNE  11-14.  1973
   TORONTO
                                         ROCHESTER
FIG. 6 continued.
(Fig. 6P), however, there was a definite pattern of higher occurrences
at stations nearest shore and in the eastern island area.  In June
(Fig. 6Q), highest values were found along the southern shore and in the
north central part of the lake, as was the case in some of the smaller
channels.

Particle counts in the 80-150 urn size channel were relatively low in
samples from the first two SB cruises (Fig. 7A,B)y and only slight
increases were noted at stations near shore and in the eastern part of
the lake during the May BC cruise (Fig. 7C).  Continued slight increases
were noted at stations in the eastern part of the lake and stations near
Niagara on the three following SB cruises  (Fig. 7D, E, F).  Samples from
the June BC cruise showed scattered very high values at stations along
the southern shore and in the eastern part of the lake (Fig, 7G).
Samples from the two following SB cruises  (Fig. 7H, I) showed a tendency
towards decrease at stations in the eastern part of the lake and increase
at stations in the west.  In July (Fig, 7J), however, values in this
size range were very high at stations along the southern and' eastern
shores and relatively low at stations in the western part of the lake.
By August, overall average values had declined (Fig. 7K) and striking
declines were evident at stations that had been high the previous
month.  High values were present at a series of stations in the
                                        57

-------
   TORONTO
MtUUCN
                              MRT  2-5,   1972
                                        ROCHESTER
                            MRT  10-12,  1972
  TOROMTO
  FIG.  7.  Areal distribution of 80-150 ym particles.
                                58

-------
                         KPT  15-19,  1972
   TORONTO
                           MRT 24-25.  1972
wwrucw
             MVCN
  D
  FIG. 7 continued.
                                       ROCHESTER
                                   59

-------
                       MRY  30  - JUNE  2, 1972
TORONTO
                   \
                                      ROCHESTER
  FIG. 7 continued,
                          JUNE 5-7.  1972
TORCMIO
          WER
                                     ROCHESTER
                                  60

-------
TORONTO
                        JUNE  12-16,  1972
                                                                  00
                                    ROCHESTER
                       JUNE  19-22,  1972
                                                                  00
                                   ROCHESTER
FIG. 7 continued.
                                 61

-------
                            JUNE  26-28,  1972
   TORONTO
        \  \
                \
                                        ROCHESTER
   TORONTO
                    \
           ^    \
MML1M
        \
            \

                      m
             •JdCWftl
             MVOI
                           JULY  10-14,  1972
                                        BOOCSTEH
    FIG.  7  continued.
                                      62

-------
                        RUG  21-24,   1972
TOROtfTO
                                                                    120.00
                                      ROCHESTER
                       OCT 30 -  NOV  3,  1972
                                       BODIES IEB
   FIG. 7 continued.
                                      63

-------
   TOftONTO
IflfULlCN
              macfrfll
              uvoi
                               FEB 5-9.   1973
                                           ROOtSTER
      M
   TORONTO
                          NOV  27  -  DEC 1.   1972
     N
                                           ROCHESTER
     FIG.  1  continued.
                                         64

-------
 TORONTO
    0
  TORONTO
MMLVM
                       KRR  19-22,  1973
                        RPR 24-28,  1973
                                       noatsten
     FIG.  7  continued.
                                      65

-------
                             JUNE 11-lH,   1973
              NJfCWtt
               UVER
FIG. 7 continued.
Hamilton-Niagara region.  Particle densities in this size range declined
drastically by October (Fig. 7L) and remained .low during the winter and
spring (Fig. 7M, N, 0, P).  A substantial increase was noted in June
samples (Fig. 7Q), but levels approaching those common the previous
year were present only at a single station in Mexico Bay.


Vertioal Distribution by Size Class

The vertical distribution of 5-10 urn particles at stations sampled on the
main lake biology-chemistry cruises is  plotted in Figure 8.  Stations
sampled during May showed relatively little vertical stratification,
although samples from stations 42,  72,  73,  59,  79,  and 90 showed  a definite
vertical trend in abundance.  Stations sampled  during June 1972 showed more
or less pronounced  vertical stratification,   except stations  26,  32,
40, 44,  62  and 75  which had  very low counts  and  no  apparent vertical
trend.   Similar vertical distribution was noted at  stations 15,  45,  45 and  54
but particle densities at these stations were somewhat higher.   Very  similar
patterns,  possibly indicative of regional water mass similarities,
were noted at stations 30 and 31 and at stations 52, 64, and 66.   All
stations sampled during July showed some evidence of vertical stratifi-
cation, and some apparent regional patterns were evident.  At stations
5, 10,  24, and 26, 5-10 jjm particles were appreciably concentrated at
                                     66

-------
    10 m while at stations 38, 40, 44, and 45 there appeared to be a distinct
    break in concentration levels at the 20 m depth,  Somewhat surprisingly,
    samples taken during August did not show as distinct vertical patterns
    aa the samples from previous months, perhaps as a result of a floristic
    shift of species in the larger size classes,  At this time similar
    patterns were noted at stations 45 and 46, although adjacent station 44
    was strikingly different.  Stations 62, 64 and 69 showed a different
    but internally consistent pattern.  Stratification of particles in this
    size class apparently broke down in October and, as would be expected,
    no trends were evident in the winter and early spring samples.  In
    April, anomolous results were obtained at station 26,  Samples from the
    June 1973 cruise showed an unusual pattern at the same station when
    particle densities that were down to 40 m then increased.  A similar
    pattern was  found at station 44.  Apparently similar vertical distribu-
    tions were found at stations 46, 62, 64, and 66, but results from this
    sampling period were, in general, much more irregular than in the same
    month the previous year.

    Vertical distributions of 10-20 and 20-40 urn particles are plotted in
    figure 9.  May samples showed significant stratification of particles
    in these size categories at stations 30, 31, 72, and 73 along the south
    shore, stations 94, 96, 97, and 98 in the eastern island area, and
    station 105  in Mexico Bay.  Other stations sampled showed little signi-
    ficant stratification.  Stratification of particles in these size ranges
                          MRT  15-19,  1972
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FIG. 8.   Vertical distribution of  5-10  ym  particles.
                                     67

-------
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                                      68

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                                     69

-------
                            JUNE  12-16,  1972
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 FIG.  8  continued.
                                              71

-------
                          RUGUST  21-24,  1972
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FIG. 8  continued.
                                    72

-------
                     RUGUST  21-24,  1972
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                                 73

-------
                         OCT 30  - NOV  3,   1972
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                                       74

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                        NOV  27  -  DEC  1.   1972
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                                      75

-------
                   NOV 27 -  DEC 1.  1972
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                           76

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                                     77

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                           78

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                                     79

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                                80

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                            JUNE   11-14.   1973
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                                       81

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                            JUNE 11-14,  1973

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FIG. 8 continued.
was rather poorly developed at stations sampled during the June 1972
cruise, and significant vertical differences were mostly restricted to
stations near shore and in the eastern part of the lake.  Samples taken
from station 75 during this cruise showed unusually high particle count
values in the near-bottom waters.  Many stations sampled during July
had highest particle count values and significant peaks in particle
density at depths ranging from 10 to 20 in, and particle densities were
higher in the upper water column at most stations sampled.  An apprecia-
ble   secondary peak was noted at 50 m at station 56.   Samples taken
during August all showed higher concentrations of particles in this
size category in the epilimnion,  and there was an extreme peak at 15 m
at station 40. Certain stations showed relatively high concentrations
in the near-bottom waters.  Concentration of particles in these size
categories was relatively low in samples taken during October, and most
stations had relatively insignificant vertical differences.  Station 15
was an exception in that vertical stratification in particle density
appeared still to be present.  Samples from the November cruise showed
unusually high particle densities in the near-bottom waters at stations
30 and 31.  Samples taken during this cruise from many of the stations
in the eastern part of the lake were unusual in that the ratio between
abundance of 10-20 and 20-40 urn particles was reversed from the normal
case throughout the rest of the year.  In February and March,  however
concentration of 10-20 ym particles exceeded the average ratio.   In
                                    82

-------
    April, samples from station 26 had very unusual values, as they did in
    the lower particle count channel, and unusually high near-bottom values
    were found at stations 45, 46, and 48.  In June 1973, particle count
    values were higher in the top 20 meters, although more variation was
    present than had been the case the previous year.  Station 26 had
    unusually high values in the deep-water samples, and surrounding stations
    had extreme peaks at 20 m (sta. 17) and 40 m (sta. 15 and 32).

    Samples taken during the May 1972 cruise (Fig. 10) showed near-surface
    concentrations of particles in the 40-80 and 80-150 ym size classes
    at stations 94, 96, and 97 in the eastern end of the lake and station
    105 in Mexico Bay.  Mid-lake stations 17, 34 and 46 showed relatively
    high subsurface values in the 10-30 m range.  In June 1972, most stations
    sampled showed stratification of particles in these size classes, with
    highest values occurring near the surface.  There were, however, a series
    of about 14 stations in the south central "cold core" region of the lake
    where counts were appreciably lower and stratification was not highly
    developed.  Stations sampled during July all showed stratification near
    the surface but no particular regional trends were evident.  In August,
    values remained relatively high, with greatest concentrations near the

                         MRT  15-19.   1972
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    FIG.  9,   Vertical  distribution  of  10-20 urn and  20-40 ym  particles.   The
    10-20 pm  channel is  represented by the solid  line  and  the upper  scale,
    the 20-40 pm channel by  the dashed line and the lower  scale.  A  star
    indicates that  an  entire profile is above the maximum  scale value.
                                    83

-------
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                                      84

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                              JUNE   12-16.   1972
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                                         85

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                             JUNE  12-16.   1972
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                                       86

-------
                               JULY   10-14,   1972
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                                          87

-------
                     flUGUST 21-24,  1972



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                                      89

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                                      90

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                  NOV 27  - DEC  i,  1972
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                           91

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                 NOV  27 - DEC  1,  1972
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                            92

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                     FEBRUflRT  5-9.   1973
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FIG. 9 continued.
                                 93

-------
                   MflRCH 19-22.  1973

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                             94

-------
                  MRRCH 19-22,  1973
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                             95

-------
                       RPRIL 214-28,  1973
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                               96

-------
                        JUNE 11-m.   1973
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  FIG. 9 continued.
                                    97

-------
                             JUNE  11-14.  1973
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FIG. 9 continued.
surface except at station 40,  where a  large peak was noted at 15 m and
station 59 where values were very  high in  the near-bottom sample.  In
October, values were reduced and stratification was less pronounced at
all stations sampled.  Subsurface  peaks were noted at station 30 (near
bottom), station 94 (20 m)  and station 99  (5 and 10 m).  As might be
expected, samples taken during November 1972 showed relatively little
vertical stratification.  Very high near-bottom values were noted at
stations 26, 30, 31,  32, 34, 36, and 38.   Similar to some of the other
channels, there was an evident change  in channel ratios at all depths
sampled at station 49 and stations 94-99 and 103 in the far eastern area
of the lake.  Stations collected during February 1973 had relatively low
values, although samples from  the  upper 20 m were significantly higher
at station 24, and 5 m peaks were  noted at stations 20 and 26.  Mid-depth
peaks were noted at stations 45, 46, 75, and 89.  In March, values were
relatively low except at stations  12,  30,  and 42 along the southeastern
shore and stations 89, 92,  and 95-97 in the eastern portion of the lake.
Samples from the April cruise  showed extreme near-bottom values at
stations 45, 46, and 48 and relatively high values at stations 95-98 in
the far northeastern end of the lake.   High and rather variable values
were found at most stations sampled during June 1973, with apparent
vertical stratification being  present  except at stations 32, 44, and 45
where particle counts were low and there was little evidence of vertical
                                    98

-------
   stratification.  Mid-depth peaks were noted at stations 17  and  77.
                        MflT 15-19,  1972
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FIG.  10.   Vertical distribution of 40-80 ym and  80-150 ym particles.   The
40-80 ym channel  is represented by the solid line and the upper scale,
the 80-150 ym  channel by the dashed line and the lower scale.  A star in-
dicates that an entire profile is above the maximum scale value.
                                    99

-------
                       MflT 15-19,  1972
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FIG. 10 continued.
                               100

-------
                     JUNE  12-16.  1972
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                            101

-------
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                             102

-------
                         JULY  lO-lil.  1972
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                                 103

-------
                     RUGUST 21-24,  1972
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                              104

-------
                   OCT 30  - NOV 3.  1972
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FIG.  10 continued.
                              105

-------
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                                  106

-------
                   NOV 27 - DEC 1,  1972
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                            107

-------
                     FEBRURRY  5-9,  1973
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 FIG. 10 continued.
                            108

-------
                     FEBRURRY  5-9,  1973
 0    MO
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                      MRRCH  19-22,  1973

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                             109

-------
                       MRRCH  19-22,   1973
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                              110

-------
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FIG. 10 continued.
                           112

-------
                      JUNE  11-Hi.  1973
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                              113

-------
 PHYTOPLANKTON  DATA

 Aveal Distribution of Total Phytoplankton in Neap-surfa.ee Waters

 Trends  in  total phytoplankton abundance in  the surface waters of Lake
 Ontario are  summarized  in Figure  11.

 Based on samples  taken  during the May 1972  cruise, there appeared to be
 a  nearshore  bloom with  largest standing crops occurring at relatively
 shallow stations  nearest shore and in the eastern part of the lake.
 Highest values were found at stations on the southeastern shore, especially
 near Sodus Bay and  in Mexico Bay, although  nearly comparable values were
 found at some  stations  in the northeastern  island area.  By the time the
 June 1972 samples were  taken, high phytoplankton standing crop levels
 had become more generally distributed in the lake and highest abundance
 values  were  found  at stations in  the northwestern sector.

 Some reduction in  abundance was noted at stations on the southern shore
 which had highest  levels the previous month.  There was also an apparently
 consistent trend  toward low total phytoplankton abundance at a series of
 stations offshore  in the south central part of the lake.  In July, average
 phytoplankton cell  counts were reduced, but there was a tendency for
 highest  values to be found at stations in the southern half of the lake.
 One particularly high abundance value was noted at station 14, near Niagara.
 A  slight further reduction in total cell abundance was noted in the
 August  samples, and highest values were found at stations in the southern
 and eastern  sectors of the lake.   In this respect the situation this month
 was somewhat similar to that found in early spring, although the tendency
 towards  extremely high values at stations nearest shore was not nearly
 as pronounced.

 A  continued reduction in total phytoplankton abundance was found in
 the October samples, and this month no pronounced regional distri-
 bution patterns were evident although peak values were generally found
 at mid-lake stations.   Total phytoplankton abundance apparently con-
 tinued to decline in November and although highest values were still
 found in the offshore waters, relatively small differences were present
 between  the stations sampled.  Lowest total abundance found during our
 study occurred in the February samples.   At this time very low phytoplank-
 ton standing crop was present at  most stations sampled, with only signif-
 icant highs at 79, 96, and 97, near Prince Edward Point.   The apparent
 initiation of the spring bloom is evident from samples collected during
March.   Highest phytoplankton cell counts are restricted to stations
 nearest shore,  except for those stations in the shallow northeastern part
 of the lake where values comparable to those found at stations nearest
 shore in the main part of the lake were found.   This  trend apparently
 continued as, by the time the April samples were taken,  all stations
                                    114

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                          MRT  15-19,  1972
                                       POCHE3TER
                          JUNE  12-16,  1972
                                                                       00
             HIKPTR
             IUVU<
                                       ROCHESTER
FIG.  11.   Areal distribution of total cell counts.
                                 115

-------
                            JULY  10-14,  1972
    TORONTO
 IWUUOI
                         RUGUST  21-24,   1972
   10POHTO
                                      ROCHESTER
FIG.  11  continued.
                                116

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                        OCT 30 -  NOV  3.  1972
   TOftOKTO
                                        ROCHESTER
                        NOV 27  - DEC  1,  1972
   TORONTO
FIG.  11 continued.
                                  117

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                        FEBRUflRT  5-9,  1973
  70ROKTO
                        MRRCH  19-22,  1973
HBVTL10H
FIG. 11 continued,
                                       ROCHESTER
                                                                   6000.00
                                 118

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                         RPRIL  2H-28,  1973
                                      ROCHESTER
   70RCOTO
                          JUNE  11-14.  1973
            Hincmv
            M«n
                                      TOOCS7ER
FIG.  11 continued.
                                119

-------
 nearest  shore  in  the main  body of  the lake and stations north and east
 of  a  line  between Prince Edward Point and Stoney Point had notably
 increased  total phytoplankton counts-   Increases were also noted at
 several  stations  in the open lake  and,  as in the previous spring,
 there was  a  tendency towards higher values in the northern half of the
 lake.  By  June 1973, high  phytoplankton abundance was present at most
 stations throughout the lake.  In  general, levels of abundance were
 greater  at offshore stations than  they  were at stations nearest shore
 although notably  low assemblage abundance was found at stations 15
 and 44 and there  appeared  to be a  consistent pattern of relatively
 low values at  stations in  the north central portion of the lake.
Areal Distribution of Major Groups in Near-surfaoe Waters

Seasonal trends in the abundance of major phytoplankton groups in the
surface  waters of Lake Ontario, averaged for all stations sampled
during any particular cruise, are shown in Figure 12.  Several interest
ing points are evident in this summary information.  The first is that
the gross composition appeared to be quite different during the two
spring periods sampled.  In 1972, diatoms were dominant during the
spring and early summer, with secondary contributions by green algae,
mostly Soenedesmus bicellularis, and microflagellates.  In 1973,
however, although diatoms were again dominant in the early spring, the
microflagellates became dominant by June and their average abundance
on a cell count basis was more than twice as high as it had been the
previous year.  Although the trends shown may be partially an artifact
of sampling periodicity, our evidence suggests that there were con-
siderable differences in major group composition of the phytoplankton
community in the two years.  The same trend is apparent in the seasonal
trends of the green algae.  In 1972 there was a strong peak,  apparently
caused by the unusual abundance of a single population, and a secondary
peak in late summer which was contributed to by a number of species.
No similar spring peak in abundance of green algae was detected in
our 1973 samples.   Our results also indicate that the peak abundance
of blue-green algae occurred unusually late in the season in 1972.  Tht
component of the phytoplankton community reached its greatest abundance
in October with a nearly synmetrical increase and decline on  either
side of the peak.

Previous studies on phytoplankton periodicity in Lake Ontario (Munawar
and Nauwerck 1971) have indicated that a late fall peak in abundance
of blue-green algae is not uncommon.  On the basis of the same study
it would appear that the relative abundance of major groups found in*
1973 may be the more typical case for Lake Ontario, since they
emphasize the importance of several species of microflagellates in
their collections.  On the other hand they report that Saenedesmus
was a spring dominant,  as it was in our 1972 collections but  not in
1973.  Thus the situation is not entirely clear,  and it is highly
probable that in a system as highly disturbed as Lake Ontario there
is no consistent yearly pattern of phytoplankton succession and the
                            120

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        1400-
     a
     to
     d
     w
     o
     w
     1
     Ed
        1000-
         800-
600
400-
          200-
                 / \
	  Bacillariophyta
	  Chlorophyta
	  Cyanophyta
	  Microflagellates
                                           A
                                           i\
            MY    JN    JL  AG  OC   NV   FB   MR   AP   JN


     FIG. 12.   Seasonal average abundance of major  phytoplankton
     group cell counts.
events of a particular year are largely determined  by yearly variations
in climatic conditions, as they appear to be in western Lake Erie
(Chandler 1942).

The fraction of total surface plankton contributed  by the major  groups  is
summarized in Figure 13.  It was necessary to scale the figures  for
different months in order to accommodate the variation in assemblage
density found at the different sampling periods.  In our May 1972 samples
diatoms were dominant at most nearshore stations in the southeastern
part of the lake.  Microflagellates comprised a larger fraction  of the
total near-surface phytoplankton at stations in the far northeastern part
of the lake and at stations along the northern shore.  While diatoms
were dominant at some offshore stations, green algae made a more signif-
icant  contribution to the total assemblage in addition to somewhat
lower and more variable fractions of microflagellates.  Although present
at most stations sampled, the blue-green algae contributed a relatively
small fraction of the total phytoplankton collected during May.   A
definite shift in the pattern of dominance was noted in the collections
                                   121

-------
                           MfiY 15-19.  1972
     TOfWWTO
 MttllLTON
                                                                        OSHEGO
             NlflGWW
              WVER
                                            ROCHESTER
^2000.00  T£MO.M   -^000.00
                          JUNE  12-16,   1972
    TOROMIO
HRMIUON
             NJRGflRP
              MVER
FIG.  13.   Areal distribution of major  phytoplankton  group cell counts.
                                     122

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    TORONTO
HflMlLT
                           JULY  10-14.   1972
              NIRGfflfl
              RIVER
_~^

      vf
       \  J \1000.00  xlooo-00  \1000.
       ^-'v/ i       ^-        *-o
                                                     • oi/ML   » CM/ML   • BG/ML    » FL/ML
                          flUGUST 21-24,   1972
    TONHIO
              NIRGHW
               RIVER
 FIG.  13 continued.
                                             ROCHESTER
            •ilOOO.OO  -^1000.00   TlOOO.OO  11000.00
                                       123

-------
    10IWTO
HPHIU10N
                         OCT 30  -  NOV  3,   1972
                WVER
                                     -veoo.oo   \60o.oo   \eoo.oo   \eoo.oo
                                      10      io      ^ o      ^-o
                                              * CM/ML   * BG/ML   «  FL/ML
     10RONTO
                          NOV  27  -  DEC   1.  1972
Ju

 A.
 w.
 HR1IUON
                NIRCflRfl
                 P1VER
             1    ^
                                       A.
                                       T600.00   \600.00   T600.00   \600.00
                                                ^ 0       *• 0       '•O
                                       . Q,/t1L   , (^ni.   , BG/ML   • FU/ML
   FIG.  13 continued.
                                           124

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                        FEBRURRT  5-9,   1973
 towwio
           NlRGflflfl
            WVER
                                                                            OSHEGO
-J.GOO.00   T.600.00    TBOO.OO   -1600.00
                                             KJCHESTCR
                          TB
                          t
                                                                         0      1 0
                                                     * OI/HL    » CM/ML    » BG/ML   » TL/ML
                        MRRCH  19-22.   1973
 TORONTO
           NIAGPRfl
            RIVER
                                                                            OSHEGO
            '.oo  yooo.oo  yooo.oo   yooo.oo

ROCHE:S1CT « oj/n.   • cn/rt.    • Bern.    •
FIG.  13 continued,
                                        125

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                           RPRIL  24-28.   1973
    TORONTO
HflHIUON
              tORGflPfl
               RIVER
          aooo.oo  \zooo.oo   \sooo.oo   -5.2000 oo
           Q       *- 0      i-O      J-
ROCHESTER • 01/M.   » GN/rtL    • BUM.    •
      TORONTO
                               JUNE  11-14.  1973
  HfifULTON
                NIRGfiftfl
                 WVEP
                                .00   ^000.00

  MCMESTER  • OI/Mk.   » CtVHL    • BO^ML    •
  FIG.  13  continued,
                                          126

-------
taken during the June 1972 cruise.   While diatoms  were dominant  at
stations in the northwestern sector of the lake and  at certain stations
in the northeastern part,  microflagellates had become a much more
relatively important part  of the flora at stations in the southeastern
sector,  A relative increase in the importance of  green algae was seen
at several stations, and they were co-dominant with the other major
groups at several stations in the far southwestern and far northeastern
parts of Lake Ontario,  There was considerable regional variation in
dominance patterns based on samples collected during July (note  scale
change).  An extreme peak in abundance of green algae was found  at
station 14 near Niagara, and this group was also relatively abundant
at certain stations along  the southern shore and at  a group of stations
in the eastern part of the lake.  Diatoms remained dominant at stations
on the western shore, between Hamilton and Toronto and at several
offshore stations in the east central part of the  lake,  Microflagellate
abundance was quite variable, although this group  dominated several off-
shore stations, particularly in the eastern half of  the lake. During
July, blue-green algae first became relatively important  in the  phyto-
plankton assemblage, particularly at stations in the far  eastern part
of the lake and at certain stations along the southern shore.

