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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facilitate further development and application of environmental
technology. Elimination of traditional grouping was consciously
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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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This report has been reviewed by the Office of Research and
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policies of the Environmental Protection Agency, nor does mention
of trade names or commercial products constitute endorsement or
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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
-------
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.
-------
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
-------
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
-------
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 '
\
\
^\.
\
\
\
_~- -
\
\
\
\
I
\
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
-------
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
-------
TOROfTO
NMUM
MRY 15-19. 1972
20000.00
ROCHESTER
TORONTO
MflT 24-25. 1972
D
FIG. 5 continued,
ROCHESTER
20000.00
41
-------
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
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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
\
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\
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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
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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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MRY 15-19, 1972
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RUGUST 21-24, 1972
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OCT 30 - NOV 3, 1972
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JUNE 11-14. 1973
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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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FIG. 9 continued.
84
-------
JUNE 12-16. 1972
0 10000.0 M 80000.0 a 60000.0 t 0000.0
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JUNE 12-16. 1972
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FIG. 9 continued.
85
-------
JUNE 12-16. 1972
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FIG. 9 continued.
86
-------
JULY 10-14, 1972
tMot eoooo eoooo
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FIG. 9 continued.
87
-------
flUGUST 21-24, 1972
so
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FIG. 9 continued.
89
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g BOOM
OCT 30 - NOV 3, 1972
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FIG. 9 continued.
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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93
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MflRCH 19-22. 1973
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FIG. 9 continued.
94
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MRRCH 19-22, 1973
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95
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RPRIL 214-28, 1973
MOM «MM CMOO MMO «XJM MOM
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FIG. 9 continued.
96
-------
JUNE 11-m. 1973
«__««« , ,««fM
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FIG. 9 continued.
97
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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
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JUNE 12-16. 1972
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JULY lO-lil. 1972
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OCT 30 - NOV 3. 1972
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NOV 27 - DEC 1, 1972
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FEBRURRY 5-9, 1973
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108
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FEBRURRY 5-9, 1973
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109
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MRRCH 19-22, 1973
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110
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RPRIL 214-28, 1973
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FIG. 10 continued.
112
-------
JUNE 11-Hi. 1973
B 100 WO WO 100 tOO WO MO WO . . WO . . WO
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FIG. 10 continued.
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
-------
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
-------
OCT 30 - NOV 3. 1972
TOftOKTO
ROCHESTER
NOV 27 - DEC 1, 1972
TORONTO
FIG. 11 continued.
117
-------
FEBRUflRT 5-9, 1973
70ROKTO
MRRCH 19-22, 1973
HBVTL10H
FIG. 11 continued,
ROCHESTER
6000.00
118
-------
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
-------
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
-------
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
-------
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
-------
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
-------
MflT 15-19, 1972
lowrno
ROCHESTER
JUNE 12-16. 1972
KOtSTER
FIG. 14. Assemblage diversity (Shannon-Weaver index)
129
-------
JULY 10-14, 1972
TORONTO
HfWVTCN
ROQtSTEfl
RUGUST 21-24, 1972
TORONTO
TOCHESTER
FIG. 14 continued.
130
-------
OCT 30 - NOV 3. 1972
\
\
\
\
\
\
A
\
\
- _ .
\
~^
\
\
A.
\
\
V
\
\
v
\
\
^S
\
\
Sos^
WWU1
,3.00
»-0
ROOCSTER
NOV 27 - DEC 1. 1972
TORONTO
FIG. 14 continued.
131
-------
FEBRURRT 5-9, 1973
TOROmO
IUVD1
MflRCH 19-22. 1973
TDFIONTO
IBOl.
ROQtSTER
FIG. 14 continued.
132
-------
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
-------
MfiY 15-19. 1972
TORONTO
tWILTON
NIAGARA
WVEft
ROCHESTER
TORONTO
JUNE 12-16. 1972
HFK1ILTON
ROCHESTER
FIG. 15. Distribution of Asterionella formosa.
135
-------
TORONTO
HRMILTON
NTRGflRfl
RIVER
JULY 10-14. 1972
ROCHESTER
TORONTO
HflMILT
NJflCflfift
RIVtft
RUGU3T 21-211. 1972
ROCHESTER
FIG. 15 continued,
136
-------
TORONTO
HRMILT
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
NIRGHW
RIVER
NOV 27 - DEC 1, 1972
ROCHESTER
FIG. 15 continued,
137
-------
FEBRURRY 5-9. 1973
TORONTO
MW1ILTON
RIVER
ROCHESTER
MRRCH 19-22. 1973
TORCNIO
HflMILT
NlfiGRRfl
Rivtn
ROCHESTER
FIG. 15 continued.
