Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
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EPA-905/3-82-002
July, 1982
ZOOPLANKTON COMMUNITY COMPOSITION
IN
GREEN BAY, LAKE MICHIGAN
by
John E. Gannon, Kathryn S. Bricker
and
F. James Bricker
Biological Station
The University of Michigan
Pellston, Michigan 49769
Grant No. R 005340 01
project Officer
David C. Rockwell
Great Lakes National program Office
536 South Clark Street
Chicago, Illinois 60605
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION V
CHICAGO, ILLINOIS 60605
U.S. Environmentaf Protection Agency '
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DISCLAIMER
This report has been reviewed by the Great Lakes National Program
Office, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views and
policies of the U.S. Environmental Protection Agency, nor does mention of trade
names or commercial products constitute endorsement or recommendation for use.
ii
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FOREWARD
The Great Lakes National Program Office (GLNPO) of the United States
Environmental Protection Agency was established in Region V, Chicago to focus
attention on the significant and complex natural resource represented by the
Great Lakes.
GLNPO implements a multi-media environmental management program drawing on a
wide range of expertise represented by Universities, private firms, State,
Federal and Canadian Governmental Agencies and the International Joint
Commission. The goal of the GLNPO program is to develop programs, practices and
technology necessary for a better understanding of the Great Lakes system and to
eliminate or reduce to the maximum extent practicable the discharge of
pollutants into the Great Lakes system. The Office also coordinates U.S.
actions in fulfillment of the Agreement between Canada and the United States of
American on Great Lakes Water Quality of 1978.
This study was supported by a GLNPO grant to the University of Michigan at
Ann Arbor for investigating the zooplankton community composition in nearshore
waters of northern Green Bay, Lake Michigan.
ill
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ABSTRACT
Zooplankton samples collected in northern Green Bay in 1977 were analyzed to
evaluate present water quality and to provide a benchmark on zooplankton
community composition for comparison with future studies. Species composition,
abundance and distribution were investigated to determine the apparent response
of the zooplankton community to water quality conditions. Although caution must
be exercised in establishing one-to-one casual relationships between zooplankton
community composition and eutrophication, trends in spatial distribution and
abundance of zooplankton in Green Bay appeared to be related to existing water
quality.
Green Bay zooplankton was characterized by a predominance of perennial
cyclopoid and calanoid copepods during May. Parthenogenetic rotifers and
cladocerans were the numerically most important components of the
zooplankton community in August and October. Rotifers were overwhelmingly most
abundant, comprising an average of 89.8% of total zooplankton during the study
period, predominant rotifers were Keratella cochlearis cochlearis, K. crassa,
—• earlinae, polyarthra vulgaris, P. major, P. remata, and Conochilus unicornis.
The most prevalent crustacean plarik~ters were~Diacyclops thomasi, Eubosmina
coregoni, Daphnia galeata mendotae and E>. retrocurva.
Two broad regions (north and south of Chambers Island in Green Bay) and two
localized areas (near the Menominee River mouth and in Little Bay de Noc,
especially near the Escanaba River) were determined by analyses of zooplankton
community composition. Zooplankton indications of eutrophication were generally
highest south of Chambers island and the lowest in the open waters of Green Gay
north of Chambers island, especially in the island passages. The most
indications of eutrophication were off the Menominee and Escanaba River mouths.
Eutrophic indicator species (e.g., Brachionus spp., Euchlanis, Pompholyx,
Trichocerca spp., Acanthocyclops vernal is and Chydorus sphaericus) were
generally rare and confined or most prevalent in the most eutrophic regions.
More prominently, the overall response of zooplankton community was an increase
in density of indiginous, eurytopic species in perturbed regions. This feature
seems to be indicative of mesotrophy in northern Green Bay and elsewhere in the
Great Lakes. The regions of different water quality in northern Green Bay as
identified by zooplankton community composition closely resembled those
determined by physicochemical and phytoplankton analyses.
IV
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CONTENTS
Foreward iii
Abstract iv
Figures vi
Tables vi i i
Acknowledgements ix
1. Introduction 1
2. Materials and Methods 2
Field 2
Laboratory 5
3. Results f>
Physicochemistry 6
Abundance and Distribution by Major Groups 7
Species Composition. 20
Seasonal and Spatial Distribution of Major Rotifera 20
Notes on Other Rotifers 43
Seasonal and Spatial Distribution of Major Micro-Crustacea.... 48
Notes on Other Micro-Crustacea 68
4. Discussion 70
References 76
Appendices 79
A. physicochemical data for May composite and August and October
discrete samples from Green Bay, 1977.
B-l. Species composition and mean and maximum abundance (Number x
10 /m) of rotifers in Green Bay. _
B-2. Species composition and mean and maximum abundance (Number/m )
of crustacean plankton in Green Bay.
v
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FIGURES
Number page
1 Generalized current patterns in Green Bay, Lake Michigan (Redrawn
from Bertrand £t al. 1976) 3
2 Location of sampling stations in Green Bay, Lake Michigan 4
3 Distribution of total rotifers 10
4 Distribution of total crustacean plankton 1.1
5 Distribution of total calanoid copepods 12
6 Distribution of total calanoid copepods, percentage of total
crustaceans 13
7 Distribution of total cyclopoid copepods 15
8 Distribution of total cyclopoid copepods, percentage of total
crustaceans 16
9 Distribution of total cladocerans 17
10 Distribution of total cladocerans, percentage of total
crustaceans 18
11 Distribution of calanoid/cyclopoid + cladoceran ratio 19
12 Distribution of Keratella cochlearis cochlearis 26
13 Distribution of Ascomorpha oval is 27
14 Distribution of Polyarthra vulgar is 29
15 Distribution of Polyarthra remata 30
16 Distribution of Polyarthra major 31
17 Distribution of Keratella crassa 32
18 Distribution of Keratella earlinae 34
19 Distribution of Conochilus unicornis 35
vi
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20 Distribution of Synchaeta stylata 36
21 Distribution of Asplanchna priodonta 37
22 Distribution of Ploesoma truncatum 38
23 Distribution of Gastropus stylifer 40
24 Distribution of Keratella cochlearis f. robusta 41
25 Distribution of Collotheca mutabilis 42
26 Distribution of Kellicottia longispina 44
27 Distribution of Keratella quadrata 45
28 Distribution of Daphnia galeata mendotae 49
29 Distribution of Daphnia retrocurva 50
30 Distribution of Daphnia longiremis 52
31 Distribution of Eubosmina coregqni 53
32 Distribution of Bosmina longirostris 54
33 Distribution of Chydorus sphaericus 56
34 Distribution of Ceriodaphnia spp 57
35 Distribution of Holopedium gibber urn 58
36 Distribution of Diacyclops thomas^ 59
37 Distribution of Mesocyclops edax 61
38 Distribution of Acanthocyclops vernalis 62
39 Distribution of Diaptomid copepodids 63
40 Distribution of Leptodiaptomus ashlandi 65
41 Distribution of Skistodiaptomus oregonensis 66
42 Distribution of Leptodiaptomus minutus. 67
43 Distribution of Eurytemora affinis 69
vn
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TABLES
Number Page
1 Zooplankton abundance by major groups in Green Bay during the
1977 sampling season. 8
2 Species composition, mean abundance (nunber x 10 /m ) and trophic
status of rotifers in Green Bay 21
3 Species composition, mean abundance (number/m ) and trophic
status of crustacean plankton in Green Bay , 23
viii
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ACKNOWLEDGMENTS
We thank Theodore Ladewski for providing computer and statistical
assistance. We also acknowledge the U.S. Environmental Protection Agency for
collecting the zooplankton samples and providing the physicochemical data.
IX
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INTRODUCTION
Green Bay, a large and shallow embayment of Lake Michigan, has undergone
dramatic changes in water quality because of pollution and eutrophication during
the past 150 years. Concurrently there has been dramatic fluctuations and
changes in fish stocks because of alterations in the bay's ecology and other
factors (e.g., exploitation, exotic species introductions, etc.). Both
pollution and fish community changes undoubtedly have had considerable impact on
zooplankton community composition in Green Bay. However, little is known
concerning changes in zooplankton in the bay because of the unavailability of
early data for comparison with more recent investigations.
In spite of the ecological and economic importance of Green Bay, zooplankton
investigations have been few and limited to the most recent decades. Balch ^t
al. (1956) collected zooplankton in lower Green Bay in 1955 but identified
organisms only as Cladocera and Copepoda. Gannon (1972, 1974) examined
crustacean plankton in Green Bay in 1969-1970 and provided the first descriptive
information on species composition, abundance and distribution. Samples from
all seasons were obtained but most stations were in the lower bay south of
Chambers Island. Data were obtained throughout Green Bay only in July, 1970.
Torke (1973) examined crustacean plankton in the lower bay on a single
date in July, 1971. Crustacean and rotifer plankton were investigated
intensively in Fox River mouth and the lower bay year round in 1973 as part of a
thermal plume study (Wisconsin Public Service Corporation 1974). Although most
rotifers were identified only to genus, this was the first investigation in
Green Bay to include rotifers.
This report concerns zooplankton community composition in Green Bay during
1977. The study was initiated by the united States Environmental Protection
Agency (U.S. EPA), Region V, as part of its water quality monitoring program.
Phytoplankton and physicochemical data were collected concurrently and are
reported in Stoermer and Stevenson (1980).
The purpose of this report is to provide a benchmark on zooplankton
composition, abundance and distribution in Green Bay for comparison with future
monitoring and surveillance efforts. Zooplankters represent the ecologically
important secondary trophic level in food web dynamics in aquatic ecosystems and
have been shown to have value as water quality indicators (Gannon and
Stemberger 1978).
The cultural, economic and limnological characteristics of Green Bay have
been reviewed extensively by Bertrand et al. (1976) . Limnological features
especially pertinent to interpreting zooplankton distributions in relation to
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water quality were discussed by Gannon (1974). the morphometry of the bay is
exceedingly diverse and appears to have played a prominent role in influencing
spatial variability of physicochemical and biological features, including
zooplankton distribution.
Green Bay is the largest embayment in the Lake Michigan basin. It is an
elongate bay oriented southwest to northeast and contains two smaller northerly
extensions, Big and Little Bay de Noc. Green Bay is 190 km long and averages 37
km wide. It has a total area of 4,116 km and volume of 62 km . in comparison
with the main portion of Lake Michigan, Green Bay is shallow with mean and
maximum depths of 16m and 50n, respectively. It is shallowest at its extreme
southern end and deepest off Washington Island. The watershed of Green Bay
contains some of the richest agricultural lands in Wisconsin. Moreover, a large
urban and industrial complex is located in the Fox River Valley south of the
bay. The Pox River is the largest tributary and is the most important source of
nutrients and other pollutive inputs to Green Bay. Other noteworthy sources of
nutrient loading are discharges from pulp and paper mills on the Oconto,
Menominee and peshtigo Rivers and domestic wastewater outfalls on the Escanaba
and Menominee Rivers (Bertrand ^t al. 1976; Tierney £t aU 1976).
Waters in the upper portion of Green Bay have a high rate of exchange with
Lake Michigan whereas the more physically isolated lower bay is primarily
influenced by inflowing Fox River water. Wind-generated currents and seiche
activity cause two counterclockwise circulation patterns to predominate in Green
Bay. The two gyres interact in the area between the Menominee River mouth and
Sturgeon Bay (Fig. 1). Fox River water is most prominent along the eastern
shore of the lower bay. All of the water entering Green Bay eventually flows
into Lake Michigan, primarily through the passages between the islands north of
the Door County peninsula. However, the residence time of Fox River water in
the bay is long. Summertime flushing rates calculated for the lower 37 km of
the bay were over 100 days (Modiin and Beeton 1970).
MATERIALS AND METHODS
Field
Zooplankton samples were collected in Green Bay in May, August and October,
1977. The samples in August and October were collected at 25 stations by U.S.
EPA personnel aboard the R/V Simons (Fig. 2). The May cruise was an abbreviated
one; Michigan Department of Natural Resources personnel collected at 18 stations
for crustacean plankton and 10 stations for rotifers, using an outboard patrol
boat. The sampling scheme focused on the northern portion of the bay (north of
Oconto, WI) and included Big and Little Bay de Noc.
For crustacean plankton, the May samples were collected with a 0.25 m
diameter, no. 6 (240 .urn) mesh conical net. A 0.5 m diameter net of the same
mesh size was used during the August and October cruises. A standardized
vertical tow was made from 10 m to the surface (or bottom to the surface at
stations less than 10 m deep). At stations deeper than 10 m, a second,tow was
taken from the bottom to the surface.
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AREA ENLARGED
N
t
GLADSTONE
Eicanabi
Rlv«r
ESCANABAI
Ford f
GARDEN
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MENOMINEE
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Figure 2. Location of sampling stations in Green Bay, lake Michigan.
4
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The standardized tow aided comparison of data between stations because
approximately the same volume of water was filtered by the net. The no. 6 net
was used because the filtration efficiency of that mesh size is near 100%
(Gannon 1972; 1980), thereby improving the accuracy of abundance calculations.
However, some of the smallest zooplankters (e.g., Chydorus sphaericus, Bosmina
longirostris, Eubosmina coregoni, Ceriodaphnia .spp., Tropocyclops pfasinus
mexicanus and cyclopoid copepodids) may escape through the mesh and be
undersampled.
Another sampling bias may be the different diameter nets used. Larger, more
agile zooplankters (e.g., calanoid copepods) may avoid the approaching 0.25 m
diameter net more readily than the larger 0.5 m diameter net. The later has
four times the surface area of the former, thereby reducing possible error due
to avoidance.
Rotifers were collected in May using a composite-type sampler which was
lowered to a depth twice the Secchi disc reading and raised to the surface. The
August and October samples were collected with a 8-liter Niskin bottle at
discrete depths, 2 m from the surface and one meter off bottom. A third sample
from an intermediate depth was taken at stations greater than 10 m deep. The
water samples from each depth were pooled and concentrated in a filtering funnel
fitted with 54 urn mesh screening (Likens and Gilbert 1970). Both rotifer and
crustacean samples were narcotized with carbonated water (Gannon and Gannon
1975) and preserved with 5% buffered formalin.
It would be desirable to sample rotifers and crustacean plankton by the same
methods. However, micro-crustaceans are too sparcely distributed to collect
with a water bottle. Consequently, it was necessary to use a plankton net to
sample these organisms. In contrast, rotifers are sufficiently concentrated to
allow reliable samples to be collected with the water bottle. Intercomparisons -
of rotifer data with chemistry and phytoplankton are most valid statistically
since these limnological variables were collected at the same depths using
identical methods.
Laboratory
Prior to micro-crustacean counts, each sample was adjusted to a constant
volume in a graduated cylinder and poured into a 4 oz jar. The cylinder was
rinsed with an additional 10 to 20 ml of tap water and this was carefully added
to the rest of the sample for a final volume of usually 100 ml. The sample was
then randomly and thoroughly mixed with a large bore, calibrated automatic pi-
pette and the subsample quickly drawn from the middle of the sample. Aliquot
sizes ranged from 1 ml to 10 ml depending on species numbers. A second, larger
aliquot usually was withdrawn for enumeration of less common species. Sub-
samples were transferred to a chambered counting cell (Gannon 1971) and the en-
tire contents usually 150-300 individuals, were enumerated at 30 to 60x under a
Wild stereo-microscope. Those organisms requiring higher magnification for
identification were mounted in polyvinyl lactophenol, stained with lignin pink
and examined at 430 or lOOOx under an American Optical compound microscope. Data
were calculated in numbers of individuals per m and percent composition. This
procedure has proved to be accurate and reproducible (Gannon 1972, 1980).