Samples taken during the August cruise showed a considerable increase
in the relative importance of green algal species, particularly  at
stations in the eastern part of the lake where they were  dominant in
the assemblages collected  at most stations,  Some  increase in the
relative importance of blue-green algae was also noted, although highest
levels occurred at scattered stations.  In October (note  scale change),
however, this group became dominant at many stations.  They were most
important at a series of stations near mid-lake, while in other  areas,
particularly in the eastern half of the lake, assemblage  abundance was
more evenly distributed among the major groups. While the green algae
generally declined in relative importance in this  set of  samples, the
diatoms again became dominant at isolated stations along  the western
and southern shores.  Somewhat surprisingly, the dominance of blue-
green algae was maintained into the November 1972  sampling period.   This
group was either dominant or co-dominant with the  diatoms at many
stations, although the latter group was significantly more abundant
than any other at many nearshore stations throughout the  lake.  By
February 1973, the blue-green algae had declined to insignificant levels
at most stations sampled although a few relatively high population
densities were still found.  Diatoms were dominant at most stations,
with relatively minor contributions from other groups.  In March,
diatoms were dominant at nearly all of the stations sampled, with
minor contributions from the other groups.  The proportion of the
total phytoplankton assemblage contributed by this group  was especially
large at stations near shore, apparently as a result of the initiation
of the spring diatom bloom.  Approximately the same situation was pres-
ent  in the April samples (note scale change),  Diatoms were dominant
at all stations, with very minor contributions from the other groups,
It did appear, however, that there was an increase in the importance
of microflagellates relative to the other minor components of the flora.
                                   127

-------
 In June there was a dramatic increase in the relative importance  of
 microflagellates.  At  the time our samples were taken,  this  group was
 dominant at most  offshore stations and co-dominant with diatoms at many
 nearshore stations.  Unlike the previous two months,  the  other two major
 groups,  particularly the green algae,  had begun to increase  and consti-
 tuted  a still minor but  appreciable part of the total phytoplankton
 flora,  especially at stations nearest shore.
 Diversity Trends  in Near-surface  Waters

 The  Shannon-Weaver index,  a  gross measure of assemblage structure, was
 calculated  for  near-surface  phytoplankton assemblages analyzed during
 the  course  of this investigation.  Although the results of any such
 integrative measure should be interpreted with caution, certain inter-
 esting patterns are present  in Lake Ontario.  The calculated diversity
 of most  samples taken during the  May cruise (Fig. 14) was uniformly
 rather high, with values less than 2.0 being found only at stations
 69,  71 and  85 in  the east  central part of the lake.  Samples taken
 during June 1972  also showed relatively high diversities at most stations
 however, values below 2.0 were found at stations 92 and 105 in Mexico
 Bay  and  at  a group of stations in the south central part of the lake,
 including shoreward stations between Rochester and Niagara and extending
 out  to mid-lake stations.  Average diversity decreased significantly
 during July, and  the apparent pattern of the previous month was
 reversed.   Most stations sampled  during this month had diversities
 less than 2.0,  and higher values were restricted to a group of near-
 shore stations  in the far western part of the lake near Hamilton and
 Toronto, stations 90, 92 and 105  in the Oswego-Mexico Bay region and
 a group  of  stations in the central portion of the lake extending from
 the north to the  south shore.  In August the average diversity at sta-
 tions sampled again increased, and values greater than 2,0 were found
 at most  stations.  Diversity values less than 2.0 were found only at
 stations 12 and 14 near Niagara,  a group of stations extending from
 8 and 19 near Toronto out to near mid-lake, and stations 54 and 56 in
 the central part of the lake.  In October,  average diversity values
were slightly depressed, and scattered values less than 2.0 were found
at stations throughout the central portion of the lake and at a few
 stations near shore.   Average diversity values remained over 2.0 in
samples collected during November 1972.   Significantly lower values
were found at a group of stations in the northwestern sector of the
lake running from the Toronto vicinity to near mid-lake, and at a
group projection from stations 72 and 73 east of Rochester northward
into the lake.  The former pattern was quite similar to that found in
the August  samples.  In February 1973, the only samples which had cal-
culated diversities less than 2,0 were mid-lake stations 46 and 77
and station 60 near Rochester.  In March, diversity values less than
2.0 were restricted to certain stations near the southern shore,
Included in this group were stations 89,  90 and 105 in the Oswego-
Mexico Bay vicinity,  station 60 near Rochester,  and station 30 east of
Niagara.   A somewhat similar case was apparent in the April samples.
                                   128

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                          MflT  15-19,  1972
  lowrno
                                      ROCHESTER
                          JUNE 12-16.  1972
                                       KOtSTER
FIG.  14.  Assemblage diversity  (Shannon-Weaver index)
                                  129

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                           JULY  10-14,   1972
   TORONTO
HfWVTCN
                                        ROQtSTEfl
                          RUGUST 21-24,  1972
   TORONTO
                                       TOCHESTER
FIG.  14 continued.
                                  130

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                        OCT  30 -  NOV  3.   1972
                                        \
\
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— -— _ .
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WWU1
    ,3.00







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                                      ROOCSTER
                        NOV  27 -  DEC  1.  1972
   TORONTO
FIG. 14 continued.
                                  131

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                         FEBRURRT 5-9,  1973
   TOROmO
             IUVD1
                         MflRCH  19-22.  1973
   TDFIONTO
IBOl.
                                      ROQtSTER
FIG.  14  continued.
                                  132

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                         RPRIL  24-28.  1973
   TORONTO
   TORONTO
                           JUNE  11-14.  1973
             now
\
\
\
v
\
v>
                                                                 >OSHEGO
                                        ROQCSTE8
,3.00






 \0
FIG. 14 continued.
                                  133

-------
 The only samples from this cruise having diversities less than 2.0 were
 collected at nearshore stations 42,  60 and 72 in the Rochester vicinity
 and station 1,  north of Hamilton.   In June 1973  a rather dramatic  rever-
 sal of the usual pattern,  somewhat similar to the case found  the previous
 July,  was noted.  Average  assemblage diversities declined substantially,
 and the only samples having diversities greater  than 2.0 were collected
 at nearshore stations,  and primarily in areas which,  on the basis  of
 our other results,  appear  to be significantly enriched.   Included  in
 this group were stations 8 and 19  near Toronto,  station 30 east of
 Niagara,  stations 42,  59,  60 and 72  in the Rochester vicinity,  station
 105 in Mexico Bay,  and  a group of  6  stations  in  the  northeastern part
 of the lake.
Aveal Distribution of Selected Species

In  the  following  section, data on  the distribution of certain species
and higher  classification groups in the near-surface waters of Lake
Ontario are presented.  We have attempted  to select those entities
which are either  particularly abundant in  the phytoplankton assemblage
or  whose occurrence may be indicative of particular water quality con-
ditions.  Data are based on samples from 1 m depth.  A brief discussion
of  the  ecological affinities of the entities treated is given along
with discussion of their abundance trends  in Lake Ontario.
Bacillariophyta

Asterionella Jbrmosa Hass.  (Fig, 15).  This species is one of the most
ubiquitous of all freshwater plankton diatoms.  It is present in nearly
all areas of the Laurentian Great Lakes.  Slight morphological differ-
ences suggest that there may be strain differences in populations
occurring in areas with grossly different nutrient supplies, but
recent revision of the genus (Koerner 1970) retains A. formosa as a
single species,  Hohn's (1969) study of plankton diatom populations
in Lake Erie suggests that this species did not drastically change in
absolute abundance during the period that Lake Erie underwent drastic
apparent reduction in water quality.  It was, however, reduced in
relative abundance.  Apparently this species can tolerate considerable
eutrophication and is favored by increased nutrient levels.

During the IFYGL sampling period on Lake Ontario it was present at
most stations sampled throughout the year.  During the May 1972 cruise,
highest populations were noted at stations relatively near shore.
Although still abundant in June of the same year, highest population
levels were noted at mid-lake stations.  Overall abundance of this
species was considerably reduced by July, although fairly high counts
were noted at a few offshore stations.  Populations reached and re-
mained at low levels during August and October 1972.   Slight increases
were noted during the November 1972 and February 1973 cruises.  The
earliest indication of a spring bloom of this species was considerably
                                   134

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                              MfiY  15-19.   1972
    TORONTO
tWILTON
             NIAGARA
              WVEft
                                           ROCHESTER
    TORONTO
                              JUNE  12-16.  1972
HFK1ILTON
                                           ROCHESTER
 FIG.  15.  Distribution of Asterionella formosa.
                                      135

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     TORONTO
 HRMILTON
              NTRGflRfl
               RIVER
                                JULY  10-14.   1972
                                             ROCHESTER
    TORONTO
HflMILT
             NJflCflfift
              RIVtft
                              RUGU3T 21-211.  1972
                                            ROCHESTER
 FIG.  15 continued,
                                       136

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    TORONTO
HRMILT
                           OCT  30  - NOV  3.  1972
                                           ROCHESTER
    TORONTO
             NIRGHW
              RIVER
                           NOV  27  -  DEC  1,  1972
                                            ROCHESTER
 FIG. 15  continued,
                                       137

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                             FEBRURRY 5-9.  1973
    TORONTO
MW1ILTON
              RIVER
                                           ROCHESTER
                             MRRCH  19-22.   1973
    TORCNIO
HflMILT
             NlfiGRRfl
              Rivtn
                                           ROCHESTER
FIG.  15  continued.
                                      138

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    TORONTO
HHIILTON
              NIflGfWt
              RIVER
                              RPRIL 24-28.  1973
                                             ROCHESTER
    TORONTO
HRMILTON
              NlflGRRfl
               RIVER
                               JUNE 11-114.  1973
                                             ROCHESTER
FIG.  15 continued.
                                        139

-------
 elevated  population densities noted  at  stations  in Prince  Edward  Point
 area during  the February sampling period.   During  March  1973,  popula-
 tion densities  of A, fovmosa remained high  at  stations in  this region,
 and  similarly elevated  levels were noted at a  few  other  nearshore
 stations.  By the April 1973 sampling interval, very  high  population
 levels were  found at most stations relatively  near shore.  As  in  the
 previous  year,  by June  1973  populations were significantly reduced at
 nearshore stations,  although remaining high in the south central  part
 of the lake.
Coscinodiscus subsalsa Juhl.-Dannf.  (Fig, 16).  If a  single diatom were
to be chosen as being indicative of  extreme disturbance in the
Laurentian Great Lakes,  this species would be a prime candidate.  It
is apparently tolerant of extreme levels of nutrient  enrichment and
conservative element contamination.  In Lake Erie it  is one of the
species which have shown the greatest increase between the 1938-1940
period and 1965 (Hohn 1969).  According to Bonn's results it was
exceedingly rare in Lake Erie prior to 1950.  Although present in Lake
Michigan, its distribution is almost entirely restricted to polluted
harbors and adjacent nearshore areas (Stoermer and Yang 1969),  Even
in highly disturbed areas its numerical abundance is  not particularly
great compared to some of the other pollution-tolerant taxa, but
because of its relatively large cells it contributes  considerably to the
biovolume of the assemblage (Hohn 1969).

Unlike most diatom species,  C.  subsalsa apparently requires relatively
high temperatures for maximum growth, and population maxima usually
occur in the late summer and fall.  During the IFYGL  sampling period
on Lake Ontario this seasonal preference was quite evident.  During
the May 1972 cruise it was found at a single station  in Mexico Bay.
In the June 1972 samples it was detected at two stations, also in the
eastern part of the lake.  In both cases population levels were very
low.   In the July 1972 samples, higher populations were found at two
stations in Mexico Bay and by August at all stations  east of Oswego
and Pt. Petre.   This species was detected also at stations 72 and 73
east of Rochester and 49 and 66 in the Presqu'ile Bay - Scotch Bonnet
Lt. area.  The latter pattern is particularly interesting since it is
repeated in the November results.   Samples taken during October 1972
showed a reduction in the number of stations occupied by C,  subsalsa,
but relatively high population levels were still present at some
stations in the eastern part of the lake.  A similar pattern was noted
in the November 1972 samples.  In February 1973 this species was noted
at a single station near Niagara and only at a few scattered stations,
primarily in the eastern part of the lake,  in March and April 1973.
The only apparent consistency in these months was its occurrence at
station 90 near Oswego.   It was not noted in our June 1973 samples.
Diatoma tenue var. elongation Lyngb. (Fig. 17),  Available information
suggests that this species was introduced into the waters of the
                                   140

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    TORONTO
HflHILTl
             NIRCflflfl
              RIVER
                              MflT  15-19.  1972
                                           ROCHESTER
    TORONTO
             NIHCflRR
              RIVCR
                              JUNE  12-16.  1972
                                           ROCtCSTLB
FIG. 16.   Distribution of  Coscinodisous subsalsa.
                                      141

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     TORONTO
HftHILT
              NlflCHW
              RIVER
                               JULY  10-14,  1972
                                            KJCWESTEB
    TORONTO
HBMILT
             NIfiGflRfl
              RIVER
                             RUGUST 21-24,  1972
                                           ROCHESTER
FIG.  16 continued.
                                      142

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    TORONTO
HflMILTi
              NlflCR'V)
               RIVER
                             OCT 30  -  NOV 3,   1972
                                              ROCHESTER
    TORONTO
HRHIL.T
              NlftGflflfl
               RIVER
                             NOV  27  -  DEC  1.  1972
                                              ROCHESTER
 FIG.  16 continued.
                                         143

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   TORONTO
            NJBCflRfi
             RIVER
                           FEBRUflRY  5-9,  1973
                                         ROCHESTER
   TOftWTO
           NlfiGFW
            RIVEfl
                           MRRCH  19-22.  1973
                                        ROCHESTER
FIG. 16 continued.
                                    144

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     TORONTO
              NlfiGfWfl
               RIVER
                              flPRIL  24-28,   1973
                                             ROCHESTER
    TORONTO
HflMILTl
             NIAGARA
              RIVER
                               JUNE  11-114,  1973
                                            ROCHESTER
FIG.  16 continued.
                                       145

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     TORON10
 HH1IUON
                               MfiT 15-19,   1972
                                           ROCHESTER
    TORONTO
HRMtLTON
             NIRGFttA
             RIVtfi
                              JUNE  12-16,  1972
                                           ROCHESTER
 FIG. 17.  Distribution of Diatoma tenue var. elongation.
                                       146

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    TORONTO
                               JULY  10-14,   1972
                                                       \   v     \
HM1IUON
              NIRGflRR
              RIVER
                                            ROCHESTER
    TORONTO
MfiMILTON
             NIRGfiflfl
              RIVtR
                             RUGUST  21-24,   1972
                                            ROCHESTER
 FIG.  17  continued.

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     TORONTO
MRMILT
              NIRGflRfl
               RIVER
                             OCT  30 - NOV  3.   1972
                                              ROCHESTER
    TORONTO
HflMILTON
              NJRGflRft
               RIVER
                             NOV  27  -  DEC  1,  1972
                                              ROCHESTER
FIG.  17 continued.
                                        148

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    TORONTO
HfiNILION
             NIRGRRfl
              RIVER
                             FEBRURRT  5-9,  1973
                                            ROCHESTER
    TORONTO
HflNILTON
             NIRGflRfi
              RIVER
                             NRRCH 19-22,  1973
                                            ROCHESTER
FIG.  17 continued.
                                      149

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HflHILTON
             NIRGflftH
              RIVER
                              nPRIL  24-28,   1973
                                            ROCHESTER
    TORONTO
                              JUNE  11-14,  1973
HflMILlOH
             NIRGKVt
              R1VIR
                                           ROCHESTER
FIG. 17  continued.
                                      150

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Laurentian Great Lakes only after a considerable degree of disturbance
had taken place.  Hohn (1969) lists it among the species which were
absent or only rarely noted in historic collections from Lake Erie but
which has become a major dominant in the past few decades,  Similarly,
Stoermer and Yang (1969) did not find it in very early collections from
Lake Michigan although it was present there as early as 1932 (Ahlstrom
1936) and became abundant as early as 1946,  At the present time it
occurs throughout Lake Michigan and is especially abundant in nearshore
waters and in polluted harbors.  It has been widely reported from Lake
Ontario (Nalewajko 1966; Michalski 1968; Reinwand 1969; Munawar and
Nauwerck 1971).  Most of these authors report D, tenue var. elongation
as being particularly abundant in winter and early spring collections.

Like many species with similar patterns of occurrence in the Great Lakes,
D. tenue var. elongation appears to be favored by elevated levels of
conservative ions (Huber-Pestalozzi 1942) as well as nutrient pollution.

In samples collected during our May 1972 sampling cruise, low level
populations of this species were noted, particularly at nearshore
stations.  Population densities exceeded 100 cells/ml in only one sample,
from Mexico Bay, collected during this cruise.  Increased population
densities were noted in collections taken during June, particularly at
stations east of a line from Oswego to Point Petre.  A continued
increase was noted in collections taken during July, with a tendency
for highest population densities to occur in the southern half of the
lake.  By August these populations had been considerably reduced and
remained at low levels during the October and November 1972 and
February and March 1973 cruises.  In April 1973, one population exceeding
100 cells/ml was noted in the eastern part of the lake, and there appeared
to be a general increase in the population density at nearshore stations.
As had been the case the pervious year, D. tenue var. elongation bloomed
at stations in the eastern part of the lake in June 1973.
Fragilaria aapueina Desm. (Fig. 18).  The world distribution records of
this species suggest that it is primarily a littoral species which can
become important in the plankton of eutrophic lakes (Huber-Pestalozzi
1942).  Hohn (1969) reports that it has become a dominant in western
Lake Erie since 1950 and may comprise as much as 90% of the total phyto-
plankton assemblage at certain stations in the island area of  that lake.
According to Stoermer and Yang (1969), low level populations were pre-
sent in historic collections from Lake Michigan, however abundant
occurrences are largely restricted to highly eutrophied areas  such as
certain harbors and southern Green Bay.  It has been noted as  being
abundant in Lake Ontario by some investigators (Nalewajko 1966; Reinwand
1969) but not reported by others.  Michalski (1968) indicates  it is
more abundant in the Bay of Quinte than in Lake Ontario proper,  Its
tendency to occur  in very large colonies leads to large uncertainties
in  estimates of its abundance made by standard plankton counting methods.

Cnly low population levels of this species were noted in our samples from
                                   151

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    TORONTO
HRKILTON
             NIRGfiRft
              RIVER
                              MflT  15-19,   1972
                                           ROCHESTER
    TORONTO
                              JUNE  12-16,   1972
            NIHGPftR
             RIVER
                                           ftOCHCSTER
  FIG.  18.  Distribution of Fragilaria oapuoi-na.
                                      152

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    TORONTO
fRIILTON
             NIRGRRH
              RIVER
                              JULY  10-14.  1972
                                           ROCHESTER
    TOROKTO
tWULT
             NlRUWl
              RIVER
                             flUGUST  21-2U.   1972
                                           ROCHESTER
  FIG. 18 continued
                                      153

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                             OCT  30 -  NOV  3.  1972
                                 817
    TOROKTO
HRMILTi
              NIRGFfW
              WVER
                                             ROCHESTER
                            NOV  27  -  DEC  U  1972.
    TORONTO
tmUTON
             NlBWtth
              WVEfl
                                             ROCHESTER
  FIG. 18  continued.
                                        154

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HmiLTON
                             FEBRURRY  5-9.  1973
             NlfiGWA
              RIVER
                                           ROCHESTER
    TORONTO
HRMILTON
                            MRRCH 19-22.  1973
             NJRGffiR
              RIVLfl
                                           ROCHESTER
  FIG. 18 continued.
                                     155

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    TORONTO
HHMIUTON
             NIRGRRfl
              RIVER
                             RPRIL  24-28,   1973
                                            ROCHESTER
    TORONTO
                              JUNE  11-1H.  1973
HfltltUON
              RIVES
                                            WJCHESTER
  FIG.  18 continued,
                                       156

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the May 1972 cruise.  In the June samples, high population densities
were noted at a few isolated nearshore stations, although this species
was not particularly abundant at most stations.  The high populations
noted the previous month had declined by July, and only a few low-level
occurrences were noted in collections from that month.  Increased
population densities were noted at several stations in the eastern part
of the lake and at station 2 near Hamilton during the August cruise.
The greatest abundance of F, capueina found during the IFYGL field
sampling period occurred during the October cruise, when very high
populations were found at two stations near the southern shore and
relatively high population densities were noted at several offshore
stations,  In samples from the November 1972 cruise, high population
densities were again restricted primarily to stations nearest shore, and
by February 1973 F. capuaina  was noted only at station 14 near Niagara
and station 90 near Oswego.  In our samples from March 1973, high pop-
ulation densities were noted at stations 79 and 96 in the eastern part
of the lake and minor increases at several other stations.  Further
increases, again primarily at stations nearest shore, were noted in
samples from the April cruise.  In June the number of stations having
high population densities of F. aapuc'ina  decreased, but one abundant
occurrence was noted off shore at station 45.
Fragilaria orotonensis Kitton.  (Fig. 19).  This species is one of the
most common and widely distributed of all freshwater plankton diatoms.
It is apparently able to tolerate a wide range of ecological conditions,
and populations are found in nearly all areas of the Laruentian Great
Lakes.  Some evidence of its adaptability is apparent in Hohn's (1969)
finding that it was one of the species whose absolute abundance had
not changed appreciably in western Lake Erie over the past several
decades.  Stoermer and Yang (1969) have speculated that its apparently
wide range of tolerance may be due to the fact that several races or
cryptospecies are included in the commonly accepted concept of the
species, but firm evidence for this is lacking.

This species was abundant at several stations in the eastern part of
the lake and some nearshore stations, particularly on the northern shore,
on the basis of samples taken during the May 1972 cruise.  Some general
increase in population density was noted during June, again particularly
in the northern half of the lake.  Apparently these populations were
reduced by July, and significant populations were found only at a few
mid-lake stations and two stations in the western end of the lake.  In
August, however, population densities apparently increased again, and
significant populations were found at most stations throughout the lake.
Population levels were reduced in samples obtained during October and
November 1973, although F, cvotonensis remained widely distributed in
Lake Ontario.  This reduction in population density apparently contin-
ued, since only a few low-level populations were found in the February
1973 samples.  Samples taken during March showed slight increases at
a few  stations relatively near shore, and by April significant popula-
tions  were again present at stations in the eastern part of the lake
                                   157

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                                MflY  15-19.  1972
     TORONTO
 HHHILTl
              NJBGflRfl
               RIVEfl
                                            ROCHESTER
    TORONTO
                               JUNE  12-16.   1972
rtPMILT
             NJRGfWR
              BIVEH
                                            ROCHESTER
 FIG. 19.  Distribution  of  Frag-Llavla  erotonensis.
                                         158

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    TORONTO
HfWlLTl
             NIBGflfW
              RIVER
                              JULY  10-14.   1972
                                            ROCHESTER
    TORONTO
                             filiGUST 21-24,  1972
             NIRGfiRB
              RIVER
                                            ROCHESTER
 FIG. 19 continued.
                                         159

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                             OCT 30 -  NOV  3.  1972
     TORONTO
HRHILTi
              NJfiGOFfi
              RIVEfl
                                            ROCHESTER
    TORONTO
NRHILTON
                            NOV 27  - DEC  i.  1972
                                            ROCHESTER
FIG.  19 continued.
                                        160

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    TORONTO
HflMILT
             NlflGflRfl
              RIVER
                             FEBRURRY  5-9,  1973
                                           ROCHESTER
    TORONTO
MRHIU
             NIRGRRfl
              RIVER
                             MRRCH  19-22.   1973
                                           ROCHESTER
 FIG. 19 continued.
                                         161

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     TORONTO
              RIVCR
                              flPRIL  24-28,  1973
                                           ROCHESTER
    TORONTO
                              JUNE  11-14,  1973
HfltllUOC
             NJHGHfW
             RIVER
                                          ROCHESTER
 FIG.  19 continued.
                                       162

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and along the north shore.  High levels of F.  crotonensis were noted at
numerous stations in the June 1973 samples, as in the previous year,


Melosira islandioa 0, Mull.  (Fig, 20),  This species is a common domi-
nant in large temperate lakes.  Although it is apparently not tolerent
of high degrees of eutrophication, it is abundant in most areas of the
Laurentian Great Lakes,  Hohn (1969) indicates that it is not present in
abundance in Lake Erie, and Holland (1968) has shown it is much less
abundant in highly eutrophic regions of Green Bay than it is in the
offshore waters of Lake Michigan.  Nalewajko (1966) found it to be
relatively much more abundant in collections from offshore stations in
Lake Ontario than it was in nearshore stations.  Most literature sources
indicate that Af. -istandioa reaches its maximum abundance at water temper-
atures   less than 12°C, and Munawar and Nauwerck (1971) found it to be
a spring dominant in Lake Ontario.