138
-------
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
-------
TORONTO
HflHILTl
NIRCflflfl
RIVER
MflT 15-19. 1972
ROCHESTER
TORONTO
NIHCflRR
RIVCR
JUNE 12-16. 1972
ROCtCSTLB
FIG. 16. Distribution of Coscinodisous subsalsa.
141
-------
TORONTO
HftHILT
NlflCHW
RIVER
JULY 10-14, 1972
KJCWESTEB
TORONTO
HBMILT
NIfiGflRfl
RIVER
RUGUST 21-24, 1972
ROCHESTER
FIG. 16 continued.
142
-------
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
-------
TORONTO
NJBCflRfi
RIVER
FEBRUflRY 5-9, 1973
ROCHESTER
TOftWTO
NlfiGFW
RIVEfl
MRRCH 19-22. 1973
ROCHESTER
FIG. 16 continued.
144
-------
TORONTO
NlfiGfWfl
RIVER
flPRIL 24-28, 1973
ROCHESTER
TORONTO
HflMILTl
NIAGARA
RIVER
JUNE 11-114, 1973
ROCHESTER
FIG. 16 continued.
145
-------
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
-------
TORONTO
JULY 10-14, 1972
\ v \
HM1IUON
NIRGflRR
RIVER
ROCHESTER
TORONTO
MfiMILTON
NIRGfiflfl
RIVtR
RUGUST 21-24, 1972
ROCHESTER
FIG. 17 continued.
-------
TORONTO
MRMILT
NIRGflRfl
RIVER
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
HflMILTON
NJRGflRft
RIVER
NOV 27 - DEC 1, 1972
ROCHESTER
FIG. 17 continued.
148
-------
TORONTO
HfiNILION
NIRGRRfl
RIVER
FEBRURRT 5-9, 1973
ROCHESTER
TORONTO
HflNILTON
NIRGflRfi
RIVER
NRRCH 19-22, 1973
ROCHESTER
FIG. 17 continued.
149
-------
HflHILTON
NIRGflftH
RIVER
nPRIL 24-28, 1973
ROCHESTER
TORONTO
JUNE 11-14, 1973
HflMILlOH
NIRGKVt
R1VIR
ROCHESTER
FIG. 17 continued.
150
-------
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
-------
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
-------
TORONTO
fRIILTON
NIRGRRH
RIVER
JULY 10-14. 1972
ROCHESTER
TOROKTO
tWULT
NlRUWl
RIVER
flUGUST 21-2U. 1972
ROCHESTER
FIG. 18 continued
153
-------
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
-------
HmiLTON
FEBRURRY 5-9. 1973
NlfiGWA
RIVER
ROCHESTER
TORONTO
HRMILTON
MRRCH 19-22. 1973
NJRGffiR
RIVLfl
ROCHESTER
FIG. 18 continued.
155
-------
TORONTO
HHMIUTON
NIRGRRfl
RIVER
RPRIL 24-28, 1973
ROCHESTER
TORONTO
JUNE 11-1H. 1973
HfltltUON
RIVES
WJCHESTER
FIG. 18 continued,
156
-------
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
-------
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
-------
TORONTO
HfWlLTl
NIBGflfW
RIVER
JULY 10-14. 1972
ROCHESTER
TORONTO
filiGUST 21-24, 1972
NIRGfiRB
RIVER
ROCHESTER
FIG. 19 continued.
159
-------
OCT 30 - NOV 3. 1972
TORONTO
HRHILTi
NJfiGOFfi
RIVEfl
ROCHESTER
TORONTO
NRHILTON
NOV 27 - DEC i. 1972
ROCHESTER
FIG. 19 continued.
160
-------
TORONTO
HflMILT
NlflGflRfl
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
MRHIU
NIRGRRfl
RIVER
MRRCH 19-22. 1973
ROCHESTER
FIG. 19 continued.
161
-------
TORONTO
RIVCR
flPRIL 24-28, 1973
ROCHESTER
TORONTO
JUNE 11-14, 1973
HfltllUOC
NJHGHfW
RIVER
ROCHESTER
FIG. 19 continued.