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Adult calanoid and cyclopoid copepods were identified to species according
to Wilson (1959) and Yeatman (1959), respectively. Calanoid copepedids were
included with the adults of that species except those in the family Diaptomidae.
Cyclopoid copepedids were not identified to genus, though most were undoubtedly
Diacyclpps. Adult harpacticoid copepods were identified to species with the use
of Wilson and Yeatman (1959) and Czaika (1974). All cladocerans were reported
at the species level except Diaphanosoma and juvenile Daphnia. Two species of
Diaphanosoma, D. leuchtenbergianum Fischer and D. brachyurum (Lieven), were
observed with the former overwhelmingly most abundant. Young instars of Daphnia
were often difficult to distinguish at the species level and, for purposes of
expediency, were pooled as Daphnia spp. juveniles. Brooks (1957) was used for
mature Daphnia, and Deevey and Deevey (1971) for Eubosmina. The family
Chydoridae was identified according to anirnov (1971) and the remaining
Cladocera were keyed according to Brooks (1959).
In preparation for rotifer counts, all samples were concentrated to 50 ml.
Each sample was thoroughly mixed with a calibrated automatic pipette immediately
before taking a subsample with the pipette from the center of the jar.
Subsamples of 1, 3 or 5 ml were taken depending on the density of organisms so
that the concentration of rotifers in each subsample included 200 to 400
individuals. Subsamples were transferred to a 5 ml plexiglass rectangular
counting cell and all rotifers were enumerated under an American Optical
compound microscope at lOOx. Each subsample was then replaced in the jar, and a
second subsample was taken and enumerated, and the two counts averaged. A
minimum of 300 rotifers per sample was routinely counted. Data were calculated
in numbers of individuals per m and percent composition at each station. The
subsampling and counting procedure was tested and proved to be accurate and
reproducible (Stemberger et al. 1979).
Identifications were made to species for most rotifers. Certain species of
the genus Synchaeta were indistinguishable by gross morphology because of their
contracted state and, therefore, identification of these organisms was
determined by examination of the hard, chitinous mouth parts after chlorox
bleach was used as a clearing agent (Stemberger 1973). The main references used
in identifying rotifers were Jennings (1903), Ahlstrom (1943), Voigt (1957) and
Stemberger (1976).
RESULTS
Phys icochem i stry
physicochemical data that were obtained concurrently with plankton
collections are listed in Appendix A. They are summarized briefly here. A more
detailed description is in Stoermer and Stevenson (1980). Data for the May
cruise were less complete than for the August and October sampling dates.
Considerable differences in the rate of warming of shallow and deep waters
of Green Bay were clearly evident during May. Warmest temperatures were off the
Menominee River mouth (23.0 C), off Sturgeon Bay (18.4 C) and in shallow Big Bay
de Noc (13.1 C). Temperatures in Little Bay de Noc ranged from 6.4 to 10.2 C.
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Offshore temperatures in Green Bay were variable ranging from 4.5 to 10.2 C,
whereas cold water (5.5 - 6.0 C) occurred in the island passages. Specific
conductance was highest (440-460 umhos) along the east coast from Sturgeon Bay
to east of Chambers island; values elsewhere ranged from 280 to 362 umhos.
Lowest Secchi disc values (1.0 - 2.5 m) were observed in Little Bay de Mbc, off
the Menominee River and along the eastern shore from south of Sturgeon Bay to
east of Chambers Island. Highest Secchi disc readings were observed in the open
waters of northern Green Bay and Big Bay de Noc (4.5 - 6.0 m) and the island
passages region (6.0m).
Summertime temperatures of about 20 to 22 C were recorded from most stations
in August, although an anomaly of 10.0 C was recorded off Sturgeon Bay.
Specific conductance gradually decreased from south to north. Values averaged
275 pnhos with the highest reading (283 jjmhos) off Oconto and the lowest (271
umhos) occurring in Big Bay de Noc and the island passages region. The opposite
trend was observed with Secchi disc readings, ranging from less than 4.0 m south
of Chambers Island to 4.5 to 5.5 m in northerly waters. Lowest readings (2.5 m)
were recorded off the Escanaba and Menominee Rivers. Reactive phosphorus
concentrations were less than 2 ppb throughout the bay but nitrate and silica
concentrations generally followed the trend for water transparency and increased
northward. Ammonia concentrations were near 4.0 ppb throughout the bay with
slightly higher values (6-7 ppb) in Big Bay de Nbc and much higher off the
Menominee River (40-50 ppb) and in Little Bay de Noc (6-22 ppb) with an
especially high anomoly (150 ppm) off the Escanaba River.
The fall cooling trend was well underway during October with water
temperatures fairly uniform (13.0 - 14.5 C) throughout the bay. Temperatures
were slightly cooler off Sturgeon Bay (12.4 C) and in Little Bay de Noc (11.5 -
13.2 C). Similar to August, specific conductance gradually decreased northward
and lower nutrient concentrations, especially nitrate and silica, coincided with
lower water transparencies. Secchi disc readings were generally lowest in
October, ranging from 1.5m near the Escanaba River to 4.0 east of Chambers
Island and in the island passages. In contrast to August, ammonia
concentrations exhibited no discernible spatial trend in October. Similar to
August, reactive phosphorus concentrations in October were less than 2 ppb.
Abundance and Distribution by Major Groups
Although rotifer and micro-crustacean data are not strictly comparable
because different sampling methods were used, it is of interest to contrast
approximate abundances of the two major groups of zooplankton in Green Bay.
Mean abundances by cruise are given in Table 1 and mean and maximum abundance
for all cruises combined are presented in Appendix B.
Population size reflected the seasonal limnological cycles in Green Bay
during the sampling periods. Lowest numbers of total zooplankton (>53,000 per
m
J5 \ _
) were observed in May and perennial cyclopoid and calanoid copepods were the
predominant crustaceans and rotifers were over 10 times more abundant than
crustacean plankton. Summertime conditions were well underway in August and
numbers of total zooplankton (>480,000 per m ) were 9 times higher.
7
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parthenogenetic breeders, the rotifers and cladocerans, that are adapted for
rapid reproduction during favorable conditions, were predominant; these
organisms represented 99.1% of total zooplankton during August. Cladocerans
represented 85% of total micro-crustaceans and 4.8% of total zooplankton.
Although the population size of calanoid copepods tripled between May and
August, its proportion relative to other zooplankton groups dropped threefold.
The population of cyclopoid copepods dropped by a third between the two sampling
dates but its relative percentage dropped tenfold. Fall cooling was well
underway by the October sampling with total numbers (>106,000 per m ) being less
than a third of August levels.
TABLE 1. ZOOPLANKTON ABUNDANCE BY MAJOR GROUPS IN GREEN BAY
DURING THE 1977 SAMPLING SEASON.
DATA ARE BASED ON THE STANDARDIZED NET TOWS FOR MICRO-CRUSTACEANS
AND THE POOLED DISCRETE-DEPTH SAMPLES FOR ROTIFERS.
THE AVERAGE DENSITY IN NUMBERS OF INDIVIDUALS PER M AND
AVERAGE RELATIVE ABUNDANCE IN PERCENT COMPOSITION OF TOTAL CRUSTACEA (%C)
AND TOTAL ZOOPLANKTON (%Z) ARE PRESENTED FOR EACH SAMPLING DATE.
May August October
O "5 O
no./m %C %Z no./m %C %Z no./nr %C %Z
Calanoid
Copepoda 650 14.1 1.2 1,880 6.8 0.4 4,120 23.8 3.9
Cyclopoid
Copepoda 3,120 67.5 5.8 2,220 8.1 0.5 4,100 23.7 3.8
Cladocera 850 18.4 1.6 23,460 85.1 4.8 9,070 52.5 8.5
Total
Crustacea 4,620 8.6 27,500 5.7 17,290 16.2
Rotifera 49,200 91.4 457,200 94.3 89,100 34.0
Total
Zooplankton 53,820 484,760 106,390
Perennial species of calanoid and cyclopoid copepods once again became relative-
ly more prevalent as parthenogenetic populations of cladocerans and rotifers
declined 2.5 and 5 times, respectively, from August to October (Table 1).
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populations of total rotifers were generally highest at stations where
higher temperature, conductivity, alkalinity and turbidity and lowest Secchi
disc transparency were observed (Appendix A, Figure 3). Rotifer numbers were
highest (15,000 per m ) at the southernmost station and along the east cost in
Green Bay during May. Numbers were highest (>1,5000,000 per m ) in August off
the Menominee and Escanaba Rivers and lowest (200,000 per m ) in northernmost
Green Bay, the island passages and Big Bay de Noc. Although total rotifer
numbers declined considerably between August and October, a similar pattern of
abundance was observed in fall with rotifers most frequent (150,000 - 200,000
per m ) in the Bay de Noes, off the Menominee River mouth and at the
southernmost station in Green Bay. Numbers of total rotifers had a significant
(.01) positive correlation with turbidity and conductivity and significant (.05)
negative correlation with Secchi disc transparency in August and October.
In contrast to the rotifers, patterns in total crustacean plankton
distribution usually did not exhibit as strong similarities to the distribution
of physicochemical variables. Nevertheless, some similar patterns of
distribution were observed IFigure 4). In May, total crustaceans were notably
most abundant (>5,000 per m ) at southerly and east coast stations in Green Bay.
By August, total crustacean plankton was highest (>25,000 per m ) off the
Menominee River and in Little Bay de Noc while lesser nunbers (near 15,000 per
m ) were observed in northernmost Green Bay stations and in the northerly island
passages. Micro-crustacean abundance was about two times higher in Little Bay de
Noc than in Big Bay de Noc. Numerical distribution of crustacean plankton was
more uniform in the well mixed waters of Green Bay in October. Numbers in
excess of 25,000 per m were still observed off of the Menominee River and in
both Bay de Noes whereas all Green Bay stations north of Chambers island
exhibited substantially lower numbers in comparison with August. Primarily
reflecting the predominance of cyclopoid copepods, the distribution of total
micro-crustaceans showed a significant (.01) positive correlation with
temperature and conductivity during May.
Calanoid copepods were most prevalent (about 1,000 per m ) at the
southernmost Green Bay station and along the east coast (Figure 5) but
proportions relative to cyclopoid copepods and cladocerans were highest
elsewhere in the bay (Figure 6) . Calanoid copepods represented 30-40% of total
crustaceans in northern Green Bay and in the Bay de Noes and 10-20% south of
Chambers Island. In August, highest numbers (3-9,000 per irr) were observed off
Sturgeon Bay and in the island passages. They were minor constituents «10%) of
total micro-crustaceans at most stations except in Sturgeon Bay and in the
island passages (20-30%). Highest numbers (mean of >4,000 per m ) were observed
in October with greatest concentrations occurring in northern Green Bay, the
island passages and in the Bay de Noes. Reflecting both higher calanoid nunbers
and a decline in cladocerans, calanoid copepods were relatively the most
abundant crustaceans in October, especially north of Chambers Island. Calanoid
copepods exhibited a significant (.05) positive correlation with Secchi disc
transparency in October.
Although cyclopoid copepods averaged over 3,000 per m in May, their
abundance ranged considerably from a few hundred per nr at most stations to
9
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Total Rotifers
Oct 1977
Figure 3. Distribution of total rotifers.
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Total Micro - Crustacea
Figure 4. Distribution of total crustacean plankton.
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Total Calanoid Copepods
ro
Oct 1977
Figure 5- Distribution of total calanoid copepods.
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Calanoid Copepods % of Total Crustacea
1977
Figure 6. Distribution of total calanoid copepods, percentage of total crustaceans.
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10-20,000 per m at southernmost and east coast stations (Figure 7). In spite
of the wide range in actual numbers, in terms of percent composition they
consistently represented 65-85% of total crustaceans throughout the study area
(Figure 8). Cyclopoid copepods were minor constiuents of the plankton community
during August with low populations of 500-2,000 per m at most stations,
representing less than 10% of total crustaceans.and 3% of the total zooplankton.
In October Cyclopoid copepods were distinctly most abundant south of Chambers
Island, ranging near 10,000 per m . in contrast, numbers rarely exceeded 2,000
per m north of the island. This pattern was also evident in terms of relative
abundance. Cyclopoid copepod abundance exhibited significant positive
correlation with temperature and conductivity during May (.01) and October
(.05).
Cladoceran populations were just beginning springtime development in May
with highest numbers (near 5,000 per m ) located off Sturgeon Bay and Chambers
Island (Figure 9). Cladocerans were absent from some stations north of Chambers
Island and in the island passages where temperatures were coldest. ' Numbers of
Cladocerans were highest (mean of 27,500 per m ; maximum of over 45,000 per m )
during August. The population was.consistently high at all stations except in
the island passages (<10,000 per m ). Whereas Cladocerans represented only from
0-30% of total crustaceans in Green Bay during May, they averaged 85% in August
(Figure 10). Cladocerans remained relatively abundant (mean of 53% of total
crustaceans) in October even though actual numbers decreased five-fold between
August and October. Highest concentrations (near 20,000 per m ) were observed
south of Chambers Island and in the Bay de Noes. Cladoceran abundance exhibited
a significant (.01) positive correlation with temperature and conductivity
during May.
Gannon et al. (1976) and Gannon and Stemberger (1978) suggested that the
ratio of calanolcf copepods to cyclopoid copepods plus Cladocerans may be useful
in detecting trends in zooplankton distribution as related to water quality
during the growing season. Calanoid copepods generally are most prevalent in
oligotrophic conditions relative to the other major crustacean groups and,
therefore, the ratio may be greater in areas of higher water quality. In
contrast, rapidly developing populations of parthenogenetic Cladocerans tend to
become predominant in more eutrophic waters, thereby resulting in a lower ratio.
Cyclopoid copepods are dominated by the eurytopic species, Diacyclops thomasi,
which also tends to become most prevalent under eutrophic conditions, hence
lowering the ratio. These trends were discernible in Green Bay during 1977
(Figure 11). The ratio was highest in the more northerly waters of Green Bay
during May and exhibited a significant (.05) positive correlation with Secchi
disc transparency. The ratio was lowest at the southernmost station and along
the east coast in Green Bay. It was uniformly low throughout Green Bay in
August, reflecting the low proportions of calanoid copepods to Cladocerans
during the peak of the summer growth period. The ratio was relatively high only
in the island passage area where water quality is greatly influenced by Lake
Michigan proper. A similar trend was observed in October. The absolute value
of the ratio was higher in October as Cladocerans became less abundant relative
to calanoid copepods. However, the absolute value of the ratio carries little
limnological significance. Only the relative trends within a given data set
appear to have interpretive value.
-------
Total Cyclopoid Copepods
Oct 1377
Figure 7- Distribution of total cyclopoid copepods.
-------
Cyclopoid Copepods % of total Crustacea
hay 1977
Oct 1977
Figure 8. Distribution of total cyclopoid copepods, percentage of total crustaceans.