Sizable populations were present in most of our samples from May 1972,
although there was a tendency for lower populations to be present at
mid-lake stations.  The highest population densities noted during our
study were found in the June 1972 samples.  At this time most stations
sampled had significant populations of Af. •Lstandtaa but there was a
tendency toward reduced population densities at stations near the
American shore, particularly in the Rochester vicinity.  By July,
populations had been strikingly reduced, and this situation continued
through the August, October and November sampling period.  Slightly
increased abundance was noted at some  inshore stations sampled in
February, and the beginning of the spring bloom period was visible  in
our March results.  In 1973, highest population densities were found in
the April samples, although there was  still a clear difference in
abundance between the  mid-lake and shoreward areas at the time the
samples were taken.  In striking contrast to the previous year's
samples, populations of this species had collapsed at all but a few
mid-lake stations by June  1973.


Nitzsohia bacata Must.  (Fig. 21).  Although the reported distribution
of  this species  is primarily restricted  to large,  tropical lakes  (Hustedt
1949), populations occurring in the Laurentian Great Lakes appear to
be morphologically identical to typical  populations.  Although Stoermer
and Yang  (1969)  have recorded this  entity  from a number  of localities
in  Lake Michigan, other reports from  the Great Lakes are  lacking.   So
far as previous  reports from Lake Ontario  are concerned, we suspect
that  this species has  been included under N. aciaularis  which it
somewhat resembles,  and perhaps Synedva  spp. which are  exceedingly
difficult to distinguish  from planktonic Nitzsohias  in  settled pre-
parations.

In  our collections this species was relatively abundant  at nearshore sta-
 tions sampled during May  1972, and  smaller populations  occurred  at  most
offshore stations.   It apparently continued to increase  in abundance at
                                   1.63

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                              MflT  15-19,  1972
     TORorno
             NIRGRRfl
              BJVER
                                           ROCHESTER
                              JUNE  12-16.  1972
    TOHONTO
Hf»MJLT
                                          ROCHESTER
 FIG.  20.   Distribution of Melosira islandica.
                                      16A

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   TORONTO
             N1RG8RP
             RIVER
                             JULY  10-14,   1972
                                           ROCHESTER
    TORONTO
HRMIUC
             NIRGfW
              RIVES
                            RUGUST  21-2»A.  1972
                                           FQCtCSTEK
  FIG. 20 continued
                                       165

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    TOflCWTO
HfltllLTi
             NJRSWfl
              fUVEfi
                            OCT  30 -  NOV 3.   1972
                                            FOOIESTEfl
    TORONTO
WILT
                            NOV 27  - DE!C  1.  1972
                                             ROCHESTER
  FIG.  20 continued.
                                       166

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    TORWTO
MflHILT
            NIRGWfl
             8IVER
                           FEBRUflRT 5-9.  1973
                                          ROCHESTER
    TORONTO
HfifllLTON
                            HflRCH  19-22.  1973
                                          BOOCSTER
  FIG. 20 continued.
                                      167

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    TOfWTO
HAMILTON
             NJBSW
              RIVEfl
                             RPRIL 24-28,  1973
                                            ROCHESTER
    TORONTO
H8WLT
             NIRGPiHR
              FUVEfl
                              JUNE  11-14,   1973
                                           ROCHESTER
 FIG. 20  continued.
                                      168

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    TORONTO
                              MflY 15-19,  1972
             NlRGflHfl
              RIVER
                                           ROCHESTER
    TORONTO
                              JUNE 12-16.  1972
             NIRGHOR
             RIVtfl
                                          ROCMES1ER
FIG. 21.  Distribution of Nitzschia baaata.
                                      169

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                             JULY  10-14.  1972
    TORONTO
WWIUOH
             RIVER
                                         TOCHESTEfl
                           HUGUST 21-24.   1972
    TORONTO
HttlILT
             RIVER
                                         ftOOCSTER
FIG. 21 continued.
                                     170

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    TORONTO
WILT
             NIRGFBR
              RIVER
                           OCT  30  - NOV  3.  1972
                                            ROCHESTER
    TORONTO
               RIVER
                            NOV 27 -  DEC  1.  1972
                                             ROCHESTER
 FIG. 21 continued.
                                        171

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                              FEBRURRT  5-9,   1973
     TORONTO
 tiflrilLTi
              NIRGflRP
               RIVEB
                                            ROCHESTER
     TORONTO
                             MflRCH 19-22.  1973
 HRNtLTi
                                           ROCHESTER
FIG. 21 continued.
                                     172

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    TORONTO
                            RPRIL 24-28.  1973
             NIRCWtfl
             RIVER
                                           ROCHESTER
    TORONTO
tlfifllU
             NlRGRflfl
              RIVER
                              JUNE  11-14.  1973
                                           fWCMESTER
FIG.  21 continued.
                                       173

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 most stations sampled during the June cruise,  and populations were present
 at most stations except a series off shore in the southern half of the
 lake.   This particular pattern was seen in several other species.   By
 July,  populations had drastically declined and only low-level populations
 were noted at scattered stations.   This trend  continued  into  August,
 when occurrences of this species were very scarce.   Abundance of ff.
 baeata increased again in October,  particularly in the far western end
 of the lake,  and scattered occurrences were noted in samples  taken
 during 1972 and  February 1973.   In March,  population densities increased
 markedly at a few stations in  the eastern  end  of the lake,  and there
 was a  slight  tendency toward higher numbers at stations  throughout the
 lake.   Populations peaked at stations throughout the lake in  April 1973,
 but began to  decline again, particularly at stations in  the eastern
 half of the lake,  in June.


 Nitz8ehia dissipata  (Kutz.) Grun.  (Fig.  22).   One of the most  common
 and widely distributed  members  of  the genus, N,  dissipata,  seems to be
 particularly  abundant in the phytoplankton of  the Laurentian  Great
 Lakes.   Although usually considered to be  primarily a benthic  rather
 than a planktonic  species (Huber-Pestalozzi 1942),  it was reported as
 a  major species  in some localities  in western  Lake  Erie  (Hohn  1969) and
 is apparently widely distributed  in Lake Michigan (Stoermer and  Yang
 1969).   According  to Stoermer and Yang's study it was not noted  in
 collections taken  prior to  1937.  Its wide distribution  in the offshore
 waters  of  the Great  Lakes is somewhat surprising,  since  some authorities
 consider it to be  primarily a species of eutrophic  habitats, and high
 population densities to be  indicative of organic pollution (Cholnoky
 1968).   It has previously been  reported  as being common  in certain
 localities in Lake Ontario  (Nalewajko 1966; Reinwand  1969).

 Although never among  the major  dominants in our  collections, this
 species  is rather  consistently  present and  displays  a distinct seasonal
 pattern.   It  was present  in relatively high numbers  in collections taken
 during May 1972, and  slightly reduced in samples taken during  the  June
 cruise although  it was  still present  at  the majority of  the stations
 sampled.   In  July, the  abundance of N. dissipata was severely  reduced
 and  occurrences were  largely restricted  to  stations  nearest shore.  This
 trend continued during  August,  with only one significant  population, at
 station  60 near Rochester, and  a few  isolated  occurrences at nearshore
 stations.  Somewhat  increased numbers were  noted  in  samples taken during
 October, and  populations were noted at several offshore  stations although
 highest  abundance was still restricted to  nearshore  stations.  Approxi-
mately the same pattern continued during the time period covered by the
 November 1972 and  February  1973 cruises, but there  appeared to be  less
 difference in population density  of  this species near shore compared  to
 mid-lake stations.  A distinct  increase  in the abundance of fj. dissipata
 was noted in  collections taken  during March, and this trend apparently
 continued into April.   By the time  stations were sampled  in June,  popula-
 tions  appeared to  be on the wane again and  population densities were,  in
 general, lower than  they had been the previous year.
                                   174

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    TORONTO
MRfirLTi
             NIRGRFW
              BIVEfl
                              MflY  15-19,   1972
                                            ROCHESTER
    TORONTO
HflMIU
                              JUNE 12-16.  1972
             NIRGflftR
              RIVER
                                            ROCHESTER


 FIG.  22.  Distribution of  Nitzsehia dissipata.
                                      175

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    TOROMO
HfWILTi
              NIRGfiflfl
              RIVEfl
                               JULY  10-1U.  1972
                                             ROCHESTER
    TOBOOTO
HBttlU
                              RJGUST
                                             ROCHESTER
 FIG. 22  continued.
                                        176

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    TOROhfTO
HRHILT
                          OCT  30  - NOV 3.   1972
                                         ROCHESTER
    TORONTO
                          NOV 27 -  DEC  1.  1972
HflWU
FIG. 22 continued.
                                    177

-------
                              FEBRURRY  5-9,  1973
     TORONTO
HflMILT
              NIBGftRfl
              RIVER
                                            ROCHESTER
    TORONTO
                             MflRCH  19-22.  1973
MflMJLTON
             NIRGWIfl
              RIVER
                                            ROCHESTER
FIG.  22 continued.
                                       178

-------
    TORONTO
HfltllLTC
             \
              RIVER
                            RPRIL  24-28.  1973
I

1
\
1 \
V
V V
\ -
\ \
\
\ \
i
^" \ v
                                           POCHtSTER

                                                                      i-OSHEGO
,25.00
    TORONTO
                              JUNE  il-14,  1973
                                           POCHE3TW
 FIG.  22 continued.
                                       179

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Nitzschia  sp.  (#2)  (Fig.  23).  This unidentified  species of Nitzsohia,
although never particularly abundant,  is apparently widely distributed
in  the phytoplankton of the Great Lakes.   Stoermer and Yang  (1969) have
recorded it from a  variety of  localities in Lake  Michigan and our obser-
vations indicate that it  is also present in the other lakes.  It some-
what resembles N. linearis Wm. Smith,  and  some records of N. lineavis
from the offshore waters  of the lake may refer to the entity we treat
here.  Despite its  consistently low levels of absolute abundance, the
distribution of this species appears to be quite  uniform and, because
of  its relatively large size,  it probably  makes an appreciable contri-
bution to  the biomass of  the sparse winter phytoplankton in Lake
Ontario.

A number of populations of this species were noted in collections
taken during the May 1972 cruise.  Population densities decreased
somewhat in our June samples,  and there appeared  to be a trend of
higher population densities in the western part of the lake.  Only
isolated low-level  occurrences were found  in the  July and August
samples.   Occurrences were noted at a  larger number of stations sampled
during August although population densities remained relatively low.
Increased  population densities were noted  at a number of stations
sampled during November 1972, and this trend was  apparently continued
in  February 1973 despite  the pronounced minimum in total phytoplankton
density which occurred this month.  Further increases in the abundance
of  this species were noted at most stations sampled on the March
cruise, and the highest population densities found at any time during
the IFYGL  sampling period occurred at stations taken during the April
1973 cruise.  The extremely high population densities noted the pre-
vious month had apparently been substantially reduced by the time the
June 1973  samples were taken, however significant populations of this
species were still present at a number of  stations.
Stephanodisous alpinus Hust. (Fig. 24).  The ecological affinities of
this species are difficult to determine because of the taxonomic
confusion which surrounds it.  It is apparently often confused with
S. astraea and its varieties and to a certain extent with smaller
species such as S. tenuis.  According to Hohn (1969) it is one of the
species which have undergone dramatic increase in Lake Erie in recent
decades.  According to Stoermer and Yang (1969) it has been present
in Lake Michigan since the 1880*s and has not enjoyed any great increase
in abundance during the period of record.  Their results indicate that
it is primarily a winter form in Lake Michigan.  Previous records from
Lake Ontario are lacking.

Isolated populations of S. alpinus were noted in collections taken
during the May 1972 cruise, particularly at mid-lake stations.  Popula-
tions apparently declined by June and remained low during July and
August.  Populations began to increase again in October.  After a slight
apparent decrease in November, population densities of S.  alpinus
increased again in February 1973 and reached their highest levels in
                                   180

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    TORONTO
HHHILT
             NlflGfWfl
              RJVER
                               MRY  15-19,  1972
                                            ROCHESTER
    TOftOKTO
                              JUNE  12-16,  1972
HRHn.7
             NIRCflRfl
              RIVER
                                            ROCHESTER


 FIG. 23.   Distribution  of Nitzsahi-a  sp,  (#2).
                                      181

-------
    TORONTO
HfiHILT
                             JULY  10-14.  1972
                                          ROCHESTER
    TORONTO
HflMILT
              RIVER
                            RUGLJST  21-24,   1972
                                          ROCHESTER
FIG.  23 continued
                                     182

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    TORONTO
HRHILTi
              NIBCflRfl
               RIVER
                             OCT  30  -  NOV 3,  1972
                                              ROCHESTER
    TORONTO
HRHILTi
              NlRGfW)
               RIVEfl
                             NOV 27  -  DEC  U  1972
                                              ROCHESTER
  FIG. 23  continued.
                                        183

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    TORONTO
HfiMILTI
             NIMflRB
              RIVER
                             FEBRURRY  5-9,  1973
                                           ROCHESTER
    TORWfTO
                             MRRCH  19-22,  1973
HRMILTON
              RIVER
                                           ROCHESTER
 FIG.  23 continued.
                                      184

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      TORONTO
 HflMILTi
              NIflGfiRfl
               RIVER
                              RPRIL  24-28,  1973
                                                                  73
                                            ROCHESTER
    TORONTO
HflMILT
                               JUNE  11-14,  1973
                                           ROCHESTER
 FIG.  23  continued.
                                     185

-------
                               MRT 15-19,   1972
     TOftONTO
 HRHIL70N
             NJPGW
              RIVER
                                           ROCHESTER
    TORONTO
HflMIUON
             RIVER
                              JUNE  12-16,  1972
                                           ROCHESTER
 FIG. 24.  Distribution of Stephanodiscus alpinus.
                                     186

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     TORONTO
 MPMILTi
              NlfiCHW
               RIVER
                                JULY  10-m,  1972
                                            ROCHESTER
    TORONTO
MflMILTl
              RIVER
                             fiUGUST  21-24,   1972
                                            ROCHESTER
  FIG.  24 continued.
                                      187

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                             OCT 30  - NOV  3,   1972
     TORONTO
HAMLTi
              HI WWW
               RIVER
                                             ROCHESTER
    TORONTO
HRMILTl
             NIRGflflfl
              RIVER
                            NOV  27 -  DEC  1.  1972
                                             ROCHESTER
  FIG. 24  continued,
                                        188

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    TORONTO
HRMILTON
             NIRGHW
              RIVER
                            FEBRURRY  5-9,   1973
                                           ROCHESTER
    TORONTO
HflMILTON
                             MRRCH  19-22,  1973
             N1RWRA
              WVER
                                           ROCHESTER
  FIG.  24  continued
                                        189

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     TORONTO
 HRHrUON
              NJflGRRR
               RIVER
                              RPRIL  24-28.  1973
                                            ROCHESTER
    TORONTO
NRHIUON
             macaw
              RJVER
                              JUNE 11-14.  1973
                                           ROCHESTER
  FIG.  24 continued.
                                      190

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samples taken during March.  In April, population densities declined
drastically except at a few stations in the western part of the lake,
and by June this species was essentially absent.  5. alpinus is,  thus,
one of the few taxa present in Lake Ontario which shows a consistent
increase in absolute abundance during the winter months.


Stephanodisous binderanus (Kutz.) Krieg. (Fig. 25).  The presence of
significant quantities of this species is considered to be indicative
of degraded water quality conditions in the Laurentian Great Lakes.
Hohn (1969) indicates that it increased greatly in abundance in Lake
Erie between 1940 and 1965.  In Lake Michigan it has caused significant
problems at municipal water plants (Vaughn 1961), primarily in the late
winter and early spring.  According to Stoermer and Yang (1969),  S.
bindefanus is not indigenous to Lake Michigan but is now present in the
nearshore waters in considerable abundance during the spring and main-
tains populations in polluted harbors year-round.  Most recent studies
of Lake Ontario phytoplankton indicate that it has been abundant in
recent years.  It is difficult to arrive at a clear picture of recent
and, particularly, historic trends because of the taxonomic confusion
which surrounds most of the smaller species of Stephanodiscus.

Like many of the phytoplankton species which have invaded the Great
Lakes, S. binderartus appears to be favored by both eutrophic conditions
and considerable conservative element contamination (Huber-Pestalozzi
1942).  Some authorities (Cholnoky 1968) consider it to be primarily
a brackish water form.  Our records indicate that its optimum tempera-
ture for growth is around 9°C, and most world distribution records
indicate that it occurs in maximum abundance in the spring and fall.

During the IFYGL sampling period on Lake Ontario, S. bindeixmus was
relatively abundant in samples taken from nearshore stations and stations
in the far eastern part of the lake during the April 1972 cruise.  At
this time it was either present in only low abundance or entirely absent
from mid-lake stations.  In samples taken during June  1972, abundance
declined somewhat in the Rochester-Oswego area and in the far eastern
part of the lake, but very high population densities were noted at
nearshore stations in the northwestern part of the lake and at several
offshore stations.  As was the case with several other species, low
abundance was noted at a group of stations offshore in the southern
part of the lake.  By the time of the July cruise, the high population
densities noted the previous month had collapsed, although low densities
of S. binderanus were still found at most stations sampled.  Only very
low abundance of this species was noted at stations during August.
Slight increases were found during the fall cruises, particularly at
stations in the far eastern part of the lake and at certain nearshore
stations closest to major cities.  Population densities remained low  in
samples taken during February and March 1973, but increased significantly
in April.  A continued increase was noted in samples taken during June
1973, but populations at no time approached the densities reached the
previous spring.
                                   191

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                               MRT  15-19,   1972
     TORONTO
HWILTON
             NJftGflfW
              WEB
                                           MCHESTEB
          1*77
                       2509.
                              JUNE  12-16.   1972
 2723
MflNILTl
             NIflGWA
              RIVER
                                           ROCHESTER
 FIG.  25.  Distribution of Stephanodiscus binderanus.
                                     192

-------
    TORONTO
HfiMILTi
             NIRGflRfl
              RIVER
                               JULY  10-14,  1978
                                            ROCHESTER
    TORONTO
HFtllUON
             HJPGHVt
              WVER
                             RUGUST 21-24,  1972
                                           ROCHESTER
 FIG.  25 continued.
                                      193

-------
                           OCT 30 -  NOV  3.  1972
    TORONTO
HRMU
                                          ROCHESTER
                           NOV  27  - DEC  1,  1972
    TOMKTO
HRMJL70N
             WVER
                                          ROCHESTER
  FIG. 25 continued.
                                      194

-------
    TORONTO
HfiMILTON
              flIVEfl
                            FEBRUARY  5^9.   1973
                                          ROCHESTER
    TORONTO
HPWUON
             RIVER
                            MRRCH  19-22.  1973
                                          WXHESTEB
  FIG.  25 continued.
                                     195

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    TORONTO
HPHIUON
             NIRGSRR
              RIVER
                             RPRIL 24-28.  1973
                                            ROCHESTER
    TORONTO
HAMILTON
              RIVER
                              JUNE  11-14.   1973
                                           ROCHESTER
  FIG.  25  continued.
                                       196

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Stsphanodiscus hantzschii Grun. (Fig.  26).  This species has long been
considered a "form characteristic of strongly eutrophied waters" (Huber-
Pestalozzi 1942), and in the classical European literature it has been
associated with water quality degradation in large, alpine lakes (Hustedt
1930).  Like several other small species of Stephanod-iscus which occur
in eutrophied habitats, it is apparently favored by conservative element
contamination and can tolerate brackish water.  It has been widely re-
ported from the Great Lakes, including the Bay of Quinte (McCombie 1967)
and Lake Ontario, where Munawar and Nauwerck (1971) cite 5. hantzschii
var. pus-ilia as being a characteristic spring bloom form.  However,
confusion regarding its taxonomy makes it difficult to discern consis-
tent patterns in its occurrence.

During the IFYGL sampling period this species was abundant at most
stations sampled during May 1972.  Population densities declined at most
stations sampled during June, and by July high population densities
were largely restricted to a few mid-lake stations.  Only scattered
occurrences of S. hantzsohii were found in samples from the August cruise,
but populations of this species increased again in samples taken during
October.  This trend continued in November, and by February 1973 rela-
tively high population densities were noted at stations near shore
in the northeastern sector of the lake.  By March there appeared to be
a definite spring bloom at stations in the northern and eastern parts
of the lake and an increase in population density at all nearshore
stations.  In our April samples, the very high population densities
noted the previous month declined somewhat, but there was a tendency
toward increase at most offshore stations, and very high population
densities were recorded at stations 20, 35, 36, and 48 along the
northern shore east of Toronto.  Population densities of this species
declined significantly again by the June cruise.
Stepkanodisaus minutus Grun.  (Fig. 27).  This species usually occurs
in the cold season phytoplankton of autrophic or mesotrophic lakes.  As
is the case with other small  species of the genus, distribution records
are difficult to interpret because of taxonomic problems.  Stoermer
and Yang  (1969) indicate that it is common in Lake Michigan and parti-
cularly abundant in eutrophied nearshore areas and harbors.