162
-------
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
-------
MflT 15-19, 1972
TORorno
NIRGRRfl
BJVER
ROCHESTER
JUNE 12-16. 1972
TOHONTO
Hf»MJLT
ROCHESTER
FIG. 20. Distribution of Melosira islandica.
16A
-------
TORONTO
N1RG8RP
RIVER
JULY 10-14, 1972
ROCHESTER
TORONTO
HRMIUC
NIRGfW
RIVES
RUGUST 21-2»A. 1972
FQCtCSTEK
FIG. 20 continued
165
-------
TOflCWTO
HfltllLTi
NJRSWfl
fUVEfi
OCT 30 - NOV 3. 1972
FOOIESTEfl
TORONTO
WILT
NOV 27 - DE!C 1. 1972
ROCHESTER
FIG. 20 continued.
166
-------
TORWTO
MflHILT
NIRGWfl
8IVER
FEBRUflRT 5-9. 1973
ROCHESTER
TORONTO
HfifllLTON
HflRCH 19-22. 1973
BOOCSTER
FIG. 20 continued.
167
-------
TOfWTO
HAMILTON
NJBSW
RIVEfl
RPRIL 24-28, 1973
ROCHESTER
TORONTO
H8WLT
NIRGPiHR
FUVEfl
JUNE 11-14, 1973
ROCHESTER
FIG. 20 continued.
168
-------
TORONTO
MflY 15-19, 1972
NlRGflHfl
RIVER
ROCHESTER
TORONTO
JUNE 12-16. 1972
NIRGHOR
RIVtfl
ROCMES1ER
FIG. 21. Distribution of Nitzschia baaata.
169
-------
JULY 10-14. 1972
TORONTO
WWIUOH
RIVER
TOCHESTEfl
HUGUST 21-24. 1972
TORONTO
HttlILT
RIVER
ftOOCSTER
FIG. 21 continued.
170
-------
TORONTO
WILT
NIRGFBR
RIVER
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
RIVER
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 21 continued.
171
-------
FEBRURRT 5-9, 1973
TORONTO
tiflrilLTi
NIRGflRP
RIVEB
ROCHESTER
TORONTO
MflRCH 19-22. 1973
HRNtLTi
ROCHESTER
FIG. 21 continued.
172
-------
TORONTO
RPRIL 24-28. 1973
NIRCWtfl
RIVER
ROCHESTER
TORONTO
tlfifllU
NlRGRflfl
RIVER
JUNE 11-14. 1973
fWCMESTER
FIG. 21 continued.
173
-------
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
-------
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
-------
TOROMO
HfWILTi
NIRGfiflfl
RIVEfl
JULY 10-1U. 1972
ROCHESTER
TOBOOTO
HBttlU
RJGUST
ROCHESTER
FIG. 22 continued.
176
-------
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
-------
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
-------
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
-------
TORONTO
HRHILTi
NIBCflRfl
RIVER
OCT 30 - NOV 3, 1972
ROCHESTER
TORONTO
HRHILTi
NlRGfW)
RIVEfl
NOV 27 - DEC U 1972
ROCHESTER
FIG. 23 continued.
183
-------
TORONTO
HfiMILTI
NIMflRB
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORWfTO
MRRCH 19-22, 1973
HRMILTON
RIVER
ROCHESTER
FIG. 23 continued.
184
-------
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
-------
TORONTO
MPMILTi
NlfiCHW
RIVER
JULY 10-m, 1972
ROCHESTER
TORONTO
MflMILTl
RIVER
fiUGUST 21-24, 1972
ROCHESTER
FIG. 24 continued.
187
-------
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
-------
TORONTO
HRMILTON
NIRGHW
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
HflMILTON
MRRCH 19-22, 1973
N1RWRA
WVER
ROCHESTER
FIG. 24 continued
189
-------
TORONTO
HRHrUON
NJflGRRR
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
NRHIUON
macaw
RJVER
JUNE 11-14. 1973
ROCHESTER
FIG. 24 continued.
190
-------
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
-------
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
-------
TORONTO
HPHIUON
NIRGSRR
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
HAMILTON
RIVER
JUNE 11-14. 1973
ROCHESTER
FIG. 25 continued.
