v>EPA
United States
Environmental Protection
Agency
Region 5
Great Lakes National
Program Office
230 South Dearborn Street
Chicago, Illinois 60604
EPA-905/3-90-003
GLNPO Report No 01-91
December 1989
Phytoplankton and
Zooplankton in Lakes
Erie, Huron, and
Michigan: 1985
Do not WEED. This document
should be retained in the EPA
Region 5 Library Collection.
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Phytoplankton and Zooplankton Composition,
Abundance and Distribution and Trophic Interactions: Offshore Region of
Lakes Erie, Lake Huron and Lake Michigan, 1985
Volume 1 - Interpretive Report
by
Joseph C. Makarewicz and Theodore Lewis
Department of Biological Sciences
State University of New York at Brockport
Brockport, New York 14420
and
Paul Bertram
Great Lakes National Program Office
United States Environmental Protection Agency
230 South Dearborn Street
Chicago, Illinois 60604
August 1989
U.S. En,.
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Abstract
With the acknowledgement that biological monitoring was fundamental to
charting ecosystem health (Great Lakes Water Quality Agreement 1978), EPA's
program was developed for Lakes Erie, Huron and Michigan to: 1) monitor
seasonal patterns, ranges of abundance and, in general, structure of the phy-
toplankton and zooplankton communities; 2) relate the biological components to
variations in the physical, nutrient and biological environment; and 3) assess
the annual variance to allow better long-term assessments of trophic structure
and state. Several offshore stations (7-10 per cruise) on several cruises
(5-6) during the spring, summer and autumn of 1985 were sampled.
By examining changes in the phytoplankton and zooplankton in relation to
water chemistry, evidence was found suggesting little change in the trophic
status of Lakes Huron and Michigan while an improvement in the trophic status
of Lake Erie was evident. The offshore region of Lake Michigan is experienc-
ing changes in phytoplankton and zooplankton composition consistent with
nutrient control and top-down control by fish. Even so, the biomass of
phytoplankton and zooplankton and the trophic status of the lake have not
changed significantly. The appearance and establishment of Daphnia pulicaria
in offshore waters of Lake Huron suggest a change in the forage fish base.
Plankton composition has changed little since the 60's. However, dramatic
reductions in biomass of nuisance and eutrophic indicator species have
occurred. These changes are consistent with expectations of long-term nutri-
ent control. However, a change in piscivory is evident that has apparently
allowed the establishment of the large cladoceran Daphnia pulicaria. The
exotic predaceous cladoceran Bythotrephes cederstroemii has become established
in all three lakes.
ii
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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.
iii
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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 ecosys-
tem 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 Great Lakes Water Quality Agreement of 1978
between Canada and the United States of America.
This report presents results of the phytoplankton and zooplankton
portions of the water quality surveillance program conducted by GLNPO on Lakes
Michigan, Huron and Erie in 1984 and in winter of 1985. Results of the
physical and chemical portions of the surveillance program may be found in a
companion report:
Rockwell, David C., D. K. Salisbury and B.M. Lesht. 1989.
Water Quality in the Middle Great Lakes: Results of the 1985
USEPA Survey of Lakes Erie, Huron and Michigan.
Publication Number EPA-905/6/89-001. Great Lakes National Program
Office.
Environmental Protection Agency, Chicago, Illinois
iv
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ACKNOWLEDGEMENTS
Diane Oleson, Anna Brooks, Mike Letson and Lisa Kilroy inputed the raw
data into the computer. We thank them for their time and effort. Portions
of this report were completed while the primary author was on a Fulbright
Fellowship at the Max Planck Institute fur Limnologie. We thank Winfried
Lampert, Director of the Institute for his hospitality.
GLNPO gratefully acknowledges the contribution to this study of the
Bionetics Corporation, with whom GLNPO contracted for assistance in the col-
lection of samples and for the identification and enumeration of the phyto-
plankton and zooplankton. In particular, we extend appreciation to Norman A.
Andresen, Mark A. Lamb, Louis L. Lipsey, Donna Page and Heather K. Trulli.
Funds for this report were provided by U.S.E.P.A., Great Lakes National
Program Office under Grant Number R005007-01.
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TABLE OF CONTENTS
Page
Abstract ii
Disclaimer iii
Foreward iv
Acknowledgments v
Table of Contents vi
List of Tables ix
List of Figures xiii
OVERVIEW 1
SUMMARY
Lake Michigan 2
Lake Huron 7
Lake Erie 11
INTRODUCTION 16
METHODS
Sampling Sites 18
Chemistry 18
Phy toplankton 19
Zooplankton 20
Data Organization 21
Definitions 21
RESULTS AND DISCUSSION - LAKE MICHIGAN
Phytoplankton 23
Picoplankton 23
Annual Abundance of Major Algal Groups 23
Seasonal Abundance and Distribution of Major Algal Groups..24
Regional and Seasonal Trends in the Abundance of
Common Taxa 25
Historical Changes in Species Composition 29
Geographical Abundance and Distribution 33
Indicator Species 34
Historical Changes in Community Abundance 35
Zooplankton 37
Annual Abundance of Zooplankton Groups 37
Seasonal Abundance and Distribution of Major Zooplankton
Groups 37
Geographical Abundance and Distribution of Zooplankton
Groups 38
Common Species 39
Historic Changes in Species Composition 39
Crustacea 39
Rotifera 43
Historical Changes in Zooplankton Biomass 44
Indicators of Trophic Status 44
Trophic Interactions 46
vi
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RESULTS AND DISCUSSION - LAKE HURON
Phy toplankton 50
Annual Abundance of Major Algal Groups 50
Picoplankton 50
Seasonal Abundance and Distribution of Major Algal
Groups 51
Geographical Abundance and Distribution of Major Algal
Groups 52
Regional and Seasonal Trends in the Abundance of Common
Taxa 53
Historical Changes in Species Composition 56
Indicator Species 57
Historical Changes in Community Abundance and Biomass 58
Zooplankton 59
Annual Abundance of Zooplankton Groups 59
Seasonal Abundance and Distribution of Major
Zooplankton Groups 60
Common Species 60
Changes in Species Composition 61
Rotifera 63
Geographical Abundance and Distribution of
Zooplankton Groups 64
Indicators of Trophic Status 65
Historical Trends in Abundance 67
Trophic Interactions 68
RESULTS AND DISCUSSION - LAKE ERIE
Phytoplankton 70
Picoplankton 70
Annual Abundance of Major Algal Groups 70
Seasonal Abundance and Distribution of Major
Algal Groups 71
Geographical Abundance on Distribution Major
of Major Algal Groups 72
Regional and Seasonal Trends in the Abundance
of Common Species 72
Changes in Species Composition 76
Indicator Species 77
Historical Changes in Community Biomass 78
Zooplankton 80
Annual Abundance of Zooplankton Groups 80
Seasonal Abundance and Distribution of Major
Zooplankton Groups 80
Geographical Abundance and Distribution of
Zooplankton Groups 81
Common Species 82
Changes in Species Composition 83
East-West Species Distribution 86
vii
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Indicators of Trophic Status 87
Historical Changes in Abundance 89
Trophic Interactions 90
Comparison of Lakes Michigan, Huron and Erie 96
LITERATURE CITED 98
TABLES 110
FIGURES 169
VOLUME 2. DATA SUMMARY REPORT. Summary sheets of phytoplankton
and zooplankton data ATTACHED MICROFICHE
viii
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TABLE LEGENDS
TABLE 1 Latitude and longitude of plankton sampling
stations , 1985 110
TABLE 2 Plankton sampling dates for Lakes Michigan,
Huron and Erie in 1985 Ill
TABLE 3 Sample dates and stations for Lake Erie,
1985 Ill
TABLE 4 Sample dates and stations for Lake Huron,
1985 112
TABLE 5 Sample dates and stations for Lake Michigan 113
TABLE 6 Statistical comparison of zooplankton abundance
and biomass from north-south transects, Lake Erie..114
Table 7 Statistical comparison of phytoplankton abundance
and biomass from north-south transects, Lake Erie...114
TABLE 8 Average biological and chemical- parameters
(April-November) from a 1-m depth for Lakes Erie,
Michigan and Huron, 1985 115
TABLE 9 Relative abundance of major phytoplankton
divisions in Lake Michigan, 1983, 1984 and 1985 116
TABLE 10 Number of species and genera observed in each
algal division or grouping in Lake Michigan,
1983 , 1984 and 1985 117
TABLE 11 Abundance of Rhizosolenia eriensis in Lake
Michigan in 1983, 1984 and 1985 118
TABLE 12 Summary of common phytoplankton species occurrence
in Lake Michigan, 1983 119
TABLE 13 Summary of common phytoplankton species occurrence
in Lake Michigan, 1984 121
TABLE 14 Summary of common phytoplankton species occurrence
in Lake Michigan, 1985 123
TABLE 15 Comparison of abundance of Cyclotella species
at offshore sites in August of 1970, 1983, 1984 and
1985, Lake Michigan 124
TABLE 16 Distribution of indicator diatom species in Lake
Michigan 125
TABLE 17 Relative abundance of zooplankton in Lake Michigan..126
TABLE 18 Summary of common zooplankton species occurrence
in Lake Michigan during 1985 127
TABLE 19 Early August Cladoceran abundance in 1954, 1966,
1968, 1983, 1984 and 1985 in Lake Michigan 128
ix
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TABLE 20 Early August Copepoda abundance in 1954, 1966,
1968, 1983, 1984 and 1985 in Lake Michigan 129
TABLE 21 Average crustacean zooplankton biomass for 1976,
1984 and 1985, Lake Michigan 130
TABLE 22 The ratio of calanoids to cyclopoids plus
cladocerans geographically in Lake Michigan,
1983, 1984 and 1985 131
TABLE 23 Correlation of phytoplankton with total phosphorus
concentrations and zooplankton abundance
within individual cruises in Lake Michigan 132
TABLE 24 Number of species and genera observed in each
algal division or grouping, Lake Huron, 1983,
1984 and 1985 133
TABLE 25 Relative abundance of major phytoplankton
divisions in Lake Huron, 1983, 1984 and 1985 133
TABLE 26 Abundance of Rhizosolenia eriensis in Lake
Huron, 1983, 1984 and 1984 134
TABLE 27 Summary of common phytoplankton species occurrence
in Lake Huron during 1983 135
TABLE 28 Summary of common phytoplankton species occurrence
in Lake Huron during 1984 136
TABLE 29 Summary of common phytoplankton species occurrence
in Lake Huron during 1985 138
TABLE 30 Phytoplankton common in 1985 but not in 1983 and
1984, Lake Huron 140
TABLE 31 Distribution of indicator diatom species in
Lake Huron 141
TABLE 32 Relative abundance of zooplankton in Lake Huron 141
TABLE 33 Summary of common zooplankton species occurrence
in Lake Huron during 1985 142
TABLE 34 Comparison of mean crustacean abundance for the
sampling period in 1971 (April-November),
1974/75 (April-November), 1983 (August-October),
1984 (April-December) and 1985 (April-November),
Lake Huron 143
TABLE 35 Abundance of Bythotrephes cederstroemi by season
and geography in 1985, Lake Huron 144
TABLE 36 Mean abundance of rotifers in Lake Huron in
1974, 1983, 1984 and 1985 144
TABLE 37 Ratio of Calanoida to Cladocera plus Cyclopoida
in Lake Huron, 1983, 1984 and 1985 145
TABLE 38 Comparison of the plankton ratio (Calanoida/
Cyclopoida+Cladocera) between the northern
stations of Lake Huron and Lake Michigan 145
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TABLE 39 Abundance of selected zooplankton species in northern
and southern Lake Huron in 1984 and 1985 145
TABLE 40 Correlation of phytoplankton abundance with
total phosphorus concentrations and zooplankton
abundance within individual cruises, Lake
Huron 146
TABLE 41 Number of species and genera observed in each
algal division or grouping, Lake Erie, 1983,
1984 and 1985 145
TABLE 42 Number of species identified and percentage of
species belonging to various taxonomic groups,
Lake Erie 147
TABLE 43 Relative abundance of major phytoplankton divisions
in Lake Erie, 1983-1985 148
TABLE 44 Phytoplankton and zooplankton biomass, total
phosphorus, and chlorophyll a concentrations
in the Western, Central and Eastern Basins
of Lake Erie, 1983 , 1984 and 1985 149
TABLE 45 Location of maximum abundance of selected species
in 1983 , 1984 and 1985, Lake Erie 150
TABLE 46 Summary of common phytoplankton species occurrence
in Lake Erie, 1983 151
TABLE 47 Summary of common phytoplankton species occurrence
in Lake Erie, 1984 153
TABLE 48 Summary of common phytoplankton species occurrence
in Lake Erie, 1985 155
TABLE 49 Phytoplankton common in 1985 but not in 1983 and
1984, Lake Erie 157
TABLE 50 Average abundance and biomass of Rhizosolenia
eriensis, Oedogonium sp. and Amphidinium sp.,
Lake Erie, 1985 157
TABLE 51 Importance of Asterionella formosa during the
spring of 1984 and 1985, Lake Erie 158
TABLE 52 Mean maximum biomass of selected common phyto-
plankton species in 1970, 1983, 1984
and 1985 , Lake Erie 159
TABLE 53 Distribution of indicator diatom species in the
western basin of Lake Erie 160
TABLE 54 Trophic status of the western, central and eastern
basins of Lake Erie in 1970 and 1983-85 160
TABLE 55 Relative abundance of zooplankton in Lake Erie 161
TABLE 56 Summary of common zooplankton species occurrence
in Lake Erie during 1984 162
xi
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TABLE 57 Common zooplankton species observed in either 1983,
1984 or 1985 but not in all three years, Lake Erie..163
TABLE 58 Abundant (1967) and predominant (1983-1985) rotifer
species in 1967, 1983 and 1985, Lake Erie 164
TABLE 59 Occurrence of eutrophic zooplankton indicator
species in Lake Erie, 1984 and 1985 165
TABLE 60 Ratio of calanoids to cladocerans plus cyclopoids
in Lake Erie, 1983 to 1985 165
Table 61 Correlation of phytoplankton abundance with total
phosphorus concentration and zooplankton abundance
within individual cruises, Lake Erie 166
TABLE 62 Number of common phytoplankton species shared by
Lake Michigan, Lake Huron and three basins in Lake
Erie 167
TABLE 63 Number of shared species with Relative Percent
Difference and percent of shared species with
RPD > 1 based on biovolume of common phytoplankton
species in Lakes Michigan, Huron and Erie in 1985...168
xii
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FIGURE LEGENDS
FIGURE 1. Lake Erie plankton sampling stations., 1985
FIGURE 2. Lake Huron plankton sampling stations, 1985 170
FIGURE 3. Lake Michigan plankton sampling stations, 1985 171
FIGURE 4. Seasonal phytoplankton abundance and biovolume
trends in Lake Michigan, 1985 172
FIGURE 5. Seasonal distribution of algal divisions in Lake
Michigan, 1985 173
FIGURE 6. Seasonal distribution of Cryptomonas ovata, Lake
Michigan 174
FIGURE 7. Seasonal distribution of Rhodomonas lens, Lake
Michigan 175
FIGURE 8. Mean seasonal distribution of Gymnodinium helveticum,
Lake Michigan 176
FIGURE 9. Average abundance of Cyclotella comensLs from 1983
to 1985 177
FIGURE 10. Annual geographical distribution of major algal
divisions in Lake Michigan, 1985 178
FIGURE 11. Annual geographical distribution of major algal
divisions in Lake Michigan, 1985 179
FIGURE 12. Geographical distribution of phytoplankton abundance
on all cruises, Lake Michigan, 1985 180
FIGURE 13. Historical abundance of phytoplankton in Lake
Michigan 181
FIGURE 14. Seasonal zooplankton abundance in Lake Michigan,
1985 182
FIGURE 15. Seasonal fluctuation (numerical) of zooplankton
groups in Lake Michigan, 1985 183
FIGURE 16. Seasonal fluctuation (biomass) of zooplankton
groups in Lake Michigan, 1985 184
FIGURE 17. Geographical distribution of Diaptomus sicilis in
Lake Michigan, 1985 185
FIGURE 18. Geographical distribution of selected zooplankton
in Lake Michigan, 1985 186
FIGURE 19. Geographical distribution of selected zooplankton
in Lake Michigan, 1985 187
FIGURE 20. Geographical distribution of zooplankton phyla
in Lake Michigan, 1985 188
FIGURE 21. Historical trends in zooplankton biomass during July
and August, Lake Michigan 189
xiii
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FIGURE 22. Relationship between mean weighted phytoplankton
size, mean weighted Crustacea size and Crustacea
and Daphnia abundance, 1985 190
FIGURE 23. Seasonal phytoplankton abundance and biovolume
trends in Lake Huron, 1985 191
FIGURE 24. Seasonal distribution of algal (% biovolume)
divisions in Lake Huron, 1985 192
FIGURE 25. Annual geographical distribution of major algal
divisions in Lake Huron, 1985 193
FIGURE 26. Seasonal geographical distribution of phytoplankton
biomass , Lake Huron, 1985 194
FIGURE 27. Geographical and seasonal distribution of Diatoma tenue
var. elongatum, Lake Huron 195
FIGURE 28. Geographical and seasonal distribution of Synedra
ulna var. chaseana, Lake Huron 196
FIGURE 29. Geographical and seasonal distribution of Rhodomonas
lens , Lake Huron 197
FIGURE 30. Geographical and seasonal distribution of Agmenellum
quadruplicatum, Lake Huron 198
FIGURE 31. Historical offshore biomass trends in Lake Huron 199
FIGURE 32. Seasonal zooplankton biomass and abundance
in Lake Huron, 1985 200
FIGURE 33. Seasonal fluctuation (numerical) of zooplankton
groups in Lake Huron, 1985 201
FIGURE 34. Seasonal fluctuation (biomass) of zooplankton
groups in Lake Huron, 1985 202
FIGURE 35. Geographical distribution of Daphnia pulicaria
from 1983 to 1985, Lake Huron 203
FIGURE 36, Geographical distribution (abundance) of major
zooplankton groups in Lake Huron, 1985 204
FIGURE 37. Geographical distribution (biomass) of major
zooplankton groups in Lake Huron, 1985 205
FIGURE 38. Geographical distribution of Diaptomus minutus,
D. ashlandi and D. sicLlis from 1983 to 1985,
Lake Huron, 1985 206
FIGURE 39. Geographical distribution of Holopedium gibberum,
Daphnia galaeta mendotae and Daphnia pulicaria
from 1983 to 1985 207
FIGURE 40. Geographical distribution of Conochilus unicornis,
Kellicottia longispina and Keratella cochlearis
from 1983 to 1985 208
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FIGURE 41. Geographical distribution of Notholca squamula,
Gastropus stylifer and Synchaeta spp. from 1983
to 1985, Lake Huron 209
Figure 42. Crustacean abundance of Lake Huron, 1970-1985 210
Figure 43. Abundance of Rotifera in Lake Huron, 1974-1985 211
FIGURE 44. Relationship between mean weighted phytoplankton
size, mean weighted Crustacea size and Crustacea
and Daphnia abundance, 1983 212
FIGURE 45. Relationship between mean weighted phytoplankton
size, mean weighted Crustacea size and Crustacea
and Daphnia abundance, 1984 213
FIGURE 46. Relationship between mean weighted phytoplankton
size, mean weighted Crustacea and Daphnia abundance,
1984 214
FIGURE 47. Relationship between mean weighted phytoplankton
size, mean weighted Crustacea size and Crustacea
and Daphnia abundance, 1985 215
FIGURE 48. Seasonal phytoplankton abundance and biovolume
trends in Lake Erie, 1985 216
FIGURE 49. Seasonal distribution of algal divisions in Lake
Erie, 1985 217
FIGURE 50. Annual geographical distribution of major algal
divisions in Lake Erie, 1985 218
FIGURE 51. Geographical distribution of phytoplankton
abundance on all cruises , Lake Erie, 1985 219
FIGURE 52. Geographical distribution of phytoplankton
biomass on all cruises, Lake Erie, 1985 220
FIGURE 53. Geographical distribution of Rhizosolenia eriensis,
Lake Erie, 1985 221
FIGURE 54. Geographical distribution of Amphidinium sp.,
Lake Erie, 1985 222
FIGURE 55. Geographical distribution of Oedogonium sp.,
Lake Erie, 1985 223
FIGURE 56. Seasonal fluctuation of weighted mean phytoplankton
biomass from 1970 to 1985, Lake Erie 224
FIGURE 57. Regression of phytoplankton biomass versus time
in western Lake Erie 225
FIGURE 58. Phytoplankton biomass versus time for the Western,
Central and Eastern Basins of Lake Erie 226
FIGURE 59. Time trend in annual cruise mean concentration of
corrected chlorophyll a since 1970, Lake Erie 227
FIGURE 60. Time trend in annual cruise average of total phosphorus
since 1970, Lake Erie 228
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FIGURE 61. Seasonal zooplankton abundance and biomass in
Lake Erie, 1985 229
FIGURE 62. Seasonal abundance distribution of zooplankton
groups in Lake Erie, 1985 230
FIGURE 63. Seasonal biomass distribution of zooplankton
groups in Lake Erie, 1985 231
FIGURE 64. Geographical distribution (numerical) of
zooplankton groups in Lake Erie, 1985 232
FIGURE 65. Geographical distribution (biomass) of
zooplankton groups , Lake Erie, 1985 233
FIGURE 66. Geographical distribution of selected zooplankton
species in Lake Erie, 1985 234
FIGURE 67. Geographical distribution of selected zooplankton
in Lake Erie, 1985 235
Figure 68. Geographical and seasonal distribution of Chydorus
sphaericus 236
Figure 69. Geographical and seasonal distribution of Bythotrephes
cederstroemi 237
Figure 70. Geographical and seasonal distribution of Cyclops
vernalis 238
FIGURE 71. Crustacean zooplankton abundance since 1939 in
the western basin of Lake Erie 239
FIGURE 72. July and August abundance of Cladocera and
Copepoda in the western basin of Lake Erie
since 1939 240
FIGURE 73. Seasonal fluctuation of weighted mean Crustacea
(nauplii excluded) abundance from 1970 to 1985,
Lake Erie 241
FIGURE 74. Zooplankton biomass versus time for the Western,
Central and Eastern Basins of Lake Erie 242
FIGURE 75. Seasonal fluctuation of Rotifera in the western
basin of Lake Erie from 1939 to 1985 243
FIGURE 76. Projected abundance of fishable walleye in western Lake
Erie (Ohio waters) 244
FIGURE 77. Sport angler harvest of walleye from the central
basin of Lake Erie 245
FIGURE 78. Time trend of autumn emerald and spottail shiner
abundance in the central basin and alewife from
the western basin of Lake Erie. 246
FIGURE 79. (A)Seasonal total algal and filamentous algal biomass
and mean weighted edible algal size in 1985; (B) the
seasonal mean crustacean size and Daphnia spp. and adult
Calanoida abundance, 1985 247
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FIGURE 80. Comparison of the phytoplankton composition of Lakes
Michigan, Huron and Erie, 1985. Bac - Bacillariophyta,
Chi = Chlorophyta, Chr - Chrysophyta, Cry -
Cryptophyta, Cya - Cyanophyta, Pyr - Pyrrophyta,
Uni - Unidentified 248
FIGURE 81. Comparison of the phytoplankton composition of the
basins of Lake Erie, 1985. Bac - Bacillariophyta,
Chi - Chlorophyta, Chr - Chrysophyta, Cry -
Cryptophyta, Cya Cyanophyta, Pyr - Pyrrophyta,
Uni = Unidentified 249
FIGURE 82. Percent similarity of common phytoplankton species,
1985 250
FIGURE 83. Comparison of the zooplankton composition of Lakes
Michigan, Huron and Erie, 1985 251
FIGURE 84. Comparison of annual zooplankton ratios in Lakes
Michigan, Huron and Erie 252
xvii
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OVERVIEW
With the acknowledgement that biological monitoring was fundamental to
charting ecosystem health (Great Lakes Water Quality Agreement 1978), EPA's
program was developed for Lakes Erie, Huron and Michigan to: 1) assess the
annual variance to allow better long-term assessments of trophic structure and
state and 2) relate the biological components to variations in the physical,
nutrient and biological environment. The program has proven successful. By
examining changes in the phytoplankton and zooplankton in relation to water
chemistry, evidence was found suggesting little change in the trophic status
of Lakes Huron and Michigan while an improvement in the trophic status of Lake
Erie was evident within the past ten years. The offshore region of Lake
Michigan is experiencing changes in phytoplankton and zooplankton composition
consistent with nutrient control and top-down control by fish. Even so, the
biomass of phytoplankton and zooplankton and the trophic status of the lake
have not changed significantly. The appearance and establishment of Daphnia
pulicaria in offshore waters of Lake Huron suggest a change in the forage fish
base. Plankton composition has changed little since the 60's. However, dra-
matic reductions in biomass of nuisance and eutrophic indicator species have
occurred. These changes are consistent with expectations of long-term
nutrient control. However, a change in piscivory is evident that has appar-
ently allowed the establishment of the large cladoceran Daphnia pulicaria.