-------
Total Cfadocerans
Oct 1377
Figure 9. Distribution of total cladocerans.
-------
Cladocerans % of total Crustacea
CO
Oct .1977
Figure 10. Distribution of total cladocerans, percentage of total crustaceans
-------
Calanoid-fCyclopoid
Copepods / Cladocerans v
VD
Oct 1977
Figure 11. Distribution of calanoid/cyclopoid + cladoceran ratio.
-------
Species Composition
During the sampling period, 49 rotifer species were collected from Green
Bay (Table 2). Since rotifers have received so little investigation in Green
Bay, all but the most common, ubiquitous species listed herein constitute new
records for this region. However, all of them are indiginous to the Great Lakes
region (Stemberger 1979).
Predominant species were Keratella cochlearis cochlearis, I(. crassa, K.
earl inae, K. quadrata, Polyarthra vulgar is, P. maj'or, j>. remata~and ConochTlus
unicornis. Approximately 33 species, including all of the predominant ones, are
characteristic of the limnetic waters of Lake Michigan. The remainder (e.g.,
Brachionus, Euchlanis, Lophocaris, Lepadella, Trichotria, Tylotrocha,
Trichocerca and Testudinella) are primarily benthic and littoral forms that
appear in the plankton of nearshore waters especially near river mouths.
Typical of elsewhere in the Great Lakes, congeneric species are common in Green
Bay. Ten genera were represented by two or more species, including a maximum of
five species and two forms in Keratella and five species each in Brachionus,
Polyarthra and Trichocerca.
Green Bay contained 35 species of crustacean plankton in 1977, including
seven calanoid copepods, four cyclopoid copepods, two harpacticoid copepods and
17 cladocerans (Table 3). As in the rotifers, congeneric crustacean species
were prevalent with three each of Leptodiaptomus and Daphnia and two each of
Canthocamptus, Diaphanosoma, Ilyocryptus and Ceriodaphnia. Approximately 22
species are characteristic of Lake Michigan limnetic wate'rs, including
predominant Diacyclops thomasi, Leptodiaptomus ashlandi, L^ minutus,
Sk istod iaptomus oregonensis, Ho loped i urn gibberum, Cericdaphnia lacustris, C_^
quadrangula, Daphnia g_al£ata mendotae, D_._ retrocurva, p_._ longiremis, Bosmina
longirostris and Eubosmina coregoni. Most of the leastTprevalent species (e.g.,
Canthocamptus, Ilyocryptus, Alona, Camptocercus and Eurycercus) are littoral and
benthic species which occasionally are collected in the plankton of nearshore
waters. Chydorus sphaericus is primarily a littoral species but becomes common
in the plankton when clumps of blue-green algae are present; it was one of the
more abundant species in Green Bay.
Seasonal_gnd jpatial Distribution of Major Rotifera
Polyarthra vulgaris and Keratella cochlearis cochlearis were the most
abundant rotifers in Green Bay during 1977. Polyarthra vulgaris had a mean
abundance for all sampling periods of 99,200 per m (Appendix B, Table B-l). It
was most prevalent (mean of 220,900 per m3) in August when it constituted 48.3%
of total rotifers. _Ke_ratella cochlearis cochlearis had a mean abundance for all
sampling periods of 35,600 perlir^and~aTso was most prevalent in August (mean of
59,100 per m ), representing 12.9% of total rotifers. Typical of nearly all
rotifers in Green Bay, both £. vulgaris and j<. c_. cochlearis were low in
abundance (mean of 1,800 and 1,100 per m , respectively) in May and population
levels had declined considerably from summer values by October (mean of 28,200
and 29,700 per m , respectively) (Table 2).
In spite of its low abundance in May, Keratella cochlearis cochlearis
20
-------
TABLE 2. SPECIES COMPOSITION, MEAN ABUNDANCE (NUMBER X 10 /M3) AND
TROPHIC STATUS OF ROTIFERS IN GREEN BAY.
DATA ARE POOLED DISCRETE-DEPTH SAMPLES
FROM ALL STATIONS IN EACH SAMPLING PERIOD.
THE ABUNDANCE OF SPECIES LESS THAN 100 INDIVIDUALS/MJ
IS REPRESENTED BY A PLUS SIGN (+)
Class Monogonata
Order ploima
Family Brachionidae
Subfamily Brachioninae
Brachionus angular is Gosse
B. budapestinensis Daday
B. calciflorous Pallas
B. quadridentatus Hermann
Euchlanis dilatata Ehrbg.
Kellicottia longispina (Kellicott)
Keratella cochlearis cochlearis (Gosse)
K. cochlearis f. hispida (Lauterborn)
K. cochlearis f . robusta (Lauterborn)
K. crassa Ahlstrom
K. earlinae Ahlstrom
K. hiemalis Carlin
K. quadrata (O.F. Muller)
Lophocaris salpina (Ehrbg.)
Notholca acuminata (Ehrbg.)
N. foliacea (Ehrbg.)
N. laurentiae Stemberger
N. squamula (O.F. Muller)
Trichotria tectractis (Ehrbg.)
May
0.0
+
0.2
0.0
0.0
2.3
1.8
0.0
0.9
0.0
+
9.1
14.7
0.0
+
1.4
1.2
1.4
+
Aug.
0.3
+
0.0
+
0.2
4.1
59.1
4.9
2.5
22.1
18.1
0.0
2.2
0.0
0.0
0.0
+
0.1
0.0
Oct.
0.0
0.0
0.0
0.0
+
0.1
28.2
1.1
0.9
1.5
1.8
0.0
+
+
0.0
0.0
0.0
+
0.0
Trophic
Status*
E
E
E
E
E
0
ET
ET
ET
ET?
ET?
ET?
ET
I
0
0
0
O
I
Subfamily Colurinae
Lepadella ovalis (O.F. Mailer) 0.0 + 0.0
Family Lecanidae
Monostyla lunaris (Ehrbg.) 0.0 + 0.0 E
Family Trichocercidae
Trichocerca cylindrica (Imhof)
T. multicrinis (Kellicott)
T. porcellus (Gosse)
T. rousseleti (voigt)
T. similis (Ehrbg.)
0.0
0.0
0.0
0.0
0.0
3.6
7.3
5.1
1.1
-t-
0.1
1.0
2.2
0.2
+
E
E
E
E
E
(continued).
21
-------
TABLE 2. (continued).
Class Monogonata
Order Ploima
May
Aug.
Family Gastropidae
Ascomorpha ecaudis Perty
Ascomorpha oval is (Bergendal)
Gastropus stylifer (Imhof)
Family Tylotrochidae
Tylotrocha monopus (Jennings)
Family Asplanchnidae
Asplanchna priodonta Gosse
Family Synchaetidae
Ploesoma hud son i (Imhof)
P. lentlculafe Herrick
J>. truncatum (Levander)
Polyarthra dol ichoptera Idelson
£• §y£yJE£§E5 Wierzejski
Z- g|gjp_r Burckhardt
£. remata Skorikov
Z* vjjlgar'is Carlin
Synchaeta jcitina Rousselet
S_. pectinata Ehrbg.
~
S_. spp.
Family Testudinellidae
Fninia long i seta (Ehrbg.)
¥_. terminalis (plate)
Pompholyx _sulcata Hudson
jlggtud^inella patina (Hermann)
Family Conochilidae
jgonochilus unicornis (Rousselet)
Family Collothecidae
^Collotheca mutabilis (Hudson)
• glagica Itousselet
Total Rotifers
0.0
0.0
0.1
0.0
0.4
0.0
0.0
5.0
0.0
0.0
0.7
1.1
0.0
4.5
0.0
2.0
0.0
0.1
0.0
0.0
2.2
0.0
0.0
49.2
2.3
3.3
1.9
0.2
1.1
2.2
+
2.1
15.7
42.7
220.9
0.1
0.0
4.1
0.0
4.8
0.2
22.8
1.7
0.4
457.2
Oct.
0.0
0.4
0.1
0.0
0.8
Trophic
Status*
M
M
ET
M
ET
+
+
+
+
+
5.3
10.8
29.7
0.1
+
0.0
0.0
+
0.0
0.6
0.0
3.5
0.5
+
89.1
ET
ET
ET
0
M?
M?
ET
ET
I
M?
M?
I
E
0?
E
I
ET
M?
M?
*Trophic Status: ET = Eurytopic; E = Eutrophic; M = Mesotrophic;
0 = Oligotrophic; I = insufficient information. Compiled from Gannon
and Stemberger (1978), Stemberger (1979) and other sources.
22
-------
TABLE 3. SPECIES COMPOSITION, MEAN ABUNDANCE (NUMBER/M )
OF CRUSTACEANS AND TROPHIC STATUS FROM STANDARDIZED NET TOWS IN GREEN BAY.
DATA ARE FROM ALL STATIONS IN EACH SAMPLING PERIOD. -
PRESENCE OF A SPECIES IN NUMBERS LOWER THAN 10 INDIVIDUALS/M
IS INDICATED BY A PLUS SIGN (+)
Subclass Copepoda
Order Calanoida
Limnocalanus macrurus Sars
Eurytemora affinis (Poppe)
Epischura lacustris Forbes
Leptodiaptomus sicilis Forbes
L. ashlandi Marsh
L. minutus Lilljeborg
Skistodiaptomus oregonensis Lilljeborg
Diaptomid copepodids
Order Cyclopoida 3
Acanthocyclops vernal is Fischer
Diacyclops thomasi Forbes 2
Mesocyclops edax (Forbes)
Tropocyclops prasinus mexicanus Kiefer
Cyclopoid copepodids
Order Harpacticoida
Canthocamptus robertcokeri M.S. Wilson
C. staphyl inoides Pearse
Subclass Branchipoda
Order Cladocera
Family Leptodoridae
Leptodora kindtii (Focke)
Family Polyphemidae
Polyphemus pediculus (L.)
Family Sididae
Diaphanosoma spp.
Family Macro thricidae
Ilyocryptus acutifrons Sars
I. spinifer Herrick
May
650
+
+
0
20
250
100
230
50
,120
120
,830
20
70
80
+
0
+
850
0
0
+
0
0
Aug.
1,880
0
180
10
+
460
130
100
970
2,220
330
1,420
350
40
90
+
+
0
23,460
60
80
190
0
+
Oct.
4,120
0
20
20
20
160
50
60
3,790
4,100
220
3,000
510
120
150
+
0
+
9,070
20
0
80
+
0
Trophic
Status*
0
I
ET?
0
M
M
ET
E
ET
ET?
ET?
I
I
ET
ET
ET?
I
I
(continued)
23
-------
TABLE 3. (continued).
Family Holopedidae
Holopedium gibberum Zaddach
Family Daphnidae
Ceriodaphnia lacustris Birge
C_. quadrangula Muller
Daphnia galeata mendotae Birge
D. retrocurva Forbes
D. longiremis Sars
Daphnia spp. juvenile instars
Family Bosminidae
Bosmina longirostris (Muller)
Eubosmina coregoni (Baird)
Family Chydoridae
Alona quadrangularis (Muller)
Camptocercus rectirostris Schodler
Chydorus sphaericus (Muller)
Eurycercus lamellatus (Muller)
Total Crustacea
May
50
0
0
70
+
0
140
130
420
0
+
40
0
4,620
Aug.
3,370
590
1,370
6,300
5,230
1,720
30
1,350
2,770
0
400
0
27,560
Oct.
160
30
30
1,150
2,040
500
0
300
3,470
0
1,280
17,290
Trophic
Status*
ET?
E
E
ET
ET
M-0
E
I
ET
I
E
ET?
*Trophic Status: ET = Eurytopic; E = Eutrophic; M = Mesotrophic;
0 = Oligotrophic; I = Insufficient information. Compiled from Gannon
and Stemberger (1978) and other sources.
-------
exhibited a discernible distribution pattern that had a significant (.05)
negative correlation with Secchi disc transparency, it was relatively most
abundant at the southeastern stations in Green Bay and in Little Bay de Noc
(Figure 12). In August, K. c_. cqchlearis had the most ubiquitous distribution
of any rotifer during the study period.It ranged from 20,000 per m near the
Cedar River to 109,400 per m at a station off the Menominee River. Greatest
concentrations (mean of >80,000 per m ) were observed in the four stations off
the Menominee River but similarly high values (>60,000 per m ) were observed at
stations throughout Green Bay, off Sturgeon Bay and in Big Bay de Noc. Tn
contrast to most rotifer species during August* K. cochlearis cochlearis was
more prevalent in Big Bay de Noc (72,500 per m3) than in Little Bay de Noc
(24,0000 per m ). in October, numbers of _K. c. cochlearis were low
(10,000-25,000 per m ) in upper Green Bay north of Chambers Island but were
still relatively high (40,000-80,000 per nr) in lower Green Bay, off the
Menominee River and in Big Bay de Noc. Numbers were low (12,000-20,000 per m )
in lower Little Bay de Noc but high (100,000 per m ) at the upper "most station
(Figure 12). Its abundance and distribution showed a significant (.05 in August
and .01 in October) positive correlation with alkalinity and turbidity and a
negative correlation with Secchi disc transparency in summer and fall.
The distribution of Ascomorpha oval is most closely resembled that of K.
cochlearis cochlearis (Figures 12 and 13). Ascomorpha ovalis was just appearing
in the plankton during May but by August reached a mean abundance of 2,300 per
m and was most prevalent off the Menominee River and in Big Bay de Noc. Its
greatest abundance (8,300 per m ) was observed near the Menominee River mouth.
In contrast numbers elsewhere in Green Bay ranged from less than 1,000 to more
than 3,000 per m . Numbers averaged 1.5 times higher in Big Bay de Noc than in
Little Bay de Noc. Its abundance and distribution exhibited a significant (.01)
positive correlation with turbidity (.01) and a significant (.05) negative
correlation with Secchi disc transparency (.05). Although numbers of A. ovalis
were much reduced (mean of 400 per m ) by October, it still showed a tendency
for greater abundance off the Menominee River and its distribution exhibited a
significant (.01) positive correlation with conductivity and negative (.05)
correlation with Secchi disc transparency.
Nine species (Polyarthra vulgar is, j>. remata, _p. major, Conochilus
unicornis, Keratella crassa, K. earlinae, Synchaeta stylata, Asplanchna
priodonta and ploesoma truncatun) exhibited similar pattern of distribution
(Figures 14-22). They were all just appearing in the plankton during May but by
August were distributed throughout the study area with marked population
concentrations off the Menominee River mouth and in Little Bay de Noc. Since
Polyarthra vulgaris was the most abundant species in this group, it will be
discussed first.
Polyarthra vulgaris was found at scattered locations during May (mean of
1,100 per m )"but, nevertheless, its distribution showed a significant (.01)
negative correlation with Secchi disc transparency. By August, it was^ high in
abundance through the study area, reaching a maximum of 613,500 per m" at a
station off the Menominee River mouth. Population peaks were observed in Little
Bay de Noc (>300,000 per m ) and off the Menominee River (MOO,000 per m ).
Numbers were also high (near 250,000/m ) in Green Bay from Chambers island north
25
-------
KerateHa c. cochlearis
rv>
Figure 12. Distribution of Keratella cochlecufis
-------
Ascomorpha ovalis
Figure 13. Distribution of Ascomoppha ovalis.