196
-------
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
-------
TORONTO
HPMILTON
NIRGFRfl
RIVER
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
HflhILTON
NlfiOW)
RIVER
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 27 continued,
205
-------
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
-------
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
-------
TORONTO
MfiMILTON
NIRGfifW
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
HHMILT
NIftGflflfl
RIVER
MRRCH 19-22. 1973
ROCHESTER
FIG. 28 continued,
212
-------
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
-------
TORONTO
HPHILTON
NJRGRRB
RIVES
JULY 10-14. 1972
ROCHESTER
TORONTO
HRHIL10N
RIVER
RUGUST 21-24, 1972
IWCMESTER
FIG. 29 continued.
215
-------
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
-------
I3JJ
TORONTO
HHMILTON
RIVEft
RPRIL 24-28, 1973
,077 "C 1148
ROCHESTER
JUNE 11-14, 1973
HAMILTON
RIVCR
ROCHESTER
FIG. 29 continued.
218
-------
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
-------
MflY 15-19, 1972
TORONTO
HWIUT
ROChESTEfl
Tonomo
WHIUTON
NTfiGflflfl
RIVER
JUNE 12-16. 1972
POCHCSIEfl
FIG. 30. Distribution of
220
-------
TOfWIO
hRMTLT
NJPCfWfl
RIVER
JULY 10-114. 1972
ROCHESTER
TWWIO
MWILT
flUGUST 21-214. 1972
WJCHESIEfl
FIG. 30 continued.
221
-------
TORONTO
HWITUtl
NIRGRfW
RIVER
OCT 30 - NOV 3. 1972
ROCHESTER
TORorrro
tlflttlU
NlRGftflfi
PIVER
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 30 continued.
222
-------
TORONTO
HPNILT
FEBRURRT 5-9, 1973
ROCHESTER
TORONTO
MflRCH 19-22, 1973
MIRGfWl
RIVER
ROCHESTER
FIG. 30 continued,
223
-------
RPRIL 24-28, 1973
TORONTO
NJRGflRP
RIVER
ROCHESTER
TORONTO
HflNILT
N1RGHW
RIVER
JUNE 11-14, 1973
ROCHESTER
FIG. 30 continued.
224
-------
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
-------
TORONTO
HRMILTON'
MflY 15-19, 1972
WJOCSTEfl
TORONTO
JUNE 12-16, 1972
HW11LT.
ROCHESTER
FIG. 31. Distribution of Synedva ostenfeldii.
226
-------
10RONTO
NlflWR
RIVER
JULY 10-14. 1972
hOCtCSTEfl
TORONTO
RUGUST 21-24. 1972
FIG. 31 continued,
227
-------
TORONTO
HflMILTi
NIflSRfW
RIVER
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
HW1ILTI
MIRGRHR
RIVEfl
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 31 continued.
228
-------
TORONTO
tfltlILT
NlflGflRR
RIVER
FEBRUflRT 5-9. 1973
ROCHESTER
TORONTO
MBHILT
NIflGfWfi
RIVER
MflRCM 19-22, 1973
ROCHESTER
FIG. 31 continued,
229
-------
Towro
hFWILTi
MWWfl
RIVER
flPRIL 24-28. 1973
fttEHESTER
TORONTO
MBNILTI
NJRCflflfl
RIVEB
JUNE 11-14. 1973
ROCHESTER
FIG. 31 continued.
230
-------
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
-------
JULY 10-14. 1972
TORONTO
NlftGflflfl
RIVER
ROCHESTER
fiUGUST 21-24, 1972
TORON10
HflMILTON
ROCHESTER
FIG. 32 continued.
232
-------
TORONTO
MRMILT
NJRGfiRR
RIVER
OCT 30 - NOV 3. 1972
ROCHESTEB
TOfWWTO
NOV 27 - DEC 1, 1972
hWIILTl
NIRGWR
RIVCR
fOCMCSTCO
FIG. 32 continued.
233
-------
FEBRURRT 5-9, 1973
TORONTO
NIRGWW
RJVER
ROCHESTEB
TOIWO
HWIILT
HfiRCH 19-22. 1973
NJR'JfW)
RIVEfl
ROCrCSTCT
FIG. 32 continued,
234
-------
TORONTO
NJRGflRft
RIVER
fiPRIL 24-28. 1973
ROCHESTER
TORONTO
JUNE 11-1H. 1973
HRMtLT
NJRGflfift
RIVEB
noctesrcB
FIG. 32 continued.
235
-------
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
-------
TORONTO
HBMILT
NlflCflflfl
RIVER
MflT 15-19, 1972
ROCHESTER
TORONTO
MflWLTi
JUNE 12-16. 1972
RIVER
FIG. 33. Distribution of Ankistifodesmus falaatus.