The exotic predaceous cladoceran Bythotrephes cedarstroemii has become
established in all three lakes.
The following summaries for Lakes Michigan, Huron and Erie outline the
major observations of the 1985 intensive sampling of the offshore region. As
such, the 1983 (Makarewicz 1987), 1984 (Makarewicz 1988) and 1985 studies
provide a basis for long-term monitoring of the structure and functioning of
the Great Lakes.
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SUMMARY
Lake Michigan
1. Compared to 1983 and 1984, when 379 and 327 phytoplankton species were
observed, there was a substantial reduction in the number of species observed
(238) in 1985. Since there were no significant differences in the sampling
regime and water chemistry between years, the differences in species number
observed are attributed to changes in personnel responsible for enumeration
and identification. The number of zooplankton species observed were the same
in 1984 and 1985 (52).
2. Picoplankton represented 85.5% (1984: 82.9%.) of the total abundance but
only 1.6 % (1984: 1.4%) of the algal biomass. Because the picoplankton have
not been historically considered in the Great Lakes, they are not included in
abundance and biomass trends reported.
3. Even though there was a decrease in the number of species identified from
1984 to 1985, the average phytoplankton and zooplankton abundances (mean+S.E.)
were not significantly different between 1984 and 1985 (phytoplankton: 1985 -
2,841±241 cells/mL; 1984 - 3,602±244) (zooplankton: 1985 - 34,950±4,085 organ-
isms/m3; 1984 - 59,764±8,284) for the study period. Mean algal and zooplank-
ton biomass were 0.45±0.043 g/m3 (1984: 0.55±.038) and 47.9±5.2 mg/m3 (1984:
33.2±4.9) for the study period.
4. As in Lakes Erie and Huron in 1983 and 1984, diatoms possessed the great-
est number of species (90) and biomass (63.9% of the total) in 1985. Similar
to 1984, the Cryptophyta accounted for the second highest biomass in 1985.
5. Unlike 1984, but similar to 1983, diatoms were dominant in the spring and
autumn accounting for as much as 80% of the phytoplankton biomass. During
August, the prevalence of diatoms decreased dramatically to 8% (1983: 10%) of
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the biomass. Unlike 1984, a seasonal succession of the plankton was observed
by August of 1985 similar to the one observed in 1983, where Cryptophyta,
Pyrrophyta and Cyanophyta succeeded the diatoms.
6. The large drop in diatom biomass observed in August of 1983 and 1985 was
not observed in 1984. The occurrence of a bloom of Rhizosolenia eriensis
during 1984, not observed in 1983 and 1985, was the major cause of the domi-
nance of diatoms in August of 1984. The prevalence of R. eriensis appears to
determine whether or not a divisional succession occurs during the summer.
7. The 1985 sampling pattern differed from 1983 and 1984 in that the far
northern stations (Stations 56, 57, 64 and 77) and the most southern stations
(Station 6) were not sampled. In 1983 and 1984, abundance of phytoplankton
decreased from the most northern station to Station 57 and remained the same
southward to the most southerly station, where it increased slightly. With
the absense of the most northern and southern stations in the 1985 sampling
pattern, total phytoplankton abundance was not significantly different between
the northern and southern half of the lake in the 1985. However, Cyanophyta
abundance was significantly higher in the southern basin compared to the
northern basin in 1985.
8. The phytoplankton composition of Lake Michigan has changed. The following
subdominant or dominant species have decreased in abundance from the 60's and
70's: Cyclotella michiganiana, Cyclotella stelligera, Melosira islandica,
Synedra acus and Ankistrodesmus falcatus. Oscillatoria limnetica has
increased in abundance. Abundance of Rhizosolenia eriensis increased in 1984
after a general decrease since the 60's and 70's, but decreased in 1985.
9. Considerable variability in dominant diatoms has occurred from 1983 to
1985. In 1984, the dominant diatom species included the mesotrophic forms
Tabellaria flocculosa and Fragilaria crotonensis and the oligotrophic forms
Cyclotella ocellata and Rhizosolenia eriensis. Comparing the 1984 data to the
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1983 cruises where mesotrophic forms were predominant, the same mesotrophic
forms were present in 1984 along with the oligotrophic indicators. In 1985 a
considerable change occurred in the predominant diatom species. The species
of Cyclotella and Tabellaria flocculosa were present but were not dominant or
common. The eutrophic indicator Stephanodiscus niagarae was the dominant spe-
cies on a biomass basis, while Rhizosolenia longiseta and the mesotrophic
indicator species Melosira islandica were dominant on a numerical basis. Only
Melosira italics subsp. subartica and Fragilaria crotonensis were predominant
diatom species in 1983, 1984 and 1985.
10. The ratio of mesotrophic to eutrophic algal species (trophic ratio) sug-
gests a eutrophic status for nearshore waters in 1977, while the offshore
waters in 1970-71, 1983, 1984 and 1985 would be in the
oligotrophic-mesotrophic range.
11. Based on the classification scheme of Munawar and Munawar (1982), Lake
Michigan's algal biomass in 1983 (0.42 mg/m3), 1984 (0.55 mg/m3) and 1985
(0.45 mg/m3) suggests an oligotrophic status for the offshore waters of Lake
Michigan.
12. Phytoplankton abundance of the offshore waters appears to have increased
from 1962-63 to 1976-77 but has not significantly changed from 1976 to 1985.
Because of the difference in enumeration methodology used in the 1962-63 study
compared with the other surveys, the suggested increase in algal abundance
from 1962-63 to 1976-77 has to be interpreted cautiously.
13. The trend in zooplankton biomass was similar to the phytoplankton trend
between 1976 and 1985 in that no significant change in zooplankton biomass was
observed.
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14. The Rotifera possessed the largest number of species (29, 1984 and 1985)
and relative abundance 39.9% (1984: 67.5%). The Rotifera contributed only
1.1% (1984: 2.6%) of the biomass, while the Calanoida, rather than the Cladoc-
era as in 1984, accounted for 67.4% of the zooplankton biomass.
15. Abundance of zooplankton generally increased from north to south in 1984.
The far northern stations (64 and 77) had a significantly higher abundance
than the rest of the lake in 1984. In 1985 this pattern was not observed due
to a change in the sampling regime which did not include these stations.
16. In 1983, 1984 and 1985, the dominant rotifer composition was similar to
the nearshore and to Ahlstrom's (1936) offshore composition.
17. The species composition of the predominant rotifers suggests an oligo-
trophic offshore assemblage. Further support is provided by the high relative
abundance of Diaptomus sicilis and Limnocalanus macrurus and the occurrence of
Senecella calanoides, all oligotrophic crustacean indicator species.
18. The plankton ratio (Calanoida/Cladocera + Cyclopoida) was high relative
to Lake Erie but lower than Lake Huron. In general, the ratio was high and
similar indicating a similar high quality of water throughout the offshore
area sampled.
19. The changing nature of the zooplankton community of Lake Michigan was
evident from 1983 to 1985. The abundance of Daphnia pulicaria, first observed
in 1978, dropped from 376/m3 in 1983 to 78/m3 in 1984, but increased in 1985
to 161/m3. Abundance of D. galeata in 1984 and 1985, rare in 1966 and 1968,
was 2-3 times the density observed in 1954 (1200/m3). Abundance of the large
cladoceran Leptodora kindtii appears to be increasing from 1954. In general,
the larger cladocerans, calanoids and cyclopoid copepods, observed to have
decreased in the early 60's, had increased in abundance to values similar to
those in August of 1954.
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20. The presence of the oligotrophic rotifer association, the presence of the
oligotrophic crustacean indicator species Diaptomus sicilis and LLmnocalanus
macrurus, the predominance of mesotrophic diatom species, the similarity of
the plankton ratio on the north-south axis and a phytoplankton and zooplankton
abundance and biomass between those of the eutrophic Lake Erie and oligo-
trophic Lake Huron suggest that the offshore waters of Lake Michigan are cur-
rently in the oligotrophic-mesotrophic range (i.e. meso-oligotrophic). A
similar conclusion was reached in 1983 and 1984. Only the dominance (biomass)
of Stephanodiscus niagarae, a eutrophic indicator, in 1985 suggests otherwise.
21. A significant change in zooplankton composition has occurred with the
establishment of Daphnia pulicaria in the entire offshore region of Lake Mich-
igan. Decline of the alewife population has apparently reduced predatory
pressure from alewife releasing the suppressed large-bodied zooplankton such
as Daphnia pulicaria (Scavia et al 1986). In addition, abundances of Lepto-
dora kindtii, Daphnia galeata mendotae, Diaptomus ashlandi and Cyclops bicus-
pidatus have returned to or exceeded abundances observed in 1954 during a
period of low alewife abundances.
22. The mean seasonal size of the edible phytoplankton community decreased as
the abundance of the herbivorous Daphnia spp. increased.
24. Correlation analysis suggests that the increases in Daphnia galeata men-
dotae, as well as D. pulicaria, have exerted greater grazing pressures on the
phytoplankton community.
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SUMMARY
Lake Huron
1. Compared to 1983 and 1984, when 329 anA 315 phytoplankton species were
observed, there was a substantial reduction in the number of species observed
(213) in 1985. Since there were no significant differences in the sampling
regime and water chemistry between years, the differences in species number
observed are attributed to changes in personnel responsible for enumeration
and identification. The number of zooplankton species observed in 1983 (58),
1984 (53) and 1985 (57)were similar.
2. Picoplankton accounted for 92.3% (1984: 83.9%) of the total abundance but
only 3.4% (1984: 1.4%) of the biomass. This finding is similar to that of
1983 and 1984. Because the picoplankton have not been historically considered
in the Great Lakes, they are not included in abundance and biomass trends
reported.
3. Even though there was a decrease in the number of species identified from
1984 to 1985, the average phytoplankton and zooplankton abundances (mean+S.E.)
were not significantly different between 1984 and 1985 (phytoplankton: 1985 -
2,020±113 cells/mL; 1984 - 2,772±196) (zooplankton: 1985 - 67,668±9,390 organ-
isms/m3; 1984 - 55,400+7,200) for the study period. Mean algal and zooplank-
ton biomass were 0.34±.021 g/m3 (1984: 0.38±0.10) and 59.2±7.03 mg/m3 (1984:
27.3±2.3) for the study period.
4. As in 1984, diatoms possessed the greatest number of species (120) and
biomass (67.4% of the total, 1984: 62.9%). Similar to 1984, the Chrysophyta
was the second most important division (10.0% of the total; 1984: 9.7%).
5. Considering biomass, the diatoms were dominant throughout the study period
accounting for as much as 78% but never less than 42% of the biomass. The
large drop in the relative importance of diatoms in August of 1983 was again
observed in 1985 but not in 1984. A bloom of Rhizosolenia eriensis in August
7
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of 1984, not observed in 1983, was considered a major cause of the dominance
of diatoms throughout the summer of 1984. Even though a bloom of J?. eriensis
did occur in 1985, a drop in the mid-summer importance of diatoms occurred.
6. Average phytoplankton biomass decreased from the northern Lake Huron sta-
tions to -Station 32, where abundance increased and then decreased slightly
southward.
7. In general, offshore species composition of phytoplankton has changed
little since the early 70's. StephanodLscus minutus was not common in 1971,
1974, 1975, 1980, 1983 and 1985. In 1984, it was common with an average
density of 19.4 cells/mL because of the inclusion of winter samples. Abun-
dance averaged 63 cells/mL in February.
8. From 1983 to 1985, the dominant diatom assemblages were species character-
ized as indicators of oligotrophic or mesotrophic conditions.
9. The ratio of mesotrophic to eutrophic algal species (trophic ratio) has
not changed since 1971. This suggests that the trophic status of the offshore
waters of Lake Huron has not changed since 1971.
10. As in 1984, the Rotifera possessed the largest number of species (30,
1984: 31) and relative abundance (40.3%, 1984: 56.0%). The Calanoida (48.5%,
1984: 42.0%) dominated on a biomass basis followed by the Cladocera (26.3%,
1984: 27.5%). Rotifera contributed only 1.5% (1984: 2.5%) of the zooplankton
biomass.
11. Species composition of zooplankton was similar in 1971, 1974, 1983, 1984
and 1985. Abundance of Diaptomus ashlandL and D. sicilis has increased
steadily since 1971, while abundance of D. minutus and D. oregonensis has
increased since 1984. The oligotrophic indicator species, Limnocalanus macru-
rus, appeared not to have significant changes in abundance since 1971. Abun-
dance of Bosmina longirostris has steadily decreased since 1971.
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12. Daphnia pulicarla was first observed in offshore waters in 1983. Average
abundance has steadily decreased since 1983. Within the Cladocera, rank abun-
dance dropped from third in 1983 to fifth in 1984 and fourth in 1985.
13. A new cladoceran species, Bythotrephes cederstromil, was observed in the
offshore waters of Lake Huron. By 1985, it had become established throughout
the lake.
14. The rotifer community was dominated by an assemblage indicative of oligo-
trophic conditions from 1983 to 1985. In addition, the calanoid Diaptomus
sicilis, an oligotrophic indicator, was fairly abundant.
15. The plankton ratio (Calanoida/Cladocera + Cyclopoid) was high compared to
Lake Erie but similar for the entire offshore region, which suggests a similar
high quality of water over the entire offshore region except for the far
northern Station 61 and perhaps Station 6 at the south end of the lake.
16. The presence of the oligotrophic rotifer assemblage, the domination of
the calanoids, the fairly abundant oligotrophic Diaptomus sicilis, and the low
zooplankton abundance compared to those of Lakes Erie and Michigan, suggest
the offshore waters of Lake Huron in 1983, 1984 and 1985 were oligotrophic.
17. Zooplankton abundance of the offshore waters of Lake Huron in 1970,
1974/75, 1983, 1984 and 1985 was not significantly different.
18. The consistency of the trophic ratio and algal biomass through time, the
insignificant difference in zooplankton abundance from 1970-1985, the occur-
rence of oligotrophic and mesotrophic algal indicator species, the oligo-
trophic zooplankton assemblage and the similarity of the plankton ratio over
the entire offshore suggest that no significant change in the trophic status
of the offshore waters of Lake Huron has occurred since 1970.
19. With a mean algal biomass of 0.35, 0.38 and 0.42 g/m3 for 1985, 1984 and
1983, respectively, Lake Huron would be classified as oligotrophic by the
classification scheme of Munawar and Munawar (1982).
9
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20. The appearance of Daphnia pulLcarLa in Lake Huron suggests that the
zooplankton community has been released from size-selective planktivory.
21. The correlation of phytoplankton abundance with total phosphorus and
zooplankton abundance within individual cruises suggests that "top down" and
"bottom up" control of the trophic web of lake ecosystems exists simulta-
neously and varies with season.
10
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SUMMARY
LAKE ERIE
11
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SUMMARY
Lake Erie
1. The phytoplankton assemblage of 1985 was comprised of 369 species (1984:
356, 1983: 372) representing 101 genera. The zooplamkton assemblage of 1985
comprised 80 species (1984: 81, 1983: 66) representing 44 genera.
2. Picoplankton accounted for 83.6% (1984: 89.6%) of the total abundance. A
similar finding was observed in 1983. Because the picoplankton have not been
historically considered in the Great Lakes, they are not included in abundance
and biomass trends reported.
3. Mean phytoplankton and zooplankton abundance (mean-/-S .E.) were 4,483+570
cells/mL (1984: 6,187±750, 1983: 5,331±462) and 221,577±26,988 (1984:
159,600±25,300) organisms/m3 for the study period. Average biomass of phyto-
plankton and zooplankton was 1.22±.ll and 0.106±0.0098 g/m3, respectively
(1984: 0.86±.08 and .053±.0062 g/m3).
4. Phytoplankton biomass varied within Lake Erie. The Western basin pos-
sessed a greater biomass (1.62±0.33 g/m3) than the Eastern (0.54±0.08 g/m3)
and Central (1.38+0.15 g/m3) basins. Zooplankton abundance increased in a
similar fashion into the Western basin in 1984 and 1985 but not zooplankton
biomass.
5. Diatoms possessed the greatest number of species (162, 1984: 171) and
biomass (63.2%, 1984: 47.8% of the total) in 1985. Compared to 1970, a sig-
nificant change in diversity of phytoplankton has occurred. In 1970 only 21
diatom species were observed that accounted for 53% of the biomass. The
Chlorophyta possessed the largest number of species (78) in 1970.
6. Diatoms were dominant in April and May and were succeeded by the Chloro-
phyta in August. By November, the diatoms were again dominant. A similar
seasonal pattern was observed in 1983 and 1984.
12
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7. The historically highly productive Western basin has had a steady decrease
in algal biomass from 1958 to 1985. Similarly, chlorophyll a levels have
decreased in all basins, but most dramatically in the Western basin. However,
algal biomass is still higher in the Western basin than in the Central and
Eastern basins.
8. Lakewide, the mean weighted algal biomass was 3.4, 1.5, 0.8 and 1.26 g/m^
in 1970, 1983, 1984 and 1985, respectively. A 56 to 76% reduction in algal
biomass has occurred in offshore waters of the lake from 1970 to 1983-85.
9. Although occurrences of common and dominant species were similar in 1970,
1983, 1984 and 1985, dramatic decreases in the biomass of these species were
evident. For example, a 96% reduction in the maximum biomass of the nuisance
species Aphanizomenon flos-aquae has occurred since 1970. The eutrophic indi-
cator species Stephanodiscus binderanus and Fragilaria capucina have had a
>90.% reduction in maximum biomass.
10. Asterionella formosa has not been prevalent in Lake Erie since prior to
1950. In the 1984 spring cruises, A. formosa was the dominant species on a
biomass basis. In 1985 A. formosa was not prevalent in the spring and was not
a common species. Melosira islandica, a mesotrophic indicator was not common
in 1983 and 1985 but common in 1984.
11. Evidence of a shift in trophic status since 1970 is provided by a compari-
son of predominant diatom indicator species in 1970, 1983, 1984 and 1985. The
number of eutrophic species has decreased, while the number of mesotrophic
species has increased.
12. The Rotifera possessd the largest number of species (49, 1984: 48) and
relative abundance (70.8, 1984: 80.1%) of the zooplankton. On a biomass
basis, the Rotifera represented only 5.5% (1984: 13.6%) of the zooplankton
biomass while the Cladocera contributed 35.1% (1984: 40.5%) of the biomass.
13
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13. A shift in zooplankton composition is occurring with a new species Daph-
nia pulicaria being observed for the first time in 1984. On a biomass basis,
D. pulicaria was the dominant Cladocera in the lake with a major bloom in
August of 1984. In 1985 it was not even a common species. Another new spe-
cies, Bythotrephes cederstroemL, was observed throughout the entire lake in
October of 1985. Although not a common species in 1985, its large size and
its potential to effectively crop down Daphnia populations and thus affect
lower trophic levels make it a species of interest.
14. By virtual of its high abundance in the Western Basin in 1985, the eutro-
phic cyclopoid Cyclops vernalis was considered to be a common species in 1985.
Prior to 1985, it appeared to be decreasing in abundance.
15. A decrease in summer Cladocera and Copepoda abundance in the Western
Basin is suggested from 1961 to 1985. Rotifera abundance in the Western Basin
has increased since 1934. A number of eutrophic rotifer indicator species had
abundances restricted to or significantly higher in the Western Basin. The
plankton ratio also suggests a more productive status for the Western Basin.
16. There is a lack of dominance of eutrophic rotifer indicator species for
the entire lake. This suggests that Lake Erie in 1984, as well as 1985, as a
unit is not eutrophic. The number of dominant eutrophic algal species has
decreased, while the number of dominant mesotrophic species has increased;
that is, the trophic ratio has increased, suggesting an improvement in water
quality.
17. Evidence of a shift in trophic status of Lake Erie since 1970 is provided
by the trophic ratio, the plankton ratio, phytoplankton and zooplankton indi-
cator species, declines in total abundance and biomass of total phytoplankton
and zooplankton since the mid-60's and 70's, declines in abundance of nuisance
species and eutrophic species, declines in total phosphorus and chlorophyll a,
and the current total biomass and abundance of plankton.
14
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18. The trophic condition of Lake Erie appears to be improving. However,
compared to Lakes Huron and Michigan in 1983 and 1984, biomass of phytoplank-
ton and zooplankton was higher, the plankton and trophic ratios were lower,
and the phytoplankton and zooplankton species compositions suggest a more
productive status for Lake Erie.
19. Based on the classification schemes of Vollenweider (1968) and Munawar
and Munawar (1982) utilizing maximum and average algal biomass, the Western
Basin would be meso-eutrophic, the Central Basin mesotrophic, and the Eastern
oligo-mesotrophic. This conclusion reached in 1984 and 1985 is supported by
other indicators of the trophic status noted above.