During the IFYGL sampling period it was present at most stations sampled
during the May 1972 cruise and tended to increase, particularly at
stations  in the northern half of the lake, by June.  Population
densities declined at all except a few mid-lake stations sampled
during July, and by August only isolated low-level populations were
present.  Low population densities continued at all sampling intervals
through February 1973.  In March, however, this species began to
increase, and by April substantial populations were present at most
stations  sampled, with highest population densities occurring at the
shoreward stations.  Counter  to the trend shown by many diatom species,
high  population densities were again noted at stations sampled during
June  1973.
                                   197

-------
twin ON
                              MflY  15-19.  1972
              RIVER
                                          ROCHESTER
    •TORONTO
                             JUNE  12-16.  1972
WMLTON
             NJflGfiRFI
             RIVER
                                          ROCHESTER
  FIG. 26.  Distribution of Stephanodiseus hantzschii.
                                     198

-------
     TORONTO
HRMILIW
              NJRGRfW
              RIVER
                               JULY  10-14,  1972
                                            fiOCMESTER
    TORONTO
                             flUGUST  21-24,   1972
HRMILTON
             HIRGflfW
              RIVER
                                            ROCMESTER
  FIG.  26 continued,
                                       199

-------
                              OCT  30 -  NOV  3,   1972
     TORONTO
HHIILTl
              MIRGRftR
               RIVER
                                              ROCHESTER
    TORONTO
                             NOV 27  -  DEC  1,   1972
MW1ILTON
             NIRGHRR
              RIVER
                                             ROCHESTER
 FIG. 26 continued.
                                        200

-------
    TORONTO
              \
HAMILTON
              NIRGRRft
               RlVtft
     TOWWTO
                               FEBRURRT  5-9,   1973
                                                                                v<
                                                                             e if
               \
\
1
\
r- '
4.
*.
\
'
V 1
X .
tf
ROCHESTER
901
MfiRCH 19-22, 1973 «<>T\
911 \\
\ ^
^Jl— -^^X^-, £
	 ^ — ^ s — L b^
^^A
\
\
^ V
3 V_ \ * \
" — \ \ V
                                                                             >OSHEGO
  \
120.00


  0
                                                                       706
HAMILTON
              NIftGWl
   FIG.  26 continued,
                                               POCHESTER
                                                                                 v<
                                                                      \
>03HEGO
                                           201

-------
                  RPRIL 24-28,  1973
           499
   TORONTO
                         ^\\
HHMILTON
        NIftWWI
         RIVER
                           ROCHESTER
  TORONTO
                   JUNE 11-m. 1973
HflMILTON
                           ROCHESTER
 FIG. 26 continued.
                         202

-------
                               MRY  15-19,   1972
     TORONTO
HftllLTON
             NJfiGfW)
              RIVER
                                            ROCHESTER
                              JUNE  12-16,   1972
    TORONTO
MfniLTON      	

             Nifmw1
              RIVER


                                           ROCHESTER



  FIG.  27.  Distribution of Stephanodiscus minutus.
                                      203

-------
     TORONTO
HAMILTON
                               JULY  10-14,   1972
              HIRGfifW
              RIVER
                                            ROCHESTER
    TORONTO
HAMILTON
                             RUGUST  21-24,   1972
             NJRWTO
              RIVER
                                            ROCHESTER
 FIG.  27  continued.
                                       204

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    TORONTO
HPMILTON
             NIRGFRfl
              RIVER
                            OCT  30 -  NOV  3.  1972
                                             ROCHESTER
    TORONTO
HflhILTON
              NlfiOW)
              RIVER
                            NOV  27 -  DEC  1.  1972
                                             ROCHESTER
  FIG. 27  continued,
                                        205

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    TORONTO
             NlflGRRfl
              RIVER
                             FEBRUflRT 5-9.  1973
                                            ROCHESTER
    TORONTO
                             MflRCH  19-22.   1973
H9HILTON
             NIPCfiRR
              RIVER
                                           ROCHESTER
 FIG. 27 continued.
                                     206

-------
                              fiPRIL 24-28,  1973
                   1093
     •TORONTO
 HRMILTON
              NIRGWft
               PJVtfl
                                            ROCHESTER
                               JUNE  11-11,  1973
HftMtLTON
             HIRGflRB
              RIVER
                                           ROCHESTER
  FIG. 27 continued.
                                      207

-------
 Stephanodiscus subtilis (Van Goor)  A.  Cl.  (Fig.  28).   The distribution
 and  ecology of this  very small and  delicately structured  member  of  the
 genus  is  very poorly known.   According to  Cleve-Euler  (1951)  it  reaches
 its  highest population densities  in highly eutrophic and  "slightly  salty"
 waters.   According to Stoermer and  Yang (1969) it  is abundant  in
 eutrophied  nearshore waters  and polluted harbors around Lake Michigan.
 Apparently  it has not been reported previously from Lake  Ontario although
 it may have been included in counts of other  small members of  the genus.

 In our May  1972 samples, relatively high population densities  of this
 species were found at nearshore stations in the southeastern sector of
 the  lake.   By June this  distribution pattern  had changed  rather  dramati-
 cally, with highest  population densities being found at stations in the
 northern  half of the lake.   On the  basis of samples collected  during
 July,  populations tended to  decrease in the coastal areas in the
 eastern part  of the  lake, while remaining  high at  nearshore stations in
 the western part and  at certain mid-lake stations  in the  eastern part.
 By August population densities were significantly  reduced except at a
 limited number of stations in  the vicinity of Rochester.  Abundance
 remained  rather low  at stations sampled during August, except  for
 stations  2  and 3 near Hamilton.  Relatively low population densities
 of this species were  found at  stations  sampled during November,  and
 this apparent decline continued during  February 1973.  On the  basis of
 samples from  the March cruise,  it appeared that a  nearshore bloom of this
 species was developing, but  this trend  was not evident in the  April
 samples.  The June 1973 samples showed  increased population densities
 of S. subtilis at stations in  the southwestern part of the lake, but
 the abundance of this species  never  approached the levels found  the
 previous spring.


 Stephanodisaus tennis Hust.  (Fig, 29).   This species appears to  be
 associated with highly eutrophied waters in the Laurentian Great Lakes.
 Hohn (1969) lists it  as one  of  the  species which increased greatly in
 abundance in western  Lake Erie in recent decades.  It has apparently
 undergone similar increase in  the eutrophied nearshore regions and
 polluted harbors bordering Lake Michigan (Stoermer and Yang 1969).  On
 the basis of electron micrographs published by workers investigating
 the problem (Vaughn 1961) it appears that this species is, in  fact,
 "the organism tentatively identified at S.  hantzschii" which caused,
 together with S. binderanus3  considerable problems at the Chicago
 filtration plant during the  1960's.  It  has been widely reported from
 Lake Ontario  (Nalewajko 1966,  1967; Michalski 1968; Reinwand 1969;
Munawar and Nauwerck  1971) and on the basis of these reports it appears
 to be consistently a dominant  element of the spring diatom bloom.  Sim-
 ilar to other small species  of Stephanodiscus which have become abundant
 in the Laurentian Great Lakes  in relatively recent years,  this organism
 appears to be favored by elevated levels of conservative ions  as well
 as increased nutrients.

 In our May 1972 samples, population densities were high at stations
                                  208

-------
     TOROfTFO
MfiHIUON
              NJfiGflflfl
              RIVER
                               MflT  15-19,   1972
                                            ROCHESTER
    TORONTO
                               JUNE  12-16,   1972

                                                151]
t«1ILTON
             NJBGORfl
              RIVER
                                            ROCHESTER
  FIG. 28.   Distribution of Stephanodi-saus subtilis.
                                       209

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                               JULY  10-14.   1972
     10?ON70
HH1ILTON
             NlftGffifl
              RIVER
                                            ROCHESTER
HRMILTOM
             NIRGRTtfl
              RIYtR
                             RUGUST  21-24,  1972
                                            ROCHCSTLR
  FIG.  28 continued.
                                      210

-------
 HflMJLlON
                             OCT  30  -  NOV  3,   1972
              NIRGRRft
               WVEft
                                             ROCHESTER
    TORONTO
HflMILTON
             NIRGWW
              RIVER
                             NOV  27 -  DEC  1,   1972
                                            ROCHESTER
  FIG. 28  continued.
                                       211

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     TORONTO
MfiMILTON
             NIRGfifW
              RIVER
                              FEBRURRY  5-9,   1973
                                            ROCHESTER
    TORONTO
HHMILT
             NIftGflflfl
              RIVER
                             MRRCH 19-22.  1973
                                           ROCHESTER
  FIG. 28 continued,
                                      212

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    TORONTO
HAMILTON
             NIRGWfl
             MVER
                            RPRIL  24-28,  1973
                                          ROO1ESTW
    TOfWfOO
                             JUNE  il-14.  1973
HAMILTON
                                          ROCHESTER
  FIG. 28 continued.
                                     213

-------
     TORONTO
             NJflGHW
              RIVER
                               MflY  15-19,  1972
                                            ROCHESTER
    TORONTO
HfiMIUON
             NlflGRRft
              RIVER
                              JUNE  12-16,  1972
                                           ROCHESTER
 FIG.  29.  Distribution of Stephanodisous tennis.
                                     214

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     TORONTO
 HPHILTON
             NJRGRRB
              RIVES
                               JULY  10-14.  1972
                                            ROCHESTER
    TORONTO
HRHIL10N
              RIVER
                             RUGUST  21-24,  1972
                                            IWCMESTER
  FIG.  29  continued.
                                      215

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     icwwno
HftMILION
              NIflGflfifl
               RIVER
                             OCT  30  -  NOV 3.   1972
                                             ROCHESTER
    TORONTO
HflMIUQN
              MlflGKVl
              RJVER
                             NOV  27 -  DEC  1,  1972
                                             ROCHESTER
 FIG.  29 continued.
                                       216

-------
    TOWJNTO
MH1ILTON
             NlftCfiRH
              RIVER
                             FEBRURRT  5-9,   1973
                                           ROCHESTER
    TORONTO
HflHILTON
                             MRRCH  19-22.   1973
             NIftGWW
              RIVtR
                                            ROCHESTER
 FIG.  29 continued.
                                       217

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                                                                 I3JJ
     TORONTO
HHMILTON
              RIVEft
                              RPRIL  24-28,  1973
                                    ,077         "C   1148
                                            ROCHESTER
                               JUNE  11-14,  1973
HAMILTON
              RIVCR
                                            ROCHESTER
  FIG. 29 continued.
                                       218

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 nearest  shore in the  southeastern  sector  of  the  lake  and very  low at most
 stations.   By the June  sampling  period  somewhat  elevated counts were
 noted  at offshore stations,  but  the  very  high population densities noted
 at nearshore stations the  previous month  had been drastically  reduced.
 Populations continued to decline except at a few nearshore  stations
 between  Hamilton and  Toronto in  July, by  August  only  a  few  low level
 occurrences were noted.  During  the  October  cruise, increased  population
 densities were noted  at several  stations  in  the  western end of the lake,
 but by the November cruise only  very low  population densities  were pre-
 sent at  the stations  sampled.  A slight increase in the abundance of this
 species, particularly in some of the stations nearest shore, was found
 in the February 1973  samples in  spite of  reduced total  phytoplankton
 abundance during this month.  Samples taken  during March 1973  indicated
 the beginning of a nearshore spring  bloom of this species,  particularly
 at station 60 near Rochester,  and  by April very  high  population densities
 were found at most nearshore stations in  the eastern  half of the lake.
 Population densities  were  significantly reduced  at all  stations sampled
 during June, except'stations 7 and 8 near Toronto.

                    IT
 Surirella angusta Kutz.  (Fig.  30).  The abundance and wide  distribution
 of this  species in the  phytoplankton of Lake Ontario  is extremely unusual.
 Although several species of the  genus are successful  in the plankton of
 large  lakes, most previous studies would  indicate that  S. angusta  is
.primarily benthic in  habitat preference.   Skuj-a(1956) lists it in  his
 discussion of the Swedish  limnoplankton,  but emphasizes that it  is very
 rare and probably accidental in  such collections. Huber-Pestalozzi
 (1942) does not even  mention it  in his  extensive treatment  of  the
 planktonic members of the  genus.  Stoermer and Yang  (1969)  list  it  from
 a number of localities  in  Lake Michigan,  but always  in  very low abun-
 dance.  Hohn (1969) lists  it as  occurring in Lake Erie, but does not
 indicate that it was  particularly  abundant in his collections. Previous
 investigations of Lake  Ontario phytoplankton (Munawar and Nauwerck  1971),
 however, list it as one of the major winter  dominants.  Although  the
 population densities  achieved by this species are not particularly great,
 it may be of considerable  ecological importance  because of  its relatively
 great  cell volume and because it is  apparently most  abundant when  other
 species  are at their  yearly minimum. The factors which allow this
 species, which is usually  associated with benthic habitats  in eutrophic
 systems, to become important in  the  plankton community  of Lake Ontario
 are not  readily apparent.

 In our collections from May 1972,  S. angusta was present  at most  stations
 and quite abundant at many offshore  stations.  It declined  drastically  in
 the June samples and  remained very scarce in the July and August  collec-
 tions.  Slightly increased population levels were noted in  October col-
 lections, particularly at  stations relatively near  shore.   This trend
 continued in the November  collections,  and into February  1973, when
 total  phytoplankton abundance was  at its yearly low.   Population densities
 of this  species remained relatively high in our March collections,  and
 reached  their seasonal peak in  April 1973.   By June 1973,  population
                                    219

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                              MflY  15-19,  1972
     TORONTO
 HWIUT
                                           ROChESTEfl
    Tonomo
WHIUTON
             NTfiGflflfl
              RIVER
                              JUNE  12-16.  1972
                                           POCHCSIEfl
FIG. 30.   Distribution of
                                      220

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    TOfWIO
hRMTLT
             NJPCfWfl
              RIVER
                              JULY 10-114.   1972
                                           ROCHESTER
    TWWIO
MWILT
                            flUGUST 21-214.  1972
                                           WJCHESIEfl
FIG. 30 continued.
                                      221

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      TORONTO
 HWITUtl
               NIRGRfW
                RIVER
                              OCT  30  -  NOV  3.  1972
                                               ROCHESTER
     TORorrro
 tlflttlU
               NlRGftflfi
                PIVER
                              NOV 27  -  DEC  1.   1972
                                               ROCHESTER
FIG.  30 continued.
                                         222

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    TORONTO
HPNILT
                           FEBRURRT  5-9,  1973
                                         ROCHESTER
    TORONTO
                           MflRCH  19-22,  1973
            MIRGfWl
             RIVER
                                          ROCHESTER
 FIG.  30 continued,
                                      223

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                              RPRIL  24-28,   1973
     TORONTO
              NJRGflRP
               RIVER
                                            ROCHESTER
     TORONTO
 HflNILT
              N1RGHW
              RIVER
                               JUNE  11-14,  1973
                                            ROCHESTER
FIG. 30  continued.
                                       224

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levels had been reduced again to insignificant levels.
Synedra ostenfeldii (Krieg.) A. Cl. (Fig, 31).  This species is one of
the planktonic members of the genus which regularly occurs in colonies
under optitnal growth conditions.  Individual cells are also found,
especially following periods of peak abundance.  The distribution and
ecological affinities of this species are relatively poorly known.
According to Cleve-Euler (1953) it is common in eutrophic lakes and
rivers in Europe.  Stoermer and Yang (1969) indicate that it is widely
distributed in Lake Michigan with highest population densities occurring
in eutrophied nearshore areas.  Apparently it has not been reported
previously from Lake Ontario specifically, although it is undoubtedly
contained in several reports of the genus.

Although S. ostenfeldli was never particularly abundant in our collec-
tions, numerous occurrences were noted, and it seems to demonstrate a
pronounced seasonal pattern of occurrence.  Samples from the first
cruise in May 1972 had few occurrences, although relatively large
populations were noted at a few nearshore stations, particularly in
the southeastern sector of the lake.  Many more occurrences were noted
in June samples, and highest population densities were found at stations
in the eastern part of the lake which had not been sampled the previous
month.  Although occasional occurrences of this species were noted, its
abundance remained low throughout the summer, fall, and winter sampling
cruises.  Samples taken during March 1973 showed slightly increased
numbers, and a definite increase, particularly at stations in the far
eastern part of the lake, was noted during April.  Abundance increased
further in June, with highest population densities occurring at offshore
stations in the southern half of the lake.
Tabellca"ia fenestrata (Lyngb.) Kutz. (Fig. 32).  This species is among
the most common and widely distributed of the freshwater plankton diatoms.
It occurs in abundance throughout the Laurentian Great Lakes and seems
tolerent of most conditions.  According to Hohn (1969) it is one of the
taxa whose absolute frequency has not changed markedly in western Lake
Erie in recent decades, although its relative abundance has decreased
because of the introduction of exotic dominants.  Considerable contro-
versy  surrounds the taxonomy of this taxon (Knudson 1952; Koppen 1973),
and the apparent extreme range of adaptability of this species may be
due to failure to recognize the true genetic entities involved.

During the IFYGL sampling period, this species was present at most
stations in the northern part of the lake during the May 1972 sampling
cruise and at a few other stations near shore.  The same pattern
continued during June, when there appeared to be a well defined zone of
non-occurrence of T. fenestvata at offshore stations in the  southern
half of  the lake.  These populations apparently declined and, by the
time of  the July cruise, high population densities were largely restricted
to a few offshore stations.  The single exception to this was station  19,
                                   225

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     TORONTO
 HRMILTON'
                              MflY  15-19,  1972
                                          WJOCSTEfl
    TORONTO
                              JUNE 12-16,  1972
HW11LT.
                                          ROCHESTER
FIG.  31.   Distribution of Synedva ostenfeldii.
                                   226

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  10RONTO
           NlflWR
           RIVER
                         JULY 10-14.  1972
                                      hOCtCSTEfl
   TORONTO
                         RUGUST  21-24.  1972
FIG.  31 continued,
                                 227

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     TORONTO
 HflMILTi
              NIflSRfW
               RIVER
                              OCT  30  -  NOV  3.  1972
                                              ROCHESTER
    TORONTO
HW1ILTI
              MIRGRHR
               RIVEfl
                             NOV  27 -  DEC  1.  1972
                                              ROCHESTER
 FIG. 31  continued.
                                      228

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    TORONTO
tfltlILT
             NlflGflRR
              RIVER
                             FEBRUflRT 5-9.  1973
                                            ROCHESTER
    TORONTO
MBHILT
             NIflGfWfi
              RIVER
                             MflRCM 19-22,  1973
                                            ROCHESTER
FIG.  31  continued,
                                    229

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    Towro
hFWILTi
             MWWfl
              RIVER
                             flPRIL  24-28.  1973
                                           fttEHESTER
    TORONTO
MBNILTI
             NJRCflflfl
              RIVEB
                              JUNE  11-14.  1973
                                           ROCHESTER
 FIG. 31 continued.
                                   230

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    TORONTO
HRHILT
             NJRGfllW
              RIVER
                              MRY  15-19,  1972
                                           ROCHESTER
    TORONTO
HfiHFUTI
             NJRGfWI
              RIVER
                              JUNE  12-16.   1972
                                            ROCHESTER
 FIG.  32.  Distribution of Tabellaria fenestrata.
                                    231

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                              JULY  10-14.  1972
     TORONTO
             NlftGflflfl
              RIVER
                                           ROCHESTER
                            fiUGUST 21-24,  1972
    TORON10
HflMILTON
                                          ROCHESTER
FIG.  32 continued.
                                     232

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    TORONTO
MRMILT
              NJRGfiRR
              RIVER
                             OCT 30  - NOV  3.  1972
                                             ROCHESTEB
    TOfWWTO
                             NOV  27 -  DEC  1,  1972
hWIILTl
              NIRGWR
              RIVCR
                                             fOCMCSTCO
 FIG. 32  continued.
                                         233

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                             FEBRURRT 5-9,  1973
     TORONTO
             NIRGWW
              RJVER
                                          ROCHESTEB
    TOIWO
HWIILT
                            HfiRCH  19-22.  1973
             NJR'JfW)
             RIVEfl
                                          ROCrCSTCT
FIG. 32 continued,
                                      234

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   TORONTO
             NJRGflRft
             RIVER
                            fiPRIL  24-28.  1973
                                           ROCHESTER
    TORONTO
                              JUNE  11-1H.  1973
HRMtLT
             NJRGflfift
              RIVEB
                                           noctesrcB
 FIG. 32 continued.
                                        235

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 near Toronto.   The decline  in  abundance of T,  fenestrata  continued  into
 August,  vhen  appreciable  population densities  vere noted  only  at  a  few
 aid-lake stations and  stations in  the  far western end  of  the lake.   In
 October, however, population densities again increased at most stations.
 Population densities remained  similarly high in samples taken  during
 November,  however there appeared to be a trend toward  higher abundance
 at  stations in  the southern and eastern sectors of the lake at this
 time.  By  February 1973,  population levels of  T.  fenestrata were  con-
 siderably  reduced, as was total phytoplankton  density,  except  at
 stations 96 and 97 in the far  eastern  part of  the lake.   Reduced
 abundance  was noted also  in samples taken in March and  April,  with a
 tendency for highest population density to occur at  stations nearest
 shore.   Some increase in  abundance  of  T.  fenestrata.  was noted  in
 June 1973  samples, however in  1973  populations appeared to be  higher
 on  the southern shore,  unlike  June  1972.
 Chlorophyta

Ankistrodesmus falcatiie (Corda) Ralfs  (Fig. 33).  Populations of this
 entity in Lake Ontario are somewhat unusual in  that they generally fall
 in  the lower size range commonly attributed to  the species.  Munawar
 and Nauwerck (1971),  in their treatment of Lake Ontario phytoplankton,
 separated A. falcatits var. spiril'Liformi.s G. W. West from the nominate
variety.  All of the populations we have observed, however, tend to be
 intermediate in size and lack the characteristic shape of variety
spirtll-ifornris and we chose to treat them under  the nominate variety.

Ankistrodesmus falcatus has been reported from many areas in the
Laurentian Great Lakes, but high population densities are usually
found only in eutrophied areas.

Low level populations were noted at most stations sampled during the
Hay 1972 cruise,  and  high population densities occurred at several
nearshore stations between Niagara and Rochester.  Population densities
of this species increased at most stations sampled during June 1972.
Highest densities were present at stations in the far western region
of the lake near Hamilton and on the southern shore,  with exception of
the stations near Niagara, where abundance was notably reduced.  In
this month there appeared to be a consistent pattern of low population
densities of this species at stations running from Niagara offshore
in the southern half  of the lake.  Unlike most species associated with
the spring bloom, A.  falcatus never achieved particularly high abun-
dance in the eastern sector of the lake.  Samples taken during July
showed a general reduction in density of A.  falcatus, although signifi-
cant populations were still present at stations nearest shore in the
eastern part of the lake and in Mexico Bay.   Although previous investi-
gations have characterized Ankistrodesmus spp. as summer (Munawar and
Nauwerck 1971) or fall (Michalski 1968) forms, populations were con-
siderably reduced in our August samples and remained at low levels  in
samples taken during the fall and winter cruises.  The same situation
                                  236

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    TORONTO
HBMILT
             NlflCflflfl
              RIVER
                              MflT  15-19,  1972
                                           ROCHESTER
    TORONTO
MflWLTi
                              JUNE 12-16.   1972
              RIVER
  FIG.  33.   Distribution of Ankistifodesmus falaatus.
                                       237

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     TOflCTTO
 HftMJLT
              NJflGflfifl
              RIVER
                               JULY  10-14.   1972
                                            ROCHESTEfl
    TORONTO
HWILTi
             NIflCflflfl
              RIVER
                             flUGUST 21-24,  1972
                                           ROCHtSTER
  FIG.  33  continued,
                                       238

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    Tonowro
BfiMILT!
             KlflCfiflfl
              RIVEfl
                            OCT 30  - NOV  3.  1972
                                            ROCHESTER
    TORONTO
HflhIU
             MJflCflflfl
              flivtn
                            NOV 27  - DEC  1.  1972
  FIG. 33  continued.
                                       239

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     TORONTO
             NJRCfiflfl
              RIVEfi
                             FEBRUflRT  5-9.  1973
                                           ROCHESTER
    TORONTO
HAMILTON
              RIVCB
                             MflRCH  19-22.  1973
                                          ROCHESTER
  FIG.  33 continued.
                                      240

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  TORONTO
           NJflSflflfl
            RIVER
                          RPRIL 24-28.  1973
                                         ROCHESTER
  TORONTO
           NIRGfWfl
            KIVEfl
                            JUNE  11-14,  1973
                                         ROOCSTLR
FIG. 33 continued.
                                      241

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 obtained during the early spring sampling periods in 1973, and it was
 not until June  1973 that a few samples with population densities
 comparable to those found throughout the lake were found at stations
 near Niagara.  If the lake-wide bloom of this species noted the previous
 year was repeated,  this apparently did not take place until after
 termination of our  sampling period.
 Botryoeoccus braun-ii Kutz.  (Fig.  34).   This species has unusual distrib-
 ution,  occurring in both eutrophic and oligotrophic lakes in consider-
 able quantities (Hutchinson 1967).  Mature and scenescent colonies
 accumulate large quantities of fats and oils and tend to float near
 the surface.   This,  plus the fact that mature colonies are quite large,
 leads to uncertainties in estimates of its abundance made by standard
 phytoplankton enumeration methods.  Although the distinctive colonies
 are visible in net  plankton collections taken from almost any locality
 in the  Laurentain Great Lakes during the late summer and fall,  it is
 rarely  reported in  quantitative studies.

 In our  collections  its occurrence was  very restricted.   A single
 occurrence at about  75 cells/ml was noted at station 35 in May.   Aside
 from this,  all other occurrences  noted came from the month of August.
 During  this sampling period  B.  braun-ii was present in considerable
 quantities  at a number of stations sampled,  particularly in the eastern
 and  northeastern parts of the lake.