237
-------
TOflCTTO
HftMJLT
NJflGflfifl
RIVER
JULY 10-14. 1972
ROCHESTEfl
TORONTO
HWILTi
NIflCflflfl
RIVER
flUGUST 21-24, 1972
ROCHtSTER
FIG. 33 continued,
238
-------
Tonowro
BfiMILT!
KlflCfiflfl
RIVEfl
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
HflhIU
MJflCflflfl
flivtn
NOV 27 - DEC 1. 1972
FIG. 33 continued.
239
-------
TORONTO
NJRCfiflfl
RIVEfi
FEBRUflRT 5-9. 1973
ROCHESTER
TORONTO
HAMILTON
RIVCB
MflRCH 19-22. 1973
ROCHESTER
FIG. 33 continued.
240
-------
TORONTO
NJflSflflfl
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
NIRGfWfl
KIVEfl
JUNE 11-14, 1973
ROOCSTLR
FIG. 33 continued.
241
-------
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
-------
MRT 15-19. 1972
TORONTO
RUGUST 21-24, 1972
HRNIUON
NJWWW
wvtn
ROCHESTER
FIG. 34. Distribution of Botvyoooocus bvaunii.
243
-------
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
-------
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
-------
TORONTO
WMILT
NJBGPRfl
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
tWIJLTON
MRRCH 19-22. 1973
ROCHESTER
FIG. 35 continued,
246
-------
TORONTO
HfiMILT
NIflGfflfi
RIVER
RPRIL 24-28, 1973
ROCHESTER
TORONTO
HRf.tLTON
NIBGPRft
RIVtR
JUNE 11-14. 1973
ROCHESTER
FIG. 35 continued.
247
-------
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
-------
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
-------
JULY 10-14. 1972
5172
TORONTO
HAMILTON
NJRCW
RIVER
TOBOKTO
RUGUST 21-24, 1972
HfiMILTON
NIHGWW
RIVER
nooesien
FIG. 36 continued.
250
-------
TORONTO
HflMILTON
NJflGflRft
RIVER
FEBRUflRT 5-9, 1973
TOOCSTER
TORONTO
MflRCH 19-22. 1973
HRHILTON
NIBGflflfl
IUVER
ROCHESTER
FIG. 36 continued,
252
-------
TORONTO
HRNILTON
NIR6HW
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
HAMILTON
NIRGflflft
RIVER
JUNE 11-14, 1973
ROCHESTER
FIG. 36 continued
253
-------
TORONTO
MflrtlLTON
NIBCWR
RIVER
MRY 15-19, 1972
ROCHESTER
TORONTO
NFV1ILTON
NlflCflflfl
RIVEfl
JUNE 12-1G. 1972
FIG. 37. Distribution of Oooystis spp.
254
-------
TORONTO
NIAGARA
RIVER
JULY 10-14. 1972
ROCHESTER
TORONTO
RUGUST 21-24. 1972
NlRGfflfl
RIVER
ROCHESTER
FIG. 37 continued.
255
-------
TORONTO
MflMILTl
NJPGftRfl
RIVER
OCT 30 - NOV 3, 1972
ROCHESTER
MftMILT
NlflGflflft
RIVLfl
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 37 continued.
256
-------
TORONTO
tlWIILTI
NIPGfWfl
RIVER
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
HflMLT
NIAGARA
RIVER
MRRCH 19-22, 1973
ROCHESTER
FIG. 37 continued.
257
-------
TORONTO
HfirtlLION
NJRGflflft
RIVER
RPRIL 24-28, 1973
ROCHESTER
TORONTO
MftMILTON
NJBSflfifi
PI VCR
JUNE 11-14. 1973
ROCHESTER
FIG. 37 continued
258
-------
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
-------
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
-------
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
-------
TORONTO
HftMILT
NIAGARA
RIVEB
OCT 30 - NOV 3. 1972
NOV 27 - DEC 1. 1972
TORONTO
NJH6PPP
PIVEfl
FIG. 39 continued,
262
-------
TORONTO
HfltllLT
RIVER
FEBRUflRY 5-9, 1973
ROCHESTER
TORONTO
HHIILTl
N1W3W
RIVER
MRRCH 19-22. 1973
ROCHESTER
FIG. 39 continued,
263
-------
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
-------
TORONTO
HH1ILTON
NIRGHW
RIVER
JUir 10-14. 1972
ROCHESTER
TORONTO
fiUGUST 21-24, 1972
NIRGWW
RIVtR
ROCHESTER
FIG. 40 continued.