20. Models, experimentally verified, of size-structured plankton communities
predict shifts to small algae at low biomass of small grazers and shifts to
larger algae as larger sized grazers or biomass increase. This was observed
in Lake Erie during the summer. The size of the algal community is inversely
related to the abundance of Crustacea and Daphnia (r2--0.787) and size of the
Crustacea. This inverse relationship was also observed in 1983 (r2--0.943)
and 1984 (r2=-0.441).
21. The decreases in phytoplankton abundance, chlorophyll, total phosphorus
and turbidity are consistent with expectations of long-term nutrient control.
However, the significant changes in the composition of the zooplankton commu-
nity with the appearance and establishment of the large cladoceran Daphnia
pulicaria are attributed to a change in planktivory. The planktivorous
emerald and spottail shiners have dramatically declined, perhaps due to a
resurgence of the walleye and the salmonine stocking programs.
15
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INTRODUCTION
The project reported here was initiated by the United States Environmental
Protection Agency, Great Lakes National Program Office (GLNPO), to analyze
phytoplankton and zooplankton samples taken in 1985 from the offshore waters of
Lakes Erie, Huron and Michigan. Along with the report on water chemistry
(Rockwell et al 1989), the two reports represent the results of the 1985
Surveillance Program designed to evaluate the progress of the phosphorus remedial
control efforts. This program is an outgrowth of the Great Lakes International
Surveillance Program (GLISP) (International Joint Commission 1975), the purpose
of which is to comply with the provisions of the 1978 Canada-United States Water
Quality Agreement that calls for periodic monitoring of the Great Lakes to
determine the degree to which the objectives of the agreement are being met.
Nutrient loading of lakes and rivers, navigation, fish management policies,
fishing, shoreline alteration, contaminant production and, in general, economic
development, ultimately affect the lake ecosystem. Effects of perturbations
are not always known and can not always be monitored individually in large,
complex systems such as the Great Lakes. Biological monitoring is an integrative
monitoring strategy (Johannson et al 1985). Ecosystems respond to stress with
compensatory changes in community structure and function mediated at the population
level (Boesch and Rosenberg 1981). Therefore, changes in ecosytem health can
be detected by monitoring changes in the biotic community (Nicholls et al 1980,
Dillon et al 1978).
Any monitoring program must first document the state of the ecosystem,
namely, the species composition, biomass and production of each community com-
ponent, including the normal range of temporal and spatial variation. The
second step is to examine the relationship and interactions amongst the ecosystem
16
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components in order to interpret and possibly predict future changes in community
structure or function. Thus, the value of such monitoring programs goes far
beyond its surveillance capabilities; it can form the backbone for research
activities, thereby encouraging a detailed understanding of the system.
An in-depth planktonic (phyto- and zooplankton) comparison is presented
based on extensive seasonal lake-wide surveys. This comparison was achieved
by the application of standard and consistent identification, enumeration and
data-processing techniques of plankton that were collected from the offshore
waters of Lakes Huron, Michigan and Lake Erie. The primary objectives of this
report include: (1) To organize plankton data for use in eutrophication models;
(2) To characterize the composition and abundance of the phytoplankton and
zooplankton for comparison with past conditions to the extent that they are
known; (3) To provide firm documentation with which future assessment of the
changes in water quality of the lakes can be made; (4) To characterize the water
quality by studying the abundance and autecology of phytoplankton and zooplankton;
and (5) To characterize within and between year plankton variance to allow
better long-term assessments of plankton structure.
17
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METHODS
Sampling Sites
Phytoplankton and zooplankton samples from Lakes Erie, Huron and Michi-
gan were collected by GLNPO personnel during six cruises during the spring,
summer and autumn of 1985. Phytoplankton were also collected during an
additional late spring cruise on Lakes Michigan and Huron. Collection dates
and station locations of routine plankton sampling are given in Tables 1-5 and
in Figures 1-3. The far northern stations (Stations 47, 56, 64, 77) and the
most southern station (Station 6) in Lake Michigam, sampled in 1983 and 1984,
were not sampled in 1985 because of refinements in the monitoring program.
Locations of sampling sites on Lake Huron were not consistent for the year
(Table 4). Instead, alternate east-west stations were sampled (e.g. 54 or
53, 45 or 43; Fig. 3) on various cruises. For geographic analyses, east-west
stations were combined, assuming that no significant difference in species
abundance and composition existed between east-west stations in Lake Huron, to
give a single north-south transect. Because abundance of phytoplankton and
zooplankton between north-south stations (30,31,32; 43,42; 38,37,36; 15,63;
9,10) were not significantly different in Lake Erie, north-south stations were
averaged to give a single east-west transect (Table 6 and 7). All sites are
part of the Great Lakes International Surveillance Program.
Chemistry
Only selected water quality variables collected during the study are
presented in this report. Results of the complete water chemistry investiga-
tion are reported elsewhere (Rockwell et al 1989). Methods used were standard
procedures (Rockwell et al 1989).
Phytoplankton
An 8-liter PVC Niskin bottle mounted on a General Oceanics Rossette
sampler with a Guildline electrobathythermograph (EBT) was used to collect
18
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phytoplankton. One-liter composite phytoplankton samples were obtained by
compositing equal aliquots from samples collected at depths of 1, 5 , 10 and
20m as allowed by depth. Vertical distribution samples were taken at 1m, 5m
and 10-m intervals to the bottom. Phytoplankton samples were immediately
preserved with 10 mL of Lugol's solution, while formaldehyde was added upon
arrival in the laboratory. The settling chamber procedure (Utermohl 1958) was
used to identify (except for diatoms) and enumerate phytoplankton at a magni-
fication of 500x. A second identification and enumeration of diatoms at 1250x
was performed after the organic portion was oxidized with 30% H202 and HN03.
The cleaned diatom concentrate was air dried on a #1 cover slip and mounted on
a slide (75x25mm) with HYRAX mounting medium.
Identifications and counts were done by Dr. Norman A. Andresen, R.
Flakne, M. Lamb, L. Lipsey, R. Harvey, D. Wagner, K. Verhage, J. Kranzfelder
and S. Radzyminski of the Bionetics Corporation. The cell volume of each
species was computed by applying average dimensions from each sampling station
and date to the geometrical shape such as sphere, cylinder, prolate spheroid,
etc., that most closely resembled the species form. At least 10 specimens of
each species of each sample were measured for the cell volume calculation.
When fewer than 10 specimens were present, those present were measured as they
occurred. For most organisms, the measurements were taken from the outside
wall to outside wall. The protoplast was measured with loricated forms, while
the individual cells of filaments and colonial forms were measured. For com-
parative purposes, biovolume (unH/L) was converted to biomass (mg/m^) assuming
the specific gravity of phytoplankton to be 1.0 (mm^/L-mg/m^) (Willen 1959,
Nauwerck 1963).
Zooplankton
A Wildco Model 30-E28 conical style net (62-um mesh net; D:L ratio -
1:3) with 0.5-m opening (radius-0.25m) was used to collect a vertical zoo-
19
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plankton sample at each station. Vertical tows were taken from 20m to the
surface. At Lake Erie stations, where water depth was less than 20m, the tow
was taken from 1m above the bottom to the surface. Filtration volume and
towing efficiency were determined with a Kahl flow meter (Model OOSWA200)
mounted in the center of the net. Filtration efficiency averaged 86.4, 74.5
and 93.3%, respectively, for Lakes Erie, Huron and Michigan for the entire
sampling season. Following collection, the net contents were quantitatively
transferred to 500-mL sample bottles, narcotized with club soda and preserved
with 5% formalin.
Zooplankton data from Lake Michigan Cruise #5, 21-23 August 1985, were
unrealistically high compared to the samples taken just three days before on
Cruise #4, 17-20 August 1985. Net efficiencies for Cruise #5 were exceedingly
low (37.9% for the 20m hauls) compared to Cruise #4 (92.5%). Phytoplankton
abundance during Cruise #5 was not abnormally high suggesting that the low
efficiencies were caused by some other factor. In the data sheets, there was
a note questioning the reliability of the flow meter. Since a set of samples
were taken just three days before, Cruise #5 was not included in the analysis
reported here.
Identification and enumeration of zooplankton follow Gannon (1971) and
Stemberger (1979) and were performed by J.L. Schmitz and L.A. Stokes of the
Bionetics Corporation. Raw counts were converted to number/mL by Bionetics,
Inc. The volume of each rotifer species was computed by using the geometrical
shape that most closely resembled the species (Downing and Rigler 1984). It
is essential that the measurements are made on the population being studied
since they vary in different habitats for some species up to 100% and more
(Bottrell et al 1976). For each cruise, length of at least 20 specimens of
each rotifer species was measured in each lake. Width and depth were also
measured on one date for each lake to develop length-width and length-depth
20
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ratios for use in the simplified formulas of Bottrell et al (1976). Assuming
a specific gravity of one, volume was converted to fresh weight and to dry
weight assuming a ratio of dry to wet weight of 0.1 (Doohan 1973) for all
rotifer species except Asplanchna spp. A dry weight/wet weight ratio of 0.039
was used for Asplanchna spp. (Dumont et al 1975).
Because of the considerable variability in length and thus weight encoun-
tered in the Crustacea, the dry weights of Crustacea were calculated using
length-weight relationships (Downing and Rigler 1984). Average length of
crustaceans (maximum of 20 for each station) was determined for each station
of each cruise. A comparison of calculated weights to measured weights of
Crustacea in Lake Michigan suggests good agreement at the minimum weight range
(Makarewicz 1988). The weight of the Copepoda nauplii followed Hawkins and
Evans (1979).
Data Organization
Abundances and dimensions of each species of phytoplankton and zooplank-
ton were entered into a Prime 6350 computer using the INFO (Henco Software,
Inc., 100 Fifth Avenue, Waltham, Mass.) data management system. Biomass was
calculated for phytoplankton and zooplankton and placed into summaries for
each sampling station containing density (cells/mL), biovolume (um^/mL) and
relative abundances of species. In addition, each division was summarized by
station.
Definitions
Common phytoplankton species were defined as having an abundance of
>0.5% of the total cells or >0.5% of the total biovolume.
Common zooplankton species were defined as having >0.1% of the total
abundance or >1.0% of the total biomass. Rotifer species were considered
common if they accounted for >1.0% of the total abundance.
Species diversity refers simply to the number of species observed.
21
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Dominance refers to a community property reflected in the relative abun-
dance pattern of a species. A species was considered to be dominant if it
possessed the highest relative abundance or biomass of a taxonomic grouping
(e.g. Division).
Importance refers to a group of measurements by which the species in a
community can be compared (Whittaker 1975). Abundance or biomass was the
importance value used in this report.
22
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RESULTS AND DISCUSSION
LAKE MICHIGAN
Phytoplankton
The species list (Table Al) and summary tables of abundance (Table A2)
and biovolume (Table A3) are in Volume 2 - Data Report (ATTACHED FICHE). A
summary of selected water chemistry parameters is presented in Table 8.
Picoplankton
Picoplankton abundance in 1985 (mean - 16,685; maximum of 5.9 x 10^
cells/mL) was not dissimilar from 1984 (mean - 18,409; maximum of 4.3 x 10^
cells/mL) or from 1983 (mean - 23,607; maximum of 1 x 10^ cells/mL). On a
numerical basis, the picoplankton represented 85.5% of the total cells in 1985
but because of their small biomass, only 1.6% of the total biovolume. Their
relative numerical dominance in 1985 was comparable to 1983 (89.4%) and 1984
(82.8%) (Makarewicz 1987, 1988). Historically the picoplankton have not been
considered in evaluations of the plankton community of Lake Michigan. Their
high abundance tends to distort relative abundance values and does not allow
reasonable comparisons with the historical data. For this reason, they are
not considered further in this discussion.
Annual Abundance of Major Algal Groups
The phytoplankton assemblage of 1985 was comprised of 222 species repre-
senting 79 genera from eight divisions (Table 9). Compared to 1983 and 1984,
a sizeable reduction in the number of genera (1983 - 90 genera; 1984 - 91) and
species (1983 - 336 species; 1984 - 327 species) was observed. Much of the
reduction in species occurred with the diatoms. 167 and 166 species of dia-
toms were observed in 1983 and 1984, respectively, while only a total of 90
species was observed in 1985. With no significant changes in the sampling
regime and water chemistry between years, these differences are attributable
to changes in personnel responsible for enumeration and identification that
23
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occurred during this year.
Similar to 1983 and 1984, the Bacillariophyta possessed the largest
number of species (90) and biovolume (64.0% of the total, Table 9 and 10),
while the second largest number of species (41), as in 1983 and 1984, was
observed for the Chlorophyta (Table 10). Similar to 1983 and 1984, the Cryp-
tophyta accounted for the second highest biovolume (17.2%). Highest overall
densities were attained by the Cyanophyta (34.4% of the total). The
Pyrrophyta had a much lower biovolume in 1984 and 1985 than in 1983 (Table
10). Unidentified organisms represented 31.1% of the total organisms identi-
fied.
The annual average phytoplankton density and biomass in 1985 were
2,841±241 cells/mL (mean±S.E.)(3,602±244 cells/mL, 1984; 3,159±203 cells/mL,
1983) and 0.45 g/m3±0.043 (0.52 g/m3±.038, 1984; 0.41±.05 g/m3, 1983),
respectively.
Seasonal Abundance and Distribution of Major Algal Groups
Seasonally, abundance (cells/mL) was low during the spring and
increased slightly by June. Because sampling in the present study was
designed to monitor the early pre-bloom conditions, the spring bloom observed
in May, June and July of 1976 (Bartone and Schelske 1982) was not observed in
1984 (Makarewicz 1988) or 1985 (Fig. 4). Similar to 1984, a secondary
abundance maxima was observed in August (Fig. 4a) but was not observed in the
biovolume seasonal distribution in 1985 (Fig. 4b). During August, a general
downward trend in biomass occurred. Because samples were not taken in Octo-
ber, the large autumn peak observed in 1983 (Makarewicz 1987) was not observed
in 1984 (Makarewicz 1988) or 1985. Similarly, a fall bloom was not observed
in 1976 by Bartone and Schelske (1982). This was attributed either to a weak
bloom that was not observed or to the occurrence of the bloom at a time when
samples were not taken.
24
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Considering biovolume, the Bacillariophyta were dominant in the spring
and fall accounting for as much as 80% of the phytoplankton biovolume (Fig.
5). The large drop in biovolume of Bacillariophyta (to 8%, -10% in 1983)
observed in August of 1985 and in 1983, was not observed in 1984 (Makarewicz
1987, 1988). Makarewicz (1988) attributed the predominance of the diatoms
throughout the summer of 1984 to a bloom of Rhizosolenia eriensis. A bloom of
R. eriensis was not observed in 1983 or 1985 (Table 11), suggesting that the
prevalence of R. eriensis determines whether or not a divisional succession
occurs as suggested by Makarewicz (1987).
The small decrease in diatoms in August of 1984 corresponded with an
increase in the Cryptophyta, while in 1983 the major decline in diatoms corre-
sponded with an increase in the Pyrrophyta (Makarewicz 1987, 1988). In 1985,
the decrease in diatoms corresponded with a major increase in the Cryptophyta,
Pyrrophyta and the Cyanophyta (Fig. 5). A shift in biovolume composition was
observed in 1976 with diatoms decreasing to 17% in August when greens and
blue-green algae predominated (Bartone and Schelske 1982).
Regional and Seasonal Trends in the Abundance of Common Taxa
The definition of common species (Makarewicz 1987, 1988) has been revised
to accommodate the removal of the picoplankton. Common species (Table 12 -
14) were arbitrarily defined as those possessing a relative abundance of >0.5%
of the total cells or >0.5% of the total biovolume. Using the new definition,
the data from 1983 (Table 12) and 1984 (Table 13) were revised. Eight new
common species were observed in 1985 from 1983 and 1984. Two of these spe-
cies, Cymatopleura solea var. apiculata and Stephanodiscus sp.#9, were
actually rare - abundance being less than 0.2 cells/mL. Because of their
large size, these species attained a biomass exceeding 0.5% of the total bio-
mass. Because of the similarity of the 1985 common species list to the 1983
and 1984 list, a species by species description of autecology and regional and
25
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seasonal trends are not warranted here and can be referred to in Makarewicz
(1987, 1988). Only new common species, with the exception of Cymatopleura
solea var. apLculata and Stephanodiscus sp.#9, are discussed below.
Cryptophyta
Chroomonas acuta Uterm.
Stoermer and Kopczynska (1967a&b) did not identify flagellates to the
species level but did conclude that their abundance was low. In the nearshore
zone in 1970, abundance of Chroomonas sp. reached 68.6 cells/mL (Stoermer
and Tuchman 1979). In Green Bay, Chroomonas spp. was sporadically represented
in May and August (mean - 58.9 cells/mL)(Stoermer and Stevenson 1979). The
intensive study of 1976 and 1977 that included the offshore region did not
report this genus (Rockwell et al 1980). However, the authors report that the
results may be affected by the low magnification (400x) used in enumeration
and identification. It is apparent that abundance of this genus has been high
in Lake Michigan. Average abundance in 1983 (7.9 cells/mL) and 1984 (7.4
cells/mL) was comparable to 1985 (16.3 cells/mL)(Table 14). A maximum abun-
dance of 155 cells/mL was observed on the 17-20 August, 1985 cruise.
Cryptomonas ovata Ehr.
Stoermer and Kopczynka (1967b) reported cryptomonads and other flagel-
lates as a numerically minor component of the total plankton in Lake Michigan
in 1963. However, Munawar and Munawar (1975) found that flagellates
contributed between 6 and 31% of the biomass in 1973. Claflin (1975) also
found small flagellates (particularly Bhodomonas spp. and Cryptomonas spp.) to
be very abundant in 1971. In the nearshore zone, C. ovata abundance
averaged 28.6 cells/mL with a maximum of 98.4 cells/mL in 1977 (Stoermer and
Tuchman 1979). In the intensive survey of 1977 (Rockwell et al 1980) that
included the offshore, as well as the nearshore, abundance of C. ovata ranged
from 60 cells/mL in April to 101 cells/mL in August. Although a common spe-
26
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cies in 1985 by virtue of its large size, abundance averaged only 1.7 cells/mL
with a maximum of 25 cells/mL (Table 14). Abundance was also low in 1983 (1.6
cells/mL) and 1984 (2.1 cells/mL). No obvious geographical pattern was
observed (Fig. 6). Except for the 1963 work, Cryptowonas appears to be preva-
lent at times within Lake Michigan.
Cryptomonas rostratiformis Skuja
This species was not reported by Stoermer and Kopczynska (1967a&b),
Stoermer and Tuchman (1979), Stoermer and Stevenson (1979) or Rockwell et al
(1980) in the nearshore and offshore or in the waters of Green Bay. Abundance
in 1983 (mean - 1.4 cells/mL) and 1984 (mean - 0.3 cells/mL) was similar to
1985 (1.2 cells/ mL). In 1985, it was most prevalent throughout the lake in
May and August. Maximum abundance was observed in early May at Station 19
(12.3 cells/mL).
Rhodomonas lens Pasch. & Rutt.
Rhodomonas minuta and R. minuta var. nannoplanktica have been the forms
of Rhodomonas observed in Lake Michigan. Although an exhaustive search of the
literature was not performed, a review of the generally cited comprehensive
phytoplankton studies of Lake Michigan (Stoermer and Kopczynka 1967a, Claflin
1975, Munawar and Munawar 1975, Rockwell et al 1980, Stoermer and Tuchman
1979, Makarewicz 1987, 1988) did not reveal any other previous occurrences of
this species except for the work done in 1983 (mean - 8.3 cells/mL), 1984
(mean - 8.7 cells/mL) and 1985 (Makarewicz 1987, 1988, this study). Although
a common species in 1985 by virtue of its large size, abundance averaged only
25.1 cells/mL with a maximum of 139 cells/mL (Table 14). Seasonally, maxima
in abundance occurred in the spring and autumn (Fig. 7)
27
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Cyanophyta
Anabaena sp.
Species of Anabaena were present in low quantities (<5 cells/mL) in the
fall, but rare during the spring of 1962-63 (Stoermer and Kopczynska 1967a).
Stoermer and Tuchman (1979), working in the nearshore of Lake Michigan,
reported Anabaena flos-aquae as the prevalent species of Anabaena (mean - 24.5
cells/mL). Other forms of Anabaena were not identified, but densities were
low (<0.5 cells/mL). Similarly, abundance of Anabaena flos-aquae was high
(mean - 79.4 cells/mL) in Green Bay in 1977 (Stoermer and Stevenson 1979). In
the intensive study of Lake Michigan, which also included offshore waters,
filamentous bluegreens were considered relatively unimportant (Rockwell et al
1980). Abundance in 1983 (mean - 8.0 cells/mL) and 1984 (mean - 12.0
cells/mL) was slightly lower than 1985 (mean - 21.8 cells/mL)(Table 14). An
isolated bloom that occurred in August at Station 47 (1,309 cells/mL) was the
cause of the increase reported in 1985 from 1983.
Pyrrophyta
Gymnodinium helveticum f. achroum Penard
Historical information on this species is inadequate for comparison to
the 1985 data. Stoermer and Stevenson (1979) did report G. helveticum (0.67
cells/mL) present in Green Bay in 1977. Stoermer and Tuchman (1979), working
irt the nearshore zone of southern Lake Michigan in 1977, reported an average
abundance of 0.64 cells/mL (Maximum - 20.7 cells/mL) for Gymnodinium spp. In
1985, average abundance of G. helveticum var. achroum and Gymnodinium sp. was
0.8 cells/mL (Table 14). Occurrence of G. helveticum f. achroum in 1985 was
restricted to southern Lake Michigan during the spring (Fig. 8).
28
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Historical Changes in Species Composition
Division Trends
In August of 1962, an analysis of samples from southern Lake Michigan
revealed that the diatoms were numerically dominant (Stoermer and Kopczynka
1967a). Relative abundance of diatoms was never lower than -70% of the total
assemblage at all stations. By 1969 green, blue-green and golden brown algae
were the major phytoplankton components (Schelske and Stoermer 1972). Simi-
larly, Schelske et al (1971) observed that blue-green and green algae consti-
tuted 56 to 85% of the phytoplankton during August and September. In a
detailed study of southern Lake Michigan, Stoermer (cited in Tarapchak and
Stoermer 1976) observed that blue-green algae contributed up to 80% of the
phytoplankton cells in August of 1971.
Another shift in algae composition was evident by 1977. Relative abun-
dance of blue-greens dropped to 22.9% in August. However, flagellates (-42%)
rather than diatoms (22%) were the dominant group of algae (Rockwell et al
1980). A similar composition to 1977 was observed in August of 1984 (diatoms
- 12.2%, blue-greens = 16.4%, unidentified flagellates - 42.1%) when pico-
plankton were not included in the analysis (Makarewicz 1988). From 1983 to
1985, in addition to the cyanophytes being more prevalent than the diatoms,
the chrysophytes were numerically more important than the diatoms (Table 9).