 Coelastnm micvopovian  Nag.  (Fig.  35).   This species  is  apparently quite
 widely  distributed in  the Laurentian Great Lakes,  but only reaches
 appreciable abundance  in eutrophic regions.   Taft  and Taft (1971)
 reports  it  from western Lake  Erie,  and we have observed it in collec-
 tions from  several localities  in  Lakes Michigan  and  Huron.   In  these
 lakes it occurs  in greatest abundance  in  shallow,  eutrophied  areas
 such as Green Bay and  Saginaw Bay.   It has been  reported  from Irondequoit
 Bay of Lake Ontario  (Tressler  et  al. (1953)  and  as a  spring dominant
 in the open lake by Munawar and Nauwerck  (1971).   Several  other records
of Coelastrwn sp. from Lake Ontario are likely referrable  to  this
 species.

 It was not noted in our collections from  the May and June  1972 cruises,
and only isolated occurrences  in  the opposite ends of the  lake were
noted in July.  By the  time the August  samples were taken, however,
most stations sampled had populations  of C. microporwri, and it was
quite abundant at stations in  the  eastern  half of the lake.  The
population density of this species was  greatly reduced  in  samples
 taken during October, and only a  few populations were found in the
November samples.  A single occurrence was noted in samples taken
during February, and it was apparently absent from samples taken
during March and April 1973.   In June  1973 a single, extremely high
occurrence was noted at station 59 near Rochester.
                                   242

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                             MRT  15-19.   1972
    TORONTO
                          RUGUST  21-24,  1972
HRNIUON
            NJWWW
            wvtn
                                        ROCHESTER
 FIG.  34.  Distribution of  Botvyoooocus bvaunii.
                                   243

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     TORONTO
 HRMLTQN
             NlBOTRfl
              RIVER
                               JULY  10-1U.  1972
                                           ROCHESTER
    TORONTO
                             nUGUST 2i-2U.   1972
HRMILT
             MlflGflftfl
             RIVER
                                           ROCHESTER
 FIG. 35.  Distribution of Coelastrum micvoporum.
                                     244

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    TORONTO
HRMLTi
             NIRGPRfl
              RIVER
                            OCT  30  - NOV  3,   1972
                                             ROCHESTER
    TORONTO
t«1IU70N
              N1WWW
              RIVEft
                            NOV  27  -  DEC  1.   1972
                                             ROCHESTER
 FIG.  35 continued,
                                       245

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     TORONTO
 WMILT
             NJBGPRfl
              RIVER
                              FEBRURRY 5-9,  1973
                                           ROCHESTER
    TORONTO
tWIJLTON
                             MRRCH  19-22.  1973
                                          ROCHESTER
 FIG.  35 continued,
                                   246

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    TORONTO
HfiMILT
             NIflGfflfi
              RIVER
                             RPRIL 24-28,  1973
                                            ROCHESTER
    TORONTO
HRf.tLTON
             NIBGPRft
              RIVtR
                               JUNE  11-14.   1973
                                             ROCHESTER
 FIG.  35 continued.
                                      247

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 Gloeoaystis planctoniaa  (West & West) Leram.  (Fig. 36).  This species has
 been reported from a variety of habitats in  certain regions of Europe
 (Skuja 1956) and, although not widely reported from the Great Lakes,
 we have found it to be one of the more abundant green algae in the
 plankton of Lake Michigan.  Skuja  (1948) has given an excellent account
 of the life cycle stages of this species, and we suspect that some of
 the previous reports of Chlovella spp., Chlamydomonas globosa Snow,
 and Gloeooystis gigas (Ku'tz.) Lag. from Lake Ontario may be referrable
 to it.

 Moderate levels of abundance of this species were noted at stations
 along the southern shore in samples from the May 1972 cruise.   By the
 time of the June cruise it had become widely distributed and populations
 were noted at most stations sampled, although there was a consistent
 pattern of non-occurrence at offshore stations in the southern half
 of the lake east of Niagara.   High population densities were again
 noted in samples from the July cruise,  especially in the southwestern
 sector of the lake and at isolated stations in the eastern part.   An
 extremely high abundance of this species was found at station 14  near
 Niagara at this time.   Somewhat  reduced population densities were
 noted in the August samples,  although the species was still present in
 significant quantities,  particularly at stations in the northeastern
 part  of the lake.   Abundance  of  G.  planatonica declined considerably
 in the October samples,  and only scattered,  low levels of  occurrence
 were  noted in samples  from the November 1972 cruise and from the
 February,  March and April cruises  in 1973.   Slightly increased  levels
 of abundance of  G. ptanctonioa were noted in samples taken during June
 1973,  but  population densities never approached  those found the previous
 spring.
 Oocystis  spp.  (Fig. 37).   The major  population included  in  this  category
 is 0. parva West & West,  although minor  populations  of some of the  other
 smaller species of the genus are present.   Such species  are a ubiquitous
 part of the summer phytoplankton in most parts  of  the Laurentian Great
 Lakes.  In most offshore  regions population levels of Oocystis spp.
 remain at low  levels, although high  population  densities may be
 present in the more eutrophic regions.

 The entities included in  this category showed a pronounced  seasonality
 in our samples.  Scattered, low level populations  were found in May,
 June, and July 1973 samples.  August samples showed a lake-wide  bloom,
 with a trend toward highest population densities in the  eastern  portion
 of the lake.  Abundance of the species progressively declined during the
 October and November sampling periods, and only  scattered,  low level
 populations were found in the 1973 samples.
Pediastrum glanduliferum Benn. (Fig. 38).  Although not widely reported
from the Laurentian Great Lakes, this is apparently a fairly widely
distributed euplanktonic species.
                                   248

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    TORONTO
HRHIUON
             NJRGfttR
              RIVER
                              MRY  15-19,   1972
                                           ROOCSTER
    TORONTO
                              JUNE.  12-16.  1972
MflnlLTON
             NlfWHW
              RIVER
                                           ROCHESTER

 FIG. 36.   Distribution of Gloeooystis planatoniea.
                                       249

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                              JULY  10-14.  1972
          5172
    TORONTO
HAMILTON
             NJRCW
              RIVER
    TOBOKTO
                            RUGUST 21-24,  1972
HfiMILTON
             NIHGWW
             RIVER
                                          nooesien
 FIG.  36 continued.
                                   250

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     TORONTO
 HflMILTON
              NJflGflRft
              RIVER
                              FEBRUflRT  5-9,  1973
                                            TOOCSTER
    TORONTO
                             MflRCH  19-22.  1973
HRHILTON
             NIBGflflfl
              IUVER
                                           ROCHESTER
 FIG. 36  continued,
                                     252

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    TORONTO
HRNILTON
             NIR6HW
              RIVER
                             RPRIL 24-28.  1973
                                            ROCHESTER
    TORONTO
HAMILTON
             NIRGflflft
              RIVER
                               JUNE  11-14,  1973
                                            ROCHESTER
FIG.  36 continued
                                       253

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     TORONTO
 MflrtlLTON
              NIBCWR
               RIVER
                               MRY  15-19,  1972
                                            ROCHESTER
    TORONTO
NFV1ILTON
             NlflCflflfl
              RIVEfl
                              JUNE 12-1G.  1972
FIG.  37.  Distribution of Oooystis  spp.
                                     254

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   TORONTO
            NIAGARA
             RIVER
                             JULY  10-14.  1972
                                          ROCHESTER
   TORONTO
                           RUGUST  21-24.  1972
            NlRGfflfl
             RIVER
                                          ROCHESTER
FIG. 37 continued.
                                       255

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      TORONTO
 MflMILTl
              NJPGftRfl
               RIVER
                              OCT  30  -  NOV 3,   1972
                                              ROCHESTER
MftMILT
             NlflGflflft
              RIVLfl
                             NOV 27  -  DEC  1.   1972
                                             ROCHESTER
 FIG.  37 continued.
                                         256

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    TORONTO
tlWIILTI
             NIPGfWfl
              RIVER
                             FEBRURRY  5-9,  1973
                                            ROCHESTER
    TORONTO
HflMLT
             NIAGARA
              RIVER
                             MRRCH  19-22,   1973
                                            ROCHESTER
 FIG. 37  continued.
                                        257

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      TORONTO
 HfirtlLION
               NJRGflflft
               RIVER
                                RPRIL  24-28,  1973
                                              ROCHESTER
    TORONTO
MftMILTON
             NJBSflfifi
              PI VCR
                                JUNE  11-14.  1973
                                            ROCHESTER
 FIG. 37  continued
                                        258

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    TORONTO
tmt-TON
             NIRGfiflfl
              RIVER
                             JULY  10-14.  1978
                                          ROCHESTER
                            RUGUST  21-2'4.  1972
                                                                       r*/
    TORONTO
                                                                     P it
HflMILTON
             NIRGHW
- • t x .
*• V
~— V v
U"
nrtrurcrra
\
V

k
V

\.
\)
^OSHEGO
,350.00
^0
 FIG. 3& •   Distribution of Pediastvwn glandulifenon.
                                     259

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 Its distribution in our samples from Lake Ontario is remarkably
 restricted,  A single occurrence was noted at station 14 near Niagara
 in July.  In August it was abundant at all stations east of Oswego
 and Pt. Petre and somewhat smaller populations were found at nearshore
 stations ranging west from this region.  No occurrences were noted in
 samples from cruises either before or after these two months.
 Phaootus lenticularis  Ehr. (Fig. 39).  This unusual chlorophycean
 flagellate has not been widely reported from the Great Lakes and
 relatively little is known about its distribution and ecological
 preference.   We have found occasional populations in the in the upper
 lakes but it is usually a minor element of the flora.  It is abundant
 in the summer plankton of some of the larger inland lakes in Michigan.
 In his review of the Swedish freshwater phytoplankton, Skuja (1956)
 indicates that it is widely distributed and is especially abundant in
 the summer.   This tendency is strikingly apparent in our results.

 Significant  populations of this species were not noted in our samples
 from May and June 1972.   In July,  populations were noted at two stations
 In Mexico Bay.   By August it had apparently undergone a lakewide bloom
 since significant populations were found at nearly every station
 sampled during  the August 1972 cruise.   In the rest of the months
 sampled,  relatively small populations were noted with some tendency
 for largest  populations  to occur at  stations in the far eastern part
 of the lake  and  at stations nearest  shore in other parts of the lake.


 Soenedesmus  bioellularis  Chodat  (Fig.  40).   Very little is known about
 the distribution and ecological  affinities of this small species of
 Soenedesmus  in the  Laurentian  Great  Lakes.   We have not found  records
 of  it  from Lake Ontario,  although  specimens referred  to S.  bijuga
 and  its varieties  (Ogawa  1969; Munawar  and  Nauwerck 1971)  may  be
 included  in  S. bioellulavis  as treated  here.

 This species was very abundant at  stations  sampled  during  the  first
 biology-chemistry  cruise  of  the  IFYGL during  May  and  no particular
 geographical trends in its distribution were  apparent.   It  continued
 to  be very abundant at stations  sampled during  the  June cruise,  but
 at  this time there appeared  to be a  consistent  tendency toward reduced
 numbers at stations nearest  the  south shore of  the  lake.  Unlike most
 of  the species of green algae noted  in the  Lake Ontario phytoplankton,
S. b-iGellutapis had a pronounced summer minimum and the July and
August samples contained relatively  insignificant populations.  A
 slight increase in abundance was found in samples collected during
October, and small populations were  also found in November 1972 and
 February 1973 cruises.  Nearly stable populations were apparently
present during March and April and, although significant increases
 in population density were noted at a few stations in the western
part of the  lake in June, the abundance of  this species never
approached the levels found  the previous spring.
                                   260

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    TORONTO
HflMILT
             NIRGfWJ
              RIVER
                              JULY 10-14.  1972
                                           ROCHESTER
    TORONTO
                            flUGUST  21-24,  1972
HAMILTON
             NIRGflflfl
              RIVER
                                           ROOtSTEH
 FIG. 39.  Distribution of Phxcotus  lentieularis.
                                      261

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    TORONTO
HftMILT
             NIAGARA
              RIVEB
                           OCT  30  - NOV  3.  1972
                           NOV  27  -  DEC  1.  1972
    TORONTO
            NJH6PPP
             PIVEfl
FIG. 39 continued,
                                      262

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    TORONTO
HfltllLT
              RIVER
                            FEBRUflRY  5-9,  1973
                                           ROCHESTER
    TORONTO
HHIILTl
             N1W3W
              RIVER
                            MRRCH 19-22.  1973
                                           ROCHESTER
FIG.  39 continued,
                                         263

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     TORONTO
 MfiMILTi
              NlflWTO
              RIVER
                              flPRIL  24-28,  1973
                                            ROCHESTER
    Tonomo
HftlILT
             NIAGARA
              RIVER
                              JUNE: 11-14.  1973
                                            ROCHESTER
FIG.  39 continued.
                                          264

-------
                              MflT  15-19,  1972
    TORONTO
HW1ILTON
             NlftGflftf)
              RIVER
                                           ROCHESTER
HfiHlLT
             NJRGHV)
              RIVER
                              JUNE  12-16.  1972
                                           ROCHESTER
 FIG.  40.  Distribution of Saenedesmus bicellularis.
                                         265

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    TORONTO
HH1ILTON
             NIRGHW
              RIVER
                               JUir  10-14.  1972
                                           ROCHESTER
   TORONTO
                             fiUGUST  21-24,   1972
            NIRGWW
             RIVtR
                                           ROCHESTER
FIG. 40  continued.
                                      266

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    TORONTO
              RIVEB
                           OCT  30  - NOV  3.  1972
                                           ROCHESTER
    TORONTO
hflrtlLTON
             NlflOW*
              RIVtB
                           NOV  27  -  DEC  1.   1972
                                            ROCHESTER
 FIG. 40 continued.
                                           267

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     TORONTO
 tWIILTON
              NlflCffifl
               RIVER
                              FEBRURRT  5-9,  1973
                                            ROCHESTER
    TORONTO
HRHILT
                             MNRCH  19-22,  1973
             NIRGWfl
              RIVER
                                           ROCHESTER
 FIG.  40 continued.
                                          268

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    TORONTO
HRMRTOM
             NIRGRRR
              WVEft
                             flPRIL 24-28,  1973
                                            ROCHESTER
    TOROKIO
MFWILTON
                              JUNE 11-14.  1973
             NIRGfiRft
              RIVER
                                            ROCHESTER
 FIG. 40 continued.
                                          269

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 Soenedesmus quadrieauda var,  longispina  (Chodat) G. M, Smith (Fig, 41).
 According  to Skuja  (1956) this  taxon is most common in small ponds, and
 is rarely  found in  abundance  in larger lakes.  This is somewhat surprising
 since our  observations would  tend to indicate that it is common in the
 more eutrophied portions of the Laurentian Great Lakes.  It has been
 recorded as being widely distributed in western Lake Erie (Tiffany 1934;
 Taft and Taft 1971).  Soenedesmus quadvieauda var. maxi-mus was listed
 from Irondequoit Bay of Lake  Ontario (Tessler et al, 1953) and the
 nominate from stations in the open lake by Nalewajko (1966).  Although
 not particularly abundant in  our collections, this taxon is consistently
 present over a considerable part of the IFYGL sampling period.

 Only two isolated populations of S.  quadrioauda var. longisp-ina were
 noted in collections taken during the May 1972 sampling cruise.  Both
 occurred at nearshore stations in the southeastern sector of the lake.
 In samples taken during the June cruise an increased number of  occurren-
 ces were noted,  still mostly at nearshore stations,   Similar distribu-
 tion was noted in the July samples,  with occurrences being restricted
 to stations nearest  the south shore.   In August populations of  S.
 quadvioauda var.  longispina occurred at most  stations in the far eastern
 part of the lake,  with isolated occurrences at stations along the
 northern shore and in the offshore waters.  This species was much more
 generally distributed in our October samples  although it still  appeared
 at stations nearest  shore or in the eastern part of  the lake.   Populations
 declined in the  November samples with significant populations being
 largely restricted to offshore stations,  although levels near those  of
 the previous month were maintained at  stations  8 and  19,  near Toronto.
 Only a  single population was noted in samples from the  February cruise
 and  this species was not  recorded  from  samples  taken during  March.
 Isolated populations occurred  in samples  taken during April  at  stations
 nearest  the southern shore,  and  the population density  of S.  quadriaauda
 var.  longispina increased significantly in samples taken during June
 1973 particularly  from  stations  nearest the southern  shore.


 Scenedesnrus quadvieauda var. quadrispina  (Chodat) G. M. Smith (Fig. 42).
 This entity is quite easily  separated from the previous one  on  classical
 taxonomic characteristics, however, in  light of  the known plasticity of
 such characteristics under different culture conditions  (Trainor and
 Hilton 1963; Trainor 1966; Trainor and Roskosky 1967) it is  tempting
 to speculate that both may be  ecophenes of the same genetic  entity.  The
 very limited distribution of 5.  quadrioauda var. quadriepina  might be
 interpreted as supporting such a supposition, but our observations do
 not furnish a plausible basis  for resolving the question.  In any case,
 the difference in distribution of the two morphological entities must
 reflect  environmental differences at the stations sampled.

 No occurrences of 5.  quadrioauda var. quadm-spina were noted during the
 first two IFYGL biology-chemistry cruises.  Limited populations were
 found in July at stations in opposite ends of the lake.  In August,
however, appreciable populations were found at most stations in the
                                  270

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    TORONTO
             NlRGPRfi
              RIVER
                              MRY  15-19,  1972
                                           ROCHESTER
     TORONTO
 HWILTON
              NlWWRfl
              RIVER
                              JUNE  12-16,  1972
                                           ROCHESTER


FIG. 41.  Distribution of Scenedesmus  quadricauda var.  longispina.
                                     271

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                              JULY  10-14.  1972
  (WILTON
             MKPf*
              WVER
     10RON70
HRWU
                            RUGUST 21-211,  1972
                                        ROCHESTfR
FIG. 41 continued.
                                  272

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    TORONTO
HPMILT
              NIWWW
               RIVER
                             OCT 30  - NOV  3,
                                             ROCHESTER
    TORONTO
HRntLTON
              NIRGFfW
               RIVER
                             NOV  21  -  DEC 1.   1972
FIG.  41 continued.
                                        273

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     IONNTO
 HBHILtl
             NIfffiHW
              RIVER
                             FEBRURRT 5-9,  1973
                                           ROCHESTER
     TORONTO
                             MRRCH  19-22.   1973
              RIVER
                                          ROCHESTER
FIG. 41 continued
                                     274

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    TORONTO
HWILTI
             NIfWW
              RIVER
                            RPRIL 24-28,  1973
                                           ROCHESTER
    TORONTO
HRMILTON
             NJflGPRfl
              RIVCT
                              JUNE  11-m,  1973
                                           ROCHESTER
FIG. 41 continued,
                                      275

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      TORONTO
  HfiMLT
               NlflGflRfl
               WVER
                                JULY 10-1U.  1972
                                             ROCHESTER
     TORONTO
 HflMIlT
              NIftGWft
               RIVER
                              RUGUST
                                            ROCHESTER


FIG. 42 .   Distribution of Seenedesmus quadrioauda var, quadrispina.
                                      276

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     TORONTO
 HRMUON
              NIBGflftfl
               RIVER
                              OCT  30 - NOV  3,  1972
                                              ROCHESTER
     TORONTO
HRMILTi
              NlflCflRfl
               RIVER
                             NOV  27  -  DEC  1,  1972
                                              ROCHESTER
FIG.  42 continued.
                                       277

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 Eastern half of the lake and at several nearshore stations in the western
 half.  These populations were considerably reduced by October, and only
 isolated occurrences at stations near Toronto and Niagara were noted in
 November, No occurrences of this taxon were noted in months sampled
 subsequently.
 Ulotkrix spp. (Fig.  43).  The dominant population included in this cate-
 gory is U.  subeonstvieta G. S. West (194 occurrences)  although counts  of
 two entities of uncertain taxonomic affinities (one with 63 occurrences
 and the other with 2) and a single record of U.  tenerrima Kutz.  have
 been included.

 Records of  this genus in the phytoplankton of the Great  Lakes are  very
 incomplete,  but personal observations  indicate that high population
 densities are largely restricted to eutrophied regions.   Nalewajko
 (1966)  has  recorded  relatively low-level populations from Lake Ontario,
 although other authors do not record it  among the more abundant  forms  in
 the phytoplankton.

 In the  light of our  results this is rather surprising.   A. few high
 levels  of occurrence were recorded from  samples  taken  during May 1972,
 but by  June  it was present in considerable quantities  at most stations
 in the  northern half of the lake and at  several  nearshore stations in
 the southern half.   These populations  apparently declined substantially
 by the  time  the July samples  were taken,  although substantial populations
 were still present at  stations 8  and 19  near  Toronto.  Abundance of
 Ulotlwix spp.  increased again in  August,  particularly  in the eastern and
 southern part  of the lake.  Extremely  high population  density was  noted
 at  station 60  near Rochester.   Population densities  declined in October
 and  this  trend  continued  through  November,  reaching  the  yearly low in
 February  1973.   Samples from  the  March cruise  showed slightly increased
 population densities of Ulothrix,  but  no  further  increase was evident
 in samples taken during April  1973.  Populations did increase substantially
 in July but never approached  the  levels  or  the wide  distribution noted in
 June 1972.
Cyanophyta

Anabaena flos-aquae (Lyngb.) Breb. (Fig. 44).  Occasional low-level pop-
ulations of this species are found throughout the Laurentian Great Lakes,
but abundant occurrences seem to be restricted to areas which have under-
gone some degree of eutrophication.  It is one of the species which has
become much more abundant in Lake Michigan in recent years although it
was recorded as rare in earlier collections (Ahlstrom 1936).  In Lake
Ontario it was recorded from Irondequoit Bay (Tessler et al. 1953), and
other records for the genus from the Bay of Quinte (Michalski 1968) and
stations in the open lake (Nalewajko 1966) probably refer, in part, to
this taxon.  Ogawa (1969) found it to be abundant at a number of open
lake stations sampled during September 1964.  This species is capable of
                                  278

-------
      TORONTO
  HH1H.TON
                                 MflT 15-19,  1972
                                             ROCHESTER
     TORONTO
HfiMILTQN
             NIAGARA
              RIVER
                                   E  12-16.   1972
                                            ROCHESTER
 FIG.  43.  Distribution of Ulothrix spp.
                                       279

-------
     TORONTO
 HR1IIT
             ' NlflGFflfl
               RIVEP
                                JULT  10-14,  1972
                                             ROCHESTER
     TORONTO
tWlILTON
              NIRGHVJ
              RIVER
                              RUGUST  21-24,  1972

                                        IMS
                                            ROCHESTER
FIG. 43  continued.
                                       280

-------
    TORONTO
HRMIUON
              NIRGPRfl
              RIVER
                            OCT  30  -  NOV  3.  1972
                                             ROCHESTER
    TORONTO
 MFWU
              WRGSRH
               RIVER
                            NOV  27  -  DEC  1,   1972
                                             ROCHESTER
FIG. 43  continued.
                                       281

-------
   TORONTO
                         FEBRURRt  5-9,  1973
             RIVER
                                         ROCHESTER
     TOROKTO
                           MRRCH 19-23,  1973
               RIVER
                                           ROCHESTER
FIG. 43 continued.
                                   282

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    TORONTO
HAMILTON
             NIAGARA
              RIVER
                             flPRIL 2U-28,  1973
                                            ROCHESTER
    TORONTO
HRHILTON
             NIRGHVI
              RIVER
                               JUNE  11-14.  1973
                                            ROCHESTER
  FIG. 43  continued.
                                      283

-------
     TORONTO
 ffiML.lt
             NJflffRfl
              R1VEB
                              JUNE  12-16,  1972
                                           ROCHESTER
    TORONTO
IWULT
             RIVER
                             JULY 10-m.   1972
                                          ROCHESTER
 FIG. 44.  Distribution of Andbaena flos-aquae.
                                     284

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    TORONTO
(Will.!
                            RUGUST 21-24,  1972
             BlVfB
                                          ROQCS7OI
    10RCKTO
MRMIL1
             NJftCHW
              RlVOt
                           OCT  30  -  NOV  3,  1972
                                           ftOOCSTEB
  FIG.  44 continued.
                                       285

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  producing  obnoxious water  blooms  and is one  of  the  taxa  contributing
  to  such nusiances  in western  Lake Erie  (Ogawa and Carr 1969),  On  the
  basis of Ogawa and  Carr's  study,  it  would  appear that this  species is
  also one of  those  capable  of  fixing  nitrogen under  conditions where
  excessive  phosphorus input led  to depletion  of  available nitrogen  in
  the system.