266
-------
TORONTO
RIVEB
OCT 30 - NOV 3. 1972
ROCHESTER
TORONTO
hflrtlLTON
NlflOW*
RIVtB
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 40 continued.
267
-------
TORONTO
tWIILTON
NlflCffifl
RIVER
FEBRURRT 5-9, 1973
ROCHESTER
TORONTO
HRHILT
MNRCH 19-22, 1973
NIRGWfl
RIVER
ROCHESTER
FIG. 40 continued.
268
-------
TORONTO
HRMRTOM
NIRGRRR
WVEft
flPRIL 24-28, 1973
ROCHESTER
TOROKIO
MFWILTON
JUNE 11-14. 1973
NIRGfiRft
RIVER
ROCHESTER
FIG. 40 continued.
269
-------
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
-------
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
-------
JULY 10-14. 1972
(WILTON
MKPf*
WVER
10RON70
HRWU
RUGUST 21-211, 1972
ROCHESTfR
FIG. 41 continued.
272
-------
TORONTO
HPMILT
NIWWW
RIVER
OCT 30 - NOV 3,
ROCHESTER
TORONTO
HRntLTON
NIRGFfW
RIVER
NOV 21 - DEC 1. 1972
FIG. 41 continued.
273
-------
IONNTO
HBHILtl
NIfffiHW
RIVER
FEBRURRT 5-9, 1973
ROCHESTER
TORONTO
MRRCH 19-22. 1973
RIVER
ROCHESTER
FIG. 41 continued
274
-------
TORONTO
HWILTI
NIfWW
RIVER
RPRIL 24-28, 1973
ROCHESTER
TORONTO
HRMILTON
NJflGPRfl
RIVCT
JUNE 11-m, 1973
ROCHESTER
FIG. 41 continued,
275
-------
TORONTO
HfiMLT
NlflGflRfl
WVER
JULY 10-1U. 1972
ROCHESTER
TORONTO
HflMIlT
NIftGWft
RIVER
RUGUST
ROCHESTER
FIG. 42 . Distribution of Seenedesmus quadrioauda var, quadrispina.
276
-------
TORONTO
HRMUON
NIBGflftfl
RIVER
OCT 30 - NOV 3, 1972
ROCHESTER
TORONTO
HRMILTi
NlflCflRfl
RIVER
NOV 27 - DEC 1, 1972
ROCHESTER
FIG. 42 continued.
277
-------
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
-------
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
-------
TORONTO
(Will.!
RUGUST 21-24, 1972
BlVfB
ROQCS7OI
10RCKTO
MRMIL1
NJftCHW
RlVOt
OCT 30 - NOV 3, 1972
ftOOCSTEB
FIG. 44 continued.
285
-------
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
-------
tORCKTO
HflMILT
NIAGARA
WVER
MRY 15-19, 1972
ROCHESTER
TOROKTO
HRMJL10N
run*
nUGUST 21-2U, 1972
FIG. 45. Distribution of Andbaena varidbilis.
287
-------
DCT 30 - NOV 3, 1972
10RO0D
HRML10N
NOV 27 - DEC 1. 1972
TORONTO
HRflJLliW
WVDl
fWOCSTER
FIG. 45 continued.
288
-------
TOTOKTO
WBCfttft
IUVER
FEBRURRT 5-9, 1973
TWOKTO
WM1L10W
RIVER
JUNE 11-1U. 1973
ROQESTEH
FIG. 45 continued.
289
-------
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
-------
TORONTO
HfiMILTi
NIBCfiflfl
RIVER
JULY 10-14, 1972
ROCHESTER
TORONTO
HftMlLTi
NlflCWfl
RIVEfl
RUGUST 21-214. 1972
ROCHESTER
FIG. 46 continued.
291
-------
OCT 30 - NOV 3. 1972
TOfWTO
NIBCRHfl
BIVEB
ROCHESTER
TORONTO
HHHILTi
NJBCflRfl
RJVEB
NOV 27 - DEC I. 1972
ROCHESTER
FIG. 46 continued.