In addition, the cryptophytes were more prevalent in 1983 and 1985. The
numerical decline of the diatoms has been attributed to the high phosphorus
loading and concomitant silica depletion (Schelske and Stoermer 1971). On a
biomass basis, however, diatoms were the dominant group in 1983, 1984 and
1985.
Species Trends
The Haptophyceae, Monoraphidium contortion (Chlorophyta), Dinobryon
sociale var. americanum (83 and 84 only)(Chrysophyta), Rhodomonas minuta var.
29
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nannoplanktica and Chroomonas norstedii (Cryptophyta), Anacystis montana var.
minor and OscLllatorLa limnetica (83 and 84 only) (Cyanophyta) were numer-
ically dominant in 1983, 1984 and 1985. Dominant diatoms in 1983 included the
numerically dominant Cyclotella comensis, Fragilaria crotonensis and Melosira
italica subsp. subartica; on a biomass basis, Tabellaria flocculosa was pre-
dominant (Makarewicz 1987). In 1984 Cyclotella comensis and Fragilaria croto-
nensis, along with Cyclotella ocellata, were numerically dominant. M. italica
subsp. subarctica was common but not dominant. On a biomass basis,
Rhizosolenia eriensis and Tabellaria flocculosa were predominant in 1984. In
1985 Rhizosolenia longLseta, Melosira islandica and Melosira italica subsp.
subartica were dominant on a numerical basis while Stephanodiscus niagarae was
the dominant species on a biomass basis. Fragilaria crotonensis was common in
1985 but not dominant.
Of the 1983, 1984 and 1985 dominant diatoms, only Fragilaria crotonensis
and perhaps Tabellaria flocculosa were major components of the diatom assem-
blage in 1962-63. Stoermer and Kopczynska (1967a) noted taxonomic difficul-
ties with Tabellaria and noted that most populations of Tabellaria "are
probably to be referred to T. fenestrata ...."
The dominant species of Cyclotella in 1962-63 was C. michiganiana.
Rockwell et al (1980) reported that Cyclotella spp. were common in 1977 but
were never dominant. A dramatic decrease in some species of Cyclotella, such
as C. michiganiana and C. stelligera, which were offshore dominants in August
of 1970, was evident by 1983 (Table 15). Cyclotella comensis, believed to be
tolerant of higher nutrient and lower silica concentrations than most members
of this genus, was the numerically dominant diatom in the offshore waters in
1983 and 1984 (Makarewicz 1987, 1988), but not 1985 (Fig. 9). Cyclotella
ocellata, a species generally associated with oligotrophic conditions, was
also dominant in 1984 but not in 1985.
30
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Yearly variation in dominance of species of Melosira was evident. Melo-
sira islandica was dominant in 1962-63. In 1983 M. Lslandica was present
(mean - 12.1 cells/mL), but M. italics subsp. subarctica (mean - 37.6
cells/mL) was more abundant. In 1984 M. islandica and M. italics subsp.
subartica had similar abundances (-10-12 cells/mL) but were not dominant (Ma-
karewicz 1988). In 1985 these two species, along with Stephanodiscus niaga-
rae, were the dominant diatoms (Table 14).
Synedra acus was common throughout the southern basin in 1977 (Rockwell
et al 1980) but represented only <0.1% of the total cells from 1983 to 1985.
Makarewicz (1987) has suggested an apparent decline in R. eriensis since
1962. In May of 1962, relatively high (100 cells/mL) populations were
observed in southern Lake Michigan (Stoermer and Kopczynska 1967a). During
May and June of 1970, mean abundances for offshore stations were 63 and 611
cells/mL, respectively (Holland and Beeton 1972). Rockwell et al (1980)
reported a mean density of 28.7 cells/mL for 1?. eriensis during June of 1977.
Abundance in 1983 was 2.6 cells/mL for the entire lake. A bloom (133
cells/mL) in the northern Station 77 did occur in October. In 1984, mean lake
abundance increased to 18.2 cells/mL, but decreased to 3.3 cells/mL in 1985.
Similar to species of Melosira, considerable yearly variation in abundance of
Rhizosolenia from 1983 to 1985 was observed.
Ankistrodesmus falcatus increased in abundance to 1977 and had decreased
by 1983. Ahlstrom (1936) reported this species as rare, but Stoermer and
Kopczynska (1967a) noted that it had increased by 1962-63 (range - 20-60
cells/mL). Rockwell et al (1980) suggested that by 1977 it had increased
further (range 20-160 cells/mL). In 1983 this species was observed only
once during the study at Station 32 (6.5 cells/mL) and was not observed in
1984 and 1985.
Dominant chrysophytes in 1962-63 were Dinobryon divergens, D. cylindricum
31
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and D. socials (Stoermer and Kopczynska 1967a). Rockwell et al (1980)
reported them as dominant or subdomlnant offshore. With the exception of D.
cylindricum in 1984, D. divergens, D. cylindricum and D. sociale were common
species in 1983 and 1984. None of these chrysophytes was common in 1985
(Table 14). As in 1983 and 1984, the haptophytes were numerically the domi-
nant group within the chrysophytes in 1985.
Dominant and common cryptophytes between 1983 and 1985 included
Cryptomonas erosa var. reflexa, C. erosa and Rhodomonas minuta var. nanno-
planktLca. Stoermer and Kopczynska (1967b) and Stoermer (1978) reported these
species as uncommon in Lake Michigan, but Vollenweider et al (1974) noted
these species as commonly found. Similarly, Munawar and Munawar (1975), Cla-
flin (1975) and Rockwell et al (1980) had reported C. erosa and R. minuta var.
nannoplanktica to be dominant, abundant and perhaps increasing in number. From
the 1983, 1984 and 1985 work, it is apparent that C. erosa was numerically
uncommon but on a biomass basis was the most important cryptophyte (second in
1984, Makarewicz 1988) (Table 14). Evaluation of abundance of R. minuta in
earlier studies was not possible because it was grouped into phytoflagellates,
flagellates or simply Rhodomonas. What can be reported about Rhodomonas
minuta var. nannoplanktica is that in 1983, 1984 and 1985 it was the dominant
cryptophyte on a numerical basis.
Oscillatoria Iimnetica has become more prevalent in the lake. Ahlstrom
(1936) and Stoermer and Kopczynska (1967a) listed 0. mougeotii as the only
species of this genus abundant in their collections. Stoermer and Ladewski
(1976) reported that 0. Iimnetica had generally increased in abundance in Lake
Michigan. Rockwell et al (1980) observed that 0. Iimnetica was common
throughout the basin in April and June and was especially abundant in Septem-
ber of 1977 at certain stations. 0. Iimnetica was the numerically dominant
offshore blue-green algae in 1983 (Makarewicz 1987), was second and third in
32
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abundance in 1984 (Makarewicz 1988) and 1985 (Table 14), respectively. Ana-
cystis montana var. minor was the dominant blue-green algae in 1984 and 1985
(Table 14).
Geographical Abundance and Distribution
The 1985 sampling pattern in Lake Michigan differed from 1983 and 1984
(Makarewicz 1987, 1988) in that the far northern stations (Stations 57, 56 64
and 77) and the most southern station (Station 6) were not sampled not allow-
ing a comparative geographical analysis between years. In 1985 total phyto-
plankton abundance was not significantly different between the northern and
southern half of the lake. A peak in abundance did occur at Station 27 caused
by the high abundance of picoplankton at this station (Fig. 10). A similar
peak at Station 27 occurred in the geographic biomass distribution pattern,
except that the peak was caused by diatoms (Fig. 11). Cyanophyta abundance
was significantly (P<0.05) higher in the southern basin compared to the north-
ern basin. Station 47 at the northern end of the sampling pattern also had a
high Cyanophyta abundance.
No obvious geographical abundance pattern was observed in the other
algae divisions. Considering biomass, a different pattern emerges (Fig. 11).
Chrysophyta biomass progressively increases from north to south. As with
abundance, blue-green biomass increases south of Station 27. Compared to the
rest of the lake, Pyrrophyta and Cyanophyta biomass are high at Station 47.
Seasonally, the two summer cruises possessed a geographical abundance
pattern similar to the mean annual phytoplankton distribution with abundance
peaks at Station 27 (Fig. 12). The.peak at Station 27 during the summer was
caused by a bloom of picoplankton (spheres). No obvious geographic patterns
were observed during the spring and fall cruises (Fig. 12).
33
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Indicator Species
Stoermer and Yang (1970), in a comparison of modern and historic
records, reported that taxa characteristic of disturbed situations were rap-
idly increasing in relative abundance in Lake Michigan in the 60's. In the
nearshore area, a shift in oligotrophic forms to those which dominate under
eutrophic conditions was evident. Occurrence of certain eutrophic species was
also evident in offshore waters (Stoermer and Yang 1970).
Dominant diatom species in the offshore waters in 1983 were Cyclotella
comensis, C. comta, Tabellaria flocculosa, Fragilaria crotonensis and Melosira
italics subsp. subartica (Makarewicz 1987). The same five diatoms were domi-
nant in 1984 with the exception of C. comta and the addition of Khizosolenia
eriensis and Cyclotella ocellata (Makarewicz 1988). In fact, R. eriensis
accounted for -25% of the total biomass of phytoplankton during 1984.
Rhizosolenia eriensis may be an opportunistic species which is able to
rapidly develop fairly high abundances when conditions are favorable (Stoermer
and Ladewski 1976). Stoermer and Yang (1970) listed R. eriensis with the
oligotrophic offshore dominants, which includes C. ocellata, but noted that R.
eriensis seemed to occur in greater abundance in areas that have received some
degree of nutrient enrichment. Tabellaria flocculosa and F. crotonensis are
mesotrophic forms, while the ecological affinities of C. comensis are poorly
understood. Cyclotella comensis was formerly found in primarily oligotrophic
areas (Stoermer and Stevenson 1979) under some nutrient stress (Stoermer and
Tuchman 1979) . Dominant diatom species in the offshore waters in 1985 were
Stephanodiscus niagarae, Melosira islandica, Rhizosolenia longiseta, Melosira
italica subsp. subarctica and Fragilaria crotonensis.
Compared to 1983 (Makarewicz 1987) when mesotrophic diatoms species
were predominant, the same mesotrophic forms were present in 1984 along with
oligotrophic indicators (Makarewicz 1988). A change occurred in 1985 in the
34
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predominant diatom species. The species of Cyclotella and Tabellaria floccu-
losa predominant in 1983 and 1984 were present but were not dominant or com-
mon. The eutrophic indicator species Stephanodiscus niagarae was the dominant
species on a biomass basis, while Rhizosolenia longiseta and the mesotrophic
indicator species Melosira islandica were dominant on a numerical basis. Only
Melosira italica subsp. subarctica and Fragilaria crotonensis were predominant
diatom species observed in 1983, 1984 and 1985.
The indicator diatom species and the distribution of them (trophic ratio)
(Table 16) suggest a eutrophic status for nearshore waters in 1977,
mesotrophic-eutrophic for offshore waters in 1970-71, and an oligotrophic-
mesotrophic range for offshore waters in 1983, 1984 and 1985. With the low
mesotrophic/eutrophic ratio in 1970-71 (M/E - 2.3) as compared to 1983, 1984
and 1985 (mean M/E =6.8), it is tempting to suggest a slightly more meso-
trophic status in more recent years. The M/E ratio has to be interpreted
conservatively as it is influenced somewhat by the definition of the
predominant species (e.g. 1% of biomass). Nevertheless, the trophic status
as determined by indicator species and the M/E ratio agrees well with the 1976
assessment based on particulate phosphorus concentrations that place the open
lake waters of Lake Michigan in the oligotrophic-mesotrophic range (Bartone
and Schelske 1982).
Historical Changes in Community Abundance
A comparison of abundance trends over the entire lake was not possible
because of the lack of comparable offshore data prior to 1983. Figure 13
plots the 1962-63 and the 1976-77 data of Stoermer and Kopczynska (1967a and
b) and Rockwell et al (1980), which are representative of the southern portion
of the lake. Only a range of abundance is available for 1962-63, while the
mean, standard error and range are plotted for the other data. Because pico-
plankton were not counted prior to 1983, they are removed from the 1983, 1984
35
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and 1985 data presented in Figure 13. Although a mean is not available, it is
apparent that phytoplankton abundance increased from 1962-63 to 1976-77. From
1976 to 1983 to 1985, abundance was not significantly different (P<0.05).
Based on the classification scheme of Munawar and Munawar (1982) which uti-
lizes the mean phytoplankton biomass as an indicator of trophic status, Lake
Michigan would be classified as oligotrophic in 1985, as it was in 1984
(Makarewicz 1988). However, the trophic ratio and composition of indicator
species suggest a mesotrophic status.
36
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LAKE MICHIGAN
Zooplankton
Annual Abundance of Zooplankton Groups
Species lists (Table A4) and summary tables of abundance (Table A5) and
biomass (Table A6) are in Volume 2 - Data Report (ATTACHED FICHE). The zoo-
plankton assemblage of 1985 comprised 52 species representing 29 genera from
the Calanoida, Cladocera, Cyclopoida, Harpacticoida, Mysidacea and Rotifera.
Compared to 1984, the same number of species was observed in 1985, which
represented a 21% reduction from the number of species observed in 1983. The
total number of genera has declined steadily from 43 in 1983 to 34 in 1984 to
29 in 1985. This difference is mostly attributable to a decrease in the
number of Rotifera species observed.
As in 1983 (Makarewicz 1987) and 1984 (Makarewicz 1988), the Rotifera
possessed the largest number of species (29) and relative abundance (39.9%).
Unlike 1984, the Calanoida, rather than the Cladocera, accounted for a major
portion (67.4%) of the Zooplankton biomass (Table 17). The Rotifera contrib-
uted only 1.1% of the total biomass (Table 17). Average density and biomass
for the study period were 34,950±4,085 organisms/m3 (mean+S.E.) (1983 -
69,353, 1984 - 59,764) and 47.9± 5.2 mg/m3 (mean+S.E.)(1984 - 33.2±4.9).
Seasonal Abundance and Distribution of Major Zooplankton Groups
The seasonal abundance patterns were virtually identical between 1985
and 1984 (Makarewicz 1988, Fig. 14) with a maximum in abundance observed in
August of each year. The secondary maximum observed in October of 1983 (Maka-
rewicz 1987) was not observed in 1984 and 1985, This difference is apparent
and is probably related to the difference in the seasonal sampling pattern
between years. Samples were not taken in September and October of 1984 and
1985.
Seasonally, abundance and biomass of all groups, except the Calanoida,
37
-------
were higher in August as compared to the early spring and late fall (Figs. 15
and 16). The lack of a maximum in total zooplankton biomass (Fig. 14) during
August is attributed to the low Calanoida biomass observed during this period.
The high abundance of Cyclopoida, Cladocera and Copepoda nauplii in August of
1984 (Makarewicz 1988) and 1985 was not observed in 1983 (Makarewicz 1987).
Geographical Abundance and Distribution of Zooplankton Groups
A definite trend of increasing zooplankton abundance occurred from
south to north in Lake Michigan in 1984 (Makarewicz 1988). Specifically,
zooplankton abundance at the far northern Stations 64 and 77 was higher than
in the rest of the lake. Abundances of Rotifera, Cladocera and Copepoda
nauplii were all higher at these far northern stations. Biomass, however, was
similar southward from Station 77 to Station 18, after which biomass decreased
southward. These patterns were not observed in 1983 (Makarewicz 1987) or in
1985. In 1985, the far northern sites (Stations 64 and 77) and the most
southern site (Station 6), where the differences in abundance were observed in
1984, were not sampled.
Previous work has suggested that abundance of several species of
zooplankton peaked at the far northern stations (Makarewicz 1987, 1988). Con-
ochilus unicornis, Bosmina longirostris, EubosmLna coregonL, Notholca lauren-
tiae, N. squamula, N. foliacea, Holopedium gLbberum, Polyarthra vulgaris (1984
only) and P. remata (1984 only) all had abundance peaks at the far northern
end of the lake in 1983 and 1984. Similarly, abundance of Diaptomus sicilis
was higher in southern Lake Michigan (Makarewicz 1987) in 1983 and 1984.
Abundance of D. sicilis appeared to be higher in the southern basin (Fig. 17)
in 1985. Similarly, C. unicornis and H. gibberum had higher abundances at
Station 47; the most northern station samples in 1985 (Fig. 18). Because
samples were not taken at the far northern stations in 1985, it was not possi-
38
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ble to fully evaluate geographical trends for the entire lake. In general,
the limited geographical data available in 1985 suggest little difference in
abundance of the stations sampled (Fig. 20).
Common Species
Common Crustacea species (Table 18) were arbitrarily defined as those
possessing a relative abundance of >0.1% of the total abundance or 1.0% of the
total biomass. Rotifera species were considered common if they accounted for
>1.0% of the total zooplankton abundance or biomass. The number of common
species (1983 - 25 species; 1984 - 24 species; 1985 - 22) and common species
composition were essentially the same between 1983 and 1985. Some of the
compositional difference can be attributed to the rotifers and the differences
in sampling schemes between years. For example, Notholca foliacea, N. lau-
rentiae, Polyarthra remata, Bosmina longirostris and Holopedium gibberum were
common in 1984 but not in 1983 and 1985. In 1985 the far northern stations,
where these organisms predominated, were not sampled.
Historic Changes in Species Composition
Crustacea
Numerous recent studies (Williams 1966; Johnson 1972; Gannon et al 1982a,
1982b; Evans et al 1980) of the nearshore region of Lake Michigan exist, along
with data from as far back as 1927 (Eddy 1927). Several researchers have
compared the nearshore with the offshore zooplankton in discussions of eutro-
phication of the entire lake. Comparisons of the inshore with the offshore
stations should be viewed with caution because effects are not necessarily due
to eutrophication or fish predation (Evans et al 1980).
Although no intensive zooplankton studies of the offshore waters of the
entire lake basin have taken place, some offshore studies of Lake Michigan
zooplankton do exist. Wells (1960, 1970) sampled Crustacea with a number 2
(366um) net on four dates in June, July and August in 1954, 1966 and 1968 from
39
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the offshore region off Grand Haven, Michigan. On six dates (March 1969 to
January 1970), Gannon (1975) collected crustaceans with a 64-um mesh net from
the offshore and inshore of Lake Michigan along a cross-lake transect from
Milwaukee to Ludington. In September of 1973, northern Lake Michigan was
sampled with a 250-um mesh net (Schelske et al 1976). Also, Stemberger and
Evans (1984) provided abundance data (76-um net) for a few zooplankters from
offshore waters of the southeastern Lake Michigan area.
The data of Wells (1960, 1970) and Gannon (1975) are useful but have to
be used with caution. A 366-um and a 250-um net are probably quantitative for
larger crustaceans but certainly would not be for smaller crustaceans such as
Chydorus sphaericus, Bosmina longirostris, Eubosmina coregoni, Ceriodaphnia
spp., Tropocyclops prasinus and copepods (Makarewicz and Likens 1979).
The zooplankton populations in Lake Michigan underwent striking size-
related changes between 1954 and 1966 (Wells 1970). Species that declined
sharply were the largest cladocerans (Leptodora kindtii, Daphnia galeata
mendotae and D. retrocurva), the largest calanoid copepods (Limnocalanus
macrurus, EpLschura lacustris and Diaptomus sicilis) and the largest cyclopoid
copepod (Mesocyclops edax). Medium-sized or small species (D. longiremis, H.
gibberum, Polyphemus pediculus, Bosmina longirostris, Ceriodaphnia sp.,
Cyclops bicuspidatus, Cyclops vernal is, Diaptomus ashlandi) increased in num-
ber, probably in response to selective alewife predation. After the alewife
dieback, M. edax and D. galeata mendotae were still rare in 1968 when the
composition of the zooplankton community shifted back toward one similar of
1954 (Wells 1970).
In northern Lake Michigan during September of 1973, predominant species
were Daphnia galeata mendotae, D. retrocurva, Limnocalanus macrurus, Diaptomus
oregonensis, Eubosmina coregoni and Diaptomus sicilis. Cyclopoid copepods
were a minor component of the fauna in 1973 (Schelske et al 1976).
40
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The changing nature of the zooplankton community of Lake Michigan was
evident in 1983. Daphnia galeata mendotae, D. pulicarla and D, retrocurva
were the second, third and fourth most abundant cladocerans in the lake (Maka-
rewicz 1987). D. galeata mendotae and D. retrocurva were again the prominent
daphnids in 1984 along with the dominant cladoceran Bosmina longirostris. In
1985 D. galeata mendotae, Daphnia pulicaria and Daphnia retrocurva were the
common cladocerans. Bosmina longirostris the dominant cladoceran in 1983 and
1984, was not even a common species in 1985. This is partialy attributed to
the dropping of the far northern stations where this organism predominated in
1983 and 1984. However, removal of the far northern stations from the 83 and
84 data still suggests an increase in B. longirostris from the 60's (Table
19). Annual abundance of Daphnia pulicaria dropped from an average of 376/m3
in 1983 to 78/m3 in 1984 and increased to 161/m3 in 1985. In August of 1983,
abundances of D. galeata, rare in 1966 and 1968, were half of those in 1954
(1,200/m3) and 2-3 times the 1954 abundance in 1984 and 1985 (Table 19).
The 1983 August abundance of Daphnia retrocurva was similar to the
August 1966 abundance rather than to those of 1954 or 1968. However, maximum
abundance in October of 1983 (3,161/m3) was comparable to the 1954 or 1968
observations. Perhaps related to the low abundance of D. retrocurva in August
of 1983 was the appearance of the large (~2 mm) (Evans 1985) cladoceran Daph-
nia pulicaria, which reached a maximum abundance in August. When D. pulicaria
dropped in abundance in 1984, D. retrocurva abundance increased to a density
comparable to those of 1954 and 1968 (Table 19). Similarly in 1985, D. retro-
curva abundance decreased when D. pulicaria abundance increased (Table 19)
Evans (1985) recently reported that JD. pulicaria was first observed in
Lake Michigan in 1978. Abundance remained low in southeastern Lake Michigan
until 1982 and 1983 when they dominated the offshore summer Daphnia community
and at an offshore station southwest of Grand Haven, Michigan. In 1983 this
41
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species was the dominant cladoceran in the offshore waters of Lake Michigan
(Makarewicz 1987). Mean annual station abundance in 1983 reached 1,741 organ-
isms/m3 in early August with a maximum of 6,056/m3. In 1985 August abundance
of D. pulicaria increased to 694/m3 from a mean of 248/m3 in 1984 (Table 19).
The large cladoceran Leptodora kindtii appeared to be increasing in
abundance from 1954 to 1984 (Makarewicz 1988, Table 19). Although average
abundance was down in 1985 compared to 1984, abundance in 1985 was still
higher than in the 60's. Eubosmina coregoni has also increased in abundance
since 1954 (Table 19). Abundance of B. longirostris and the larger Holopedium
gibberum decreased significantly from 1984 to 1985. In fact, abundances
observed in 1985 were similar to 1954, 1966 and 1968. The decrease in abun-
dance from 1984 to 1985 of H. gibberum, but not B. longirostris, is related to
the deletion of the far northern sampling stations routinely sampled in 1983
and 1984. The decrease in B. longirostris appears to be real and not due to
the changes in the sampling regime.