-------
to Washington Island. Concentrations were lowest (<100,000 per m ) in the
island passages and in Big Bay de Noc (Figure 14). In spite of obvious
population peaks off the Menominee River mouth and in Little Bay de Noc,
concentrations were relatively high elsewhere in Green Bay so that no
significant correlations between physicochemical variables and P. vulgaris
distribution were observed. By October, the population had declined (mean of
29,700 per m ) considerably from summer levels but numbers were still relatively
high in comparison with other rotifers. Polyarthra vulgaris was quite uniformly
distributed throughout the study area and, therefore, no significant
correlations were observed with physicochemical variables.
Two other species of Polyarthra, I>. remata and £. major, were also
prominent members of the rotifer community in Green Bay. The three species
collectively constituted 61.1 and 51.4% of total rotifers during August and
October respectively (Table 2). The distributional patterns of the three
species were similar (Figures 14-16).
Polyarthra remata was low in abundance (mean of 700 per m ) during May.
It was found in low numbers at scattered locations-throughout the study area
but exhibited one large concentration (6,600 per m ) off the Escanaba River
mouth in Little Bay de Noc. By August, it was well distributed throughout the
bay in high (mean of 42,700 per m ) numbers. Its greatest abundance (164,600
per m ) was located nearest the Menominee River mouth. Highest concentrations
included the cluster of stations around the Menominee River mouth and in Little
Bay de Noc (Figure 15). Lowest (<2,000 per nr) numbers were observed in the
island passages region. A substantial reduction in numbers (mean of 10,800 per
nr) had occurred by October and the population was quite uniformly distributed
with slightly higher numbers noted in Big Bay de Nbc.
Polyarthra majpj: was not observed during May but was moderately abundant
(mean of 15,700 per m ) in August. Its highest numbers (60,000 per m ) were
located off the Escanaba River and population concentrations were prominent in
Little Bay de Noc and off the Menominee River mouth (Figure 16). Similar^to £.
remata, by October P_. major was found in low numbers (mean of 5,300 per m )
throughout the study area with a slightly higher concentration in Big Bay de
Noc.
Kerate!la crassa was not present in May but developed moderately high (mean
of 22,100 per nr)populations in August. It reached a maximum of 94,800 per m
at the station nearest the Menominee River mouth and, indeed, exhibited a
pronounced population peak in that region (Figure 17). Numbers of K. crassa
were notably higher south of Chambers island and were especially low north of
Washington Island and in the Bay de Noes. Although numbers were much lower
(mean of 1,500 per m ) in October, K. crassa was slightly more prevalent off the
Menominee River mouth and at the southernmost station in Green Bay. The
abundance and distribution of K. crassa was significantly correlated with
physicochemical variables in August and October. It exhibited significant (.05)
positive correlation with alkalinity and conductivity and significant (.05 in
August and .01 in October) negative correlation with Secchi disc transparency.
The distribution of j<. earlinae was similar to that of K. crassa except JK.
28
-------
Polyarthra vulgaris
ro
Figure. 14. Distribution of Polyapthpa vulgap-is.
-------
Polyarthra remata
UJ
o
Figure 15- Distribution of Polyartkpa remata.
-------
Polyarthra major
1 Oct 1977
Figure 16. Distribution of Polyarthra major.
-------
Keratella crassa
Figure 17. Distribution of KeTatella orassa.
-------
earlinae also exhibited an additional population concentration in Little Bay de
Noc in August (Figure 18). Keratella earlinae was rare and scattered in the
study area during May and developed a moderately high (18,100 per m ) population
in August. It was notably most abundant off the Menominee River mouth where all
stations averaged over 35,000 per m . The population was relatively high
(15-25,000 per m ) in Little Bay de Nbc and in Green Bay south of Washington
Island. In October, averaged ten-times smaller (mean of 1,800 per irr) and
highest numbers (near 7,000 per m ) were observed in Green Bay south of Chambers
Island and off the Menominee River mouth. Similar to K^ crassa, the
distribution of _K. earlinae showed significant (.01) positive correlation with
alkalinity, conductivity and turbidity and significant (.01) negative
correlation with Secchi disc transparency in August and October.
Conochilus unicornis averaged 2,200 per m during May and was slightly more
prevalent south of Chambers Island in Green Bay and in Little Bay de Noc (Figure
19). The distribution of Conochilus in May showed significant (.01) positive
correlation with temperature and conductivity. The population averaged ten
times higher (mean of 22,800 per ml in August and was highest off the Menominee
River mouth (50,000 to 81,200 per m ) and in Little Bay de Noc (mean of
approximately 47,000 per m ). in October, Conochilus population was reduced to
an average of 3,500 per m and was slightly more prevalent north of Washington
Island and in the Bay de Noes. The distribution of Conochilus in August and
September did not reveal any statistically significant correlations with
physicochemical variables.
Synchaeta stylata was observed only during the August sampling period when
it reached a mean abundance of 4,100 per m (Table 2). The only consistent
distributional pattern for this species was relatively high abundance at the
cluster stations near the Menominee River mouth (maximum abundance of 20,800 per
m ). It was also more prevalent near the Ford and Cedar River mouths and near
Sturgeon Bay than elsewhere in Green Bay (Figure 20). No statistically
significant correlations with physicochemical variables were obtained.
The two predaceous rotifers, Asplanchna priodonta and ploesoma truncatum,
exhibited population maxima near the Menominee River mouth and in Little Bay de
Noc (Figures 21 and 22). In contrast to most of the preceding species, these
rotifers had peak numbers recorded in Little Bay de Noc rather than off the
Menominee River mouth during August.
Asplanchna priodonta was present in low abundance (mean of 400 per m )
in May and was most prevalent at the southeasternmost stations in Green Bay.
Its distribution exhibited significant (.01) positive correlation with
temperature and conductivity during spring only, in August, its population
averaged 1,900 per m and numbers greater than 4,000 per m were observed in
Little Bay de Noc, off the Menominee River mouth and at the southernmost station
in Green Bay (Figure 21). Maximum numbers (11,000 per m") were recorded off the
Escanaba River mouth. By October, the population averaged 800 per m and did
not exhibit any notable pattern of distribution.
ploesoma truncatum was absent in May but developed a population averaging
2,200 per m in August. It exhibited highest concentrations in Little Bay de
33
-------
Keratella earlinae
uo
Oct 1977
Figure 18. Distribution of
eavl-inae.
-------
-------
Synchaeta stylata
Figure 20. Distribution of Synohaeta stylata.
-------
Asplanchna priodonta
Oct 1977
Figure 21. Distribution of Asplanshna priodonta.
-------
Ploesoma truncatum
Oct 1977
Figure 22. Distribution of Ploesoma trvineatum.
-------
Nbc and off the Menominee River but numbers closest to the river mouths were
relatively low. The highest number (12,500 per m ) was observed in lower Little
Bay de Noc while lesser numbers (3,000 per m ) were observed nearest the
Escanaba River mouth. Likewise, nearest the Menominee River mouth, less than
1,000 per m were observed while the cluster of nearby stations had an average
of 3,300 per m (Figure 22). In October, the population was extremely reduced
(mean of <100 per m3) and scattered in distribution. No statistically
significant correlations between E>. truncatum distribution and physicochemical
variables were attained.
The preceding rotifer species have all exhibited a general pattern of
greatest abundance in southernmost Green Bay, off the Menominee River mouth and
in Little Bay de Noc. in contrast, Gastropus stylifer and Keratella cochlearis
f. robusta were most prevalent in Big Bay de Noc and in the island passages
region between Green Bay and Lake Michigan proper (Figures 23 and 24).
Gastropus stylifer was rare in May and October but was found throughout the
study area in August with mean numbers of 2,300 per m . The population size was
generally less than 1,000 per m everywhere except in Little Bay de Noc (mean of
about 3,000 per m ), Big Bay de Nbc (mean of about 13,700 per m ) and in the
island passages region (mean of about 7,900 per m ). Maximum abundance (19,500
per m ) was at the uppermost station in Big Bay de Noc. The distribution of G_.
stylifer showed significant positive (.01) correlation with alkalinity and
conductivity and significant (.05) negative correlation with Secchi disc
transparency. Although the population was extremely low (mean of 100 per m ) in
October, the same statistical correlations were obtained.
Keratella cochlearis f. robusta was observed at scattered locations in May
(mean of 900 per m ) and was most abundant (6,000 per m ) near Chambers Island.
In August, it was low in abundance everywhere except in the island passages
region (mean of about 9,500 per m ) and Big Bay de Noc (mean of about 5,000 per
m ). The station in Rock island passage had the highest concentration (14,000
per m ) of this species (Figure 24). Its distribution showed a significant
(.05) negative correlation with alkalinity, conductivity and turbidity and a
significant (.05) positive correlation with Secchi disc transparency. The
distribution of this species was considerably different in October but similar
statistically significant relationships with physicochemical_variables were
obtained. Numbers of this species were highest (6,000 per m ) at the
southernmost station in Green Bay and other areas of concentration were off the
peshtigo River and near Chambers Island during October (Figure 24).
Collotheca mutabilis was not a numerically abundant species but its
distribution was rather unique in Green-Bay. It was not present during May but
had a mean concentration of 1,700 per m during August. It was the only rotifer
species whose highest numbers were found in the open waters of northern Green
Bay. Its population peak (6,800 per m ) was observed at the station west of
Washington island (Figure 25). Collotheca was low in abundance (mean of 500 per
m ) in October but it was still most prevalent in the open waters of northern
Green Bay.
Kellicottia longispina is one of the few rotifers whose distribution
exhibited statistically significant correlations with temperature. Its
39
-------
Gastropus stylifer
1977
Figure 23. Distribution of Gastropus stylifer.
-------
Keratella cochlearis f. robusta
1977
Get 1977
Figure 24. Distribution of Keratella ooehleapis f. robusta.
-------
Collotheca mutabilis
Oct 1977
Figure 25. Distribution of Collotheea mutdbilis.
-------
distribution in May was patchy; it was absent along the east coast of Green Bay
except for an anomolous high concentration (6,000 per m ) near Chambers Island.
Low numbers (mean of 2,100 per m ) were observed along the west coast of the
bay, in the Bay de Noes and the island passages region. Its distribution showed
significant (.01) positive correlation with temperature and conductivity during
spring. In contrast, it was negatively correlated (.01) with temperature during
the warmer water temperatures of summer and fall. In August, Kellicottia had a
mean abundance of 4,100 per m and reached a maximum abundance of 34,300 per m
in the cold temperature anomoly off Sturgeon Bay (Appendix A). It was
distributed throughout the study area with slightly higher concentrations at
offshore stations iFigure 26). The population by October was extremely reduced
(mean of 100 per m ) but its distribution still showed a significant (.01)
negative correlation with temperature.
Keratella quadrata was the only major rotifer species in Green Bay that was
most abundant during May (mean of 14,700 per m ). it was prevalent, from
Chambers Island southward where it reached a maximum abundance of 62,000 per m
at the southernmost station (Figure 27). Its distribution exhibited a
significant (.01) positive correlation with temperature and conductivity during
May. The population of !<._ quadrata was low in numbers (mean of 2,200 in August
and <100 per m in October) and scattered in distribution and no statistically
significant correlations were obtained during summer and fall.
Notes on Other Rotifers
Most of the numerically important rotifers in the preceding section
exhibited the pattern of highest population concentrations off the Menominee
River mouth and in Little Bay de Nbc. These species are all limnetic and
eurytopic forms (Table 2). Other limnetic species (i.e., Keratella cochlearis
f. hispida, Filinia longiseta, polyarthra euryptera and ploesoma lenticulare)
exhibited a similar distributional pattern.
Keratella cochlearis f.. hispida was absent in the plankton in May but had a
mean abundance of 4,100 per m during August, it was observed at all stations
in August but was noticeably most prevalent off the Menominee River mouth where
its maximum abundance (19,800 per m ) was recorded (Appendix B, Table B-l). A
second population peak was not present in Little Bay de Nbc or elsewhere in the
study area, its distribution showed a significant (.01) positive correlation
with turbidity and alkalinity and a significant (.05) negative correlation with
Secchi disc transparency. In October, its population was reduced (mean of 1,100
per m ) and restricted in distribution. This species was still most prevalent
in the vicinity of the Menominee River mouth. Besides a few individuals in
uppermost Little Bay de Nbc, K. cochlearis f. hispida was not observed north of
Washington Island. Similar to August, its distribution in October showed
significant (.01) positive correlation with conductivity and alkalinity and a
significant (.05) negative correlation with Secchi disc transparency.
Filinia longiseta exhibited a similar distributional pattern. It was not
present in the plankton in May but reached a mean population of 4,800 per m in
August. Only a few individuals were observed in northern Green Bay and Little
Bay de Noc and it was absent from the island passages region and Big Bay de Noc.
-------
Kellicottia longispina
Figure 26. Distribution of Kellioottia long-Lspina.
-------
Keratella quadrata
Oct 1977
Figure 27. Distribution of Kevatella quadrata.
-------
It was by far most abundant (maximum of 34,400 per m) at the cluster of
stations off the Menominee River mouth. Numbers were low elsewhere in the
southern portion of the study area. Its distribution exhibited a significant
(.01) positive correlation with conductivity and turbidity and negative
correlation with Secchi disc transparency. It was observed only off the
Escanaba River in October.
Polyarthra euryptera was absent during May and developed mean numbers of
2,100 per m3 in August. Low numbers were observed in Little Bay de Noc and
throughout Green Bay except for the population peak (maximum of 10,400 per m )
near the Menominee River mouth. It was absent from Big Bay de Noc and the
island passages region. £. euryptera was found only near Chambers Island in
October.
Ploesoma lenticulare was also absent during May but reached mean numbers of
1,100 per m in August.Its maximum abundance (5,500 per m ) was nearest the
Menominee River mouth and a lesser peak (3,300 per m ) was observed off the
Escanaba River. Otherwise, it was low in numbers throughout Green Bay and
absent from Big Bay de Noc. Curiously, it was found (a few individuals at a
single station) only in Big Bay de Noc in October.
Other species which exhibited this general distributional pattern are
littoral forms (e.g., Brachionus spp., Euchlanis, Pompholyx and Trichocerca
spp.) that appear in the plankton under eutrophic conditions (Gannon and
Stemberger 1978).
Brachionus spp. were observed only at a few stations. Brachionus
budapestinensis and ]3. calciflorous were seen only at the southeasternmost
stations in Green Bay during May.Brachionus guadridentatus was observed only
off Sturgeon Bay and EJ. angularis (3,100 per m ) and B. budapestiensis (1,300
per m ) were collected only near the mouth of the Menominee River during August
(Appendix B, Table B-l). Brachionus calciflorus distribution exhibited
significant (.01) positive correlation with temperature and conductivity.
Similarly, EL angularis showed significant (.05) positive correlation with
conductivity and turbidity and negative (.01) correlation with Secchi disc
transparency.
Likewise, similar relationships were observed with Euchlanis and Pompholyx.
Euchlanis dilitata was observed only at the station nearest to the Menominee
River mouth (1,300 per m ) in August and it exhibited significant (.05) positive
correlation with the higher turbidity there. Pompholyx sulcata was collected
only in August near the Menominee River mouth (maximum of 2,300 per m ) near
Sturgeon Bay and off Chambers island (Appendix B, Table B-l). Its distribution
showed significant (.05) positive correlation with alkalinity and turbidity and
negative correlation (.01) with Secchi disc transparency.