292
-------
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
-------
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
-------
TORONTO
HflKJLT
NIflGflfift
RIVER
JULY 10-14. 1972
ROCHESTER
TORONTO
WWILT
NIRGflflft
RJVEB
RUGU5T 21-24, 1972
ROCHESTER
FIG. A7 continued,
297
-------
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
-------
Tcatwro
HflMJLia
RUGUST 21-24. 1972
ROCHESTER
TORONTO
NlftCWW
RIVER
OCT 30 - NOV 3. 1972
ftOCHSSTffl
FIG. 48 continued,
302
-------
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
-------
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
-------
tttULT
NJRCtWfl
RIVER
MflY 15-19, 1972
POCHESIER
TOKWTO
fiUGUST 21-24, 1972
IBHIUTB
Riven
FIG. 50. Distribution of Gomp'hosp'haepia laaustris'.
305
-------
TOWO
KW1LTOJT
OCT 30 - NOV 3, 1972
\
ROCHESTER
JUNE 11-14, 1973
poacsitn
FIG. 50 continued.
306
-------
TOfiQKTO
NlflCBRfl
RIVER
MPT 15-19. 1972
ROCHESTER
TORONTO
MWILT
NJPGflHB
Riven
JUNE 12-16, 1972
KOC3TEH
FIG. 51. Distribution of Gomphosphaeria wichurae.
307
-------
TOfWTO
HBMn.70
RIVER
JULY 10-lii. 1972
ROCHESTER
flUGUST 21-21, 1572
TOWfrTTO
FIG. 51 continued.
308
-------
OCT 30 - NOV 3. 1972
TORONTO
ROCHESTER
NOV 27 - DEC 1. 1973
TORONTO
\
\
\
HRMILTO
NlflGfiRR
\
ROQCSTEft
FIG. 51 continued.
309
-------
TORONTO
tWULTO
NlflGflfW
BIVER
FEBRUflRT 5-9. 1973
ROOCSTEfl
TORONTO
MflRCH 19-22. 1973
KRHIUTO
NISGHflfi
ROCHESTEB
FIG. 51 continued.
310
-------
NIHCflflfl
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
MflMILT
NlfiCflRft
RIVER
JUNE 11-14. 1973
ROCHESTER
FIG. 51 continued.
311
-------
TORONTO
MRNIU
NlflGNW
RIVER
MPT 15-19, 1972
KJCHESTEfl
TOPONTO
MfWILT
RIVEfl
JUNE 12-16. 1972
KEHESTEfl
FIG. 52. Distribution of Oscillatoria limnetica.
312
-------
JULY 10-14, 1972
TORONTO
HN4ILTI
NTW3RRB
RIVER
ROCHESTER
TORONTO
HRHtU
HJRGHWJ
RIVtfl
flUGUST 21-24, 1972
ROCttSTER
FIG. 52 continued.
313
-------
TORONTO
HWIILTi
OCT 30 - NOV 3. 1972
ROCHESTER
TWONTD
NlfiGWW
RIVEfl
NOV 27 - DEC i. 1972
BOCMESTLfi
FIG. 52 continued.
314
-------
TORONTO
HflflILT
NIflGRBfl
WVEP
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
HWILT
flJVEfi
MRRCH 1S-23. 1973
ROCHESTER
FIG. 52 continued.
315
-------
lORorno
fiPRIL 24-28. 1973
ROCHESTER
JUNE 11-14. 1973
N1HGWR
RIVEft
ROCHESTEfl
FIG. 52 continued,
316
-------
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
-------
TORONTO
HftMILTO
NlflGflflfl
RIVEft
MflT 15-19. 1972
ROCHESTER
TDWJWTO
HflMILTC
RJVEfi
JUNE 12-16. 1972
ROCHESTER
FIG.- 53. Distribution of Cryptomonas erosa.
318
-------
TORONTO
HAMTLTI
NlflGflRfl
RIVER
JULY 10-1H, 1972
ROCHESTER
TORONTO
MflMILT
NlflGflRfl
RTVEfl
fiUGUST 21-24, 1972
ROCHESTER
FIG. 53 continued.
319
-------
TORONTO
HflHJLTi
NJflGWW
RIVER
OCT 30 - NOV 3, 1972
ROCHESTER
TORONTO
HfiMILT
NlflGflflfl
RIVER
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 53 continued.
320
-------
TORONTO
HfiHILTi
KlflGflflfi
RJVEB
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
HflMILTl
MflRCH 19-22, 1973
ROCHESTCR
FIG. 53 continued.
321
-------
TORONTO
KRHILT
NJftGflflfl
RJVEB
RPRJL 24-28. 1973
ROCHESTER
TORONTO
HWtlLT
JUNE 11-14, 1973
ROCHESTER
FIG. 53 continued.