Cyclops bicuspidatus was the dominant cyclopoid in 1983, 1984 and 1985
with Diaptomus ashlandi or D. sicilis being the dominant calanoid (Makarewicz
1987, 1988, Table 20). Abundance of Mesocyclops edax was low in August of
1983, 1984 and 1985 compared to 1954. However, abundance of this species has
obviously increased since the 60's and appears to be approaching levels
observed in 1954. Abundance of M. edax in early October of 1983 reached a
level comparable to 1954 (151 organisms/m3, mean station abundance).
Diaptomus minutus appears to have decreased in abundance since 1968,
while D. oregonensis abundance remained similar to 1954 (Table 20). August
abundance of D. sicilis increased from 1968 to 1984 and then decreased in
1985. This decrease was not due to the change in sampling stations in 1985
(Table 20). Abundance of Limnocalanus macrurus was lower during August of
1983 and 1985 than in 1954-68. However, abundance in 1984 was similar to
42
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1954 and 1966. The abundance of EpLschura lacustris in August was low in 1983
and 1984 relative to 1954, but not in 1985, when abundance was similar to
1954. Mean station abundance reached 111 organisms/m^ in late October of
1984.
Between 1983 and 1985, the large cladocerans, calanoids and cyclopoid
copepods, observed by Wells (1970) to have decreased sharply in the early
60's, had increased in abundance to densities similar to those in August of
1954. In some instances, abundance was not as high in August but was as high
at other times of the year. In addition, a new large cladoceran, Daphnia
pulicaria, has become established in the offshore waters of Lake Michigan.
The resurgence of larger zooplankton in Lake Michigan is probably
related to the sharp decline in the abundance of the planktivorous alewife in
1982 and 1983. The lakewide catch of adult alewifes was only 31% of that of
1982 and only 12% of the 1981 catch. Bloater chubs are replacing the alewifes
and have been experiencing a dramatic increase in abundance since 1970 (Wells
and Hatch 1983). Bloaters above -18 cm in size primarily feed on Mysis and
Pontoporeia. Only smaller individuals feed on zooplankton (Wells and Beeton
1963). The decrease in B. longirostris may be related to interference compe-
tition (Vanni 1986) expected from the resurgence of large daphnids in Lake
Michigan.
Rotifera
Rotifer studies reported in the literature are primarily from the near-
shore region of the lake. In the nearshore, Keratella cochlearis, Polyarthra
vulgar is, Kellicottia longLspina, Synchaeta stylata and Synchaeta tremula were
dominant in 1926-27 (Eddy 1927). Keratella and Polyarthra were the dominant
genera in 1962 (Williams 1966), while K. cochlearis and P. vulgaris were domi-
nant in 1970 (Johnson 1972). Gannon et al (1982a) noted that the following
rotifers were predominant in 1977: Keratella cochlearis, K. crassa, Conochilus
43
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unicornis, Kellicottia longispina, Polyarthra vulgaris and P. remata.
Abundance of rotifers in Lake Michigan generally decreased from the
nearshore into the offshore (Gannon et al 1982a, Stemberger and Evans 1984)
although the species composition of the nearshore and offshore was relatively
similar. In 1983 the predominant offshore rotifers were in descending order:
Polyarthra vulgaris, Synchaeta sp., Keratella cochlearis, Polyarthra major,
Kellicottia longispina, Keratella crassa, Gastropus stylifer and Colletheca
sp. (Makarewicz 1987). The predominant rotifers in 1984 and 1985 were Kera-
tella cochlearis, Kellicottia longispina, Polyarthra vulgaris and Synchaeta
sp. (Makarewicz 1988, Table 18). The dominant rotifer composition of 1983 to
1985 is similar to the nearshore and to Ahlstrom's (1936) offshore observa-
tions of predominant species (Keratella cochlearis, Synchaeta stylata and
Polyarthra vulgaris).
Historical Changes in Zooplankton Biomass
Offshore crustacean zooplankton biomass data is available from 1976
(Bartone and Schelske 1982) for northern Lake Michigan. No information is
presented on sampling intensity or technique. A comparison with the 1984 and
1985 biomass data (Table 21) revealed that no significant difference in
crustacean biomass exists between 1976 and 1984/1985.
Another longer sequence of data is described by Scavia et al (1986).
Except for 1977, 1982, 1983 and 1984, zooplankton samples were primarily from
an offshore station (40-m depth) west of Benton Harbor, MI. A comparison of
the mean offshore 1984 and 1985 lake-wide biomass data to Scavia's station
indicates good agreement (Fig. 21). From Figure 21, there appears to be no
obvious trends in zooplankton biomass.
Indicators of Trophic Status
Zooplankton have potential value as assessors of trophic status (Gannon
and Stemberger 1978). Rotifers, in particular, respond more quickly to envi-
44
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ronmental changes than do the crustacean plankton and, therefore, are more
sensitive indicators of changes in water quality. Composition of the rotifer
community (Gannon and Stemberger 1978) can be used to evaluate trophic status.
In 1983 the six predominant rotifers in descending order of relative
abundance were P. vulgaris, Synchaeta sp., K. cochlearis, P. major, K. longis-
pina and C. unicornis, while in 1984 an 1985 the predominant rotifers were K.
cochlearis, K. longispina, P. vulgaris and Synchaeta sp. The 1983 and 1984
rotifer composition suggests an oligotrophic association. A rotifer community
dominated by Polyarthra vulgaris, Keratella cochlearis, Conochilus unicornis
and Kellicottia longispina has been considered to be an association indicative
of an oligotrophic community by Gannon and Stemberger (1978).
The high relative abundance of Diaptomus sicilis and Limnocalanus
macrurus (Table 18) and the occurrence of Senecella calanoides (l.O/m3, 1984;
0.8/m3, 1985), all oligotrophic indicators (Gannon and Stemberger 1978,
McNaught et al 1980a), also suggested oligotrophic offshore conditions for the
entire lake.
The calanoid/cyclopoid plus cladoceran ratio has been used as a measure
of trophic status in the Great Lakes (Gannon and Stemberger 1978, McNaught et
al 1980a). Calanoid copepods generally appear best adapted for oligotrophic
waters, while cladocerans and cylopoid copepods are relatively more abundant
in eutrophic waters. In 1983 and 1984 along the north-south transect, the
plankton ratios were high and similar, except at the far north and the south-
ern extreme of the lake (Table 22). In 1985 the calanoida/cyclopoid plus
cladoceran ratio was high and similar with a slight increase from north to
south. Makarewicz (1988) suggested that a lower quality of water occurred
south of Station 18 and north of Station 57 in 1983 and 1984. In addition,
the eutrophic rotifer indicator species Trichocerca pusilla and Trichocerca
multicrinis were observed exclusively at Station 6 and the northern stations,
45
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reinforcing the idea that a lower water quality exists at these locations.
Because the northern stations (Stations 57, 64 and 77) and Station 6 were not
sampled in 1985, further discussion on geographical differences observed in
previous years is not possible.
The low plankton ratios (0.20 - .41; Table 22) in 1983 and 1984 at the
far northern end of Lake Michigan (Stations 64 and 77) were very similar to
those observed in 1973 at the Straits of Mackinac (Gannon and Stemberger
1978). Gannon and Stemberger (1978) implied that more eutrophic conditions
exist within this area of a low calanoid to cladoceran plus cyclopoid ratio.
Abundance of the oligotropic LLmnocalanus macrurus and DLaptomus sicilis was
significantly lower in these far northern stations, while Eubosmina coregoni
and Bosmina longirostris, often associated with more productive conditions,
increased at the far northern stations in 1983 and 1984 (Makarewicz 1988) . In
addition, several mesotrophic algal species were more predominant at the
northern stations (Makarewicz 1988).
With a zooplankton abundance between those of Lakes Erie and Huron (Table
8), the presence of an oligotrophic rotifer association, a plankton ratio
between those of Huron and Erie, the domination of the calanoids and the
fairly abundant presence of the oligotrophic indicator species DLaptomus sici-
lis and LLmnocalanus macrurus, the offshore waters of Lake Michigan in 1985
are best characterized as mesotrophic/oligotrophic. A similar conclusion
utilizing zooplankton abundance and species composition was drawn in 1984.
Phytoplankton composition and abundance and water chemistry suggest a similar
trophic status (This Study).
Trophic Interactions
Between 1975 and 1984, gradual declines in spring total phosphorus and
summer epilimnetic chlorophyll a are reported (Scavia et al 1986). However,
long-term changes of phytoplankton and zooplankton biomass are not apparent in
46
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this study. Perhaps, the minimal changes observed in chlorophyll a are not
reflected in the high variability phytoplankton and zooplankton estimates.
Scavia et al (1986) points out that the changes in total phosphorus and chlo-
rophyll a are consistent with expectations of nutrient load control.
However, the significant lake-wide changes in zooplankton and
phytoplankton composition may not be expected from nutrient control. A spe-
cies new to the plankton assemblage, Daphnia pulicaria, is at least a sub-
dominant organism within the offshore. In addition, Leptodora kindtii,
Daphnia galeata mendotae, Diaptomus ashlandi and Cyclops bicuspidatus have
returned to and exceeded abundances observed in 1954 during a period of low
alewife abundance.
Scavia et al (1986) suggests that predatory pressure from alewife
suppressed large-bodied zooplankton until the early 1980's. Decline of the
alewife population as the major forage fish (Jude and Tesar 1985, Wells and
Hatch 1983) has been linked to the increasing population of stocked salmonines
in Lake Michigan (Stewart et al 1981, Jude and Tesar 1985). The decrease in
alewife abundance has reduced size-selective predation on larger zooplankton
allowing larger zooplankton to return (Scavia et al 1986, Wells 1970, Kitchell
and Carpenter 1986).
Table 23 lists correlation coefficients of phytoplankton abundance
versus total phosphorus and zooplankton for each cruise. For each cruise, 11
stations covering the entire length of the lake were sampled over a short
period of time. Interpretations of the correlations were as follows: A
negative correlation between a zooplankton group and phytoplankton implied
grazing pressure on phytoplankton, while a positive correlation between total
phosphorus and phytoplankton abundance would suggest an enhancement of phyto-
plankton abundance due to phosphorus availability. Except for the late autumn
cruises, correlation of total phosphorus to phytoplankton abundance was weak.
47
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As suggested by Scavia et al (1986), D. pulicaria appears to have a
negative impact on phytoplankton abundance especially during mid-August when
abundance is high. Interestingly, when Daphnia galeata mendotae is added to
the correlation analysis, the correlation coefficient increases from -.25 to
-.60 suggesting that D. galeata mendotae is also having a major effect on
phytoplankton abundance and size during August. A similar correlation existed
in 1984 (Makarewicz 1988). This would be an added effect in that D. galeata
has increased since 1954 apparently in response to decreased selective pres-
sure by the alewife. The calanoids appear to exert grazing pressure through-
out the sampling season but more heavily in the spring (Table 23).
The causes of the changes in species composition of phytoplankton are
much more difficult to evaluate. Changes in herbivore species composition
could affect algal species composition. Certain zooplankton feed on a wide
variety of algae of different sizes and shapes, and with or without sheaths
(Gliwicz 1980, McNaught et al. 1980b, Porter and Orcutt 1980). Other zoo-
plankton are highly selective in the algal types ingested. Cellular forms are
ingested more readily than filamentous or spinuosus forms and zooplanktonic
filtration rates, growth and survivorship are greater when feeding on cellular
forms (Porter 1973, Arnold 1971). Selective grazing and utilization can
remove species, reduce population size and change the size composition in the
algal community. Figure 22 demonstrates the apparent effect of Daphnia abun-
dance on the mean size of Lake Michigan phytoplankton community. The size of
the edible algae (non-filamentous and colonial forms) decreased during the
summer and early autumn when Daphnia were present. A decrease in Daphnia
appeared to result in an increase in edible plankton size. However, biomass
of filamentous algae did not increase as might be expected by the Bergquist et
al (1985) model. Alternatively, grazer utilization of an algal species can
result in enhancement of primary productivity of that species by increased
48
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selection for faster growing genotypes (Crvunpton and Wetzel 1982).
Nutrient effects can also affect composition of phytoplankton. For
example, Asterlonella is a successful competitor at high Si/P ratios, Fragil-
laria can dominate at intermediate ratios and Stephanodiscus grows well when
Si/P ratios are low (Kilham and Kilham 1978; Kilham and Tilman 1979; Tilman
1978, 1980). At high Si/P ratios, diatoms can effectively out compete blue-
green algae (Holm and Armstrong 1981). Similarly, as silica is reduced and
combined nitrogen declines, green algae can compete less effectively with
nitrogen-fixing blue-greens (Smith 1983). Effects on phytoplankton composi-
tion from both top-down and bottom-up routes are expected but are difficult to
separate in this descriptive study.
49
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LAKE HURON
Phytoplankton
Species lists (Table A7) and summary tables of abundance (Table A8) and
biovolume (Table A9) are in Volume 2 - Data Report (ATTACHED FICHE). A sum-
mary of water chemistry parameters is presented in Table 8.
Picoplankton
Picoplankton abundance in 1985 (mean - 22,923; maximum of 4.4 x 10^) was
not dissimilar from 1983 (mean - 19,343; maximum of 6.3 x 10^ cells/mL) and
1984 (mean - 14,396; maximum of 3.5 x 10^ cells/mL). On a numerical basis,
the picoplankton represented 92.3% of the total cells in 1985 but because of
their small biomass, only 3.4% of the total biovolume. Their relative numer-
ical dominance in 1985 was comparable to 1983 (86.6%) and 1984 (83.9%) (Maka-
rewicz 1987, 1988). Historically, the picoplankton have not been considered
in evaluations of the plankton community of Lake Huron. Their high abundance
tends to distort relative abundance values and does not allow reasonable com-
parisons with the historical data. For this reason, they are not considered
further in this discussion.
Annual Abundance of Major Algal Groups
The phytoplankton assemblage of 1985 wag comprised of 213 species repre-
senting 70 genera from eight divisions (Table 24). Compared to 1983 and 1984,
a sizeable reduction in the number of species (1983 - 35%; 1984 - 32% and
genera (1983 - 20%; 1984 - 24%) was observed. With no significant changes in
the sampling regime and water chemistry between years, these differences are
attributable to changes in counters that occurred in this year.
The annual average phytoplankton density and biovolume in 1985 (mean±S.E.)
were 2,020 ±113 cells/mL (2,567±178 cells/mL, 1983; 2,772±196 cells/mL, 1984)
and 0.34+.021 mm3/L (0.37±.040 mm3/L, 1983; 0.39±.039 mm3/L, 1984), respec-
tively. Similar to 1983 and 1984, the Bacillariophyta possessed the largest
50
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number of species (120) and biovolume (67.4% of the total, Table 25), while
the second largest number of species (32) was observed for the Chlorophyta
(Table 24). The Chrysophyta accounted for the second highest biovolume
(10.0%). The relative biovolume of the Cryptophyta in 1985 (9.3%) was similar
to 1983 (8.5%) and 1984 (9.2%) while Chlorophyta biovolume was higher than
1984 but similar to 1983 (Table 25). Cyanophyta biovolume was higher in 1985
than 1984. Pyrrophyta biovolume was considerably lower in 1985 than in 1983
and 1984 (Table 25). Highest overall densities were attained by the Cyano-
phyta (19.5% of the total abundance) and the Bacillariophyta (18.2% of the
total abundance). Unidentified organisms represented 26.1% of the total
cells.
Seasonal Abundance and Distribution of Major Algal Groups
Seasonally, abundance (cells/mL) increased from April to a maximum
(31,428 cells/mL) in mid June (Fig. 23). After a decline in abundance during
early August, algal abundance increased in late August, similar to 1984 (Maka-
rewicz 1988). Unlike 1984, abundance increased by the autumn sampling dates.
The seasonal biovolume distribution generally followed the seasonal abundance
distribution (Fig. 23). Abundance was not significantly different between the
late spring and fall (Fig. 23).
Considering biovolume, the Bacillariophyta were dominant throughout the
study period accounting for as much as 78.2% but never less than 41.7% of the
phytoplankton biovolume (Fig. 24). The large drop in the relative importance
of diatoms in August of 1983 (to ~30% of the total biovolume, Makarewicz
1987), which was not observed in 1984, was observed in August of 1985 (41.7%
of the total biovolume). The bloom of Rhizosolenia eriensis in August of
1984, which was suggested as the cause of the dominance of the diatoms
throughout the summer of 1984 (Makarewicz 1988), was again observed in 1985
(Table 26) even though there was a drop in relative importance of diatoms.
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With the decrease in importance of diatoms, the Chrysophyta, as in 1984,
accounted for 29% of the biovolume by late August. Diatoms regained their
spring predominant position by autumn (Fig. 24). As in 1984, the Cryptophyta
appeared to increase in importance during the study period.
Geographical Abundance and Distribution of Major Algal Groups
In 1983 the mean phytoplankton abundance for the sampling period gener-
ally decreased from north to south to Station 15, where abundance increased
and then decreased slightly southward (Fig. 26 in Makarewicz 1987).
Asterionella formosa, Cyclotella comensis, C. comta, and C. ocellata all had a
higher biomass at Station 61 in 1983 (Makarewicz 1987). A similar algal
geographical distribution was not observed during 1984 (Makarewicz 1988) but
was observed in the 1985 geographical biomass distribution (Fig. 25). Algal
biomass decreased from northern Lake Huron to Station 32 (northeast of Saginaw
Bay), where biomass increased and then decreased south of Station 27. This
geographical pattern was determined by the diatoms (Fig. 25). The Chryso-
phyta, Chlorophyta, Pyrrophyta and Cyanophyta had a higher biomass south of
Station 32 than north of Saginaw Bay (Fig. 25). Cyanophyta biomass was
generally higher in northern Lake Huron, except for Station 61, and decreased
precipitously to Station 32 before increasing in southern Lake Huron (Stations
27, 12, 9 and 6).
The annual geographical pattern of higher algal biomass south of Station
32 was generally observed seasonally during the spring and fall cruises and
somewhat evident for the summer cruise (Fig. 26). The annual pattern of a
decrease in algal biomass from the northern Station 54 to the centrally
located Station 37 was observed only during the spring and summer but not the
autumn (Fig. 26). The increase in biomass south of Station 27 in the spring
was caused predominately by diatoms and somewhat by chrysophytes. The
increase in biomass north of Station 32 was caused solely by diatoms. During
52
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the summer, the increase in biomass south of Station 27 was caused by an
increase in chrysophytes (mainly Chrysosphaerella longispina), while north of
Station 32 , the diatoms were the cause of the biomass increase. In the
autumn, the small but general increase in biomass in southern Lake Huron was
generally caused by the cryptophyte, Rhodomonas minuta var. nannoplanktica.
Regional and Seasonal Trends in the Abundance of Common Taxa
The definition of common species (Makarewicz 1987, 1988) has been revised
to accommodate the removal of the picoplankton. Common species (Table 27 -
29) were arbitrarily defined as those possessing a relative abundance of >0.5%
of the total cells or >0.5% of the total biovolume. Using the new definition,
the data from 1983 (Table 27) and 1984 (Table 28) were revised. Seven new
common species were observed in 1985 from 1983 and 1984 (Table 30).
Because of the similarity of the 1985 common species list to the 1983 and
1984 list, a species by species description of autecology and regional and
seasonal trends are not warranted here and can be referred to in Makarewicz
(1987, 1988). Only new common species are discussed below.
Bacillariophyta
Diatoma tenue var. elongatum Lyngb.
This species is widely distributed in the Great Lakes. Its greatest
abundance generally occurs in areas that have undergone significant eutrophi-
cation (Stoermer and Kreis 1980). In 1974 significant population densities
were generally restricted to stations in Saginaw Bay and stations near shore.
Average density in southern Lake Huron in 1974 was 0.94 cells/mL with a
maximum abundance of 77,5 cells/mL (Stoermer and Kreis 1980).
In 1983 and 1984, abundance averaged 5.4 and 1.3 cells/mL, respectively.
Maximum and average abundance in 1985 was 23 (Station 9, June) and 2.2
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cells/mL, respectively. Abundance was higher at those stations (92 and 27)
just south and east of Saginaw Bay during the spring (Fig. 27). A bloom was
evident throughout the lake in early June (Fig. 27).
Synedra ulna var. chaseana Thomas
Stoermer and Yang (1970) considered this species to be an oligotrophic
offshore dominant in the Great Lakes. Abundance in southern Lake Huron in
1974 was 2.2 cellls/mL with a maximum bloom of 25 cells/mL (Stoermer and Kreis
1980). In 1983 and 1984, this organism was not observed. In 1985, average
abundance was low (0.2 cells/mL) and maximum abundance reached only 4
cells/mL. Because of this organism's relatively large size (411um x 3.9Sum x
3.00um), it has a high biomass relative to its abundance. Biomass was highest
during June in the northern waters of Lake Huron (Fig. 28).
Cryptophyta
Rhodomonas lens Pasch. & Rutt.
Stoermer and Kreis (1980), in their intensive survey of southern of Lake
Huron in 1974, did not observe this species. Average abundance in 1984 and
1985 was similar (3.4 cells/mL-1983, 26.4 cells/mL-1984, 24.2 cells/mL-1985).
A bloom (maximum - 90 cells/mL) of this species was evident throughout the
lake in late April (Fig. 29).
Cyanophyta
Agmenellum quadruplicatum (Menegh.) Breb.
Huber-Pestalozzi (1938) notes that isolated specimens of A. quadrupli-
catum are found in a wide variety of habitats but that it often becomes abun-
dant in waters which are organically enriched. Stoermer and Ladewski (1976)
state that records of distribution from the Great Lakes are insufficient to
determine its range of occurrence. In southern Lake Huron, average abundance
54
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was low in 1974 (0.87 cells/mL) with a maximum bloom of 238 cells/mL
(Stoermer and Kreis 1980). Abundance in 1984 (15.4 cells/mL) was similar to
the average abundance in 1985 (29.9 cells/mL). A maximum abundance of 1,145
cells/mL (Table 29) occurred at Station 27 in June. The August bloom of this
species appeared to be restricted to southern Lake Huron (Fig. 30).
Anabaena sp.
No species of Anabaena were identified in 1985. In 1974 at least two
species, Anabaena flos-aquae and Anabaena subcylindrica were observed. In
1974 A. flos-aquae reached a densitiy as high as 55.9 cells/mL (mean - 20.6
cells/mL) in southern Lake Huron (Stoermer and Kreis 1980). Mean abundance of
all species of Anabaena in 1983 (2.1 cells/mL) and 1984 (1.4 cells/mL) was
lower than 1985 (12 cells/mL). Abundance appears to have increased in 1985
from 1983 and 1984 but generally to have decreased from 1974.