None of the five species of Trichocerca were present in the plankton during
May but three species (T. multicrinis, T. "porcellus and T. cylindrica)
were prevalent during August. Trichocerca multicrinis was observed at all
stations with mean numbers of 7,300 per m . it was most abundant (maximum of
18,700 per m ) in the cluster of stations off the Menominee River mouth. A
46
-------
lesser peak (near 9,000 per m3) occurred in Little Bay de Noc while it was least
prevalent in the island passages region and Little Bay de NOc. Trichocerca
cylindrica reached a mean of 3,600 per m . Although it was found at nearly all
stations, it was only abundant (maximum of 15,600 per m ) in the cluster of
stations near the Menominee River mouth. It was least prevalent in northernmost
Green Bay, the Bay de Noes and the island passages region. Trichocerca
porcellus was patchy in its distribution. It developed mean numbers of 5,100
per m with a maximum (16,400 per m ) at the lowermost station in Big Bay de
Noc. Numbers ranged from 2-4,000 per nr in the vicinity of Menominee River
mouth, 2-12,000 per m in Green Bay north of Chambers Island and 5-11,000 per nr
in Little Bay de Noc.. By contrast, jr. porcellus was still moderately abundant
(mean of 2,200 per m ) in October. Trichocerca multicrinus and T. cylindrica
(mean of 1,000 and 100 per m , respectively) were most prevalent south of
Chambers island in October. Trichocerca rousseleti was much less abundant (mean
of 1,100 and 200 per m respectively) in August and October. It was slightly
more prevalent west of Chambers Island and in Little Bay de Noc in August and
scattered in low numbers at eight stations in October. Trichocerca similis was
observed only nearest the Menominee River mouth in August^
In contrast with the preceding species, a number of limnetic forms, mostly
with springtime population maxima, did not exhibit the pattern of highest
numbers in the vicinity of the Menominee River mouth or in Little Bay de Noc.
These species include Notholca spp., jSynchaeta spp. and Polyarthra dolicoptera.
Pour species of the cold water stenothermic Notholca were observed and they
occurred almost exclusively during May and exhibited no discernible
distributional pattern. Notholca foliacea was observed in low numbers (mean of
1,400 per m ) throughout the study area with a maximum abundance (6,300 per m )
recorded off of Sturgeon Bay. Similarly, Notholca squamula (mean of 1,400 per
m_) was scattered at one-half of the stations with maximum abundance (7,900 per
m ) at the southernmost station in Green Bay. Notholca laurentiae was observed
in low numbers at most locations (mean of 1,200 per m) with a maximum (3,900
per m ) recorded near the Menominee River. A few individuals of NL. acuminata
were collected only at the Menominee River mouth in flay. Only a few N. squamula
and N. laurentiae were observed at scattered locations on other sampling
periods.
In addition to Synchaeta stylata (Figure 19) , S. pectinata, SI. kitina and
Synchaeta spp. (= J3. asymmetrica -f S_. lakowitziana) were observed in Green Bay.
As in Notholca, these species of Synchaeta exhibited low and rather uniform
distribution in Green Bay. Synchaeta pectinata reached a mean abundance of
4,500 per m in May and was observed at all stations with maximum numbers
(10,000 per m ) near Chambers Island. Synchaeta spp. was observed everywhere in
low numbers (mean of 2,000 per m ) during May and was most prevalent (3,900 per
m ) off the Menominee River mouth. A few individuals of_S. kitina were found at
a few, discontinuous locations in August and October.
Polyarthra dolicoptera, in contrast to the other representatives of this
genus in Green Bay, was most abundant (mean of 5,000 per m ) in May. It was
observed everywhere but in the island passages region. Abundance was patchy
with highest numbers (maximum of 13,300 per m ) near Chambers Island and lesser
47
-------
peaks off the Escanaba River (6,900 per m ), in Big Bay de Noc (11,100 per m )
and at the southernmost Green Bay station (12,600 per m ). In contrast, numbers
in upper Green Bay were low (1,500 per m ).
The remaining species were all collected as single specimens or a few
individuals. Most (e.g., Lepadella oval is, Lophocaris salpina, Monostyla
lunaris, Testudinella patina, Trichotria tectractis and Tylotrocha monopus) are
littoral and benthic species that were observed as single individuals at one or
two stations, mostly during August (Table 2). Others were limnetic forms which
were rare and usually discontinuous in distribution, ploesoma hudsoni was
observed as single specimens in May and October but was collected at four
stations in August (mean of 200 per rrr). it occurred only in northern Green Bay
and off Sturgeon Bay. Collotheca pellagica was found only at three stations in
August and two in September. In August, it occurred along the east coast of
Green Bay from Sturgeon Bay to the tip of the Door Peninsula, reaching a mean
and maximum abundance of 400 and 6,300 per m6, respectively, in October, it was
observed in low numbers only in the island passages region. Ascomorpha ecaudis
was represented by a single specimen in upper Green Bay during August.
Seasonal and Spatial Distribution of Major Micro-Crustacea
An examination of the crustacean plankton data revealed that patterns of
distribution are more readily discernible using percentage composition rather
than numbers per unit volume. A similar conclusion was reached in processing
micro-crustacean data from the Straits of Mackinac and southern Lake Michigan
(Gannon ^t aU 1976, Gannon ^t al_. 1982). Consequently, distribution of
micro-crustaceans will be discussed primarily in terms of percentage composition
in this section.
Three species of Daphnia (D. retrocurva, D. galeata mendotae and D.
longiremis were among the most prevalent cladocerans in Green Bay. Daphnia
galeata mendotae was the most abundant (mean of 2,500 per m ) cladoceran and all
three species represented a mean of 28% of total crustaceans during the study
period (Table B-2). Although each species, exhibited a noticeable
distributional pattern (Figures 28-30), these daphnids did not exhibit
consistent correlations with physicochemical variables.
Daphnia galeata mendotae had a mean abundance of 70 per m during May
(Table 3). It was absent only from the open, waters of northern Green Bay and
was most prevalent south of Chambers Island and in Big Bay de Noc (Figure 28).
Highest numbers (1,650 per m ) were observed east of Chambers Island. Its
distribution during May exhibited a significant (.01) positive correlation with
temperature and conductivity, it was abundant (mean of 6,300 per m ) during
August, and in contrast toJD. retrocurva, D. galeata mendotae was relatively
most prevalent (mean of 9% of total crustaceans) in the island passages region
(Figures 28 and 29). It was still quite prevalent (mean of 1,150 per m )
throughout the study area in October and was slightly more abundant in the open
waters of northern Green Bay.
Daphnia retrocurva, the second most abundant cladoceran, was just beginning
its springtime population growth during May (mean of <10 per m ) and was
48
-------
Daphnia galeata mendotae
vo
Oct 1977
Figure 28. Distribution of Daphnia galeata mendotae.
-------
Daphnia retrocurva
vn
o
Figure 29- Distribution of Daphnia retvocwva.
-------
observed at scattered locations. In August, it reached a mean abundance of
5,230 per m (Table 3) and was most prevalent (28,270 per m ) at the innermost
station in Little Bay de Nbc (Figure 29). It was relatively high (20 to over
50% of total crustaceans) at all stations except in the island passages region
(mean of 15%). By October, its population was substantially lower (mean of
2,040 per m ) but its distributional pattern was similar to August. No
significant correlations were obtained in May and August but during October its
distribution showed a significant (.01) positive correlation with turbidity and
negative correlation with Secchi disc transparency.
Daphnia longiremis had not appeared in the plankton in May but was
relatively abundant (mean of 1,720 per m ) in August. It was most prevalent in
Green Bay between Chambers and Washington Islands and in Little Bay de Noc. It
was still found throughout the study area in October but at reduced population
levels (mean of 200 per m ). it was slightly more abundant west of Chambers
Island than elsewhere (Figure 30). The distribution of D. longiremis showed no
significant correlations with physicochemical variables.
In contrast with the daphnids, Eubosmina coregoni and Bosmina longirostris
exhibited more discernible distributional patterns that were more consistently
correlated with physicochemical variables. Eubosmina coregoni (mean of 2,220
per m ) was relatively more abundant than Bosmina longirostris (mean of 590 per
m ). Eubosmina was the third most abundant cladoceran during the study period.
Eubosmina (mean of 420 per m ) was distributed throughout Green Bay in May
with highest numbers at southeasternmost stations (Figure 31). Its distribution
in May exhibited a significant (.01) positive correlation with temperature and
conductivity and a significant (.05) negative correlation with Secchi disc
transparency. The population of Eubosmina reached a mean of 2,770 per m in
August with numbers noticeably highest off the Menominee River mouth and in
lower Green Bay. Its maximum abundance (27,380 per m ) was observed at the
southernmost station in Green Bay. The distribution of Eubosmina during August
showed a significant (.01) positive correlation with alkalinity, conductivity
and turbidity and a significant negative correlation with Secchi disc
transparency. In contrast with most cladocerans, Eubosmina was relatively
abundant (mean of 3,470 per m ) in October. It was well distributed throughout
the study area in October and did not show any significant correlations with
physicochemical variables.
Bosmina lonqirostris was low in abundance (mean of 130 per m ) and
scattered in distribution during May. It was relatively more prevalent in
Little Bay de Noc and off the Cedar River but its distribution showed no
significant correlations with physicochemical variables. In August, Bosmina was
common (mean of 1,350 per m ) throughout the study area. It was most prevalent
off the Menominee River mouth and in Little Bay de Noc and least abundant in the
island passages region (Figure 32). The distribution of Bosmina during August
exhibited a significant (.05) positive correlation with alkalinity and
conductivity and a significant negative correlation with Secchi disc
transparency. Its population was considerably reduced (mean of 300 per m ) in
October and quite uniformly distributed. Bosmina was slightly more prevalent
south of Chambers Island and its distribution showed a significant (.01)
51
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Daphnia longiremis
Oct 1977
Figure 30. Distribution of Daphnia
-------
Eubosmina coregoni
VJl
UJ
Oct 1977
Figure 31. Distribution of Eubosmina aoregoni.
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Bosmina longirostris
Scale
Oct 1377
Figure 32. istrlbution of Bosmina
-------
positive correlation with temperature and conductivity.
Chydorus sphaericus exhibited one of the most prominent distribution
patterns of any crustacean in Green Bay. It was low (mean of 40 per m ) in
abundance during May and observed only south of Chambers island in Green Bay in
the Bay de Noes. Its distribution showed a significant (.01) positive
correlation with temperature and conductivity. In August, it was rare in the
open waters of northern Green Bay and in the island passages region and was
noticably most prevalent off the Menominee River mouth and at the southernmost
stations in Green Bay (Figure 33).~ It reached a mean of abundance of 400 per m
and was most abundant (1,890 per m6) off the Menominee River mouth and in lower
Green Bay. The distribution of Chydorus during August exhibited a significant
(.01) positive correlation with alkalinity, conductivity and turbidity and a
significant negative correlation with Secchi disc transparency. Similar to
Eubosmina, Chydorus reached its highest numbers (mean of 1,280 per m ) in
October. As in August, Chydorus was most prevalent off the Menominee River
mouth and in southernmost Green Bay, but it was also relatively abundant in the
Bay de Noes. Maximum abundance (4,540 per m ) was recorded at the lowermost
station in Green Bay whereas highest relative abundance (45% of total
crustaceans) was observed off the Escanaba River in Little Bay de Noc. As in
August, it was lowest in abundance in the open waters of northern Green Bay and
in the island passages region (Figure 33).
Ceriodaphnia lacustris and _C. guadrangula were both absent in May and were
rare and scattered in distribution in_0ctober. However, they were relatively
abundant (mean of 590 and 1,370 per m , respectively) in August. Both species
were most prevalent off the Menominee River mouth. Ceriodaphnia quadranaula was
also abundant in Green Bay north of Chambers Island and Ceriodaphnia lacustris
was prevalent in Little Bay de Noc. Both species were least abundant in the
island passages region (Figure 34). The distribution of C_. quadrangula showed a
significant (.05) positive correlation with alkalinity and conductivity and jC.
lacustris was correlated (.01) with conductivity (+) and Secchi disc
transparency (-).
The distribution of Holopedium gibberum was unique among the cladocerans.
It was the only species exhibiting greatest"relative abundance in northern Green
Bay and the island passages region. It was found in low numbers (mean of 50 per
m_) only in the Bay de Noes during May and was low in abundance (mean of 160 per
m ) and scattered in distribution in October. In August, it represented 30-40%
of total crustaceans in the Bay de Noes and 10-20% in northern Green Bay and
among the island passages. Maximum abundance (3,340 per m ) was observed in
Little Bay de Noc. Lowest numbers were south of Washington Island except for
one anomolous recording (510 per m ) near the Menominee River mouth (Figure 35).
Diacyclops thonasi was the predominant cyclopoid copepod in Green Bay. It
was one of the most abundant (mean of 2,420 per m ) crustaceans and one of the
few species_that was prevalent during all three sampling periods. It averaged
2,830 per m and represented a mean relative abundance of 61% of total
crustaceans in May. It was well distributed throughout the study area during
May (Figure 36). In August, D. thomasi, was least abundant (mean of 1,420 per
m ) and was slightly more prevalent in northern Green Bay and off Sturgeon Bay
55
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Chydorus sphaericus
Oct 1977
Figure 33- Distribution of Chydorus spha,evious.
-------
Ceriodaphnia spp.
Oct 1977
Figure 3^. Distribution of Ceviodaplmia spp..
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Holopedium gibberum
VJl
co
197-7
Figure 35. Distribution of Eolopedium gibberum.
-------
Diacyclops thomasi
1977
Figure 36. Distribution of Diaoyolops thomas-L.
-------
Bay than elsewhere. Highest numbers (mean of 3rOOO per m ) were observed in
October when the population was decidedly most prevalent off the Menominee River
mouth. The distribution of D. thomasi showed a significant (.01) correlation
with temperature in May and August. In contrast, the correlation (.01) with
temperature in October was positive. No significant correlations with chemical
variables was observed except conductivity (+ at .05) in October.
Immature cyclopoid copepods were not identified to species, but most of
the immatures were likely Diacyclops thomasi because of the overwhelming
predominance of this species. Only the larger instars were probably captured by
the net. Nevertheless, some noteworthy distributional patterns were evident.
Only a few individuals were observed at most stations during May except in
southeastern Green Bay where numbers ranged from 140 to 890 per m . Their
distribution in May exhibited a significant (.o5) positive correlation with
conductivity. In August, they were observed everywhere except in Big Bay de
Noc. Relatively high numbers (200-510 per m ) were observed only near the
Menominee River mouth. Distributional correlations were significant (.01) with
alkalinity (+), conductivity (+), turbidity (+) and Secchi disc transparency
(-). Highest mean numbers (150 per m ) were observed in October when the
population was distributed throughout the study area but noticeably most
abundant off the Menominee River and in southeastern Green Bay. The
distribution of cyclopoid copepodids in October showed significant positive
correlation with temperature (.05) and conductivity (.01).