  This species was not noted in samples from the  May  1972  cruise, and
  only a few isolated  populations were noted in the June samples.  It
  was found  in considerable  abundance  at  a number of  stations in the
  eastern part of the  lake during July,   In  August it was  particularly
  abundant at station  90 near Oswego and  at  several stations near
  Niagara.   Somewhat smaller population densities were noted at several
  stations in the eastern part  of the  lake and at isolated nearshore
  stations along the northern shore.   Only a few  isolated populations were
  found in samples from the October cruise, and this species was not
 recorded from any of the subsequent  cruises.


 Anabaena vaviabilis Ku'tz.   (Fig.  45).   The identity of this small species
 of Anabaena is somewhat questionable.  Although it is apparently very
 widely distributed  in both fresh and saline water (Huber-Pestalozzi
 1938),  previous records from the Laurentian Great Lakes are lacking.
 It forms gas  vacuoles and  may contribute to water blooms, and Ogawa
 and  Carr (1969)  have demonstrated that laboratory strains of this
 species are capable of fixing nitrogen.

 A single isolated population was noted in collections taken during the
 May  1972 cruise, but it was not  noted in June and  July.   In August,
 however, high population densities of this  species were noted at  a
 number  of stations  in the  southern half  of  the lake  and less abundant
 occurrences at  several stations  nearest  the northern shore.   A few
 isolated occurrences  were  found  in samples  from  the  October and
 November 1972 cruises and February 1973  cruises. This species was  not
 found in samples from the March  and April cruises but it  did occur  at
 a few stations in the eastern  half of the lake during June  1973.
Anooystis eyonea Dr. and Daily  (Fig.  46).   This species is one of the
blue-green algae capable of forming nusiance-producing water blooms.
It is present in many highly eutrophied areas in the Great Lakes, but
reliable quantitative estimates of its abundance are not common.  This
is partially because it tends to occur in ephemeral blooms and the cells
usually are contained in large colonies, which renders obtaining accu-
rate estimates of its abundance very difficult.

Like most bloom forming species of blue-green algae, A.  cyanea usually
reaches its peak abundance during the warmest months of the year.  In
this respect, its seasonal distribution in Lake Ontario during the
IFYGL sampling period is highly unusual.  In May 1972 a single isolated
population was noted at station 90 near Oswego.  In June somewhat higher
                                  286

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    tORCKTO
HflMILT
            NIAGARA
             WVER
                             MRY  15-19,  1972
                                          ROCHESTER
   TOROKTO
HRMJL10N
             run*
                           nUGUST  21-2U,  1972
 FIG. 45.  Distribution of Andbaena varidbilis.
                                       287

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                           DCT 30 -  NOV  3,  1972
     10RO0D
 HRML10N
                          NOV 27 -  DEC  1.  1972
    TORONTO
HRflJLliW
             WVDl
                                         fWOCSTER
 FIG. 45 continued.
                                      288

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    TOTOKTO
            WBCfttft
             IUVER
                          FEBRURRT  5-9,  1973
    TWOKTO
WM1L10W
             RIVER
                           JUNE  11-1U.  1973
                                        ROQESTEH
 FIG.  45 continued.
                                     289

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     TORONTO
 MflHILT
              NJflCflRfl
               RIVEfl
                                MflY  15-19,   1972
                                             ROCHESTER
    TORONTO
HfiMILTOf
             NJflGfiftfl
              RIVER
                               JUNE  12-16.  1972
                                            ROCHESTER
FIG.  46.  Distribution of Anaaystis ayanea.
                                        290

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     TORONTO
 HfiMILTi
              NIBCfiflfl
               RIVER
                                JULY  10-14,  1972
                                             ROCHESTER
    TORONTO
HftMlLTi
             NlflCWfl
              RIVEfl
                              RUGUST 21-214.  1972
                                            ROCHESTER
 FIG. 46 continued.
                                        291

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                              OCT  30  -  NOV 3.   1972
      TOfWTO
              NIBCRHfl
               BIVEB
                                              ROCHESTER
    TORONTO
HHHILTi
             NJBCflRfl
              RJVEB
                             NOV 27  - DEC  I.  1972
                                            ROCHESTER
FIG.  46 continued.
                                        292

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    TOKXTTO
MfiHILT
              RIVER
                            FEBRUflRY 5-9,  1973
                                           ROCHESTER
    TORONTO
HflHILTI
             NJBGRRfl
              RIVER
                             MflRCH  19-22.  1973
                                           ROCHESTER
 FIG. 46  continued.
                                        293

-------
     romwro
 HflfULTI
              NJflGflflfl
               RIVER
                              flPRIL 24-28,   1973
                                            ROCHESTER
    TORONTO
MflMIUC
             NIRGRRfl
             RIVEB
                              JUNE 11-14,   1973
 FIG. 46 continued.
                                      294

-------
populations were noted at the same station,  at station 85 adjacent to it,
and at station 10 in the far end of the lake.   In July a single population
was detected at station 3, and in August,  when population densities might
be expected to be relatively high, this species was not noted in any of
our samples.  In October, however, high population densities of A.
oyanea were noted at a number of stations.  By November populations had
declined except at stations 72 and 73,  east of Rochester.  Only single
Isolated populations were noted during February, March, and June gampling
periods in 1973.


Anaoystis inoevta Dr. and Daily (Fig. 47),  This small species contains
gas vacuoles and, according to Drouet and Daily (1956), may form blooms.
It is, however, rarely associated with nuisance conditions in the Great
Lakes.  Unlike many other species of blue-green algae in the Great Lakes
it tends to reach peak abundance during cooler months of the year, es-
pecially during the fall cooling period.  In reviewing the records of
its occurrence available to us, it would appear that it is most
successful under conditions where silica depletion limits diatom growth.

In Lake Ontario during the IFYGL field sampling period it was abundant
at stations in the eastern part of the lake in May, with only isolated
low-level populations being detected at other stations.  During the
June sampling cruise, conversely, sizable populations were found only
at stations in the far western part of the lake with a few low-level
occurrences at mid-lake stations and In Mexico Bay.  Populations
dropped to very low levels during the July sampling period, but a few
isolated abundant occurrences were noted at widely separated stations
during August 1972.  Only occasional occurrences were noted during the
rest of the months sampled, and it did not return to the levels of
abundance noted the previous spring.
Aphanizomenon flos-aquae (L.) Ralfs (Fig. 48).  This species is capable
of causing extreme nuisances under bloom conditions.  Its distribution
in the Laurentian Great Lakes is largely restricted to highly eutrophied
areas.  Although it is a conspicuous element of net collections from
such areas, estimates of its abundance made by standard phytoplankton
counting methods are subject to large uncertainties because of its
growth habit.  It has been reported as being abundant in Irondequoit Bay
(Tressler et al. 1953) and the Bay of Quinte  (McCombie 1967; Michalski
1968) but, although it is visibly present in  the surface waters of some
regions of Lake Ontario proper, it has not often been reported from
stations in the open lake.  Ogawa (1969), however, found it to be
abundant at a number of stations sampled in September 1964.

In our collections a single occurrence was noted at station 105 in
Mexico Bay during June 1972, and relatively high abundance of this species
was noted at this station and a few others in the eastern part of the  lake
during August.  Scattered populations were also noted in samples taken
during October, but this species was apparently absent from subsequent
samples.
                                   295

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     TORONTO
              NJBCflftfi
               RIVER
                                MRT  15-19.   1972
                                            ROCHESTER
    TORONTO
HflMILTl
             NJflGfWf)
              RIVER
                               JUNE  12-16,  1972
                                           ROCHESTOT
FIG.  47.   Distribution of Anacystis  i,ncevta.
                                      296

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    TORONTO
HflKJLT
             NIflGflfift
              RIVER
                               JULY  10-14.  1972
                                            ROCHESTER
    TORONTO
WWILT
             NIRGflflft
              RJVEB
                             RUGU5T 21-24,  1972
                                           ROCHESTER
 FIG. A7 continued,
                                       297

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     TORONTO
 MfiHJU
              NlRGflfifi
               RJVEfl
                              OCT  30  -  NOV 3.   1972
                                              ROCHESTER
    TORONTO
HflHlLT
              NJfiCflRP
              RIVE8
                             NOV  27  -  DEC  1.  1972
                                             ROCHESTER
FIG.  47 continued.
                                        298

-------
    TOflOMTO
HflMILTl
             NIRCflflfl
              RJVEfl
                            FEBRURRT 5-9,  1973
                                          BOCHESTEB
    TORONTO
             RI/Efl
                            MflRCH  19-22,  1973
                                                                           00
                                          ROCHESTER
FIG. A7 continued.
                                      299

-------
      TORONTO
 HRHILTC
              NJflGflflfl
               RJVEB
                               RPRIL  24-28,   1973
                                             ROCHESTER
    TOflOKTO
HHMIUC
             NJRCfiRfl
              RIVEB
                               JUNE  ll~lii.  1973
                                            ROOESTEfl
FIG. 47  continued.
                                       300

-------
     TORONTO
HrCULTG
             NJflCFftn
              RIVER
                              JUNE 12-16,  1972
                                           ROCHESTffl
    TORONTO
WUUON
             NJBCffW
             fUVUl
                              JULY  10-14,  1972
                                           ROCHESTER
    FIG.  48.   Distribution of Aphanizomenon flos-aquae.
                                        301

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   Tcatwro
HflMJLia
                           RUGUST  21-24.  1972
                                          ROCHESTER
    TORONTO
             NlftCWW
              RIVER
                           OCT 30 -  NOV 3.  1972
                                           ftOCHSSTffl
    FIG.  48  continued,
                                         302

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Gomphosphaeria aponlna Kutz.  (Fig,  49).   According to Huber-Pestalozzi
(1938) this species is a facultatively planktonic form which is widely
distributed in large and small lakes and also occasionally occurs in
brackish water.  Although records are insufficient to assess its general
distribution in the Laurentian Great Lakes,  it has been reported from
western Lake Erie (Taft and Taft 1971) and we have observed occasional
populations in Lake Michigan.

The occurrence of G. aponina in Lake Ontario during the IFYGL sampling
period was strikingly limited.  It was noted only in samples from the
October 1972 cruise when relatively high population densities were noted
at several stations in the eastern part of the lake.
Gomphosphaeria laeustris Chodat (Fig. 50).  This very common and widely
distributed member of the genus is found throughout the Laurentian
Great Lakes and is often one of the more abundant species of the sparse
summer plankton of the upper lakes.  Although it was recorded from
stations in Lake Ontario collected in September 1964 by Ogawa (1969),
it was not reported in more recent surveys.

In our collections, a single population was noted from samples collected
during May 1972.  It was not found in samples taken during June and
July, but was relatively abundant at scattered stations collected during
August.  Similar occurrences were found in October, but it was absent
from collections taken on subsequent cruises until June 1973, when a
few isolated populations were again collected.
Gomphosphaeria wichurae  Dr. and Daily (Fig. 51).  According to Drouet
and Daily  (1956), this species often forms conspicuous blooms during
the warmer months of the year in freshwater lakes.  Partially because
of the confusion that surrounds the taxonomy of this species, previous
records of its occurrence in Lake Ontario and the other Great Lakes are
difficult  to determine.  It would appear, however, that it is usually
associated with eutrophic conditions and is potentially a nuisance-
producing  form.

In our samples, only isolated low-level populations were detected
during May through August 1972.  In October, however, large populations
were  noted at most offshore stations in the northwestern sector of the
lake  and at a few stations in other regions.  Although populations were
somewhat reduced in samples from the November cruise, they were again
noted at many stations, primarily in the western portion of the lake.
A few stations sampled during February 1973 still contained significant
levels of  this species, but it continued to decline  in abundance  and
only  isolated occurrences were noted in March and April.  It was  not
noted in our June 1973 samples.
 Osoillatoria limnetica  Lemm.   (Fig.  52).   This species is by far the
                                   303

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                           OCT  30  - IMOV 3,  1972
    TOtWTO
HfWJUC
            N/RSWfl
             RIVER
                                         ROCHESTER
FIG.  49.   Distribution of Gomphosphaeria aponina.
      most common member of the genus in our collections.  According to Huber-
      Pestalozzi (1938)  it is a common  euplanktonic form which often occurs
      in polluted water.  It apparently has not been widely reported from the
      Great Lakes, although Munawar and Nauwerck (1971)  record it as being
      an abundant form in the fall plankton of Lake Ontario,  and Nalewajko
      (1966)  lists several occurrences of the very similar 0.  planktonioa.
      Wol.,  also from Lake Ontario.

      Relatively small populations of this species were  noted in our collec-
      tions from the May 1972 cruise.  In June, however,  it was one of the
      dominant species at many stations in the northern  part of the lake.
      The very abundant  populations noted the previous month had declined
      by July,  although there was one particularly high  abundance occurrence
      noted at station 19 near Toronto, and the species  was quite uniformly
      distributed throughout the lake.   There was,  however,  a trend towards
      lower population densities at offshore stations in the southern half
      of the  lake, a pattern which was  repeated by several other taxa.
      Relatively low population densities were noted at  stations sampled
      during  August,  with a tendency for highest abundance to occur at
      stations along the southern shore.   Population densities were also
      low during October,  but populations seemed to be evenly distributed
                                     304

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tttULT
            NJRCtWfl
             RIVER
                            MflY  15-19,  1972
                                          POCHESIER
    TOKWTO
                           fiUGUST 21-24,  1972
IBHIUTB
             Riven
 FIG. 50.  Distribution of Gomp'hosp'haepia laaustris'.
                                       305

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    TOWO
KW1LTOJT
                         OCT  30  - NOV 3,  1972
                         \
                                       ROCHESTER
                          JUNE  11-14,  1973
                                      poacsitn
 FIG. 50 continued.
                                     306

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    TOfiQKTO
             NlflCBRfl
              RIVER
                              MPT  15-19.  1972
                                           ROCHESTER
    TORONTO
MWILT
             NJPGflHB
              Riven
                              JUNE  12-16,  1972
                                           KOC3TEH


 FIG.  51.  Distribution  of  Gomphosphaeria wichurae.
                                       307

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    TOfWTO
HBMn.70
             RIVER
                            JULY  10-lii.  1972
                                         ROCHESTER
                           flUGUST  21-21,  1572
    TOWfrTTO
 FIG.  51  continued.
                                     308

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                            OCT 30 -  NOV 3.  1972
     TORONTO
                                           ROCHESTER
                           NOV  27 - DEC  1.  1973
    TORONTO
                 \
                 \
                      \
HRMILTO
             NlflGfiRR
\
                                          ROQCSTEft
FIG.  51  continued.
                                      309

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    TORONTO
tWULTO
             NlflGflfW
              BIVER
                             FEBRUflRT 5-9.  1973
                                           ROOCSTEfl
    TORONTO
                            MflRCH 19-22.   1973
KRHIUTO
             NISGHflfi
                                          ROCHESTEB
 FIG.  51 continued.
                                      310

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             NIHCflflfl
              RIVER
                            RPRIL  24-28.   1973
                                           ROCHESTER
    TORONTO
MflMILT
             NlfiCflRft
              RIVER
                              JUNE  11-14.  1973
                                           ROCHESTER
FIG.  51 continued.
                                       311

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     TORONTO
 MRNIU
             NlflGNW
              RIVER
                               MPT 15-19,   1972
                                           KJCHESTEfl
    TOPONTO
MfWILT
             RIVEfl
                              JUNE  12-16.  1972
                                          KEHESTEfl


 FIG.  52.   Distribution of  Oscillatoria limnetica.
                                      312

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                              JULY  10-14,   1972
    TORONTO
HN4ILTI
             NTW3RRB
              RIVER
                                           ROCHESTER
    TORONTO
HRHtU
             HJRGHWJ
              RIVtfl
                             flUGUST 21-24,  1972
                                            ROCttSTER
 FIG. 52 continued.
                                       313

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     TORONTO
HWIILTi
                            OCT 30 -  NOV 3.   1972
                                           ROCHESTER
    TWONTD
             NlfiGWW
             RIVEfl
                           NOV  27  - DEC  i.  1972
                                           BOCMESTLfi
FIG. 52 continued.
                                      314

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    TORONTO
HflflILT
             NIflGRBfl
              WVEP
                            FEBRURRY  5-9,  1973
                                          ROCHESTER
    TORONTO
HWILT
              flJVEfi
                            MRRCH  1S-23.   1973
                                           ROCHESTER
FIG.  52 continued.
                                      315

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lORorno
                        fiPRIL 24-28.  1973
                                     ROCHESTER
                         JUNE 11-14.  1973
         N1HGWR
          RIVEft
                                     ROCHESTEfl
FIG. 52 continued,
                                    316

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throughout the lake,  Approximately the same situation was evident from
samples taken on the November 1972 and February and March 1973 cruises,
Slightly increased population densities ot 0,  lirmetica  were noted in
April samples from stations along the northern shore and in the north-
eastern part of the lake,  A marked increase in the abundance of this
species was noted in most samples from the June 1973 cruise, although
significantly lower values were recorded from a cluster of stations
(26, 32, 44, and 45) near the mid-region of the lake.
Cryptophyta

Cryptomonas evosa Ehr. (Fig, 53).  This large member of the genus is
widely distributed in the Great Lakes, usually, however, in relatively
low numbers.  According to Huber-Pestalozzi (1968) it is a  eurytopic
organism, occurring both in oligotrophic lakes and often, in abundance,
in eutrophic and slightly saline habitats.  According to Munawar and
Nauwerck  (1971) it was present in all seasons in Lake Ontario during
1970, with greatest abundance in the spring and fall.

In our samples, appreciable populations were present at most stations
sampled during May 1972.  By June very large populations had developed
in the eastern part of the lake, particularly at nearshore stations
on  the southern shore.  By July these populations had collapsed, and
numbers of C. erosa remained low throughout the remainder of 1972.  It
should be noted that a few examples of it were found at most stations
sampled,  but usually in such low numbers that they are completely
insignificant when scaled against the high populations found in June.
In samples taken during February 1973, appreciable populations of this
species occurred at many of the stations sampled, and slight increases
were noted in samples taken during the March and April cruises.  These
populations, however, never approached the densities found the previous
year and, contrary to the situation the previous year, had declined
significantly by the time the June samples were taken.
 Pyrrophyta

 GTenodi-ni-im and Gyrmodiniian spp.  (Fig.  5^ ).   This  composite  category
 includes the smaller species of these two genera which could not  be
 identified satisfactorily in our collections.  Such species  are usually
 a minor component of the offshore phyioplankton of the Laurentian Great
 Lakes.   Munawar and Nauwerck (1971)  have indicated that these organisms
 are an appreciable part of the Lake   Ontario phytoplankton in the summer
 and fall.

 Relatively high levels of occurrence were noted at numerous  stations
 throughout the lake in our May 1972  samples.  Levels of abundance declined
 somewhat by June, although occurrences were still noted at most stations
 and relatively high population densities were present at a few of the
 stations sampled.  Population densities increased again in July,
                                    317

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      TORONTO
  HftMILTO
               NlflGflflfl
                RIVEft
                                 MflT  15-19.  1972
                                              ROCHESTER
     TDWJWTO
 HflMILTC
               RJVEfi
                                JUNE  12-16.   1972
                                             ROCHESTER
FIG.- 53.   Distribution of Cryptomonas erosa.
                                        318

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     TORONTO
 HAMTLTI
              NlflGflRfl
               RIVER
                               JULY  10-1H,   1972
                                             ROCHESTER
     TORONTO
MflMILT
              NlflGflRfl
               RTVEfl
                              fiUGUST 21-24,  1972
                                            ROCHESTER
FIG. 53  continued.
                                        319

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     TORONTO
HflHJLTi
              NJflGWW
               RIVER
                             OCT  30  -  NOV  3,   1972
                                              ROCHESTER
     TORONTO
 HfiMILT
              NlflGflflfl
               RIVER
                             NOV  27  -  DEC  1.   1972
                                              ROCHESTER
FIG.  53 continued.
                                         320

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      TORONTO
  HfiHILTi
               KlflGflflfi
               RJVEB
                               FEBRURRY 5-9,  1973
                                            ROCHESTER
     TORONTO
 HflMILTl
                              MflRCH  19-22,  1973
                                           ROCHESTCR
FIG. 53 continued.
                                      321

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     TORONTO
 KRHILT
              NJftGflflfl
               RJVEB
                              RPRJL 24-28.  1973
                                            ROCHESTER
     TORONTO
 HWtlLT
                               JUNE  11-14,  1973
                                            ROCHESTER
FIG. 53 continued.
                                       322

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    TORONTO
HPMILTON
              RIVER
                             MRY 15-19,   1972
                                          ROOESTCR
    TORONTO
HRHILTON
                             JUNE  12-16.  1972
                                          ROCHESTER
FIG. 54.  Distribution of Glenodiniwn and Gyrnnodiniim.
                                      323

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                               JULY  10-14,  1972
     TOK3KIO
 MflWUON
              NIRGfflfl
              RIVER
                                            ROCHESTER
     TORONTO
                             flUGUST 21-24.  1972
             NlRCflftfl
              RIVER
                                           ROCHESTER
FIG. 54 continued.
                                       324

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     TORONTO
      \
 HWILTC
          \
                           OCT 30 -  NOV 3,  1972
             NJBGfW
              WVER
\;
V———"* r

* V ^
1 \ \
\ \ \

\\
V \
I
X \^
\.
\ '
\ '
\ \
                                          WOCSTER
     TOROKTO
                           NOV 27  -  DEC  1.  1972
                                          nooesTcn
FIG. 54 continued.
                                      325

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     TOROKTO
 HRMIUT
             NJflGHW
              WVEB
                             FEBRURRY  5-9,   1973
                                           ROCHESTER
    TORONTO
                             MflRCH  19-22.  1973
MRHIUON
                                          ROCHESTER
FIG. 54 continued.
                                     326

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    TOROffTO
HRHILTI
             NIflWRR
              RIVER
                             RPRIL 24-28,  1973
                                            ROCHESTER
    TORONTO
                              JUNE  11-14.  1973
HflMILT
             NJRGflRR
              RIVER
                                            ROCHESTER
FIG.  54  continued.
                                        327

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 particularly at stations in the western half of the lake, although
 very low abundance was found at certain nearshore stations there.
 These populations had apparently crashed by the time the August samples
 were taken, as only isolated low-level occurrences were noted at stations
 in the western part of the lake and along the southern shore.  A con-
 siderable increase was noted at most stations sampled during October,
 however levels of abundance had declined again by the time the November
 1972 samples were taken.   Population densities remained low during
 February, however they increased slightly in our March samples despite
 a reduction in total phytoplankton abundance.  The populations apparently
 declined again, and only  low levels of abundance were noted in our April
 samples, with highest occurrences at stations nearest shore and in the
 eastern part of the lake.   Samples from the June 1973 cruise showed high
 abundance of these organisms at stations along the southeastern shore,
 but abundance levels never reached those noted the previous spring.


 PevLdiniwn spp.   (Fig.  55).   Members of this genus are usually present,
 though not in great abundance,  in phytoplankton samples from the
 offshore waters of the  Laurentian Great Lakes.   The taxonomy of species
 occurring in the Great  Lakes is poorly known,  and  we were not able to
 achieve satisfactory determinations of the entities in our samples,
 although more than one  population is probably involved.   Previous
 records of the distribution  of  this genus  in Lake  Ontario are essentially
 lacking,  although our data  indicate that its members contribute a
 significant  portion of  the  total phytoplankton at  certain stations during
 some  seasons of  the year.