Chlorophyta
Green coccoid - ovoid
Abundance in 1983 and 1984 averaged 1.5 cells/mL. Abundance in 1985
increased to 21.8 cells/mL with one bloom reaching 123 cells/mL. If abundance
levels increase further, identification of this organism(s) is warranted.
Monoraphidiumsetiformae (Nyg.)Kom.-Legn.
This species was not observed in the intensive study of 1974
(Stoermer and Kreis 1980). Average abundance was low in 1983 (0.2 cells/mL)
and 1984 (0.9 cells/mL) compared to 1985 (22.6 cells/mL). A bloom (maximum =
164 cells/mL) was observed at Station 32 in June of 1985.
Colorless flagellates
Stelexomonas dichotoma Lack.
This species appears to be increasing in importance within Lake
Huron. Stoermer and Kreis (1980) in their intensive study of southern Lake
55
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Huron and Makarewicz (1988) in a lake-wide study did not observe this organ-
ism. Abundance in 1984 was 3.9 cells/mL. In 1985 average abundance was 21.7
cells/mL. A maximum abundance of 237 cells/mL was observed April, 1985 at
Station 6.
Historical Changes in Species Composition
The literature pertaining to phytoplankton of the offshore waters of
Lake Huron is sparse. Fenwick (1962, 1968) published some qualitative data,
and Parkos et al (1969) listed species observed. Quantitative data from a
single offshore station in 1971 exists (Munawar and Munawar 1982, Vollenweider
et al 1974) and preliminary data covering 21 stations in 1971 are partially
analyzed (Munawar and Munawar 1979). Stoermer and Kreis (1980) reported on an
extensive sampling program in southern Lake Huron including Saginaw Bay during
1974 and provided an extensive bibliography on Huron algal research. Lin and
Schelske (1978) reported on a single offshore station sampled in 1975. An
intensive study of the entire lake basin was performed in 1980 (Stevenson
1985), but only a few offshore stations were sampled.
Diatoms have been the dominant division since 1971. Dominant diatoms
in 1971 included species of Asterionella forwosa, A. gracillima, Cyclotella
comta, C. glomerata, C. ocellata, C. michiganiana, Helosira islandica and M.
granulata. In addition, species such as Fragilaria crotonensis and Tabellaria
fenestrata were common, while cryptomonads, such as Rhodomonas minuta and
Cryptomonas erosa, contributed very heavily during different seasons. The fol-
lowing similar common diatoms were observed in 1974, 1983, 1984 and 1985:
Asterionella forwosa, Cyclotella comensis, C. ocellata, Fragilaria
crotonensis, Tabellaria flocculosa and Rhizosolenia spp. Synedra filiformis
was present in 1983, 1984 and 1985 (2.1 cells/mL) but was not as common as in
the 1974 southern Lake Huron plus Saginaw Bay data (52.4 cells/mL). The lower
abundance of C. stelligera in 1983, 1984 (Makarewicz 1987, 1988) and 1985
56
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compared to 1971 (Munawar and Munawar 1979), 1974 (Stoermer and Kreis 1980)
and 1975 (Lin and Schelske 1978) was caused by the lack of sampling during mid
and late July when this species is dominant.
Both Cryptomonas erosa and Rhodomonas minuta var. nannoplanktica were
dominant in 1971, 1974, 1983, 1984 and 1985. Dominant chrysophytes in 1971
were Dinobryon divergens and Chrysosphaerella longispina. In 1983, 1984 and
1985, these two species were common along with D. cylindricum and D. socials
(Table 29). Haptophytes were also numerically abundant. In general, the
diatom Synedra filiformis decreased in abundance after 1974, while D. cylin-
dricum and D. sociale var. americanum have increased in abundance. In gen-
eral, species composition of common offshore algae has changed little since
1971.
Indicator Species
Dominant diatoms in Lake Huron in 1983, 1984 and 1985 were Rhizosolenia
sp. (R. eriensis in 1984 and 1985), Tabellaria flocculosa (biomass) and Cyclo-
tella comensis (numerically). Four species of Cyclotella (C. comensis, C.
comta, C. kuetzingiana var. planetophora and C. ocellata) represented 9.4%,
6.6% and 7.5% of the total biomass in 1983, 1984 and 1985 (Makarewicz 1987;
1988, Table 29). R. eriensis is often grouped with oligotrophic offshore
dominants even though it may occur in greater abundance in areas receiving
some degree of nutrient enrichment (Stoermer and Yang 1970). Except for C.
comensis, whose ecological affinities are poorly understood (Stoermer and
Kreis 1980), these species are associated with oligotrophic 'or mesotrophic
conditions. Tabellaria flocculosa is commonly associated with mesotrophic
conditions (Tarapchak and Stoermer 1976).
Dominant chrysophytes (1983-1985) included Dinobryon sociale var. america-
num, D. divergens and D. cylindricum, which are often associated with several
small members of the genus Cyclotella (Schelske et al 1972, 1974) included in
57
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the classical oligotrophic diatom plankton association of Hutchinson (1967) .
Dominant cryptophytes, cyanophytes and dinoflagellates were Rhodomonas mLnuta
var. nannoplanktLca, Cryptomonas erosa (not in 1983), Anacystis roontana var.
minor and CeratLum hirundinella from 1983 to 1985.
Because of the limited number of studies of the Lake Huron offshore
phytoplankton assemblage, a limited basis for evaluating the long-term effects
of eutrophication exists. The ratio of mesotrophic to eutrophic species in
Lake Huron has not changed since 1971 (Table 31). This suggests that the
trophic status of the lake has not changed.
Those studies available (Munawar and Munawar 1979, Nicholls et al 1977a,
Schelske et al 1972, 1974) indicate that the waters of northern Lake Huron
generally contain phytoplankton assemblages indicative of oligotrophic condi-
tions. The designation of the offshore waters of southern Lake Huron as
oligotrophic based on phytoplankton composition in 1983, 1984 and 1985 is not
unlike the trophic status suggested by Stoermer and Kreis (1980) for the off-
shore waters of southern Lake Huron in 1974. This agrees well with the
trophic status as determined by the biomass classification scheme of Munawar
and Munawar (1982). With a mean biomass of 0.38, 0.42 and 0.35 g/m3 for 1983,
1984 and 1985, respectively, Lake Huron would be classified as oligotrophic.
Historical Changes in Community Abundance and Biomass
Quantitative phytoplankton data exist for the offshore waters of Lake
Huron from at least 1971. The collections of Stoermer and Kreis (1980) were
from 44 stations in southern Lake Huron and Saginaw Bay. Lin and Schelske
(1978) collected from one offshore station in 1975. In both studies, phyto-
plankton were concentrated on millipore filters rather than by the settling
chamber procedure used in the 1980 (GLNPO Data Base), 1983 (Makarewicz 1987),
1984 (Makarewicz 1988) and 1985 studies. Thus, data sets are not strictly
comparable.
58
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Munawar and Munawar (1982) collected with a 20-m integrating sampler
from April to December of 1971. Because Utermohl's (1958) procedure for enu-
meration of algae was employed, these data were directly comparable to the
1980, 1983, 1984 and 1985 data sets. Unfortunately, biomass data for only one
offshore station of Lake Huron was available for 1971 (Munawar and Munawar
1979). Phytoplankton biomass between 1971, 1980, 1983, 1984 and 1985 was not
significantly different (Fig. 31). The consistency of the mesotrophic-
eutrophic ratio through time, the similarity of dominant species and the
occurrence of oligotrophic and mesotrophic indicator species suggest little
change in the trophic status of the offshore waters of Lake Huron.
LAKE HURON
Zooplankton
Annual Abundance of Zooplankton Groups
Species lists (Table A10) and summary tables of abundance (Table All) and
biomass (Table A12) are in Volume 2 - ATTACHED FICHE. The Zooplankton assem-
blage of 1985 comprised 57 species representing 34 genera from the Calanoida,
Cladocera, Cyclopoida, Mysidacea and Rotifera. The diversity of species was
similar to 1983 (58 species, 33 genera) and 1984 (53 species, 31 genera).
The Rotifera possessed the largest number of species (30) and relative
abundance (40.3%) followed by the Calanoida and Cyclopoida. The Copepoda
nauplii accounted for 30.4% of the total Zooplankton abundance (Table 32). The
Calanoida (48.5%) followed by the Cladocera (26.3%) contributed the most bio-
mass to the zooplankton community. Rotifera represented only 1.5% of the
Zooplankton biomass. Average density and biomass were 67,668 ± 9,390 (mean +
S.E.) organisms/m3 (46,230 - 1983; 55,369 ±7,176 - 1984) and 59.2 ± 7.03
mg/m3 (mean + S.E.) (27.3 ± 2.3 mg/m3 - 1984).
59
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Seasonal Abundance and Distribution of Major Zooplankton Groups
Seasonally, abundance and biomass distributions were essentially identi-
cal (Fig. 32) with abundance and biomass increasing from the spring through
the fall and decreasing precipitously on the last sampling day in November.
The maximum in abundance and biomass observed in August of 1984 (Makarewicz
1988) was not observed in 1985.
Cladocera abundance and biomass was low in the spring and fall and high
in the summer (Fig. 33 and 34). Abundance of the nauplius stage of the
Copepoda was inversely related to the abundance of the Calanoida and Cyclo-
poida; that is, abundance of the nauplius stage decreased from June onward,
and Cyclopoida and Calanoida generally increased into the autumn. Rotifera
abundance and biomass increased from the spring to mid November and then
decreased by the last sampling date in late November (Fig. 33 and 34).
Common Species
Common Crustacea species (Table 33) were arbitrarily defined as those
possessing a relative abundance of >0.1% of the total zooplankton abundance or
1.0% of the total biomass. Rotifera species were considered common if they
accounted for >1.0% of the total zooplankton abundance or biomass. Although
the number of common species were essentially identical in 1983 (22) (Makare-
wicz 1987) and 1984 (22)(Makarewicz 1988) and 1985 (21), some small differ-
ences in common species composition were evident.
Limnocalanus macrurus and Notholca squamula, common in 1985, were not
common species in 1983, while Tropocyclops prasinus mexLcanus was not common
in 1984. Mesocyclops edax and Eubosmina coregoni were common in 1983 and 1984
but not in 1985. Polyarthra remata and Leptodora kindtii were common in 1984
but not in 1985. Daphnia retrocurva, D. schodleri and D. catawba were common
in 1983 but not in 1984 and 1985. D. catawba was observed only in the zoo-
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plankton tows that included the hypolimnion (long hauls) in 1983 (Makarewicz
1987), but data from hypolimnion tows taken in 1984 and 1985 are not included
in this report.
Changes in Species Composition
Crustacean studies of the offshore waters of the Lake Huron basin are
few in number. Patalas (1972) sampled 51 stations including Saginaw Bay in
August of 1968 with a 77-um mesh net. In 1971 eleven stations on a transect
from the Straits of Mackinac to the origin of the St. Clair River were sampled
from May to November with a 64-um net (Watson and Carpenter 1974). A 64-um
mesh net was used to sample -18 stations on eight dates from April to October
of 1974 in southern Lake Huron including Saginaw Bay (McNaught et al 1980a).
The 1980 study of Evans (1983, 1986) included stations mostly from the near-
shore rather than the offshore. The 1983 sampling cruises included 10 sta-
tions sampled (64-um mesh net) for each of the three sampling dates between
August and September. In 1984 eight stations on five cruises (64-um mesh net)
from May-December 1984 were sampled.
In August of 1968, calanoids were dominated by Diaptomus sicilis, D.
ashlandi and D. minutus (Patalas 1972). These same three species were predom-
inant in 1971, 1974/75, 1983, 1984 and 1985 with the addition of Diaptomus
oregonensis in 1983, 1984 and 1985 (Table 34). Abundance of Diaptomus
ashlandi and Diaptomus sicilis appears to have increased since 1971 (Table
34). The 1974 D. minutus abundance was similar to the 1985 abundance but
higher than either the 1971, 1983 or 1984 samples. The 1971, 1983, 1984 and
1985 data were only from offshore sites, while the 1974 data included samples
from the eutrophic waters of Saginaw Bay. The oligotrophic indicator species,
Limnocalanus macrurus, appeared not to have significant changes in abundance
(Table 34), when the limited 1983 data set are excluded.
In 1971, 1974/75, 1983, 1984 and 1985, the dominant cyclopoid was
61
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Cyclops bicuspidatus thomasi (Table 34). Tropocyclops prasinus mexicanus
increased in abundance from 1971 to 1983 (Table 34). However, a notable
decline occurred from 1983 (577/m3) to 1984 (21/m3) to 1985 (72/m3), which may
be related to the differences in the timing of the fall sampling in these two
years. Mesocyclops edax appears to have increased in abundance (Table 34)
from 1971 to 1983. Abundance was lower in 1984 and 1985 than in 1983.
Cyclops vernalis, often associated with eutrophic conditions in Lake Erie, was
higher in abundance in the 1974 data. The higher abundance in 1971 may again
have been due to the inclusion of the eutrophic Saginaw Bay stations in the
1974 data set.
Dominant cladoceran species in August of 1968 were Bosmina longirostris
and Holopedium gibberum. Similarly, H. gibberum, B. longirostris and Eubos-
mina coregoni were dominant in the August-October period in 1974. Comparison
of the offshore data from 1971 with 1984 and 1985 suggests a decrease in the
abundance of Bosmina longirostris (Table 34). A comparison to the 1983 data
is not warranted because samples were taken only during the August through
October period (Makarewicz 1987).
Quantitative data on species of daphnids were not available for 1971,
but Daphnia retrocurva, Daphnia galeata mendotae and D. longiremis were com-
monly found in Lake Huron (Watson and Carpenter 1974). The dominant daphnid
species in 1983, 1984 and 1985 was D. galeata mendotae.
Evans (1985) recently reported that Daphnia pulicaria was a new species
dominating Lake Michigan. In 1983 in Lake Huron, D. pulicaria was observed to
be the third most important cladoceran, while in 1984 it dropped to fifth in
rank abundance (Makarewicz 1987, 1988). Mean station abundance increased
from north to south with a mean density of 431 organisms/m3 for stations south
of Saginaw Bay in 1983. In 1985 abundance never reached the levels of 1983
and 1984 (Fig. 35), even though it was the second most abundant daphnid.
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D. catawba was first reported in waters of Lake Huron in 1983 (Makare-
wicz 1987). This species was not considered to be either a common or a less
common species of the Great Lakes (Balcer et al 1984). It appeared
exclusively in the long hauls from Lake Huron in 1983. A maximum abundance of
1,610 organisms/m^ was observed in August at Station 12. It was not observed
in 1984 and 1985.
Bythotrephes cederstroemi was first reported by Bur et al (1986) in Lake
Huron in December of 1984. In fact, Bur et al's report of this predaceous
cladoceran species in Lake Huron is from the data base collected by GLNPO and
reported on in Makarewicz (1988). Abundance was very low with only one
observation (3.5/m-^) in December of 1984 in southern Lake Huron (Station 12).
In 1985 this species was found throughout the lake by August and November
(Table 35). Average abundance was 4.3/m-^ with a maximum density of 72/m-^ at
Station 61 in November.
Rotifera
Stemberger et al (1979) collected rotifers with a Nisken bottle at 5-m
intervals to 20m followed by 10-m intervals to the bottom of the lake at a
number of offshore and nearshore areas. Samples were pooled and filtered
through a 54-um mesh net on the vessel. The greatest abundance of rotifers in
Lake Huron in 1974 occurred in late spring and early summer (Stemberger et al
1979), a period in which samples were taken in 1984 and 1985 but not in 1983.
Comparison of these data indicate that abundant rotifer species in 1974 and
1984/1985 were Conochilus unicornis, Polyarthra vulgaris, Keratella cochlearis
and Kellicottia longispina. C. unicornis was the dominant rotifer, while K.
cochlearis was the co-dominant in 1983 to 1985 (Table 36). Keratella coch-
learis was dominant in 1974.
Evans' (1986) study of mostly nearshore areas suggests a difference in
dominant rotifer species between the offshore and nearshore waters. Dominant
63
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rotifer species in Evans' study included in descending rank: Keratella coch-
learLs, Kellicottia longLspLna, Synchaeta sp. and Conochilus unicornis. Poly-
arthra vulgarLs and Conochilus unicornis, which were co-dominant in the
offshore waters in 1974, 1983, 1984 and 1985, were less abundant in the
nearshore waters. These differences in horizontal distribution of zooplankton
are expected in Lake Huron and are affected by the physical limnology of the
lake (McNaught et al 1980a). For example, in the warmer inshore areas,
cladocerans grow best, while calanoids tend to be found in offshore waters
(McNaught et al 1980a). Nearshore waters are also influenced by the movement
of the zooplankton-rich eutrophic waters of Saginaw Bay into the nearshore
zone south of the Bay. In general, inshore zooplankton densities are greater
than offshore densities (McNaught et al 1980a).
Geographical Abundance and Distribution of Zooplankton Groups
The mean station zooplankton abundance and biomass decreased from
Station 61 in the north to Station 32, opposite of Saginaw Bay and then
increased in southern Lake Huron (Fig. 36 and 37). The Cladocera, Calanoida,
Cyclopoida, Rotifera and the nauplius stage of the Copepoda all followed this
same pattern of decreasing abundance/biomass southward from the north to Sta-
tion 32 and then an increase southward into Southern Lake Huron. A similar
geographical abundance and biomass pattern was observed in 1983 and 1984
(Makarewicz 1987, 1988). McNaught et al (1980a) observed abundance increases
of the cyclopoid copepodites, C. bicuspidatus and T. prasinus, north to south
in southern Lake Huron.
An interesting trend exists in the 1983 and 1985 data sets. Total
zooplankton abundance from Station 12 increased northward with the exception
of Station 32 in 1983 and 27 in 1985. Station 32, located northeast, and
Station 27, located east of the mouth of Saginaw Bay, would appear to be too
far offshore to be influenced by the higher abundances in the Bay. However,
64
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Stoermer and Kreis (1980) have observed midlake stations in southern Lake
Huron to be affected by populations of phytoplankton from Saginaw Bay in 1974.
Although the transport of eutrophication-tolerant algal populations into Lake
Huron from Saginaw Bay has been mitigated in recent years (Stoermer and Ther-
iot 1985), the transport of zooplankton could still take place.
A number of zooplankton species possessed horizontal distributions that
varied along the north-south axis. These, differed between 1983, 1984 and
1985. In 1983 and 1984, Diaptomus minutus abundance was lower in the northern
portion of the lake, but not in 1985 (Fig. 38). Geographical abundance of D.
minutus, D. ashlandi and D. sicilis were similar in 1985; abundance was
higher at Stations 61 and 54 in the north and Station 9 in the south (Fig.
38). Geographically, no obvious abundance pattern of D. sicilis and D. ash-
landi were obvious in 1983 and 1984.
Abundance of Daphnia pulicaria was higher in southern Lake Huron in 1983
but not in 1984 and 1985 (Fig. 39). Yet Holopedium gibberum abundance was
consistently higher at the northern stations from 1983 to 1985. The rotifer,
Conochilus unicornis, also had a geographical abundance pattern restricted to
northern Lake Huron (Fig. 40). Notholca squamula and Synchaeta sp. had
higher abundances in southern Lake Huron in 1984 and 1985 (Fig. 41). Daphnia
galaeta mendotae, Kellicottia longispina, Keratella cochlearis and Gastroper
stylifer had no consistent geographical pattern from 1983 to 1985.
Indicators of Trophic Status
The calanoid/cyclopoid plus cladoceran ratio (the plankton ratio) has
been employed as a measure of trophic status in the Great Lakes (Gannon and
Stemberger 1978, McNaught et al 1980a). Calanoid copepods generally appear
best adapted for oligotrophic conditions, while cladocerans and cyclopoid
copepods are relatively more abundant in eutrophic waters. Using this ratio,
McNaught et al (1980a) identified the offshore waters of southern Lake Huron
65
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to have a higher quality water than the nearshore waters. Because the 1983,
1984 and 1985 samples were all from the offshore, no such comparison could be
made. However, the 1985 and the 1983 and 1984 plankton ratio was high and
variable from north to south (Table 37). The far northern station (Station
61) and perhaps the far southern station (Station 6) appear to have a lower
water quality, as indicated by the plankton ratio. A comparison of the 1983,
1984 and 1985 mean phytoplankton ratio suggests a lower quality of water at
Stations 6 and 9 and perhaps at Station 61. Water chemistry data from 1987
and 1988 suggest these southern stations have higher chloride, sulfate, total
phosphorus and turbidity levels and lower silica levels than the rest of the
lake (Makarewicz 1987, 1988).
Station 61 might be influenced by waters from Lake Michigan. The
plankton ratio at Station 61 in Lake Huron is comparable more to northern Lake
Michigan than the rest of Lake Huron (Table 38). The physical transport of
plankton populations by water currents from Lake Michigan into Lake Huron
through the Straits of Mackinac has been demonstrated (Schelske et al 1976).
A similar conclusion was arrived at in 1984 (Makarewicz 1988).
Species considered to be indicators of eutrophic waters were rare
compared to the Western Basin of Lake Erie and possessed limited distrib-
utions. Interestingly, the eutrophic indicator Filinia longiseta, was
observed at only three sites at the extreme southern (52/m^-Station 6) and
northern stations (331/m3-Station 61) and just east of the eutrophic waters of
Saginaw Bay (317/m^-Station 27). Brachionus spp. was not observed, while
Trichocerca multicrinis (91/m^) another eutrophic species was found only at
Station 90 in southern Lake Huron.
The rotifer community in 1983 (Makarewicz 1987), 1984 (Makarewicz 1988)
and 1985 was dominated by Polyarthra vulgaris, Keratella cochlearLs, Conochi-
lus unicornis and Kellicottia longispina. This association has been consid-
66
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ered to be indicative of an oligotrophic lake (Gannon and Stemberger 1978).
The offshore abundances of Holopedium gibberum, Conochilus unicornis and
Kellicottia longispina were greater north of Saginaw Bay than south of it
(Table 39) suggesting better water quality in northern Lake Huron. H. gib-
berum has been reported as an indicator of oligotrophic lakes in Sweden (Pej-
ler 1965) but was widely distributed in both oligotrophic and eutrophic waters
in the Laurentian Great Lakes region (Gannon and Stemberger 1978).
The low zooplankton abundance, compared to that of Lake Erie (Table 8),
the presence of the oligotrophic rotifer association, the domination of the
calanoids, and the fairly abundant presence of the oligotrophic Diaptomus
sicilis (McNaught et al 1980a) suggest oligotrophic offshore waters for Lake
Huron in 1983, 1984 and 1985.