Mesocyclops edax was rare (mean of 20 per m ) in May but was moderately
abundant (mean of 350 and 510 per m , respectively) in August and October. It
was observed only in southern Green Bay and in Big Bay de Noc during May whereas
in August and October it occurred throughout the study area. It was most
prevalent near the Menominee and Peshtigo Rivers, near Washington Island and in
Little Bay de Noc during August when its distribution showed a significant (.01)
negative correlation with Secchi disc transparency. In October, it was most
prevalent south of Chambers Island and in Little Bay de Noc (Figure 37). Its
distribution in October exhibited a significant (.05) positive correlation with
temperature and conductivity.
Acanthocyclops vernalis was relatively low in abundance (mean of 220 per
m ) but exhibited noteworthy distribution patterns in Green Bay. it was rare
and scattered in distribution during May except for population peaks near the
Menominee River mouth and off Sturgeon Bay (Figure 38). In August, it was most
prevalent in Little Bay de Noc and off Sturgeon Bay. It was rarest in northern
Green Bay and in the island passages region. Its distribution in August showed
a significant (.01) negative correlation with temperature. Acanthocyclops
vernalis was low in numbers at most stations during October and was most
prevalent south of Chambers Island, especially near the Menominee River mouth,
and in Little Bay de Noc. Its distribution in October exhibited a significant
(.05) negative correlation with Secchi disc transparency.
Immature diaptomid copepods were overwhelmingly the most abundant calanoid
plankters in Green Bay and, therefore, their pattern of distribution (Figure 39)
closely resembled that of total calanoid copepods (Figure 6). Diaptomid
copepodids averaged 1,600 per m and comprised a mean of 53% of total calanoids
60
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Mesocyclops edax
Oct 1977
Figure 37- Distribution of Mesoayalops edax.
-------
Acanthocyclops vernalis
Figure 38. Distribution of Aoanthooyolops vernalis.
-------
Diaptomid Copepodids
1977
Figure 39- Distribution of Diaptomid copepodids.
-------
and 9% of total crustaceans (Table B-2). They were low (mean of 50 per nr) in
abundance during May with slightly higher numbers observed in the Bay de Noes
and off Sturgeon Bay than elsewhere. Their distribution during May showed a
significant (.01) positive correlation with temperature and conductivity. A
population peak off Sturgeon Bay was still noticeable in August and, moreover,
they were most prevalent in northern Green Bay, especially in the island
passages region. They had a mean abundance of 970 per m in August and their
distribution exhibited the opposite trend from May, a significant (.01) negative
correlation with temperature. In October, diaptomid copepodids were most
abundant (3,790 per m ), representing 92% of total calanoid copepods and 22% of
total crustaceans. They were decidedly most prevalent north of Chambers Island
but no significant correlations with physicochemical variables were obtained.
Leptodiaptomus ashlandi was the most prevalent (mean of 290 per m ) adult
calanoid copepod. It was found throughout the study area (mean of 250 per m ) in
May and was decidedly most abundant (maximum of 1,790 per m ) in the island
passages region. Its distribution exhibited a significant (.01) positive
correlation with Secchi disc transparency. In August, it reached its highest
mean abundance (460 per m ) and was markedly most abundant in the island
passages area (Figure 40). Its distribution in August showed a significant
(.05) negative correlation with conductivity and turbidity. Leptodiaptomus
ashlandi was uncommon (mean of 160 per m ) but showed the same trend of highest
relative abundance in the island passages region and at open water stations in
northern Green Bay. Its distribution in October exhibited a significant (.01)
negative correlation with conductivity.
Skistodiaptomus oregonensis adults exhibited a similar pattern of
distribution to L. ashlandi and was most abundant (mean of 230 per m ) in May
and was well distributed throughout the study area. It was slightly more
prevalent in Little Bay de Noc but its distribution did not show any significant
correlations with physicochemical variables. Skistodiaptomus oregonensis was
relatively uncommon (mean of 100 per m ) in August and was most prevalent in the
island passages region (Figure 41). Its distribution exhibited significant
(.05) negative correlation_with conductivity and turbidity. Similarly, it was
uncommon (mean of 60 per m ) in October and was also relatively most abundant in
the island passages region.
Leptodiaptomus minutus displayed a similar pattern of distribution as the
preceding adult calanoid copepods. It had an overall mean abundance of 90 per
m . In May, it was prevalent (meaan of 100 per nr) everywhere but was
relatively most abundant in northern Green Bay and Little Bay de Noc. Its May
distribution showed a significant (.01) positive correlation with Secchi disc
transparency, in August, it was slightly higher (130 per m ) in mean abundance
and was decidedly most prevalent in the island passages region and at the
uppermost station in Big Bay de Noc (Figure 42). By October, it was reduced in
numbers (mean of 50 per m ) but was still most prevalent in the island passages.
Its October distribution showed a significant (.01) negative correlation with
conductivity.
Eurytemora affinis had an overall mean abundance of 70 per m . It was
least prevalent (mean of <10 per m ) in May when it was absent from Little Bay
64
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Leptodiaptomus ashlandi
1977
Figure 40. Distribution of Leptodiaptomus ashlandi.
-------
Skistodiaptomus oregonensis
Figure 4l. Distribution of Skistodiaptomus ovegonensis.
-------
Leptodiaptomus minutus
Figure 4-2. Distribution of Leptodiaptomus minutus.
-------
de Noc and all westside stations. It was relatively most abundant in Big Bay de
Noc and vicinity. The May distribution of E. affinis showed a significant (.01)
positive correlation with Secchi disc transparency. In August, it was most
abundant (mean of 180 per m ) and was most prevalent off Sturgeon Bay and in
Little Bay de Noc (Figure 43). Its August distribution revealed limnologically
inconsistent correlations with physicochemical variables. It exhibited a
significant (.01) negative correlation with temperature and a positive (.05)
correlation with Secchi disc transparency. On the other hand, it showed a
significant (.05) positive correlation with alkalinity. Its population was
reduced (mean of 20 per nr) in October and no discernible or statistically
significant distributional trends were observed.
Notes on other Micro-crustaceans
Diaphanosoma was represented by D. leuchtenberg ianum and D. brachyurum.
Only a few of the latter were observed, undoubtedly washed into the plankton
from riparian wetlands. Most of the individuals were the former but the two
species were combined during laboratory processing for the sake of expediency.
Diaphanosoma spp. had an overall mean abundance of 90 per m . None were
observed in May and highest numbers (mean of 190 per m ) were reached in August.
They were rare everywhere except in Little Bay de Noc, Big Bay de Nbc and at the
mouth of the Menominee River. Highest numbers (4,740 per m ) were recorded at
the innermost station in Little Bay de Noc where they represented 9% of total
crustaceans. In contrast, the October population (mean of 60 per nr) was most
prevalent in Green Bay north of Chambers Island, Big Bay de Noc and the island
passages region. No significant correlations between Diaphanosoma distribution
and physicochemical variables were observed.
Polyphemus pediculus was observed only in August when it developed a mean
abundance of 60 per m .Its population was decidedly most prevalent in Green
Bay north of Chambers island^ the Bay de Noes and the island passages area.
Highest numbers (1,340 per m ) were observed near St. Martin Island where it
represented 2.5% of total crustaceans. Polyphemus distribution exhibited
significant (.05) positive correlation with alkalinity, conductivity and
turbidity and negative correlation with Secchi disc transparency.
Leptodora kindtii was uncommon in August and October and absent during May.
In August, it was infrequent (mean of 60 per m ) and absent from one-quarter of
the stations. Relatively high numbers (>400 per m ) were observed only at the
innermost station in Little Bay de Noc and the southernmost station in Green
Bay. In October, it was rare (mean of 20 per m ) and observed only at six
stations. Highest numbers (130 per m ) were collected near the Menominee River
mouth and low numbers were observed at the southernmost station in Green Bay and
in the Bay de Noes. No significant correlations between Leptodora distribution
and physicochemical variables were obtained.
Tropocyclops prasinus mexicanus was the only other cyclopoid copepod
collected in Green Bay. It was uncommon (overall mean of 80 per m ) but was
observed during each sampling period, in May, it was rare (mean of 70 per m )
at most stations but it was absent from the island passages and Big Bay de Noc.
68
-------
Eurytemora affinis
1977
1977
Figure 43. Distribution of Eurytemora affinis.
-------
Highest numbers (360 per ml were recorded east of Chambers Island, it was less
prevalent (mean of 40 per ra ) in August but displayed a similar distributional
pattern. It was again absent from the island passages and Big Bay de Noc and
most abundant off Chambers Island. In contrast, it was found everywhere in
October but still in low numbers (mean of 120 per m ). Tropocyclops was most
prevalent in innermost Little Bay de Noc and in southeastern Green Bay.
Three calanoid copepods, Epischura lacustris, Leptodiaptomus sicills and
Limnocalanus macrurus, were rare in Green Bay, Epischura was observed only in
August (mean of 10 per nr) and October (mean of 20 per m ). in August, it was
collected only in the Bay de Noes and off the Cedar River in northern Green Bay.
Its distribution exhibited significant (.05) correlations with conductivity (-),
alkalinity (-) and Secchi disc transparency (+). In October, it had a similar
distribution but was also collected from the island passages. Leptod iaptomus
sicills was observed in low numbers (mean of 30 per m ) throughout the study
period, it was relatively abundant (130-140 per m ) in the southeasternmost
stations in Green Bay in May. It was observed only at the southernmost station
in Green Bay in August and was scattered along the east coast from Sturgeon Bay
to Rock island passage in October. Limnocalanus was observed only in May (mean
of <10 per m ) and only in the open waters of northern Green Bay and in Big Bay
de NOC.
the remaining micro-crustaceans are primarily benthic species that
infrequently appeared as single or a few individuals at some stations.
Camptocercus rectirostris was observed most frequently, especially in the
shallow Big and Little Bay de Noc stations during May and August. The most
benthic species (i.e., Canthocamptus robertcokeri, jS. staphylinoides,
Ilyocryptus acutifrons, !_. spinifer and Alona quadrangularis) were collected at
the station off Sturgeon Bay. Canthocamptus staphylinoides was also observed in
the Bay de Noes. Eurycercus lamellatus was collected only in Little Bay de Noc.
DISCUSSION
the species composition of zooplankton in a lake, with few exceptions,
usually remains constant for many decades, perhaps for centuries, because these
species have adapted to the physicochemical environment and have been successful
in competing with other species. A species which newly disperses to that lake
rarely can become established unless some environmental disturbance occurs.
Perturbations which change the physicochemical milieu or alter the balance of
competition between species can cause extermination of some species and allow
the appearance of others. At the present state of our knowledge,
eutrophication, size-selective predation by planktivorous fishes, and toxic
substances are the major factors that may cause changes in zooplankton species
composition and abundance. Although monitoring and surveillance programs
primarily have been designed to assess eutrophication trends, caution must be
exercised in establishing one-to-one cauusal relationships between changes in
zooplankton community composition and eutrophication (Gannon and Stemberger
1978). Nevertheless, trends in spatial distribution and abundance of
70
-------
zooplankton in Green Bay during 1977 appeared to be related to existing water
quality conditions.
Water quality patterns in Green Bay are largely dependent on the mixing of
relatively oligotrophic Lake Michigan waters with comparatively eutrophic waters
of southern Green Bay. The southern portion is shallow and more physically
isolated from Lake Michigan; it receives high nutrient inputs from the Fox River
and smaller tributaries, especially the Oconto, Peshtigo and Menominee Rivers
along the east coast (Bertrand et^ al. 1976). Because of current dynamics, Pox
River water normally moves along tRe east coast of southern Green Bay gradually
mixing with Lake Michigan water as the water mass progresses northward. Pox
River water concentrations decrease to about 10-25% at our lowermost sampling
stations south of Sturgeon Bay. Current patterns are more complex in northern
Green Bay and are less well understood. A high rate of exchange between Lake
Michigan and Green Bay waters is evident with Lake Michigan water entering
through the island passages and moving principally southward along the east
coast.
Little and Big Bay de Noc differ considerably in morphology and degree of
anthropogenic impact. Big Bay de Noc has no larger rivers, urban areas or
industrial development. The mouth of the bay is wide and rapid exchange of
water between Big Bay de Noc and northern Michigan is evident. In contrast.
Little Bay de Noc is narrow and a relatively slow rate of exchange between the
bay and northern Green Bay is suspected. Moreover, waters in Little Bay de Noc
are highly influenced by municipal and industrial discharges, principally by way
of the Escanaba River (Bertrand et al. 1976; Tierney et al. 1976).
Rotifer populations appeared to be especially responsive to water quality
conditions in Green Bay. Total rotifers were distinctly most abundant along the
east coast of Green Bay south of Chambers Island, in Little Bay de Noc
(especially off the Escanaba River) and off the Menominee River mouth.
Statistically significant correlations between high rotifer densities and high
alkalinity, specific conductance and turbidity and low Secchi disc transparency
were often observed.
The predominant rotifers exhibiting this pattern were limnetic, eurytopic
species ( i.e., polyarthra vulgaris, JP. major, JP. remata, Conochilus unicornis,
Keratella crassa, K. earlinae, Synchaeta stylata, Asplanchna priodonta and
ploesoma truncatum). Other limnetic eurytopic species of lesser abundance
(i.e., Keratella cochlearis f. hispida, Polyarthra euryptera and ploesoma
lenticulare) showed the same distributional trend. Eutrophic indicator species
were not abundant in the study area but did display the same pattern. They
included the limnetic, Filinia longiseta, and littoral species, such as
Brachionus spp., Euchlanis dilatata, Pompholyx sulcata and Trichocerca spp.
The littoral species were especially localized nearest to the Menominee and
Escanaba River mouths. On many occasions, most of the predominant and lesser
species exhibiting this pattern of abundance showed statistically significant
correlations similar to that reported for total rotifers. The predominant
response of the rotifer community was, therefore, an increase abundance of
eurytopic species with eutrophic indicator species comprising a numerically
minor component of the rotifer community.
71
-------
As noted by Gannon and Stemberger (1978), there are many eutrophic
indicator species in the rotifers but few oligotrophic ones. Based on
physicochemical data, the island passages, Big Bay de Noc and the open waters of
Green Bay north of Chambers island showed the least indications of
eutrophication. Rotifer populations in these regions were generally lowest in
abundance. Exceptions were relatively high numbers of eurytopic Keratella
cochlearis cochlearis and mestrophic Ascomorpha ovalis in Big Bay de Noc. The
only species distinctly most prevalent in these regions were Gastropus stylifer
and Keratella cochlearis f. robusta (Big Bay de Noc and island passages) and
Collotheca mutabilis (open waters of northern Green Bay). The oligotrophic
indicators, Notholca spp. and Polyarthra dolicoptera and mesotrophic (?)
Synchaeta asymmetrica, £>. kitina, S. lakowitziana and S_. pectinata were low in
numbers and scattered in distribution. ~
Kellicottia longispina is often noted in more oligotrophic waters of the
Great Lakes (Stemberger et aL. 1979; Gannon _et al_. 1982), but its distribution
may be more tuned to temperature than to chemical conditions. Keliicottia
was the only rotifer species exhibiting statistically significant correlations
with temperature, it was most prevalent in waters indicative of eutrophication
in May (positive correlation with temperature) but was least abundant in those
waters in August and October (negative correlation with temperature).
Consequently, waters least influenced by eutrophication were more conspiciously
charaterized by lesser numbers of eurytopic species and an absence of eutrophic
indicator species than by the presence of oligotrophic indicator species.