 In  our  samples from the May  1972 cruise, Peridinium was  relatively
 abundant  at  stations nearest the southern  shore and stations in the
 eastern part of  the lake.  By the  time the June samples  were taken,
 these populations had apparently declined  and  significant  population
 densities  were noted only at a  few mid-lake stations.  A similar situa-
 tion was noted  in  July, although at this time  high  population densities
 were more  common in the central  region of  the  lake  rather  than  at
 offshore  stations  in the east and west, as  they had  been  the previous
 month.  Population densities of Peridinium  increased again  in August,
 particularly  at  stations near shore in the northern  and  eastern parts
 of  the  lake.   These populations had  declined significantly by October
 and only scattered,  low-level populations were  noted.  Populations
 remained low  in  samples from the November 1972  cruise, although slight
 increases were noted at stations in  the western half of the lake.
 Only scattered,  low-level occurrences were found in February 1973
 samples, and  only  slight increases  in abundance in samples from the
 March cruise.  Population densities again increased at nearshore
 stations during  April and at stations  throughout the lake in June
 1973, but never  reached the  levels noted the previous spring.
Microflagellates  (Fig. 56)

We have included in this category all flagellated unicellular forms less
                                  328

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                              MflT 15-19.   1972
                                                           440
    TOfWMTO
tWULT
             NlRGflRfl
              MVEB
                                          ROCHESTER
                             JUNE  12-16,  1972
    TOWTO
            NlflGflRB
             RIVER
                                                                          00
                                          ROCtCSTEB
 FIG. 55.  Distribution of Peridiniwn spp.
                                       329

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      TORONTO
  MflMILTON
                               JULY  10-14,  1972
              NIflGJflfl
               RIVER
                                           ROQCSTEB
                             RUGUb'T  21-24,  1972
     TOWOTO
                                          POCMESTEH
FIG. 55 continued.
                                      330

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                           OCT  30  - NOV  3,  1972
    TORONTO
MflMILT
             NlftCflfW
              RIVEfl
                                           ROCHESTER
    TORONTO
                           NOV 27 -  DEC  1.  1972
                                           ROCHESTER
 FIG. 55 continued.
                                        331

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 TORONTO
                       FEBRURRY  5-9.  1973
           RIVEfi
                                      ROCHE3TEP
   TORONTO
HfWILI
                         MPRCH  13-22.  1973
FIG. 55 continued,
                                      332

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    TOfwro
HflrtILT
             NIRGRBfl
              RIVER
                            RPRIL 24-28.  1973
                                           ROCHESTER
    TORONTO
MWULT
             NJflGflRR
              RIVER
                              JUNE  11-14.  1973
                                           ROCHESTER
 FIG.  55 continued.
                                       333

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                               MfiT  15-19,  1972
      TORONTO
 HRMIITON
              NWWflfl
              RIVER
                                           ROCHESTER
    TOVJKTO
HPMUON
                              JUNE  12-16,  1972
                                          ROCHESTEfl
FIG. 56.   Distribution of microflagellates.
                                      33A

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                              JULY  10-14.   1972
    TORONTO
WILTON
             NJfiGWfl
              RIVER
                                            ROCHESTER
    TOBONTO
HPTirLTOH
             HlftGfTO
              WVER
                             flUGUST 81-214,  1972
                                            ROCHESTER
 FIG.  56 continued.
                                        335

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                            OCT 30  - NOV  3.  1972
    10RONTO
HflMLTON
             NlftCflRfl
              WVCR
                                                                            1200.00
                                            ROCHESTER
    TOMKTO
MflMlUON
             HlfiGPPfl
              WVER
                            NOV 27  - DEC  1.  1972
FIG.  56 continued.
                                         336

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    TOMKTO
HPMLT
             NIBGPPfl
              RIVER
                            FEBRURRY  5-9,   1973
                                                                         1200.00
                                           ROQCSTER
    TORONTO
             NlfiCffW
              RIVER
                            MflRCH  19-22.  1973
                                           ROCHESTER-
 FIG. 56 continued.
                                        337

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    IOIWTO
             RIVER
                           flPRIL 24-28.  1973
                                        ROCHESTER
                            JUNE  il-14.  1973
            R1YEK
                                                                       00
                                       ROCHESTER
FIG.   56 continued.
                                    338

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than 10 urn in largest dimension.   Identification of  preserved  specimens
of these organisms is exceedingly difficult,  and the species occurring
In the Great Lakes phytoplankton have been,  historically, very poorly
treated.  Although reliable published records are lacking, our obser-
vations indicate that organisms in this group are relatively much more
important in the Lake Ontario system than they are in the upper Great
Lakes.  The most abundant organisms in this class occurring in our
collections were Chiarnydomonas spp, (probably including zoospores of
other chlorophycean species), Chrysochromulina parva Lackey, Pedinomonas
spp., and Rhodomonas spp., although less abundant populations of other
chrysophycean flagellates were present at many stations.  As Munawar
and Nauwerck (1971) noted, Rhodomonas  was present during all seasons
and its abundance seemed to follow the general trends of total phyto-
plankton abundance.  In our collections Chrysochromulina was most
abundant in June and July, with a minor peak in populations in the fall.
Chlamydomonas spp. appeared to have a similar seasonal succession
although they tended to become abundant somewhat later and abundance
peaks were similar to other chlorophycean species.  Although Munawar and
Nauwerck indicated that Pedinomonas was primarily a summer form, in
our collections it became abundant at nearshore stations  in the early
spring  and reached peak abundance at open-lake  stations  in June.  This
is not  surprising, in that Huber-Pestalozzi  (1961)  indicates that P.
minutissima Skuja, which is probably the main species involved, is a
cold  stenotherm.

Microflagellates were abundant at  the  shallower stations during the May
1971  cruise, and high population densities were noted at stations in
many  parts of the  lake during June.  In this month, however,  there was
a consistent pattern of  low population densities at stations nearest
shore in the western part  of  the lake  between Niagara and West Point
and at  offshore stations  in  the  southern  half of the lake. Appreciable
populations of  microflagellates were still present  in July, but peak
abundances were down considerably  from June  values.  At  this  time highest
population  density occurred  at  station 1A near  Niagara.   Population
levels  of microflagellates were  further reduced in  August and only
relatively  low  population densities were  found  throughout the lake.
Average abundance of this group  increased somewhat  in October samples,
but  was low in  November  and  remained low during February and  March  1973
 cruises.   A general increase in  abundance of the group  was  noted  in the
April samples,  and notably increased densities  occurred at  several
 stations in the eastern part of  the lake.  An extreme  bloom of  these
 organisms apparently occurred at the time the June  1973 samples were
 taken,  and abundance in excess of 5000 cells/ml were noted at several
 offshore stations.  Highest  abundances at this time substantially
 exceeded any found during 1972.
 Vertical Distribution of Phytoplankton at Master Stations

 In the following sections, data are given on the vertical trends in total
 phytoplankton abundance and the abundance of major groups at different
                                   339

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 seasons.   Data are derived  from  standard  sampling depths at  the
 master  stations.

 In  general,  these data  are  relatively well  correlated with trends  in
 chlorophyll  concentration  (Table 6), and  particle counts (Table 7)
 both  for  total phytoplankton  and for particular groups during  their
 maximum growth phase, and relatively poorly correlated during  periods
 of  decline.

 The vertical distribution of total phytoplankton cell counts  at master
 stations  is  shown in Figure 57.    Open lake  stations  sampled
 during  May had relatively low and uniform counts at all depths, with a
 slight  increase in the  20 m sample from station 24.  Cell densities were
 considerably higher at  station 96, but no stratification of  cell
 densities  was evident.  In  June, cell densities were still low and
 uniform at stations 45  and  75 and somewhat higher but still  uniform
 with  depth at station 10.   At station 24, however, very large values
 were  found in samples from  the top 15 m, and samples from the lower
 depths  had higher counts than all stations except station 96.  In July,
 stations  24, 45, and 75 in  the central part of the lake had  relatively
 high  counts  in the epilimnion, with peak values occurring at 5, 10, and
 15 m.   Station 10, in the western end of the lake, and station 96, in
 the eastern  end both had lower and more vertically uniform phytoplank-
 ton counts.  In August,  cell counts were considerably reduced at the
 open-lake  stations,  with peak values occurring in the top 10 m.  At
 station 96,  on the other hand, phytoplankton density increased from
 levels noted the previous month,  with especially large values present
 in the  5 and 10 tn samples.   By October less pronounced stratification
was evident and cell counts were relatively low and irregular, even
 at station 96.   Abundance continued to decrease at the main-lake
 stations sampled during November, but remained near levels noted the
 previous month at station 96.   Phytoplankton densities were low and
 uniform at all stations sampled during February, and only slight increases
were  noted at the main lake stations during March although a large
 increase was found at station 96.  Approximately the same situation was
 present in April,  although slight increases were noted at stations 10
and 24 and values continued to increase at station 96.  By June 1973
values had increased greatly at all stations sampled,  and phytoplankton
densities were strongly stratified at all stations.   Peak values
occurred at 5 or 10 m depths and  the anomolous 30 m peak noted in the
cholorophyll results were evident from  the counts.

The vertical trends  in abundance  of the major  phytoplankton groups at
 the master stations  sampled are shown in Figures 58-61.

The diatoms  (Fig.  58)  were  the most consistently abundant at  the master
stations-   Tn May,  large populations were present  at all depths sampled
at station 96,  with  largest  concentrations occurring in the near-bottom
waters.   Abundance was much lower at stations  24 and 75 and more evenly
distributed with depth,  although  there  was a noticeable concentration
at the 20 m depth  at  station 24.   In June, largest  populations were
                                  340

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TABLE 6.  Correlation between fluorometrically determined chlorophyll a
values and cell counts in total and by category at master stations.

May
June
July
Aug.
Oct.
Nov.
Feb.
Mar.
April
June
Total
cells
ml
.8301
.8875
.6703
.6285
.6258
.8169
-.1367
.9584
.9129
.8090
Macrofla-
gellates
.9388
.7924
.6309
.4297
.6897
.8301
-.2383
.4338
.8506
.7416
Blue-
greens
.6009
.6715
.2409
.4858
.3809
.2253
.0155
.0027
.2920
.2130
Greens
-.0464
.5350
-.2323
.4960
.2635
.4017
-.1895
.1425
-.0028
.0419
Diatoms
.5409
.8508
.4507
,0568
.5475
.9218
-.1396
.9660
.9051
.7395
R@.99
,5256
.3801
.3683
.3646
.3575
.4128
.4076
.4487
.3542
.3646
TABLE  7.   Correlation of particle counts in channels measured with cell
counts as  determined by visual identification for master stations.

                 _ Particle Count Channels _
                  5-10ym  10-20ym  20-40vim  40-80pm  80-150um  5-150ym R@.99
MAY
Total  cells/ml    .7741    .7457    .6633    .4938   -.0031    .7594   .4705
Microflagellates  .7635    .8502    .8702    .7604    .0996    .8345
Blue-green        .2499    -2475    .2267    ,1266   -.1237    .2544
Green           -.2156   -.1874   -.2019   -.1466    .2030   -.2118
Diatoms           .6764    -6300    .5086    .3196   -.0842    .6609
JUNE
Total cells/ml   .7285
Microflagellates .7025
Blue-green       .5585
Green            .3683
Diatoms          .6711
.7229
.6529
.4799
.3099
.7183
.2886
.2273
.2137
.0915
.3159
.3634
.3830
.2934
.1618
.3268
.5785
.7020
,6119
.3960
.4022
.7396
.6963
.5447
.3531
.7006
                                                                      .3646
                                   341

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 TABLE 7 continued.
                                   Particle Count Channels
                 5-10um  10-20uiQ  20-40ym  40-80ym  SO-lSOpm 5-150um R(3 99
 JULY
 Total cells/ml   .5348
 Microflagellates .5945
 Blue-green       .2602
 Green           -.3168
 Diatoms          .2670

 AUGUST
 Total cells/ml   .3829
 Microflagellates .5088
 Blue-green       .1658
 Green            .2100
 Diatoms         -.1235

 OCTOBER
 Total cells/ml   .2728
 Microflagellates .2417
 Blue-green       .2185
 Green           -.0448
 Diatoms           .2871
.7348
.7318
.2267
.2469
.4458
.6425
.7234
,0668
-.3000
.3298
.2366
.4296
.0305
-.3611
-.0150
.0492
.2380
-.0129
-.3174
-.1180
.5976
.6461
.2559
-.3110
.3157
                                                     -3646
         .5539
         .5852
         .2695
         .3640
         -.0850
         .3629
         .3114
         .2550
         .0900
         .3794
.5877
.2088
.5726
.5490
.0993
.3697
.3122
.2432
.1451
,3946
.4515
.2040
.4208
.3935
.0639


.2857
.2080
.1726
.2111
.3099
.3566
.5857
.0753
.1242
.0616


.2720
,1270
.0979
,4817
,3850
.4315
.5274
.2061
.2594
.1108
.2987
.2620
.2302
.0117
,3141
 3646
.3683
NOVEMBER
Total cells/ml    .7016   .7864     .7663     .7321
Microflagellates  .6825   .7546     .7259     .6820
Blue-green        .1852   .2525     .2580     .2633
Green             .2214   .3229     .3366     .3312
Diatoms           .8451   .8974     .8618     .8155
                                     .3292
                                     .3010
                                     .0963
                                     ,2367
                                     ,3709
                           .7447
                           .7195
                           .2151
                           .2660
                           ,8765
                          • 4128
FIIBITARY
             no
sienificant correlation
                                  342

-------
TABLE 7 continued.
                                   Particle Count  Channels
5-10ym  10-20vim
                                          40-80um  80-150um 5-150um R@.99
MARCH
Total cells/ml   .7902  .9153
Microflagellates .4044  .3124
Blue-green       .1572  .0675
Green            .1607  .1080
Diatoms          .7859  .9252
                 .9235    .8723
                 .2550    .3094
                 .0561    .1074
                 .0908    .0205
                 .9370    .8821
 .1203     .8594
 .0285     ,3851
-.0336     .1324
-.1611     .1447
 .1308     .8599
.3978
APRIL
Total cells/ml   .3377  .6315    .7988    .3606
Microflagellates .1600  .5214    .7264    .3448
Blue-green       .2735  .2678    .2139    .0735
Green           -.2955 -.0203    .0195    .1111
Diatoms          .3604  .6319    .7951    .3513
                                   .0484    .5265
                                   .0810    .3669
                                   -.0007    .2908
                                   .1912   -.1937
                                   .0342    .5407
                  .3542
JUNE
Total  cells/ml    ,5649   .7377     .7200     .7507
Microflagellates  .4940   .7240     .6280     .7013
Blue-green        .3517   .1963     .1364     .2331
Green             .2305  -.0226   -.0613   -.0383
Diatoms           .2918   .6295     .8430     .7275
                                   ,6478    .6476
                                   .6854    .5836
                                   .2214    .3336
                                   .0179    .1795
                                   .3852    .4073
                  .3683
 found at station 24,  which had  an extreme  peak at  the  15 m sample depth.
 Relatively high numbers were present  at  the surface  of station 10,  but
 declined below.  Stations 45 and 75 had  lower and  more vertically uniform
 abundances of diatoms,  although there was  a concentration  in the near-
 bottom sample from station 75.   Populations at station 96  were reduced
 from the levels noted the previous month,  but the  trend towards highest
 concentrations in the near-bottom waters was still evident.  In July,
 abundance of diatoms was notably reduced at all depths sampled at station
                                    343

-------
               MflT  15-19,  1972
    0    WOO
                  6006
                            8000
                                       WOO
                                                 MOO
0
90
1

00


> 2

10


<
1
24


> 2

45
i . f-f



75
'{ '
'•
>

96
0   .WOO
  IJ I  I
   'IT
    /
 200'
      10
               JUNE  12-16,   1972
                  6000
   woo
•I—t	h
                       us
                                      woo
                                   -I—I  (•
 .woo
           7S
96
   0    6000
s
iso
 200
              JULY 10-14,  1972
      10
                  WOO
                            woo
                                      woo
                                   -l-^t—h
           75
                                           96
 FIG. 57.  Vertical distribution of  total phytoplankton cell

 counts at master stations.
                       34A

-------
          RUGUST  21-24,  1972
              WOO
            I  I  I
                                 «000
    10
                           96
         OCT 30  - NOV  3,   1972
 0   WOO
M
200
            r-t - 1
               •000
                                 «OM
    10
                    i
24
                                          MOO
         96
         NOV  27 -  DEC 1.  1972
 .'.  . .«*y   .,.  ,MM
     10
          15
75
96
FIG. 57 continued.
                     345

-------
            FEBRUflRT 5-9,  1973
  so
fi 1
 200
      10
                eooo
                1	1-
214
           6000
        -t	1	1-
  woo
t  i—t-
 75
 .MM
96
           MRRCH 19-22,  1973
   0    8000
  OB—•	1  I
                woo

 200
     10
          ^
        I  I
                 i - 1
                                  woo
                           96
           RPRIL  2^-28f  1973
  0   WOO
               •000
          woo
                                  woo
                                           woo
0
s :
iso-
200

<
10

<
24

,
45


75
)'
1
96
FIG. 57 continued.
                    346

-------
                         JUNE  11-m.   1973
                                                   •75
           FIG.  57 continued.
96 and near the surface at  station 10,  but  remained relatively high at
lower depths.   Station 24 had similarly low surface values, but a distinct
peak at 15 m.   Station 45 had a similar peak at  15 m,  but  the surface
values were larger than at  station 24.   Station  75 had relatively high
surface values also and highest concentrations at 5 m.  Samples from
August and October showed relatively low abundance of  diatoms and relatively
uniform abundance at all depths sampled, although there was a slight
increase in abundance at all depths sampled at station 96  in October.   In
November there was a significant increase in abundance of  this group at
all depths sampled at station 96,  but numbers remained low and vertically
uniform at the other stations.  In February, abundance of  diatoms was low
throughout the water column at all stations sampled.   In March a slight
increase was noted at most  depths sampled at the main  lake stations and
very high numbers were present at station 96, with peak abundance
occurring in the near-bottom samples.  Abundance of  diatoms continued to
increase at the main lake stations sampled during the  April cruise but
remained relatively uniform throughout the water column.  Abundance
remained very high at all depths sampled at station  96.  In June 1973
abundance of diatoms was considerably reduced at station 96, although
distribution through the water column remained fairly  uniform.  Numbers
increased at the offshore stations with peak abundance occurring at  10  or
15 m depth, except at station 75, where highest  abundance was  noted  in
the surface sample.

The abundance of green algae  (Fig. 59) was more seasonal than that of the
diatoms, and during most months they were a quantitatively less important
part of  the total phytoplankton assemblage.  Samples  from the May 1972
cruise showed relatively low numbers of green algae and uniform distribu-
tion throughout the water column.  In June, numbers of green algae increased
                                     347

-------
    0    4000

   01"*'* '''-*•
  50
  200
       10
 MflT  15-19,   1972

    4000        4000        4000
-H—i—i—K     —+—i—i—t-    rr+—«—»—*•
                        75
            96
               JUNE  12-16,   1972
   P .   4000
    —-
                  4000
i
 200
      10
              4000
           H—I—i—*•
   1000
-t—1—<—t-
                     \
  75
  HOM
96
               JULY  10-m.  1972
   o    .1000
      I—t—*-
  SO'
 200
      10
                           -\ — t
                             4WO
                       75
                                   .1000
                                              I
            96
FIG.  58.  Vertical distribution of diatoms at master stations.
                         348

-------
            RUGUST  21-24,  1972
                WOO
                          «ooo
          1000
          HOOO
  80
  too


4
10


•
24
V
•

us
lilt"

1
75

i
>
96
           OCT 30 -  NOV  3,  1972
                                    1000
  too
      10
         75
                    HOOO
                 i  I I ••>•
         96
           NOV  27 -  DEC 1,  1972
   so
  too
       10
              .. ffp
                        1 1 4- 1
        lilt
45
75
                                             •1000
96
FIG. 58 continued.
                       349

-------
    P    4000

   81 »  *
   SO
  ZOO
       10
             FEBRUnRY 5-9,  1973
   WOO
-t—I—t—\-
          -» — I
                           woo
                                  jtOOO
                               -I—t—I—>•
                     75
t t  yeao
                                          96
             MRRCH 19-22.  1973
                  .1000
                               uoee
0
so
\
w

•
5
10


1
24


<
US

•
<
75

\
*
96
 P    «OM)

0
  SO
  200
             flPRIL  24-28,  1973
                 «000
            4000
                                    1000
                                              1000
•
1
10

1
2U

i
US
<
:
i
75
\
/
>
>
96
FIG. 58 continued.
                      350

-------
                         JUNE  11-14,   1973
                 «000
           »D
                10
                                        i  >-
                                                    UOM

75
96
         FIG. 58 continued.
significantly although vertical distribution of  populations  was very
irregular.  The major contributor during this month was Saenedesmus
bicellularis.  Samples from July showed  reduced  numbers and  most  signifi-
cant concentrations occurred below 10 m depth.   In August there was  a
large increase in the abundance of this group at stations 10,  24, and
96 and there appeared to be a significant concentration of populations at
10-20 m depth at these stations.  Numbers were lower  and less  vertically
stratified at stations 45 and 75.  By October,  abundance of  this  group had
been reduced to very low levels except at station 96,  and remained an in-
significant part of the assemblage at all stations sampled during November
1972 and February and March 1973.  In April a slight  increase  occurred at
most stations and depths sampled.  In June, very high abundance was  found
in the 10 and 15 m samples from station 96.  At  the other stations sampled
numbers remained relatively low, but subsurface  peaks were evident.

Compared to the other groups, the blue-green algae (Fig. 60) constituted
a relatively small part of the phytoplankton assemblage in most samples
from the master stations.  Small surface concentrations were noted at
station 96 in May and at stations 10, 24, and 96 in June. In  July,
highest concentrations of these organisms occurred below 10  m  at  stations
24 and 96.  The highest concentrations noted during this study were  found
in samples from the upper 10 m at station 96 during the August cruise.
By October relatively low levels of blue-green algae  were found at all
stations and depths sampled.  Although numbers were further  reduced,
populations were noted at most stations and depths during November.   In
February, March and April 1973 this group was mostly represented  by low-
level populations of Oscillatoria spp. occurring at depth.  During the
June 1973 cruise some increase in the abundance of this group was noted
at station 96 and in the surface samples from station 24.
                                     351

-------
    0 .   HMO
  SO
  200
       »—*—*-
       10
               MflT  15-19,  1972
    uooo
-»—I—t—t-
  2U
 1000
I—t—*•
 H000
1	1	1-
4000
          75
          96
   9    1000
     I I—I—h
  toe
               JUNE  12-16.  1972
      to
                        woo
                      75
                                  HOOO
                    96
               JULY  10-14,   1972
   0    WOO
     ' '  ' '
 200
   4000
•«—1—i—h
      10
  214
                         I  I I
 HOOD
           MOOO
                     4000
          75
          96
FIG.  59.  Vertical distribution of green algae at master

stations.
                        352

-------
            RUGUST  21-24,   1972
  0    4000
  OK ' '  ' '
 so-
  <
 too
      10
   4000
-»—t—I—H
 HOOT
•••» '»

+-££
                      75
 |1000
                    96
           OCT  30  -  NOV 3,   1972
   9    4000
  oT i  t t »
H  '
 20C
      10
                 4000
  24
              HOOO        4000
           I I  t l     i I I t t
45
 75
                      4000
                   > I  I t
96
           NOV  27 -  DEC  1.  1972

   P   4000        4000        4000        4000     .  . 4000
  aoo
1 1 t 1
1
10
— 1 — t— t — 1-
«
•
1
H
1 1 t V
t
e .

'
75

•
96
 FIG. 59 continued.
                        353

-------
            FEBRURRY  5-9,   1973
   p   1000
   of—i—i—t—»-
  so
  200
      10
   uooo
-1—I—I—>-
  24
         -»	1	H
                          UOOO
75
           4000
96
            MflRCH  19-22,  1973
   0   WOO
                 WOO
            MOOO
                                   WOO
  90
  200
— 1 ' 1 • < *•
1
10

\
24

,
45

1
75
— « — »- < i.