Historical Trends in Abundance
Offshore crustacean zooplankton data collected with similar mesh size
nets (64 um) exist for Lake Huron. The 1970 study (Watson and Carpenter 1974;
88 collections) sampled the whole lake, while the 1974/75 work (McNaught.et al
1980a; 46 collections) was from southern Lake Huron. A comparison of the
cruise averages for Crustacea (excluding nauplii) (Fig. 42) suggests changes
in abundance from 1970 to 1985. However, these differences are not statis-
tically significant (P<0.05). A similar conclusion of no change in trophic
status since 1970 was reached with phytoplankton abundance.
Stemberger et al (1979) collected Rotifera samples from 44 stations in
southern Lake Huron in 1974. Samples were taken with a Nisken bottle at 5-m
intervals to 20 m and at 10-m intervals below that. After collection, samples
were immediately pooled and filtered through a 54-um net. In 1983 (Makarewicz
1987), 1984 (Makarewicz 1988) and 1985, a vertical tow (64-um net) was taken
from 20 m to the surface. Both studies are not directly comparable in that
Stemberger's et al (1979) work represented the entire water column, while the
67
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1983 and 1984 studies were basically samples from the epilimnion. The 1974 ,
1984 and 1985 sampling periods were not significantly different. A compari-
son of mean station seasonal abundance suggests that the spring abundance in
1984 and 1985 was lower than in 1974 (Fig. 42). Also, abundance of major
species was lower in 1983, 1984 and 1985 than in 1974 (Table 36). This
difference in abundance is related to two things: (1) Stemberger et al
(1979) used a smaller meshed net which gives a more accurate quantitative
sample and thus a higher abundance (Likens and Gilbert 1970); and (2) two
different segments of water were sampled and compared. For example, Makare-
wicz and Likens (1979) observed higher abundances and different species compo-
sition between the hypolimnion and epilimnion of Mirror Lake, New Hampshire.
Trophic Interactions
Within the offshore, there appears to be few changes that could be
attributed to nutrient control. Phytoplankton biomass and zooplankton abun-
dance of the offshore waters of Lake Huron in 1971, 1980, 1983, 1984 and 1985
are not significantly different. In general, offshore species composition of
phytoplankton has changed little since the early 70's. However, there has
been a significant lake-wide change in species composition of zooplankton.
Prior to 1983, there are no records of Daphnia pulicaria in Lake Huron. From
1983 to 1985, this species was the third to fifth most abundant cladoceran in
Lake Huron. The appearance of the large D. pulicaria in the Great Lakes is
generally attributed to a release from size-selective predation of forage fish
in Lake Michigan (Scavia et al 1986, Makarewicz 1988) and Lake Erie (Makare-
wicz 1988). In 1984 D. pulicaria abundance was negatively correlated with
decreased phytoplankton abundance, which suggested an additional grazing
pressure on phytoplankton stocks in Lake Huron. This may have influenced the
mean size of the phytoplankton. When abundance of Daphnia increased during
the summer of 1983, 1984 and 1985, the mean size of the phytoplankton commu-
68
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nity decreased (Fig. 44-47). In the autumn, the high negative correlation
between phytoplankton abundance and D. pulicaria and Calanoida abundance
(Table 40) suggests the diminished size of the phytoplankton community is
related to grazing of D. pulicaria and calanoids. The addition of the exotic
cladoceran species Bythotrephes to the zooplankton community may cause further
changes in both the zooplankton and the phytoplankton. Bythotrephes has been
implicated in causing a decrease in Daphnia populations in Lake Michigan (Leh-
man 1988).
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LAKE ERIE
Phytoplankton
The species lists (Table A13) and summary tables of abundance (Table
A14) and biovolume (Table A15) are in Volume 2 - Data Report (ATTACHED FICHE).
A summary of water chemistry paramters is presented in Table 8.
Picoplankton
Picoplankton abundance in 1985 (mean - 22,988 cells/mL; maximum of 1.4 x
105 cells/mL) was lower than in 1983 (33,171 cells/mL) and 1984 (38,075
cells/mL). On a numerical basis, the picoplankton represented 83.6% of the
total cells and 1.2% of the total biomass. Historically the picoplankton have
not been considered in evaluations of the plankton community of Lake Erie.
Their high abundance tends to distort relative abundance values and does not
allow reasonable comparisons with the historical data. For this reason, they
are not considered further in this discussion.
Annual Abundance of Major Algal Groups
The phytoplankton assemblage of 1985 was comprised of 369 species repre-
senting 101 genera (Table 41). The number of species and genera observed
annually have changed only a few percentage points from the 1983 to 1985. The
total number of species in 1983 (372), 1984 (356) and 1985 (369) was consider-
ably higher than the 125 to 150 species observed in all basins in 1970 (Muna-
war and Munawar 1976).
In 1985, as in 1983 and 1984, the diatoms possessed the greatest number
of species (162, 43.9% of the total species) and biovolume (63.3%) of the
total) (Tables 41 and 43), while the second largest number of species (115)
was observed for the Chlorophyta (Table 41). These diversity observations
represent significant changes from 1970, when the Chlorophyta possessed the
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largest number of species (78) and only 21 diatom species were observed (16.3%
of the species) (Table 42). However, diatoms were still the dominant group in
1970 accounting for 53% of the biomass (Munawar and Munawar 1976).
Highest relative densities were attained by the Cyanophyta (25.8%) in
1985, as well as in 1983 and 1984. In 1983 and 1985, the Chlorophyta had the
second highest biomass, while in 1984 they were fourth, slightly lower than
the Pyrrophyta and Cryptophyta (Table 43).
Seasonal Abundance and Disbribution of Major Algal Groups
The average density and biomass for the sampling period were 4,483
cells/mL (6,187 cells/mL, 1983; 5,331 cells/mL, 1984) and 1.22 g/m3 (1.35
g/m3, 1983; 0.86 g/m3, 1984) (Table 44). Seasonally, abundance (cells/mL)
peaked in late April, leveled off during August before reaching a minimum in
late November. The fall/early winter secondary maximum observed in 1984 (Ma-
karewicz 1988) was not observed in 1985 (Fig. 48a).
A different pattern emerged from the seasonal biovolume totals. Similar
to the seasonal abundance pattern, a peak in biomass occurred in April. How-
ever, biovolume was low in early August followed by a major peak in biomass
later in August (Fig. 48b). A second peak in biomass occurred in late
November (Fig. 48b). Except for the lower biomass in 1983, 1984 and 1985, the
timing of the spring and autumn biomass peaks is similar to that observed in
1970 (Munawar and Munawar 1976).
The biomass peak during the summer was due to a bloom of Actinocyclus
normanii in the Western Basin. During the summer cruise, biomass for the
Western Basin was high (3.04 g/m3) compared to the Central (0.80 g/m3)and
Eastern Basin (mean - 0.64 g/m3). A. normanii accounted for as much as 29%
of the biomass in the Western Basin on this cruise. It was not abundant in
the Central Basin and was not observed on this cruise in the Eastern Basin.
As in 1983 and 1984, diatoms were the dominant group throughout 1985
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(62.3% of the total biovolume). However, seasonally their importance varied
considerably (Fig. 49) but in a pattern similar to 1983 and 1984 (Makarewicz
1987, 1988). Diatoms were dominant during the first cruise in April (-60% of
the biovolume) and became co-dominants with the Chlorophyta in August. A
similar succession and relative importance were observed in 1970 (Munawar and
Munawar 1976) and 1983 and 1984 (Makarewicz 1987 and 1988).
Geographical Abundance and Distribution of Major Algal Groups
Abundance for the sampling period varied geographically and was similar to
the 1983 and 1984 observations (Makarewicz 1987 and 1988). Abundance gener-
ally decreased eastward (Fig. 50). The Western Basin possessed a greater
biomass (1.62 g/m3, S.E.-.27) than the Central Basin (1.38 g/m3, S.E.-.14) and
the Eastern Basin (0.54 g/m3, S.E.-.08) (Table 44). The considerably greater
abundance of the Western Basin was attributed to the picoplankton (Fig. 50).
However, the higher biomass of the Western Basin (Table 42) was due to the
greater abundance and biomass of the Bacillariophyta, Cyanophyta, Chlorophyta,
Cryptophyta and Chlorophyta in the Western Basin (Fig. 51).
As in 1983 and 1984, the general pattern of higher abundance in the
Western Basin was observed on each sampling date (Fig. 52). In 1983 at least
12 common species had higher abundances in the Western Basin (Makarewicz
1987). Similarly in 1984 and 1985, many of the same species had geographical
abundance pattern with maxima in the Western or Central Basin (Table 45). A
difference in species abundance from the various basins of Lake Erie has been
documented previously (Munawar and Munawar 1976, Davis 1969b).
Regional and Seasonal Trends in the Abundance of Common Species
The definition of common species (Makarewicz 1987, 1988) has been revised
to accommodate the removal of the picoplankton. Common species (Table 46 -
48) were arbitrarily defined as those possessing a relative abundance of >0.5%
of the total cells or >0.5% of the total biovolume. Using the new definition,
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the data from 1983 (Table 46) and 1984 (Table 47) were revised. Twelve new
common species were observed in 1985 from 1983 and 1984 (Table 49). A species
by species description of autecology and regional and seasonal trends are not
warranted here and can be referred to in Makarewicz (1987, 1988). Only new
common species are discussed below.
Bacillariophyta
Skeletonema potamos (Weber) Hasle & Evens
In Europe, this species is sometimes present in large quantities in
eutrophic lakes and appears to be favored by slightly saline conditions (Hus-
tedt 1930 cited in Stoermer and Ladewski 1976). Although this is a new common
species in 1985 compared to 1983 and 1984, abundance was slightly higher in
1983 (23.7 cells/mL) compared to 1985 (22.7 cells/mL). This species was prev-
alent in the Western Basin in 1985 and was not observed in the Central and
Eastern Basins. This species does appear to be a eutrophic indicator.
Suriella biseriata var. bifrons
This large species (96um) was not observed in 1984, while average cruise
densities were <0.1 cells per mL in 1983. In 1985 abundance averaged only
0.1 cell/mL with a maximum abundance of 7 cells/mL at Station 55 in the West-
ern Basin in November.
Rhizosolenia eriensis H.L. Sm.
Hohn (1969) concluded that R. eriensis was present in large numbers in
the Western Basin prior to 1930, had disappeared and was only occasionally
observed through the 60's. Vorce (1882) in a non-quantitative study noted R.
eriensis to be very abundant from February to May in the 1880's. Munawar and
Munawar (1976) categorized this species as a "less common" (less than 5% of
the total phytoplankton biomass) in 1970.
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In 1985 this mesotrophic species had a high biomass in the Western Basin
in April (9.1% of the total phytoplankton biomass in Cruise 1 and 2) and
November (20.6% in Cruise 5) (Fig. 53). In 1983 and 1984, this species was
not considered to be common even though abundance was higher in 1983 than in
1985 (Table 48). The high biomass in 1985 was due to a much larger size of
this species than in 1983. In 1985 only two length and width measurements
were taken. This paucity of measurements may bias the data and may affect
the interpretation of the data.
Cyanophyta
Anabaena flos-aquae
This species was frequent during summer in the Western Basin in 1970
(Munawar and Munawar 1976). Average whole lake abundance in 1983 (2.1
cells/mL) and 1984 (0.3 cells/mL) was considerably lower than the 1985 average
(36 cells/mL). Although this eutrophic species was observed in all basins
during the summer of 1985 (range - 0 to 200 cells/mL), maximum abundance was
observed in a bloom in the Western Basin (Station 57) during August that
reached 3,199 cells/mL. This one bloom is the cause of this species being
designated a common species in 1985.
Anabaena spiroides
As Anabaena flos-aquae, this eutrophic species was frequent in the
Western Basin during the summer of 1970 (Munawar and Munawar 1976). Average
abundance was substantially higher in 1985 (68.2 cells/mL) compared to 1983
(12.1 cells/mL) and 1984 (25.3 cells/mL). In fact, this species was observed
only once in 1985 at station #57 (abundance - 6,283 cells/mL).
Pyrrophyta
Amphidinium sp.
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This flagellate was a dominant species in the Central Basin during the
spring accounting for 9.7% of the total phytoplankton biomass (Fig. 54).
Although abundances in 1983 and 1985 were similar, biomass was considerably
higher in 1985 due to the considerably larger length in 1985 ( 19.1 urn - mean
length) than in 1983 (14.6 urn - mean length) (Table 50). 59 size measurements
were made between 1983 and 1985. Thus the increase in biomass appears to be
real and could be due to a new species. Amphidinium was abundant, but not
common (> %5 of the total biomass), in the Eastern Basin in 1970 (Munawar and
Munawar 1976). Prescott (1964) comments that this genus is mostly marine but
may be found in brackish water or in fresh water near the sea.
Chlorophyta
Botryococcus sp.
This organism was not observed in 1983 or 1984. Only one occurrence of
this species (1,554 cells/mL) was noted in 1985 at Station 30 in November.
Scenedesmus quadricauda
Abundance of this species has increased slightly from 1983 (mean - 11.3
cells/mL) and 1984 (14.4 cells/mL) to 1985 (22.9 cells/mL). A bloom (311
cells/mL) of this species occurred in November, 1985 at Station 55 in the
Western Basin. Munawar and Munawar (1976) in the intensive study of Lake Erie
in 1970 did not list this species as common.
Oeogonium sp.
Stoermer and Ladewski (1976) have found large populations only in highly
eutrophied areas such as western Lake Erie, Saginaw Bay of Lake Huron and a
few localities in Lake Ontario. In 1985 Oedogonium was a dominant species in
the Central Basin but in not the Western Basin (Fig. 55). In the Central
Basin, it accounted for 11.5% of the total phytoplankton biomass in Cruise 4
75
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(August). Similarly in August of 1970, this species was prevalent (10.0 % of
the total biomass) in the Central Basin (Munawar and Munawar 1976). Abundance
in 1983 and 1984 was lower than in 1985 (Table 50).
Changes in Species Composition
Davis (1969b) has reviewed the extensive earlier work on Lake Erie, while
Munawar and Munawar (1982), Gladish and Munawar (1980) and Nicholls (1981)
discuss the more recent material. Verduin (1964) has concluded that before
1950 the phytoplankton of western Lake Erie had been dominated by Asterionella
formosa, Tabellaria fenestrata and tielosira ambigua, whereas in 1960-61 the
dominant forms had been Fragilaria capucina, CoscLnodiscus radiatus (probably
Actinocyclus normanii f. subsalsa) and Melosira binderana (-Stephanodiscus
binderanus).
As with Munawar and Munawar (1976), the 1983 study (Makarewicz 1987)
confirmed Verduin's (1964) observations that those species dominant before
1950 (A. formosa, T. fenestrata and M. ambigua) continued to be less important
in the 1983 collections. Actinocyclus normanii f. subsalsa (=Coscinodiscus
rothii) and Stephanodiscus binderanus were dominant in 1961-62 (Verduin 1964)
and in 1970 (Munawar and Munawar 1976). In 1983 Actinocyclus normanii f.
subsalsa was only the fifth most prevalent diatom and in 1984 was not even a
common species (Makarewicz 1988). In 1985 it was the second most prevalent
diatom on a biomass basis (Table 48).
Fragilaria capucina was a dominant in 1961 but not in 1970. In 1983 and
1984, Fragilaria capucina was the second most prevalent diatom in the Western
Basin and in the entire lake (Makarewicz, 1987; 1988). In 1985 F. capucina
was the dominant diatom on a numerical basis with an average abundance of 188
cells/mL.
Dominant species in 1983, 1984 and 1985 were Stephanodiscus niagarae,
Fragilaria crotonensis, Fragilaria capucina, Cosmarium sp., Cryptomonas erosa,
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Rhodomonas var. nannoplanktica, OscillatorLa subbrevis, and Ceratium hirundi-
nella (Table 46-48). Asterionella formosa, Coelastrum microporum, Oscillato-
ria subbrevis, Anabaena sp., Aphanizomenon flos-aquae and Peridinium sp. were
also dominant occasionally from 1983 to 1985.
Asterionella formosa has not been prevalent in Lake Erie since prior to
1950. Verduin (1964) stated that before 1950 Asterionella formosa was a domi-
nant species in western Lake Erie. Similarly, Davis (1969b) reported Asterio-
nella as the dominant organism in the spring pulse of the Central Basin prior
to 1949. Numerous workers (Hohn 1969, Nichols et al 1977b, Munawar and
Munawar 1976, Gladish and Munawar 1980) reported a decline in A. formosa after
1950. The low abundance of A. formosa was apparent into 1983 (mean - 8.7
cells/mL, Makarewicz 1987).
Average density was 73.4 cells/mL in 1984 representing 5.6% of the
biomass (Makarewicz 1988). Maximum density in March of 1938 was 96.6 cells/mL
with a March mean of 553 cells/mL (Hohn 1969). No samples were taken in March
of 1984, but the April average was 226 cells/mL (maximum abundance - 942
cells/mL in May). In 1984 during the three cruises in April and May, Asterio-
nella formosa was the dominant spring species on a biomass basis and the
second most important diatom on a numerical basis (Table 51). In 1985 average
density was only 15.4 cells/mL.
Although occurrences of common and dominant species in 1970, 1983, 1984
and 1985 were similar, dramatic decreases in abundance of these species were
evident (Table 52). This pattern was evident in all three basins.
Indicator Species
Munawar and Munawar (1982) concluded that the species of phytoplankton
found in 1970 usually occurred in mesotrophic and eutrophic conditions. Com-
mon species in 1983 included eutrophic indicators (Fragilaria capucina, Melo-
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sira granulata, Peridinium aciculiferum, Pediastrum simplex, Scenedesmus
ecornis) and mesotrophic indicators (Stephanodiscus niagarae, Fragilaria
crotonensis, Tabellaria flocculosa) (Makarewicz 1987). A similar set of major
common species occurred in 1984, including the mesotrophic indicators Stepha-
nodiscus niagarae, Fragilaria crotonensis and Tabellaria flocculosa and the
eutrophic indicators Fragilaria capucina, Peridinium aciculiferum and
Pediastrum simplex. The eutrophic indicators Melosira granulata and Scenedes-
mus ecornis, common in 1983, were present in 1984 and 1985 but were not common
(>0.1% of the total cells or >0.5% of the total biovolume). Interestingly, a
mesotrophic indicator, Melosira islandica, not common in 1983, was common in
1984, accounting for 4.1% of the total biomass, but not common in 1985 (Table
48).
Evidence of a shift in trophic status since 1970 is provided by a
comparison of distribution of dominant diatom indicator species in 1970, 1983,
1984 and 1985 (Table 53). The number of dominant eutrophic species has
decreased, while the number of dominant mesotrophic species has increased.
The mesotrophic-eutrophic ratio suggests a shift to mesotrophic conditions for
the Western Basin.
Historical Changes in Community Biomass
Between 1927 and 1964, a large and consistent increase in the total
quantity of phytoplankton of the Central Basin had occurred (Davis 1964,
1969b). Nichols et al (1977b) observed that a decline in nearshore phyto-
plankton of the Western Basin occurred between 1967 and 1975. However, Glad-
ish and Munawar (1980) discounted this finding and suggested that no realistic
conclusion could be drawn from a comparison of biomass between 1970 and 1975.
The mean basin weighted biomass was 3.4, 1.49, 0.8 and 1.26 g/m^ in
1970, 1983, 1984 and 1985, respectively. A 56 to 76% reduction in algal
biomass has occurred in offshore waters of Lake Erie from 1970 to 1983 - 85.
78
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This reduction in biomass is evident for all seasons of the year (Fig. 56).
The historically highly productive Western Basin (Munawar and Burns 1976) has
had a steady decrease in biomass from 1958 to 1985 (Fig. 57). Similar
decreases in phytoplankton biomass were observed in the Central and Eastern
Basin (Fig. 58). Since 1975, chlorophyll concentrations have decreased in all
basins (Fig. 59). Phosphorus levels have also decreased in all basins (Fig.
60). Between 1970 and 1983-1985, dramatic reductions in maximum biomass of
common species have occurred (Table 52). For example, in the nuisance species
Aphanizomenon flos-aquae, a 96% reduction in the maximum biomass observed has
occurred since 1970. Stephanodiscus binderanus, a eutrophic indicator spe-
cies, has decreased in biomass by 90% in the Western Basin. Similary, Fragi-
laria capucina, another eutrophic indicator, has decreased (99% reduction)
dramatically within the phytoplankton community.
Based on maximum biomass concentrations (Vollenweider 1968), Munawar and
Munawar (1976) classified the Western Basin as highly eutrophic, the Eastern
Basin as mesotrophic and the central basin between the mesotrophic and eutro-
phic conditions. Using the same classification system of Vollenweider (1968):
Ultra-oligotrophic <1 g/m^
Mesotrophic 3 to 5 g/m^
Highly eutrophic >10 g/m^
the Western Basin (maximum biomass - 5.4 g/m^, Station 57, August) in 1985
would be between mesotrophic and eutrophic, the Central Basin (maximum biomass
=4.5 g/m3, Station 36, November) would be mesotrophic and the Eastern Basin
(maximum biomass =1.6 g/m-*, Station 10, April) would be between oligotrophic
and mesotrophic. Similarly, the classification scheme of Munawar and Munawar
(1982), based on mean phytoplankton biomass, suggests an improvement in water
quality between 1970 and 1983-85 (Table 54) in all basins of Lake Erie. Sim-
ilar conclusions were arrived at using the 1984 data base (Makarewicz 1988).
79
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LAKE ERIE
Zooplankton
Annual Abundance of Zooplankton Groups
The species list (Table A16) and summary tables of abundance (Table A17) and
biomass (Table A18) are in Volume 2 - Data Report (ATTACHED FICHE). Average
density and biomass (mean + S.E.) for the study period was 221,577 ± 26,988
(159,615/m3 ± 34,000 - 1984; 288,341/m3 ± 27,443 - 1983) and 105.8 ± 9.9
mg/ml (53.6 ±6.2 mg/m3 - 1984) (Table 44). The zooplankton assemblage of
1985 comprised 89 species representing 44 genera from the Calanoida, Cladoc-
era, Cyclopoida, Harpacticoida and the Rotifera. Compared to 1983 (37 genera,
66 species) and 1984 (39 genera, 81 species), a 25.8% and a 8.9% increase,
respectively, in the number of species was observed. This difference was
attributable to an increase in the number of rotifers from 1983 to 1984 (34 to
48, 49 in 1985). The increase in species numbers from 1984 to 1985 is
generally due to an increase in cyclopoid species (4 to 9).
The Rotifera possessed the largest number of species (49) and relative
abundance (70.8%) followed by the Cyclopoida and Calanoida. The nauplius
stage of the Copepoda accounted for 15.2% of the total zooplankton abundance
(Table 55). On a biomass basis, the importance of the Rotifera dropped to
5.5% of the zooplankton biomass because of their small size, while the Cladoc-
era contributed 35.1% of the biomass (Table 55). The relative abundance and
biomass patterns were fairly consistent over the past three years (Table 55).