The abundance and distribution of crustacean plankton showed discernible
distribution patterns but their densities did not exhibit as strong statistical
correlations with physicochemical variables as the rotifers. This indicates
that crustacean populations may not be so strongly influenced by water quality
conditions and that biotic factors, such as size-selective predation by
planktivores, may play a more prominent role. Nevertheless, there were some
noteworthy and consistent trends. Densities of total crustaceans were highest
south of Chambers Island and off the Escanaba and Menominee River mouths. Total
calanoid copepods were most prevalent in the Bay de Noes and in southern Green
Bay during spring but were distinctly most abundant north of Chambers Island and
in the island passages in summer and fall. In contrast, total cyclopoid
copepods were abundant everywhere in spring but most prevalent south of Chambers
Island in summer and fall. Total cladocerans were highest in abundance south of
Chambers Island and in the Bay de Noes. Reflecting these patterns, the ratio of
calanoid copepods to cyclopoid copepods plus cladocerans was highest north of
Chambers Island in spring and especially high in the island passages during
summer and fall. The same correlations of zooplankton densities and
physicochemical variables as noted for rotifers were observed for crustacean
plankton but were less frequent and consistent.
The most distinct distributional patterns and those with the most
significant correlations with physicochemical conditions were observed in
several numerically important cladocerans. Eubosmina coregoni, Bosmina
longirostris, Chydorus sphaericus, Ceriodaphnia spp., Daphnia galeata mendotae
and Leptodora kindtii were most prevalent in those regions with physicochemical
indications of eutrophication. Chydorus sphaericus and Ceriodaphnia spp. were
72
-------
particularly abundant in Little Bay de Noc and near the Menominee River mouth.
Eubosmina coregoni and Bosmina longirostris were also especially prevalent near
the Menominee River. As in the rotifers, the major response of the crustacean
community to eutrophication was an increase in density of eurytopic species
(i.e., Daphnia galeata mendptae and D. retrocurva) although eutrophic indicator
species (i.e., Bosmina longiros'tris, Ceriodaphnia spp. and Chydorus sphaericus)
was prominent also. Holopedium gibberum was the only relatively abundant
cladoceran that was most prevalent in waters (i.e., north of Chambers Island and
in the island passages) least influenced by eutrophication. Polyphemus
pediculus exhibited a similar distributional pattern but at considerably lower
densities. The distribution of Daphnia longiremis and Diaphanosoma spp. was
inconsistent in relation to water quality patterns.
Copepods most prevalent in areas with indications of eutrophication were
Diacyclops thomasi and Acanthpcyclops vernalis. Mespcyclops edax also exhibited
this trend but less prominently. The eurytopic D. thomasi was widespread in
abundance but most prevalent in the perturbed areas while the eutrophic
indicator, A. vernalis, was rare except in Little Bay de Noc, off the Menominee
River and near Sturgeon Bay. In contrast, all numerically important calanoid
copepods were most abundant north of Chambers island. Some copepods lesser in
abundance such as Eurytemora affinis and Tropocyclops prasinus mexicanus, did
not exhibit any consistent distributional patterns in relation to water quality.
Others such as Epischura lacustris and the oligotrophic indicator, Limnocalanus
macrurus, were observed only in northern waters. As in the rotifers, waters
least influenced by eutrophication had a paucity of oligtrophic and eutrophic
indicator species and contained lower densities of eurytopic species than more
perturbed waters.
In summary, four regions of differing water quality conditions can be
identified through zooplankton community composition analyses. The most
eutrophic areas were localized near the Menominee River mouth and in Little Bay
de Noc, especially near the Escanaba River mouth. These areas were
characterized by high densities of eurytopic species and the major concentration
zones for eutrophic indicator species as well. The area south of Chambers
Island was apparently enriched by diluted Fox River waters and was characterized
by high densities of eurytopic species but lesser prevalence of eutrophic
indicator species in comparison with the Menominee River mouth and Little Bay de
NOC. North of Chambers Island was characterized by lesser abundance of all
species, an absence of eutrophic indicator species and the presence of a few,
rare oligotrophic indicator species. Big Bay de Noc most resembled Green Bay
north of Chambers Island but often exhibited slightly higher numbers of
eurytopic species. This pattern seems more indicative of shallow, naturally
productive waters than of perturbation.
The most consistent feature of the zooplankton community in the northern
Green Bay area was the high densities of eurytopic species in contrast with the
comparative rarity of eutrophic and oligotrophic indicator species. This
pattern has been observed elsewhere in the Great Lakes and appears to be
indicative of mesotrophy (Gannon and Stemberger 1978). Consequently, based on
zooplankton community composition, waters north of Chambers island and in Big
Bay de Noc appear mesotrophic. Waters south of Chambers island are still
73
-------
mesotrophic, although closer to eutrophy on the trophic spectrum because of
comparatively large proportions of eutrophic indicator species in the
zooplankton community. The predominance of eurytopic and eutrophic indicator
species near the Menominee and Escanaba Riverr mouths indicate that these
localized areas are the most eutrophic in northern Green Bay.
No consistent patterns were observed in correlation coefficients between
zooplankton species abundances and concurrently collected phytoplankton in
northern Green Bay. Perhaps more rigorous statistical scrutiny would have
revealed more relationships. However, it is of interest that similar zonation
of water quality in northern Green Bay was independently determined by analyses
of zooplankton (this report), phytoplankton (Stoermer and Stevenson 1980) and
physicochemical (Rockwell et al. 1980).
The importance of this investigation is to provide a benchmark on
zooplankton community composition for comparison with future studies. Ideally,
we would also like to compare results of this study with previous
investigations. Unfortunately, it is difficult to assess the impact of past
changes in water quality and lake ecology on zooplankton because of the lack of
comparable historical data for northern Green Bay.
The first offshore zooplankton samples known to be collected in Green Bay
were procured by the U.S. Bureau of Fisheries in 1932. Unfortunately, these
samples were never analyzed and were destroyed long ago. Balch et aL. (1956)
collected crustacean zooplankton in the Fox River and extreme lower Green Bay.
No species identification were attempted and most of the samples were procured
in February. Torke (1973) collected crustacean zooplankton on a single date in
July, 1971 but all stations were south of the present study area. Consequently,
meaningful comparisons of these studies with the present investigation are not
possible. Gannon (1974) examined crustacean plankton in lower Green Bay from
the Fox River mouth north to Chambers Island in 1969 using the same mesh size
plankton net as in the present study. Additional samples were collected
throughout Green Bay, including the Bay de Noes, in July, 1970. Therefore,
these 1970 data are most comparable to this study. Similar species composition
and relative abundance were generally obtained in 1970 and 1977. However, lower
Green Bay, especially closest to the Fox River mouth contained considerably
higher densities and higher proportions of eutrophic indicator species than
northern Green Bay in 1970, indicating the substantially higher degree of
eutrophication in the lower bay in comparison with the 1977 study area. A
greater abundance of the eutrophic indicators, Chydorus sphaericus and
Ceriodaphnia spp., and the appearance of the eutrophic indicator, Acanthocyclops
vernalis, was observed in Little Bay de Noc in 1977, possibly indicating an
increase in eutrophication in that region between 1970 and 1977.
The only other zooplankton study that has been conducted in Green Bay
focused on the mouth of the Fox River (Wisconsin Public Service Corporation
1974) and, therefore, data are not very comparable to this investigation. It is
noteworthy, however, that mean densities of total zooplankton were nearly twice
as high in lower Green Bay south of Longtail Point during August, 1973 than in
northern Green Bay during 1977. Moreover, eutrophic indicator species (e.g.,
Brachionus, Filinia and Trichocerca) were predominant near the Fox River mouth
-------
but rare in northern Green Bay, indicating once again the much more eutrophic
condition in lower Green Bay.
In comparisons with other portions of Lake Michigan, it is evident that
northern Green Bay waters are more eutrophic, based on zooplankton assemblages,
than the open waters of Lake Michigan (Gannon 1972; Gannon et al. 1976).
Zooplankton composition in northern Green Bay and in the concurrent study of the
nearshore waters in southern Lake Michigan (Gannon et al. 1982) exhibited
similar mesotrophic features. However, rotifers were 2.4 times more abundant
and crustacean plankton 9.2 times less abundant in southern Lake Michigan than
in northern Green Bay during August, 1977. The relatively low abundance of
crustacean plankton and their small size composition indicates that
size-selective predation, principally by alewives, influenced community
structure of zooplankton in southern Lake Michigan (Gannon £t al. 1982).
Although the alewife population is also dense in Green Bay, the planktivores
appears to exert comparatively less influence on zooplankton species and size
composition. Gannon (1974) hypothesized that the impact of fish predation on
crustacean plankton is buffered by large recruitment of these zooplankters into
the population from higher rates of production in the eutrophic lower Green Bay
waters and from dispersal into the bay from Lake Winnebago by way of the Fox
River.
In conclusion, analysis of zooplankton assemblages was useful in detecting
regions of water quality differences in northern Green Bay. These data will
provide a benchmark from which future comparisons can be made. Detecting future
changes in the abundance and distribution of eurytopic species and detecting
shifts in composition, abundance and distribution of eutrophic and oligotrophic
indicator species can be useful in determining the biotic response to
eutrophication and nutrient control management strategies in Green Bay and
elsewhere in the Great Lakes.
75
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Ahlstrom, E. H. 1943. A revision of the rotatorian genus Keratella with
descriptions of three new species and five new varieties.Bull. Amer.
Museum Nat. Hist. 80:411-457.
Balch, R. P., K. M. Mackenthun, W. M. Van Horn and T. F. Wisniewski. 1956.
Biological studies of the Fox River and Green Bay. Wisconsin State
Coram. Water Poll., Bull. WP102, mimeo, 74 p.
Bertrand, G., J. Lang and J. Ross, 1976. The Green Gay watershed: Past/
present/Future. Univ. Wisconsin Sea Grant College Program, Tech. Rept.
No. 229, 300 p.
Brooks, J. L. 1957. The systematics of North American Daphnia. Mem. Connecticut
Acad. Arts and Sci., 13:1-180.
Brooks, J. L. 1959. Cladocera, p. 587-656. In: W. T. Edmondson (ed.) Fresh-water
Biology, 2nd Ed., Wiley, New York, 124¥~p.
Czaika, S. C. 1974. Aids to the identification of the Great Lakes Harpacticoids
Canthocamptus robertcokeri and Canthocamptus staphylinoides. Proc. 17th
Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., p. 587-589.
Deevey, E. S., Jr. and G. B. Deevey. 1971. The American species of Eubosmina
Seligo (Crustacea, Cladocera). Limnol. Qceanogr. 16:201-218.
Gannon, J. E. 1971. Two counting cells for the enumeration of zooplankton and
micro-Crustacea. Trans. Amer. Microsc. Soc. 90:486-490.
Gannon, J. E. 1972. A contribution to the ecology of zooplankton Crustacea of
Lake Michigan and Green Bay. Unpubl. Ph.D. Diss., Univ. Wisconsin, 257 p.
Gannon, J. E. 1974. The crustacean zooplankton of Green Bay, Lake Michigan.
Proc. 17th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., p.
28-51.
Gannon, J. E. 1980. Towards improving the use of zooplankton in water quality
surveillance of the St. Lawrence Great Lakes, p. 87-109. In: Proc. First
Biological Surveillance Symposium, Can. Tech. Rept. Fish. Aquatic Sci., No.
976, 191 p.
Gannon, J. E. and S. A. Gannon, 1975. Observations on the narcotization of
crustacean zooplankton. Crustaceana, 28(2):220-224.
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Gannon, J. E., K. S. Bricker and T. B. Ladewski, 1976. Crustacean zooplankton of
the Straits of Mackinac and northern Lake Michigan, in: Schelske, C. L.,
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Lakes Res. Div, Spec. Rept. No. 60, pp. 133-190.
Gannon, J. E. and R. S. Stemberger. 1978. Zooplankton (especially crustaceans
and rotifers) as indicators of water qualilty. Trans, Amer. Microsc. Soc.
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Gannon, J. E., F. J. Bricker and K. S. Bricker. 1982. Zooplankton community
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Rattulidae. Bull. U. S. Fish Comm., 1902: 272-352.
Likens, G. and J. Gilbert. 1970. Notes on quantitative sampling of natural
populations of planktonic rotifers. Limnol. Oceanogr. 15:816-820.
Modlin, R. F. and A. M. Beeton. 1970. Dispersal of Fox River water in Green Bay,
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Rockwell, D. C., D. S. DeVault III, M. F. Palmer, C. V. Marion and R. J.
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rotifers in Milwaukee Harbor and adjacent Lake Michigan. Unpuubl. M.S.
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Stemberger, R. S. 1976. Notholca laurentiae and N. michiganensis, new rotifers
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Environ. Protection Agency, Rept. No. EPA 600/4-79-021, 185 p.
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structure of rotifer communities in Lake Huron. U.S. Environ, protection
Agency, Rept. No. EPA 600/3-79-085, 159 p.