96
            RPRIL  24-28,  1973
                HMO
            KOOO
 WOO
                                            1000
c
90
\
»0

•
<
10


1
24


I
45

•
t
75
— 1 — 1 — 1 — H


96
FIG. 59 continued.
                     354

-------
                          JUNE  11-14,   1973
            N
            aoo
               .  .
                              HMO
                 10
24
             4000
75
          FIG. 59 continued.
As might be expected, the vertical distribution of microflagellates  (Fig.
61) was somewhat more restricted,  especially during  the  summer months,
than the other major groups of phytoplankton.   In May relatively high
numbers of organisms in this group were noted at station 96,  but other
stations had significantly lesser numbers.   By June  1972 abundance was
present in 5 m samples from stations 24 and 96 but numbers  remained
relatively low at other stations and depths sampled.   During  the July
cruise high abundance was noted at the 10 m depth of station  24 and  at
5 and 10 m samples from station 45.  Somewhat smaller concentrations
were found at 5 and 10 m depths at the other stations.  In  August highest
concentrations occurred in the 5 m samples  from stations 10 and 24.  Some-
what smaller numbers were noted at 10 m at  station 45 and 5 m from stations
75 and 96.  By October, numbers of this group had been reduced and
abundance was more uniformly distributed throughout  the water column.
Numbers were vertically uniform and relatively low at all stations
sampled during November 1972, except station 96 where numbers were
somewhat larger.  Abundance of this group was low at all stations and
depths sampled during February 1973, and only slight increases were
noted in March samples.  In April there was some increase at  station 96,
but numbers remained low at other stations sampled.   During June  1973
relatively high numbers of microflagellates were noted in all samples
from the top 20 m at all main lake stations, but considerably lower
numbers were present at station 96.  A notable secondary peak in abundance
occurred in the 30 m sample from station 45.
                                     355

-------
   pi — »•— t — «
        HMO
  90
  200
       10
               MRT  15-19,   1972
                   woo
  24
             uoco
          -«—I—I—h
                                       MOOD
            75
96
    P    WOO
       10
               JUNE  12-16.  1972
   vooo
I t  I—t-
                         _(—I
                            vooo
                                   -I-H
             4000
                      75
                      96
  of.
8  \
  SO
 200
      10
               JULY  10-14,   1972
   HOOP
i i  < — i-
                       MOOO
                              -. .
                     75
                      96
FIG. 60.  Vertical distribution of blue-green algae at  master


stations.
                        356

-------
          flUGUST 21-214,  1972
 ,i i re
     10
2U
                   4«£
         75
         96
          OCT  30 -  NOV  3,  1972
 so
     i >
     10
               I—»•
          •45

                                        -t—I I 1
                  96
          NOV  27  - DEC  1.  1972

               •AM        MUM       BOOB
  07 i i i~T    iii t 11    t I t  i i?   i I  t it   i  t I it
 SO
 zoo
     10
 24
US
75
96
FIG. 60 continued.
                      357

-------
             FEBRURRY 5-9,   1973
    0    4000

   01	1	1	1	H
                 4000
   50
  ZOO
      10
   1000
t t—I—t-
45
           HMO
         i—i—t-
          75
96
            MRRCH 19-22.  1973
    0   4000
                 4000
                          4000
  90
  200
                                            HOOO
1
10
1 1 1 !•
<
1 1 1 f
1
1
75
*
96
            flPRIL  24-28,  1973
                          4000
g
90
<
00<


1
10


!
24


<
45
— i — i i »•

^ <
75
-!• t I >-


96
FIG. 60 continued.
                    358

-------
             JUNE  11-14.  1973

1
10

4
24
,
,
US

'
75

1
96
FIG. 60 continued.
 200
     10
             MflY  15-19.  1972
   ._,-«    ,..  ..re   .  . . «y
                                *  i
 WOO
75
           W9
        i, t t >-
96
 80
 200
     10
             JUNE  12-16.   1972
                       I I I
75
96
 FIG. 61.  Vertical distribution of microflagellates at

 master stations.
                       359

-------
              JULY  10-m,  1972
   t    «000
  OK' ' '  '
S
  so
 100
                  HMO
      10
             HOOO
             "  «-
            us
             ION
          -I—I—I—•-
             Wit
                      96
             F1UGUST  21-24,  1972
      .woe
                  woo
                            uooo
 200
      10
              7
  24
                   V
  •15
                        KOOO
                     ^—t—»—»-
  75
                        UPM
  96
            OCT 30 - NOV  3,  1972
   f    HOOO
  01 » *  * »•
 200-
   HtOO
-t—t—I—»-
      10
   4000
-t—»—I—»-
            45

   1000
-»—t—I—I-
            75
   nooo
•tilt
            96
FIG. 61 continued.
                       360

-------
        NOV 21 -DEC 1.  1972
 P   HWO
  I  I I >
SO
    10
 4000
I I >
                       HMO
1000
1 t
   •WOO
-»—I—»—t-
                           96
          FEBRURRT 5-9,  1973
     4000
                   HOM
 SO

4
10
4
1
24

^
45

<
75

•
96
          MRRCH  19-22.  1973
6
SO
1
too
— 1 — I 1 >
•
•
•
1
10
. i t — »— t-
•
1
24
i t i i

1
15


1
7S


X
96
FIG. 61 continued.
                   361

-------
   p    woo
   Bl « «  « «
 5
 iso4
  2004
      10
             RPRIL  24-28.  1973
  yooo
24
   HOOD
I I  I I
                                     4000
 US
  4000
96
  50
i
              JUNE  11-14,  1973
                214
                                     woo
                                               uooo
                   75
                     96
FIG. 61 continued.
                     362

-------
                             DISCUSSION
Because of its geographical position,  Lake Ontario was the first of the
Great Lakes to receive substantial impact from the activities of western
man.  It has received, and continues to receive,  loadings of materials
originally introduced to other parts of the system.  This is, of course,
particularly true of conservative ions although there is undoubtedly a
considerable pass-through of more physiologically active materials.  As
a result we have only a very sketchy knowledge of what the original
quasi-equilibrium state of the system might have been.  In the case of
the primary producer communities, particularly the phytoplankton, there
has been no attempt to determine the previous composition and character-
istics of the flora as there has been in Lake Erie (Hohn 1969) and Lake
Michigan (Stoermer and Yang 1969).  In the case of Lake Ontario, recovery
of samples taken before significant environmental perturbation had
already occurred may not be possible, since the available evidence
suggests that large-scale and so far unreversed changes took place
very early in this system.

As is generally the case in the Great Lakes, the most extensive and
dramatic evidence of such change comes from the fisheries records
(Baldwin and Saalf-.ld 1962; Smith 1972; Parsons 1973).  These indicate
certain of the original top predator fish populations in Lake Ontario
collapsed several decades before similar occurrences in the upper lakes.
It would appear, in fact, that the high populations of Atlantic salmon
which were unique to Lake Ontario had essentially  been exterminated by
the turn of the century.  Although destruction of  the indigenous popula-
tions of desirable fish in the lake undoubtedly resulted from a combina-
tion of causes, some of which are only indirectly  related to changes  in
primary producer communities, the fact that subsequent attempts to
establish artificially managed populations of the  same species have met
with universal failure indicates  that fundamental  changes occurred in
the Lake Ontario ecosystem as early as the beginning of the  present
century.

Since,  as Davis  (1966) has noted, early  studies of primary producer
communities,  including phytoplankton,  from Lake Ontario are  scarce,
even compared  to the  other Great  Lakes,  the  true  nature and  magnitude of
change.in  the  open water  phytoplankton community  can  only be inferred
at  the  present time  from  comparison of slightly better known sequences
in  the  upper  lakes.   The  majority of  historic  studies which  are  avail-
able  (Burkholder and  Tressler  1932;  Tressler  and  Austin. 1940; Tucker
1948;  Tressler et al.  1953)  dealt primarily  or exclusively with  bays  or
other  areas which cannot  be  considered representative of  conditions  in
 the open  lake.   Both these studies,  and  more recent  studies  which treat
with similar  areas  or the nearshore waters  of Lake Ontario  (McCombie 1967;
Michalski 1968), however, have  reported  floras which could  only be
 interpreted  as  representative  of eutrophic  waters.   In light of reports
 of  gross  visual  pollution of the nearshore waters of Lake Ontario
 (MacKay 1930)  it would appear that  such  regions were substantially
                                  363

-------
disturbed before these studies  took place.

Although direct evidence of floristic change is lacking, it is clear that
the chemistry of the lake has been grossly altered since settlement (Beeton
1965, 1966, 1969) and that the  standing crop of phytoplankton has been
substantially increased (Schenk and Thompson 1965; Matheson and Anderson
1966; Davis 1966, 1969).  Comparison of the trends in Lake Ontario with
similar trends in the upper lakes leads to the conclusion that Lake
Ontario must be the most highly modified of the Laurentian Great Lakes
with the possible exception of  Lake Erie.  Beeton1s data suggest that
the degree of chemical change in Lake Erie and Lake Ontario are quanti-
tatively similar, although the morphometric oligotrophy (Rawson 1961) of
the latter body of water serves to somewhat modify biological effects.

Most recent studies have served to emphasize the fact that Lake Ontario
is more severely eutrophied than commonly supposed.  High levels of
phytoplankton standing crop are present in all areas of the lake during
most of the year (Chau et al. 1970; Nicholson 1970; Glooschenko et al.
1973) and primary production (Glooschenko et al. 1974) is, among the
Great Lakes, second only to Lake Erie and exceeds it during certain
seasons.  Studies of the composition and seasonal succession of the phyto-
plankton community (Nalewajko 1966, 1967; Ogawa 1969; Reinwand 1969;
Munawar and Nauwerck 1971) have revealed a flora dominated by species
either tolerant of or requiring eutrophic conditions for growth and extreme
successional patterns not characteristic of less modified regions of the
Laurentian Great Lakes.  Species belonging to the oligotrophic diatom
association (Hutchinson 1967) which are a major component of the offshore
flora in the upper lakes,  are apparently largely absent from Lake Ontario.

Studies of the nutrient chemistry of the open waters of Lake Ontario in-
dicate the presence of high levels of phosphorus and summer depletion
of both silica and nitrate.   It has been shown that phosphorus is the
primary element controlling eutrophication in the Laurentian Great Lakes,
and Schelske and Stoermer (1971, 1972) have postulated that increased
loadings of this nutrient into the system, in addition to simply increas-
ing gross productivity, substantially modify the composition and seasonal
succession of phytoplankton flora indirectly.  It appears that increased
productivity due to increased phosphorus input leads first to depletion
of silica and replacement  of the perennial diatom flora during the
summer stagnation by groups not requiring silica.   Further increases in
phosphorus loadings result in depletion of nitrogen sources in the
epilimnion during stratification and confer competitive advantage on
the nitrogen fixing species of blue-green algae.  Both the chemical and
biological results available to date suggest that Lake Ontario has already
passed the first of these  geochemical thresholds and is approaching the
second.  Indeed, as will be discussed later,  it appears that nitrogen
limitation is reflected in the composition of the late summer flora in
certain areas of the lake  at the present time.

The results of the present study largely confirm the trends and conditions
which might be deduced from previous work.  It is quite clear that, although
                                   364

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Lake Ontario is part of the same physical system,  it is floristically in
a different province from the upper lakes,  above Lake St. Clair.    The
phytoplankton assemblages  present are completely dominated by species which
are apparently not indigenous to the upper lakes and which, even  under
present conditions, are abundant only in nearshore regions which  have
suffered considerable impact from man's activities.  All of the diatom
species which Hohn (1969) found becoming predominant in western Lake
Erie as pollution increased are present in the offshore flora of  Lake
Ontario and many of them are the dominant elements of spring and
winter assemblages.  Species of green algae which are absent or present
only in very low abundance in the offshore phytoplankton of the upper
lakes completely dominate the summer and early fall flora.

Many of these species are capable of producing nuisance conditions of
various sorts.  Many of the small, colonial species of Stephanod-isous,
such as 5. bi.ndera.nus and S. tertuis, have been implicated in taste and
odor and filter clogging problems in local regions of Lake Michigan
(Vaughn 1961),  Some of the species of blue-green algae present such as
Aphanizomenon flos-aquae and Anaoystis oyanea are almost universally
associated with nuisance summer blooms in temperate lakes.  Indeed,
considering the abundance and wide distribution of potentially nuisance
producing phytoplankton species in Lake Ontario, it is somewhat sur-
prising that the most commonly reported nuisance appears to be caused
by overgrowths of benthic algae, particularly Cladophora spp.

One of the more surprising results of our study was the evident almost
total absence of certain species which are universally among the dominant
forms in the offshore waters of the upper lakes,  We noted less than
50 occurrences of all of the species of the diatom genus Cyolotella
which form the predominant association in the offshore waters of Lake
Huron and Superior and are an important component of offshore assemblages
in Lake Michigan.  Other species usually considered "characteristic" of
Great Lakes phytoplankton assemblages, such as Rhisosol&nia eviensi-s,
were very rarely noted in our samples.  So far as the diatom component
of the phytoplankton was concerned, there was a very striking similarity
between the trends in abundance of taxa found in our samples from Lake
Ontario, particularly the eastern part of the lake, and  those reported
by Hohn (1969) from western Lake Erie.  The elements of  the phytoplankton
flora which are common to both Lake Ontario and the upper  lakes are those
apparently eurytopic species such as Astei"ionella formosa, Fragilaria
crotonensi.s3 Arikistrodesmus falcatus3 Botryoaocaus braunii, Cryptomonas
evosa etc. which  enjoy almost universal distribution in  both oligotrophic
and eutrophic  lakes.  According to Hohn, the absolute abundance of some
of the diatom species  in this group did not change appreciably in
Lake Erie between  1938 and  1965, which furnishes some notion of their
tolerance.  At the present  time the  species cited  above, and several
others, appear to  be universally distributed in all areas  of the
Laurentian Great  Lakes.

Another striking  feature of  the species composition of  phytoplankton
assemblages  is the  large number of  species present  whose general  distrib-
ution  includes freshwater  habitats with considerable  conservative ion
                                   365

-------
 contamination and,  in many instances,  brackish water.   In searching the
 general literature  on phytoplankton species distribution one finds, with
 rather monotonous regularity,  dominant and subaumj.nant taxa in Lake
 Ontario described as having most abundant occurrences  in brackish and
 saline inland waters,   This serves to  emphasize the fact that,  while
 compositional changes which have occurred in the Great Lakes are  generally
 attributed  to eutrophication,  in the strict sense,  they really result
 from complex and  interacting changes in the total chemical  and physical
 milieu.   While chlorides  have  apparently increased  in  Lake  Ontario by
 over a factor of  3,  it still can hardly be considered  as brackish
 water.  It  may be,  however,  that the only species adapted to the  physical
 conditions  in the Great Lakes  come primarily from saline water, and
 any  considerable  increase in conservative ion levels selectively  favors
 increase in their abundance.   It would appear that  some general factor
 is operational, as  the same  distributional tendency is also found in
 some groups of invertebrates.

 Another  unusual characteristic of phytoplankton assemblages in  Lake
 Ontario,  compared to the  upper lakes,  is  the extreme abundance  of
 microflagellates, and  particularly apparently heterotrophic species.  The
 same observation  has been emphasized by Munawar and Nauwerck (1971).
 While autotrophic flagellates  are universally present  and occasionally
 constitute  an important part of  the phytoplankton assemblages of  the
 upper lakes,  the  extreme  abundance of  such species  and  particularly the
 relative importance  is, in our experience,  highly unusual.   Although our
 work furnishes no direct  support  for such a hypothesis,  it might  be
 inferred that the waters  of Lake  Ontario  have higher organic loadings than
 the  upper Great Lakes.  The  same  might  be inferred  from the apparently
 very high levels of  "microzooplankton"  observed in  many  of  our  samples.
 Although we made no  quantitative  estimates  of  abundance of  these  organisms
 many of  our samples  contained  astonishing numbers of ciliate protozoa
 and  small rotifers.   The  high  abundance of  such forms was one of  the
 strikingly gross qualitative differences  between prepared samples  from
 Lake Ontario and similar preparations made from  samples  from  the upper
 lakes.

 Our  results also indicate that the  seasonal  succession of phytoplankton
 in Lake  Ontario is much more pronounced than  is  characteristic for less
disturbed areas of the Great Lakes.  The  thermal bar (Nalewajko 1966)
 appears  to be an important factor  in controlling  the early spring changes
 in abundance  and composition of the phytoplankton assemblage.  Similar
 effects have  been noted in the upper lakes, but appear to be largely
 confined to the nearshore waters, whereas the spring pulse following
development of the thermal bar appears  to proceed all the way across
 Lake Ontario,  According to the available evidence  (Gachter et al. 1974)
 it appears that this strong spring pulse results in selective depletion
of nutrients  essential to the species dominant  in the spring flora, and
 sets  the stage for the development of the thermal tolerant species
 characteristic of the summer and   fall floras.   In this regard it must be
very strongly emphasized that our results probably represent an atypical
case,  so far as seasonal succession is  concerned.  As previously noted,
                                  366

-------
the spring of 1972 was unusually cold and wet.   Chandler's early work
on the western basin of Lake Erie (1940,  1942,  1944)  has demonstrated
the profound effects of local meteorological conditions on the abundance
and seasonal succession of phytoplankton  communities  in disturbed areas
of the Great Lakes,  It is readily apparent that the  successional trends
noted during the spring of 1973 are more  similar to those reported in
previous investigations than those noted  in the same  period of 1972.   It
should also be noted that any results from monthly or bi-monthly sampl-
ing periods should be treated with caution in such a  highly forced
system.  Due to the apparent high reproductive potential of many of the
dominant forms in the Lake Ontario phytoplankton assemblage, significant
peaks in abundance may have been either missed or considerably under-
emphasized.  In the present case it is obvious that samples from
September 1972 and May 1973 would have been very valuable in attempting
to determine the true pattern of seasonal succession.

Although the extreme degree of instability apparent in the Lake Ontario
system renders general conclusions somewhat difficult, certain patterns
are apparent.  There appears to be a general pattern of development
of the spring bloom and subsequent successional changes to develop first
at the eastern and western ends of the lake, then spread along the
southern shore before becoming evident along the northern shore, and
eventually the mid-lake region.  Certain species appear to follow
slightly different patterns which may be genuine or,  in some instances,
the result of the particular time frame examined by the sampling
sequence, but the overall pattern appears to be reasonably consistent.
In this regard Lake Ontario appears to differ significantly from its
nearest analog, Lake Erie, where the quantitative and qualitative aspects
of the phytoplankton flora appear to be strongly controlled by morpho-
metric and nutrient gradients  from the western  to the eastern end of the
lake.  Successional patterns in Lake Ontario compare poorly with those
noted in the upper lakes, where the only common feature appears to be
the nearshore development of a spring bloom which is apparently controlled
by the thermal bar.  Recent results indicate that a strong shift towards
summer dominance by green and  blue-green algae, somewhat  similar to
that noted in Lake Ontario although quantities  and dominant species
involved are not comparable, is now a feature of the southern basin of
Lake Michigan although this has not been noted  in previous studies.

Our results also indicate that certain regions  of the lake are more
highly eutrophied  than others.  In general, the shallow region  from  the
vicinity of Nine Mile Point around  the eastern  and northeastern  shore
to Point Petre was  the region  in which bloom conditions were  first
noted  and  where average  phytoplankton densities were largest  throughout
a significant portion of  the year.   It was also in this region  that  the
highest and most persistent populations  of extremely pollution  tolerant
forms  such as Aphanizomenon f1os-a.qu.ae and Cosconodisaus  subsalsa were
noted.   It would appear  that at least some of  these  populations may  first
develop  in the numerous  shallow bays  in  this region  and  subsequently
spread  into  the open waters of Lake  Ontario,   Although our  samples
furnish  no direct  support  for  this  supposition,  similar  occurrences  were
                                   367

-------
noted at stations in the vicinity of Presqu'ile Bay where there are exten-
sive shallows connected to the Bay of Quinte by the Murray Canal,  This
sort of "morphometric control" of phytoplankton composition, which
Gachter et al, (1974) propose as an important mechansim in eutrophied
regions of the Great Lakes, is probably also operational in our results
from other regions of the lake.  It might be suspected that strong
gradients would be present in regions of high population concentration
and consequent material loadings to the lake, such as areas near Toronto,
Hamilton, the Niagara outlet, Rochester, and Oswego.  Effects of these
regions on phytoplankton abundance and assemblage composition are indeed
apparent in our results in a large number of cases but the patterns are
less consistent than those visible in the eastern region of the lake.
In this respect it should be pointed out that while we have rather
loosely referred to stations nearest shore as nearshore samples, none of
our stations were actually In the highly impacted nearshore zone as common-
ly defined in recent work on the Great Lakes.  Although a general pattern
of the impact of these regions on phytoplankton dynamics in Lake Ontario
can be inferred from our work, critical evaluation of such impacts will
depend on the results of other IFYGL projects which have concentrated  on
nearshore boundary regions.
                                  368

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                               373

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                                  TECHNICAL REPORT DATA
                           (Pk-ax rraJ lnslructitmx on the reverse before eomplcnnjt)
 (UPORT NO
   EPA-660/3-75-004
2.
 TITLE AND SUBTITLE
 PHYTOPLANKTON COMPOSITION AND ABUNDANCE
 IN  LAKE ONTARIO DURING IFYGL
                                                          3. RECIPIENT'S ACCESSION-NO.
                              6. REPORT DATE
                               July  1974
                              6. PERFORMING ORGANIZATION CODE
 AUTHQR(S)
 E. F.  Stoermer, M. M. Bowman,  J.  C.  Kingston
 A. L.  Schaedel
                              B. PERFORMING ORGANIZATION REPORT NO.

                                 EPA-660/3-75-004
 PERFORMING ORG "VNIZATION NAME AND ADDRESS
 Great  Lakes Research Division
 The University of Michigan
 Ann Arbor,  Michigan  48105
                              1O. PROGRAM ELEMENT NO.

                                1BA026
                              11. CONTRACT/GRANT NO.

                              RB00605
?. SPONSORING AGENCY NAME AND ADDRESS
 Environmental Protection Agency
 NEPC-Grosse lie Laboratory
 Grosse lie, Michigan  48138
                              13. TYPE OF REPORT AND PERIOD COVERED
                               FINAL
                              14. SPONSORING AGENCY CODE
^SUPPLEMENTARY NOTES
61. ABSTHACT
 Based on samples collected during the International  Field Year for the  Great Lakes,
 the phytoplankton assemblage of Lake Ontario is dominated by taxa indicative of
 degraded water quality,  including many potentially nusiance producing species.   Many
 taxa characteristic of  the offshore waters of the upper Great Lakes are either absent
 from the flora or very  rare.   Compared to the upper  lakes, the flora of Lake Ontario
 undergoes extreme seasonal succession, with diatoms  predominating during the winter
 and early spring, green algae becoming abundant during the summer, and  blue-green
 algae showing a distinct fall peak.  Various species of microflagellates are a
 relatively important  element of the flora during all seasons.  Succession during the
 spring bloom appears  to be controlled by the thermal bar, and our data  suggest contro
 by depletion of essential nutrients following stratification.  Striking differences
 were apparent in samples collected on comparable dates in the spring of two successiv
 years.  These differences apparently result from exceptional weather conditions which
 prevailed during the  first saffipling period.  The distribution of species particularly
 tolerant of disturbance appeared to be controlled by both proximity to  major
 population centers and  lake morphometry.  The abundance of halophilic  species in most
 productive areas suggests effects of conservative  ion contamination as  well as
 nutrient enrichment.
7.
                               KEY WORDS AND DOCUMENT ANALYSIS
                 DESCRIPTORS
  Algae
                 b.IDENTIFIERS/OPEN ENDED TERMS  |c. CCSATI Field/Group
                  Lake Ontario, IFYGL,
                  Phytoplankton
18. DISTRIBUTION STATEMENT
  RELEASE UNLIMITED
                 19. SECURITY CLASS (This Report)
                                            21. NO. OF PAGES
                                              20. SECURITY CLASS (Thit page)
                                            22. PRICE
EPA Form JJJO-1 (9-73)
                            * U. S. GOVERNMENT PRINTING OFFICE: 1975-698-023/97 REGION 10

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