322
-------
TORONTO
HPMILTON
RIVER
MRY 15-19, 1972
ROOESTCR
TORONTO
HRHILTON
JUNE 12-16. 1972
ROCHESTER
FIG. 54. Distribution of Glenodiniwn and Gyrnnodiniim.
323
-------
JULY 10-14, 1972
TOK3KIO
MflWUON
NIRGfflfl
RIVER
ROCHESTER
TORONTO
flUGUST 21-24. 1972
NlRCflftfl
RIVER
ROCHESTER
FIG. 54 continued.
324
-------
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
-------
TOROKTO
HRMIUT
NJflGHW
WVEB
FEBRURRY 5-9, 1973
ROCHESTER
TORONTO
MflRCH 19-22. 1973
MRHIUON
ROCHESTER
FIG. 54 continued.
326
-------
TOROffTO
HRHILTI
NIflWRR
RIVER
RPRIL 24-28, 1973
ROCHESTER
TORONTO
JUNE 11-14. 1973
HflMILT
NJRGflRR
RIVER
ROCHESTER
FIG. 54 continued.
327
-------
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
-------
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
-------
TORONTO
MflMILTON
JULY 10-14, 1972
NIflGJflfl
RIVER
ROQCSTEB
RUGUb'T 21-24, 1972
TOWOTO
POCMESTEH
FIG. 55 continued.
330
-------
OCT 30 - NOV 3, 1972
TORONTO
MflMILT
NlftCflfW
RIVEfl
ROCHESTER
TORONTO
NOV 27 - DEC 1. 1972
ROCHESTER
FIG. 55 continued.
331
-------
TORONTO
FEBRURRY 5-9. 1973
RIVEfi
ROCHE3TEP
TORONTO
HfWILI
MPRCH 13-22. 1973
FIG. 55 continued,
332
-------
TOfwro
HflrtILT
NIRGRBfl
RIVER
RPRIL 24-28. 1973
ROCHESTER
TORONTO
MWULT
NJflGflRR
RIVER
JUNE 11-14. 1973
ROCHESTER
FIG. 55 continued.
333
-------
MfiT 15-19, 1972
TORONTO
HRMIITON
NWWflfl
RIVER
ROCHESTER
TOVJKTO
HPMUON
JUNE 12-16, 1972
ROCHESTEfl
FIG. 56. Distribution of microflagellates.
33A
-------
JULY 10-14. 1972
TORONTO
WILTON
NJfiGWfl
RIVER
ROCHESTER
TOBONTO
HPTirLTOH
HlftGfTO
WVER
flUGUST 81-214, 1972
ROCHESTER
FIG. 56 continued.
335
-------
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
-------
TOMKTO
HPMLT
NIBGPPfl
RIVER
FEBRURRY 5-9, 1973
1200.00
ROQCSTER
TORONTO
NlfiCffW
RIVER
MflRCH 19-22. 1973
ROCHESTER-
FIG. 56 continued.
337
-------
IOIWTO
RIVER
flPRIL 24-28. 1973
ROCHESTER
JUNE il-14. 1973
R1YEK
00
ROCHESTER
FIG. 56 continued.
338
-------
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
-------
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
-------
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
-------
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
It h
us
woo
-II (
.woo
7S
96
0 6000
s
iso
200
JULY 10-14, 1972
10
WOO
woo
woo
-l-^th
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 it-
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
-HiiK +iit- rr+«»*
75
96
JUNE 12-16, 1972
P . 4000
-
4000
i
200
10
4000
HIi*
1000
-t1<t-
\
75
HOM
96
JULY 10-m. 1972
o .1000
It*-
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
-tIt\-
-» I
woo
jtOOO
-ItI>
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
-»Itt-
2U
1000
It*
H000
1 1 1-
4000
75
96
9 1000
I IIh
toe
JUNE 12-16. 1972
to
woo
75
HOOO
96
JULY 10-14, 1972
0 WOO
' ' ' '
200
4000
«1ih
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
-»tIH
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
ofiit»-
so
200
10
uooo
-1II>-
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
-«IIh
MOOD
75
96
P WOO
10
JUNE 12-16. 1972
vooo
I t It-
_(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
-tI 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 tIt-
45
HMO
iit-
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
-III-
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
-ttI»-
10
4000
-t»I»-
45
1000
-»tII-
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
-------
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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