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Tierney, D. P., R. Powers, T. Williams and S. C. Hsu. 1976. Actinomycete
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(eds.), Report on a cruise of the R/v Neeskay in central Lake Michigan and
Green Bay, 8-14 July 1971, Center Great Lakes Stud., Univ. Wisconsin-
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78
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Appendix A. Physicochemical data for May composite and August and October discrete
samples from Green Bay, 1977- It includes the location number (L), collection
date (CD), collection depth (D, m), bottle temperature (T, C), alkalinity (A, ppm
C03), specific conductivity (C. mohms), turbidity (X), nitrate and nitrite (N, ppm),
ammonia (M, ppm), reactive silica (SI, ppm), and secchi depth (S, m). Reactive
phosphorus concentrations were less than 2 ppb. •
I CO
001 770505
002 770505
003 770505
004 770505
005 770505
006 770505
007 770517
008 770517
009 770519
010 770519
011 7705011
012 770S03
013 77050*
014 770503
015 77050*
016 770504
017 770518
018 770518
019 770518
020 710517
021 770517
022 770517
023 770517
024 770517
025 770517
001 770811
001 770811
002 770811
002 770811
003 770811
003 770311
DOfc 770811
014 7*0810
005 770811
005 770811
006 770810
006 770810
007 770810
007 770810
008 770810
003 770810
009 770810
009 770810
010 770310
•MO 770310
011 770810
011 770810
012 770810
012 770810
013 770810
013 770810
014 770810
014 770810
015 77M10
015 770810
0 16 770810
01« 770810
017 770810
017 770810
018 770810
018 770810
019 770811
019 77081 1
0 T 4 C X N
09 10.2 238
09 09.0 305
11 10.0 320
25 08.0 310
12 06.4 320
30 05.0 300
30 05.0 318
15 09.0 342
32 10.2 365
15 10.0 344
15 05.0 310
15 02.3 310
26 C4.5 000
15 05.0 315
16 06.0 280
IS 07.8 000
15 18.4 460
14 18.0 «i)0
30 11.0 380
15 05.5 330
30 05.8 320
30 06.0 320
30 07.0 338
15 09,8 348
12 13.1 362
02 20.0 1iO 271 0.8 0.03
10 20.0 110 273 0.9 0.04
02 20.0 no 272 0.6 0.05
14 18.0 109 278 1.0 0.03
02 20.0 109 284 1.2 0.06
12 19.0 110 279 1.4 0.07
02 19.5 110 277 0.7 0.07
15 18.5 110 276 0.9 0.08
02 20.0 109 274 0.7 0.05
12 20.0 109 274 0.7 0.05
02 21.5 no 274 0.7 0.05
16 18.5 110 276 0.8 0.08
02 22.5 110 275 0.6 0.02
30 10.0 110 274 0.9 U.17
02 21.0 11Q 273 0.7 0.04
10 20.5 110 274 0.8 0.05
02 22.0 113 278 0.7 0.02
33 09.0 110 277 0.9 0.22
02 21.0 113 279 0.8 0.02
7 . 10.5 111 278 1.1 C.13
Q* 21.5'113 280 0.8 0.02
14 10.0 112 279 0.8 0.03
02 21.0 11J 281 1.0 0.02
11 20.5 113 281 1.3 0.02
02 20.0 H3 279 1.0 0.02
17 15.0 110 277 1.1 a. 10
02 21.0 114 282 1. 1 0.02
20 12.5 111 276 1.5 0.16
02 20.0 1 13 280 1.0 0.02
23 10.5 111 279 0.0 0.20
2 21.0 113 283 0.9 0.02
16 11.5 112 280 1.3 0.17
2 10.0 116 278 1.0 0.20
7 09.5 107 282 0.8 0.21
02 22.0 113 278 0.7 0.02
20 11.0 111 279 1.0 0.20
02 20.0 112 277 0.6 0.02
3» 10.0 111 278 1.8 0.22
M
0.021
0.023
0.012
0.040
0.022
0.034
0. 150
0.320
0.006
0.006
0.005
0,015
0.004
0.017
0.004
0.008
0.004
0.017
0.004
0.017
0.003
0.008
0.003
0.003
0.040
0.070
0.050
0. 130
0.004
0.0 1 2
0.004
o.tno
0.007
0.006
0.004
0.010
0.003
0.018
SI
1.05
1. 18
0.70
1.65
1.06
1. 12
0.38
0.66
0.35
0.35
0.17
0.33
0. 16
0.90
0.22
0.28
0. 14
1.60
0.13
1.80
0.13
0.22
0. 13
0. 1*
0.17
0.58
0.13
1.51
0.18
2.35
0.17
2.73
2.30
2.38
0. 16
2.20
0.15
1.44
s
2,0
2.5
1.0
2.5
5.0
5.0
5.5
5.0
5.5
4.5
2^5
4.5
3.0
3.0
2.0
2.0
2.5
5.0
6.0
6.0
6.0
6.0
5.5
4.5
4.5
4.5
4.5
4.5
2.5
2.5
4.5
4.5
5.5
5.5
4.5
4.5
5.5
5.5
5.5
5.5
5.0
5.0
4.0
4.0
3.0
3.0
2.5
2.S
2.5
2.5
3.0
3.0
3. Q
3.0
3.0
3.0
3.0
3.0
4.0
4.0
4.5
4.5
I CD
fl lu ' /o«i i
020 770811
021 770S11
021 770811
022 770811
022 770811
023 770811
023 770811
024 770811
024 770811
025 770811
025 770811
001 771007
001 771007
002 771007
002 771007
003 771007
003 771007
004 771007
004 771007
005 771007
005 771007
006 771008
006 771008
007 771039
007 771008
008 771008
008 771008
009 771008
009 771008
010 771005
010 771005
011 771005
011 771005
012 771005
012 771O01
013 771005
013 771005
014 771005
014 771005
015 771005
015 771005
016 771005
016 771005
017 771008
017 771008
018 771006
018 771006
019 771006
019 771006
020 771006
020 771006
021 771006
021 771006
022 771006
022 771006
023 771006
023 771006
024 771006
024 771006
025 771006
025 771006
0
U2
37
02
21
02
11
02
23
02
17
02
08
02
C7
02
10
02
10
02
17
02
10
02
15
02
31
02
11
02
31
02
28
02
13
02
07
02
13
02
17
02
20
02
16
02
08
02
18
02
31
02
42
02
22
02
25
02
21
02
15
02
07
T A
20.0 112
10.0 112
20.0 109
15.5 110
20.0 109
20.0 109
20.0 110
12.0 110
21.0 112
15.5 111
21.0 110
20.5 110
11.5 105
12.0 104
12.3 105
12.5 106
12.7 107
12.8 107
13.2 108
13.0 108
12.5 107
12.8 107
13.5 103
13.5 105
13.7 110
13.7 110
13.0 109
13.0 109
13.5 109
13.7 110
14.0 110
14.0 m
14.0 109
14.0 106
14.0 107
14.0 108
14.5 109
14.5 106
14.5 109
14.5 109
14.5 110
14.5 111
14.5 107
14.5 11 1
12.4 m
13.0 112
13. Q 109
13.5 112
13.5 109
13.3 110
14.0 108
10.5 108
14.0 109
14.0 109
13.2 109
08.5 109
14.0 109
14.0 108
13.0 106
13.2 107
13.0 107
12.5 107
C X
274 0.6
276 1.0
271 0.6
270 0.7
272 0.7
271 0.6
271 0.6
275 1.0
271 0.9
275 1.0
271 1.0
271 1.0
261 5.3
261 5.2
273 2.3
274 2.2
279 1.8
275 2.0
272 0.8
274 0.9
275 1.3
273 1.6
273 1.5
273 2.9
276 2.0
276 2.0
274 2.6
273 3.3
276 1.0
276 1.5
278 0.7
278 0.3
276 1.2
277 1.3
273 1.0
273 1.0
276 1.3
274 1.2
280 1.5
280 1.7
281 1.3
280 2.2
284 2.2
283 2.6
277 2.1
277 2.8
276 0.9
276 2.0
275 1.0
270 1.0
270 0.7
273 0.8
272 0.8
272 0.9
272 0.8
275 0.8
272 0.8
273 0.8
275 1.2
272 1.0
271 1.5
271 1.7
N
0.06
0.23
0. 10
0.14
0.08
0.08
0.07
0.18
o.ds
0.12
a. 02
0.02
0.01
0.01
0.09
0.09
0.09
0.09
0.09
0.09
0.09
0.09
0.09
0.10
0.09
0.09
0.07
0.07
0.10
0.10
0.07
0.08
0.06
0.06
0.04
0.00
0.05
0.06
0.07
0.07
O.U6
0.06
0,0 1
0.01
0.02
0.01
0.10
0. 10
0.12
0.12
0.13
0.1B
0.12
0. 12
0.12
0.23
0.13
0.13
0.07
0.07
0.05
0.05
H SI S
0.004 0. 19 5.0
0.020 1.73 5.0
0.004 0.24 5.0
0.012 0.28 5.0
0.004 0.23 5.0
0.006 0.24 5.0
0.004 0.18 5.5
0.016 1.23 5.5
0.006 0.22 5.0
0.028 1. 18 5.0
0.007 0.31 5.0
0.005 0.31 5.0
0.003 1.02 0.3
0.002 1.21 0.3
0.004
0.002
0.013
0.010
0.007
0.008
0.010
0.011
0.004
0.004
0.004
0.005
3.003
0.002
0.004
0.003
0.003
.59 1.5
.55 1.5
.37 1.5
.39 1.5
.11 3.0
. 12 3.0
.34 2.0
.35 2.0
.15 3.0
.16 3.0
.26 2.5
.28 2.5
.OS 2.0
.08 2.0
.33 2.S
.30 2.5
.03 3.0
0.005 .08 3.0
0.001 .10 2.5
0.001 .09 2.5
0.002 -US 2.0
0.002 .46 2.0
0.002 .39 2.5
0.002 1.51 2.5
0.009 1.05 2.0
0.009 1.06 2.0
0.010 0.92 2.0
0.012 0.93 2.0
0.005 0.50 2.0
0.005 0.50 2.0
0.004 0.43 -.-
0,004 0.42 -.-
0.002-1.23 .0
0.002 1.25 .0
0.004 1.10 .0
0.004 1.04 .0
0.002 0.63 .0
0.002 1.0S .0
0.001 1.04 .0
0 001 1.01 4.0
0.001 1. 10 4.0
0.001 1.42 a.O
0.003 O.B8 -.-
0.003 1.02 -.-
0.005 1.40 3.0
0.006 1.41 3.0
0.003 1.43 2.0
0.003 1.«3 2.0
79
-------
TABLE B-l. SPECIES COMPOSITION AND MEAN AND MAXIMUM ABUNDANCE
(NUMBER x io3/M3)
OP ROTIFERS IN GREEN BAY.
SUMMARY IS BASED ON POOLED DISCRETE-DEPTH SAMPLES
FROM ALL STATIONS AND SAMPLING DATES COMBINED.
PRESENCE OF A SPECIES IN NUMBERS LESS THAN 100/M3
IS INDICATED BY A PLUS SIGN (+)
Class Monogonata
Order Ploima
Mean
Maximum
Family Brachionidae
Subfamily Brachioninae
Brachionus angularis Gosse
_B_^ budapestinensis Daday
B^ calc iflorous Pallas
ILi quadridentatus Hermann
Euchlanis dilatata Ehrbg.
Kellicottla IpngTspina (Kellicott)
Keratella cochlearis cochlearis (Gosse)
JK. cochlearis f. hispida (Lauterborn)
_K. cochlearis f. robusta (Lauterborn)
JK. erasea Ahlstrom
IS* earlinae Ahlstrom
K. hiemalis Carlin
K. quadrata (O.F. MQller)
Lophocaris salpina (Ehrbg.)
Notholca acuminata (Ehrbg.)
N. foliacea (Ehrbg.)
!i* laurentiae Stemberger
N. squamula (O.F. Mliller)
Trichotria tectractis (Ehrbg.)
Subfamily Oolurinae
Lepadella oval is (O.F. MQller)
Family Lecanidae
Monostyla lunaris (Ehrbg.)
Family Trichocercidae
Trichocerca cylindrica (Imhof)
T. multicrinis (Kellicott)
Z*. pogcellus (Gosse)
T_^ rousseleti (Vbigt)
T. similis (Ehrbg.)
0.1
0.1
2.1
35-6
2.k
1.5
9.3
7-9
1.5
3.5
0.2
0.2
0.3
1.5
3.3
2.9
0.5
3.1
1.3
2.3
3^.3
109. U
19.8
lij.O
9^.8
39.6
50.0
62.0
+
O.h
6.3
3.9
7.9
0.2
0.7
15.6
18.7
16.U
(continued).
-------
TABLE B-l. (continued)
Class Monogonata M .,
_ , _i • Mean Maximum
Order Ploima
Family Gastropidae
Ascomorpha ecaudis Perty + +
Ascomorpha ovalis (Bergendal) l.l 3.3
Gastropus stylifer (Imhof) 1.3 2.9'.^
Family Tylotrochidae
Tylotrocha monopus (Jennings) + 0.5
Family Asplanchnidae
Asplanchna priodonta Gosse 1.2 • 11. o
Family Synchaetidae
Ploesotna hudsoni (Imhof) 0.1 +
£. lenticulare Herrick o.k 5.5
j>. truncatum (Levander) 0.9 12.5
Polyarthra dolichoptera Idelson 0.9 13.3
j>. euryptera Wierzejski 0.8 io.4
£. major Burckhardt Q.k 6o.O
£. remata Skorikov 21.5 16U.6
JP. vulgaris Carlin 99.7 613.5
Synchaeta kitina Rousselet 0.1 +
£. pectinata Ehrbg. 0.1 10.0
S. stylata Wierzejski 1.6 20.8
J3. spp. 0.3 3-9
Family Testudinellidae
Filinia longiseta (Ehrbg.) 1.9 3^.U
F. terminalis (Plate) + 0.5
Pompholyx sulcata Hudson - 0.3 U.I
Testudinella patina (Hermann) + +
Family Conochilidae
Conochilus unicornis (Rousselet) 10.8 8l.2
Family Collothecidae
Collotheca mutabilis (Hudson) 0.9 6.8
C. pelagTca Rousselet 0.1 6.3
Total Rotifers 226.6 1090.6
81
-------
TABLE B-2. SPECIES COMPOSITION AND MEAN AND MAXIMUM ABUNDANCE (NUMBER/M3)
OF CRUSTACEAN PLANKTON IN GREEN BAY.
SUMMARY IS BASED ON STANDARDIZED WET TOWS FROM ALL STATIONS
AND ALL SAMPLING DATES -COMBINED.
PRESENCE OF A SPECIES IN NUMBERS LESS THAN 10/M3'
IS INDICATED BY A PLUS SIGN (+)
Mean Maximum
Subclass Oopepoda
Order Calanoida
Limnocalanus macrurus Sars
Eurytemora affinis (Poppe)
Epischura lacustris Forbes
Leptodiaptomus sicilis Forbes
L. ashlandi Marsh
L. minutus Lilljeborg
Skistodiaptomus oregonensis Lilljeborg
Diaptomid copepodids
Order cyclopoida
Acanthocyclops vernal is Fischer
Diacyclops thomasi Forbes
Mesocyclops edax (Forbes)
Tropocyclops prasinus mexicanus Kiefer
Cyclopoid copepodids
2,220
+
70
10
30
290
90
130
1,600
3,150
220
2,420
190
80
110
34,470
2,470
950
770
1,790
1,270
5,820
30,990
44,870
7,570
4,450
3,780
360
3,950
Order Harpacticoida + +
Canthocamptus robertcokeri M.S. Wilson + +
£. staphylinoides Pearse + +
Subclass Branchipoda
Order Cladocera 11,130 50,570
Family Leptodoridae
Leptodora kindtii (Focke) 30 640
Family polyphemidae
Polyphemus pediculus (L.) 30 1,340
Family Sididae
Diaphanosoma spp. 90 4 74o
Family Macrothricidae
Ilyocryptus acutifrons Sars + +
_!. spinifer Her rick + +
. (continued). ~~~~~~
82
-------
TABLE B-2. (continued)
Mean
Maximum
Family Holopedidae
Holopedium gibberum Zaddach
Family Daphnidae
Ceriodaphnia lacustris Birge
C. quadrangula Muller
Daphnia galeata mendotae Birge
D. retrocurva Forbes
D. longirenus' Sars
Daphnia spp. juvenile instars
Family Bosminidae
Bosmina longirostris (MQller)
Eubosmina coregoni (Baird)
1,190
210
470
2,500
2,420
740
60
590
2,220
3,340
3,670
13,170
8,200
28,270
13,550
5,340
8,^900
27,380
Family Chydoridae
Alona quadrangular is (Mliller) +
Camptocercus rectirostris Schodler +
Chydorus sphaericus (Mtiller) • 570
Eurycercus lamellatus (Muller) +
Total Crustacea 16,490
50
40
25,770
200
52,970
*Trophic Status: ET = Eurytopic; E = Eutrophic; M = Mesotrophic;
0 = Oligotrophic; I = Insufficient Information. Compiled from Gannon
and Stemberger (1978) and other sources.
y S. €mifcmm«mta* Pfotectiorv Apnqr
Region 5, Library (PL-12D
77 West Jackson Boulevarq, IZtn
Chicago, It 60604-3590
U.S. GOVERNMENT PRINTING OFFICE: 1983-655-120.
83
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