Seasonal Abundance and Distribution of Major Zooplankton Groups
Seasonally, abundance and biomass distribution (Fig. 61) was greatest in
August than in other times of the year. Similar seasonal patterns in abun-
dance and biomass were observed in 1983 (Makarewicz 1987) and 1984 (Makarewicz
1988). In 1983 and 1984, a second peak in abundance was observed in the
spring generally due to a pulse in rotifer populations.
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The 1985 seasonal abundance pattern (Fig. 62) of the various zooplankton
groups was similar to 1983 and 1984 (Makarewicz 1987, 1988). Cladocera and
Calanoida abundance was low in the spring, peaked in early August and
decreased the rest of the year. Similar to 1983 and 1984, Cyclopoida abun-
dance varied little (Fig. 62). Unlike 1983 and 1984, Rotifera abundance did
not peak in the spring but a population peak was observed in August as other
years (Fig. 62). The rotifer peak in 1983 and 1984 was in May, a month not
sampled in 1985. The biomass seasonal distribution pattern of the major zoo-
plankton groups generally mimicked the abundance pattern (Fig. 63).
Geographical Abundance and Distribution of Zooplankton Groups
Geographically, zooplankton abundance was similar to 1983 and 1984 (Maka-
rewicz 1987, 1988), with abundance being higher in the Western Basin and
decreasing easterly to Station 78 (Fig. 64). Within the Western Basin,
abundance and biomass peaked at the far eastern station (Station 55), rather
than the the most western station (Station 60) as in 1985. Similar to 1984,
abundance increased east of Station 78 but remained low in the Eastern Basin
(Stations 15 and 9). Similar to 1984, the Rotifera were the cause of the
high zooplankton abundance in the Western Basin although the Copepoda nauplii
also had a slightly higher abundance in the Western Basin (Stations 60, 57,
55) (Fig. 64).
In 1984 biomass was similar in all three basins of Lake Erie (Fig. 60a,
Makarewicz 1988). In 1985 this was not the situation. Average biomass was
higher in the Central Basin than in the Western or Eastern Basin (Table 44).
The low biomass in the Western Basin compared to the Central Basin was due to
a lower biomass at Station 60 of all zooplankton groups (Fig. 65). Similarly
in 1985, a low Cladocera abundance was observed at Station 60 in 1983 and 1984
(Makarewicz 1987, 1988).
Cladocera abundance peaked at Station 55 and generally decreased east-
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ward through the Central Basin to Station 31 (Fig. 64). At Station 31 a major
peak in Cladocera biomass occurred; it was caused by a bloom of Daphnia
galaeta mendotae (Fig. 65). In the Eastern Basin, Cladocera biomass (Fig. 65)
was similar to the Central Basin except for Station 31. Cyclopoida and Cala-
noida abundance was higher in the Central and Eastern Basin as compared to the
Western Basin.
Compion Taxa
Common Crustacea species (Table 56) were arbitrarily defined as those
possessing a relative abundance >0.1% of the total abundance or 1.0% of the
total biomass. Rotifera species were considered common if they accounted for
>1.0% of the total zooplankton abundance or biomass. The number of common
species in 1983 (25), 1984 (27) and 1985 (28) was similar, but there were
changes in composition of the common species (Table 57). The most notable
difference was the absence of Daphnia pulicaria from the common species list
in 1985. This species was common in 1984 but not in 1983 or 1985. Much of
the variability in common species was due to changes in common rotifer species
from year to year. A group, such as rotifers, that typically have a short
lifespan and explosive population growth over a short period would have dif-
ferent species succeeding each other very quickly. A few weeks difference in
the sampling schedule, similar to what occurs each year with the EPA
monitoring network, would result in different rotifer species being common as
observed.
Changes in Species Composition
Brooks (1969) suggested that a shift in the Lake Erie cladoceran assem-
blage was evident by 1948-49 with smaller cladocerans, such as Daphnia galeata
mendotae, D. retrocurva and Diaphanosoma sp., being more abundant than in
1938-39. In 1970 the most commonly found Daphnia species were D. retrocurva,
D. galeata mendotae and D. longiremis (Watson and Carpenter 1974); Bosmina
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longirostris and Eubosmina coregoni were more abundant (Watson and Carpenter
1974). Predominant cladoceran species in 1983 were small forms similar to
those observed in 1970. In 1983 the predominant Cladocera in descending order
were Eubosmina coregoni, Daphnia galeata mendotae, Bosmina longirostris, Dia-
phanosoma leuchtenbergianum and Chydorus sphaericus (Makarewicz 1987). In
1984, on a numerical basis, the predominant Cladocera were Daphnia galaeta
mendotae, Eubosmina coregoni, Bosmina longirostris, Daphnia pulicaria, Daphnia
retrocurva and Chydorus sphaericus (Makarewicz 1988). In 1985, on a numer-
ical basis, the predominant Cladocera in descending order were Eubosmina core-
goni, Daphnia galaeta mendotae, Bosmina longirostris, Daphnia retrocurva,
Diaphanosoma sp. and Chydorus sphaericus (Table 55). Between 1983 and 1985,
essentially the same dominant species, with the exception of D. pulicaria,
were present with minimal change in rank abundance. These small changes in
rank order may be attributed to the difference in the seasonal sampling pat-
tern between 1983 and 1985.
On a biomass basis, Daphnia pulicaria (mean biomass - 7.5mg/m^) was the
dominant Cladocera for the lake, with a major bloom in August of 1984 (Makare-
wicz 1988). Although D. pulicaria was present in August of 1985, average
lakewide biomass was low (0.7mg/m3) compared to 1984 (7.8 mg/m^). Instead in
1985, Daphnia galaeta mentodae was the dominant Cladocera (on a biomass
basis) and was most prominent in the Central and Eastern Basins (Fig. 66).
Average biomass for the study period was 13.0 mg/m^ with a maximum biomass of
23.7 mg/m^ observed at Station 31 in August.
A rare species in the offshore waters of the Western Basin in 1929-30
(Tidd 1955), Chydorus sphaericus was a prominent constituent in the 1950's
(Davis 1962) and in 1970 with a higher abundance in the Western Basin (Watson
and Carpenter 1974). In 1983, 1984 and 1985, this species contributed 0.2%,
0.1% and 0.3%, respectively, of the total abundance (Makarewicz 1987, 1988)
83
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(Table 56). Chydorus sphaericus has established itself as a common species in
Lake Erie and is prevalent in the Central Basin (Fig. 67 and 68).
Although not a common species, the discovery of Bythotrephes ceder-
stroemi in Lake Erie has attracted considerable attention from Great Lakes
researchers (Bur et al 1986, Berg and Carton 1988). Its large size (>10 mm)
and its potential to effectively crop down Daphnia populations (Lehman 1988)
and thus affect lower trophic levels, make it a species of interest. Bur et
al (1986) first reported this organism in Lake Erie in the stomachs of yellow
perch and walleye and from vertical zooplankton hauls. The vertical zooplank-
ton hauls cited, but not presented in Bur et al, are in fact the data pres-
ented here. B. cederstroemi was observed throughout the entire lake during
the October cruise (Fig. 69). Average density was 4.5/m3 with a maximum
density of 72/m3.
In Europe Bythotrephes sp. is found typically in the plankton from May to
December (Andrew and Herzig 1984, Nauwerk 1963, Hakkari 1978, de Bernadi and
Canali 1975). Although first observed in the autumn in Lake Michigan (Evans
1988), it was detected in June with highest abundance in July and August in
the second year of occurrence (Evans 1988, Lehman 1988). In addition to Lake
Erie, Bythotrephes was observed only during the autumn in Lakes Huron and
Ontario (Lange and Cap 1986, Makarewicz 1988, Makarewicz In Press). The
autumn predominance of Bythotrephes may be related to differences in the for-
age fish base of Lake Michigan compared to Erie and Ontario and to relaxation
of predator pressure during the autumn (Makarewicz In Press).
The prevalence of Cyclops vernalis has changed over the past 50 years. In
the 1930's, C. vernalis was found only in the extreme western end of Lake Erie
at the mouth of the Detroit and Maumee Rivers (Tidd 1955). By 1967 it had
spread rapidly throughout the lake (Davis 1969a). Patalas (1972) and Watson
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(1976) reported it as numerous in the Western Basin of Lake Erie during the
late 60's and 70's. This species was not observed in 1983 (Makarewicz 1987),
while in 1984 it was not common (Makarewicz 1988) but did average 25.9 organ-
isms/m^ for the entire lake. In 1985 it was a common species with an average
biomass of 1.2 mg/m^. As in 1984, it was more prevalent in the Western Basin
(Fig. 70).
The dominant cyclopoid copepod in 1970 was Cyclops bicuspidatus thomasi
with Mesocyclops edax common in the summer (Watson and Carpenter 1974). Cap
(1980) documented a shift in predominant copepods in the Eastern Basin from
calanoids in 1928 to cyclopoid copepods, mainly Cyclops bicuspidatus thomasi,
in 1974. Tropocyclops prasinus was present in low numbers (Watson and Carpen-
ter 1974). In 1983, 1984 and 1985, the same three species (C. bicuspidatus
thomasi, M. edax and T. prasinus) predominated (Makarewicz 1987, 1988, Table
56) with the addition of C. vernalis in 1985.
Abundance of Diaptontus siciloides has increased in Lake Erie (Gannon
1981). It was most prevalent in the Western Basin and western portion of the
Central Basin in the late 60's and 70's (Patalas 1972, Watson 1976). Abundant
diaptomids in the Eastern and Central Basins in 1970 were Diaptomus oregonen-
sis and D. siciloides, which were also the predominant calanoids in Lake Erie
in 1983, 1984 and 1985 (Makarewicz 1987, 1988) (Table 56). D. siciloides was
not a common species (1.0% of total zooplankton abundance) in 1984 and 1985
but was the second most abundant calanoid in both years.
Davis' studies (1968, 1969a) of the zooplankton of Lake Erie included
rotifers. Certain soft-bodied rotifers were not identified nor were the sam-
ples quantitative for rotifers as a #20 net was employed. However, it is
apparently the only lake-wide study of the offshore that included the
rotifers.
Species observed to be abundant in 1967 were Brachionus angularis, B.
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calycLflorus, ConochLlus unicornis, Keratella cochlearis, K. quadrats, Kelli-
cottia longispina, Synchaeta stylata and Polyarthra vulgaris (Davis 1968,
1969a). In 1983, 1984 and 1985, a similar group of rotifers was found (Table
58, Makarewicz 1987, 1988). In particular, Polyarthra vulgaris, ConochLlus
unicornis, Keratella cochlearis, and Synchaeta sp. were abundant in the 1967
and the 1983-1985 period (40.9% of the total zooplankton from 1983 to 1985).
East-West Species Distribution
Numerous researchers (e.g. Davis 1969a, Watson 1974, Patalas 1972, Gannon
1981) have documented the differences in species composition and abundance
from the Central, Western and Eastern basins of Lake Erie. In 1983 and 1984
(Makarewicz 1987, 1988), a number of species, mostly rotifers, had higher
abundances in the Western Basin. Abundances of rotifers were higher in the
Western Basin in 1985. However, the geographical pattern was different.
Instead of a gradient of high to low from the most western station eastward as
in 1984 (e.g. Fig. 59, Makarewicz 1988), rotifer abundance peaked at Station
55, the far eastern station of the Western Basin (Fig. 64). At present we
have no explanation for this observation. Phytoplankton abundance and chem-
istry do not correlate with the rotifer geographical abundance pattern.
Rotifera and Crustacea with geographical abundance peaks in the Western Basin
are presented in Fig. 66.
Geographically, Cyclops bicuspidatus thomasi had a geographical abundance
pattern with a maximum in the Central Basin in 1983, 1984 and 1985 (Makarewicz
1987, 1988, Fig. 67). Mesocyclops edax and Diaptomus oregonensis, which had
maxima in the Central Basin in 1983 and 1984, were more prevalent in the
Central Basin than in the Western Basin but were not obviously higher than in
the Eastern Basin (Fig. 67). Daphnia pulicaria was more prevalent in the
Central Basin in 1984 and 1985. Its abundance in Lake Erie in 1983 was
minimal. Ascomorpha ovalis, a rotifer, had a maximum in the Central Basin in
86
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1985 (Fig. 67). Holopedium gibberum (1983 and 1985), Tropocyclops prasinus
mexicanus (1983, 1984 and 1985) and CerLodaphnia lacustris were more prevalent
in the Eastern Basin (Fig. 67). Five species, Cyclopd bicuspidatus thomasi,
ConochLlus unicornis, Daphnia galaeta mendotae, Daphnia pulicaria and Diapto-
wus oregonensis, had low abundances in the Western Basin relative to the rest
of the lake (Fig. 67)
Indicators of Trophic Status
Geographical distribution of selected zooplankton in Lake Erie is consis-
tent from year to year and often unique to a basin. These geographical dis-
tribution patterns of zooplankton probably reflect environmental factors
unique to the various basins of Lake Erie. Thus zooplankton have potential
value as assessors of trophic status (Gannon and Stemberger 1978). Rotifers,
in particular, respond more quickly to environmental changes than do the
crustacean plankton and appear to be sensitive indicators of changes in water
quality (Gannon and Stemberger 1978). Brachionus angularis, B. calyciflorus,
Filinia longiseta and Trichocerca multicrinis are four rotifer species indica-
tive of eutrophy. Also, species in the genus Brachionus are particularly good
indicators of eutrophy in the Great Lakes (Gannon 1981). Of the three
dominant rotifer species in Lake Erie, Polyarthra vulgar is is a eurytopic
species; Notholca squamula is a cold stenotherm often associated with oligo-
mesotrophic lakes (Gannon and Stemberger 1978); while some species of Syn-
chaeta are eutrophic indicators (Gannon and Stemberger 1978). The lack of
dominance of eutrophic indicator species for the entire lake suggests that
Lake Erie in 1985, as a unit, is not eutrophic. This would agree with the
conclusion derived from phytoplankton indicator species and the algal biomass
classification of trophic status.
However, the eutrophic indicators Brachionus caudatus, B. calyciflorus,
B. angularis, Filinia longiseta, Trichocerca multicrinis and Trichocerca
87
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cyllndrica had abundances restricted to or significantly higher in the Western
Basin (Table 59). Total zooplankton abundance was also higher in the Western
Basin. As with phytoplankton biomass and species composition, both rotifer
abundance and species composition indicated a greater degree of eutrophy in
the Western Basin than in the Central or Eastern Basin.
Another measure of trophic status is the calanoid/cylopoid plus cladoc-
eran ratio (plankton ratio) (Gannon and Stemberger 1978, McNaught et al 1980,
Krieger 1981). Calanoid copepods generally appear best adapted for
oligotrophic conditions, while cladocerans and cyclopoid copepods are rela-
tively more abundant in eutrophic waters (Gannon and Stemberger 1978). In
Lake Erie, this ratio increased from west to east in 1983 and 1984 (Table 60)
indicating a more productive status for the Western Basin as compared to the
rest of the lake.
The higher algal biomass (Table 44) of the Western Basin as compared to
the Central and Eastern Basins was reflected in the abundance of zooplankton,
species composition and the plankton ratio. Compared to Lakes Huron and Mich-
igan in 1983 and 1984, abundance of zooplankton was greatest and the plankton
ratio was lower in Lake Erie (Table 8), indicating the higher trophic status
of Lake Erie compared to Lakes Huron and Michigan.
Historical Changes in Abundances
Zooplankton data exist for the Western Basin of Lake Erie from 1939 to
1984. The 1939 (Chandler 1940; 49 collections), 1949 (Bradshaw 1964; 30 col-
lections) and 1959 (Hubschmann 1960; daily collections July and August) col-
lections were taken with a 10-liter Juday trap equipped with a 64-um mesh net
in the Western Basin. A 1970 study by Nalepa (1972) is not included in the
analysis because it is from the far western end of the basin and may not be
representative of the entire Western Basin. The 1961 study of Britt et al
(1973) sampled twice monthly from mid-June to mid-September, while Davis
88
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(1968) used a 76-um mesh net in July of 1967. Because of the comparable net
sizes, all these studies, with the exception of Nalepa's (1972), are compara-
ble to the 1983, 1984 (Makarewicz 1987, 1988) and 1985 work.
A comparison of the April-December Crustacea means of 1939, 1949, 1983
and 1984 suggests an increase in zooplankton abundance from 1939 to 1949 (Fig.
71). Similarly, the mean abundance for July and August from 1939 to 1961
suggests a similar increase in zooplankton (Fig. 72). Both Bradshaw (1964)
and Gannon (1981) concluded similarly. Average ice-free abundances from 1949
to 1983 suggest a decreasing but insignificant downward trend (Fig. 71). The
decrease in zooplankton abundance from 1983 to 1984 was followed by an
increase in 1985 (Fig. 71). No obvious historical trend is evident from these
data. Focusing on July and August, where more data are available, an abundance
decrease in Cladocera, Copepoda and total Crustacea from the 1961 maximum
(Fig. 73) is evident.
A data point in the early 70's would be of interest. Data do exist for
the 70's. However, Nalepa's (1972) study is from the far western portion of
the Western Basin. Watson and Carpenter (1974) sampled the Western Basin, as
well as the Central and Eastern Basins in 1970. Their data are reported as a
weighted lake average and are not available to compare with other years in the
Western Basin. As the sampling method (1970; vertical hauls, 64-um mesh) is
comparable to those used in 1983 and 1984, these data are also directly compa-
rable on a lake-wide basis. A seasonal comparison of weighted lake-wide means
suggests little change in zooplankton abundance during the spring and autumn
from 1970 to 1983-85 (Fig. 73). Abundance of zooplankton has generally
increased from 1983 to 1985 (Fig. 74).
The 1939 and 1961 rotifer samples were collected with a 64-um mesh net,
as in the 1983 through 1985 work. An increase in Rotifera abundance in the
Western Basin is suggested since 1939 (Fig. 75).
89
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Trophic Interactions
Long-term changes of phytoplankton and zooplankton abundance were appar-
ent. A 56 to 76% reduction in lake-wide offshore algal biomass has occurred
from 1970 to 1983 to 1984. Total phosphorus and chlorophyll a levels in each
basin decreased (Figs. 59 and 60). Similarly, where comparable data are
available, zooplankton abundance and biomass decreased in the Western Basin.
With the N/P ratio currently exceeding 30 to 1, apparently due to P-control,
nuisance blue-green algae species, such as Aphanizomenon flos-aqua, decreased.
These changes are consistent with expectations of long-term nutrient control.
There are, however, significant changes in the composition of the zoo-
plankton community that can not be attributed solely to nutrient control. The
appearance of the large cladoceran Daphnia pulicaria in Lake Erie was evident
in 1983 and 1984 (Makarewicz 1988). Its dominance with a major bloom in
August of 1984 was surprising for it suggested changes in planktivory in Lake
Erie (Wells 1970, Brooks and Dodson 1965, Carpenter et al 1985, Scavia et al
1986). D. pulicaria was present in 1985 (mean - 44/m^) but because abundance
was lower than in 1984 (mean - 492/m^), it was not considered a common species
(Table 56).
A recovery in the walleye fishery of Lake Erie is evident by the increas-
ing harvest and abundance (Fig. 76 and 77). Annual walleye harvest rapidly
increased from 112,000 fish in 1975 to 2.2 million fish in 1977 in the Ohio
Lake Erie waters (Western and Central Basins) (Ohio Department of Natural
Resources 1989). Annual harvests since 1978 have stayed high but ranged from
1.7 million to the record 4.1 million in 1984 (Ohio Department of Natural
Resources 1989). Central Basin harvests have increased dramatically from
1982-1988 (Fig. 77). The initial recovery of the walleye fishery is attrib-
uted to the closing of the walleye fishery in 1970 due to mercury contamina-
tion and to the exclusion of commercial fishing for walleyes in U.S. waters
90
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since 1972 (Kutkahn et al 1976).
In addition, salmonid stocking programs exist in New York, Pennsylva-
nia, Ohio and Ontario. New York, which has the largest stocking program, had a
target stocking of -1 million fish in 1987 (F. Cornelius, Personal
Communication). Lake trout, Chinook and Coho salmon and various strains of
rainbow/steelhead trout are stocked in New York waters. These fish are primar-
ily feeding on smelt (NYSDEC 1987). Seasonal diets of walleye closely fol-
lowed changes in forage-fish availability (Knight et al 1984). Between 1979
and 1981 in the Western Basin of Lake Erie, walleye ate (100% by volume) age-1
shiners Notropis atherinoides (emerald shiner) and N. hudsonius (spottail
shiner) in spring but switched to age-0 clupeids (60-90%) Dorosoma cepedLanum
(gizzard shad) and Alosa pseudoharengus (alewife) in late July. Clupeids and
shiners composed 25-70% and 10-40%, respectively, of the diets of age-1 or
older walleyes in autumn (Knight et al 1984). There does appear to be a
difference in walleye foraging from west to east. Recent stomach analyses of
walleye from New York and Pennsylvania waters indicate that smelt represent
90% of their diet (NYSDEC 1987 and R. Kenyon, Personal Communication). Smelt
are not abundant in the Western and Central Basins.
Dramatic changes have occurred in the forage species of Erie. It is
apparent that alewife, spottail shiner and emerald shiner have declined in the
Western and Central Basins (Fig. 78) and in Pennsylvania waters (R. Kenyon,
Personal Communication). The decline of spottail and emerald shiners between
1982-1985 is impressive in view of the massive increase in walleye harvest in
the Central Basin since 1982 (Fig. 77). Fishery biologists have no specific
reason for this decline. Besides predation, other possible causes of the
decline include climatic factors, turbidity changes, toxic chemicals and the
commercial bait industry. Whatever the cause, a decrease in planktivorous
shiners has occurred.
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Emerald and spottail shiners feed heavily on microcrustacea, some midge
larvae and algae (Scott and Grossman 1973, Smith and Kramer 1964, McCann
1959). Evidence gathered by Gray (1942) in Lake Erie during December indicated
that Diaptomus, Daphnia, Cyclops and Bosmina were all important in the diet of
the emerald shiner but at different times of the day. Dymond (1926) noted
that in the spottail shiner of Lake Nipigon, Daphnia formed 40% of the diet
although Bosmina, Sida and Leptodora were also eaten. A good study on shiner
diets is needed.
There is good evidence that planktivorous fish abundance has changed as
a result of the walleye resurgence but perhaps also from the salmonid stocking
program in Lake Erie. Release from planktivore pressure has led to the estab-
lishment of the large Daphnia pulicaria in Lake Erie by 1984 (Makarewicz
1988). The causes of the decrease in D. pulicaria abundance in 1985 (44/m3)
from 1984 (492/m3) are not known. It my be related to the establishment and
occurrence of Bythotrephes cederstroemii in Lake Erie during this study year
(this study). Lehman (1988) has suggested that Daphnia populations in Lake
Michigan have decreased in response to Bythotrephes predation. However,
Bythotrephes was observed in Lake Erie only in the autumn of 1985 (Fig. 69).
Other top-down effects are difficult to evaluate. For example, the
decrease in Aphanizomenon flos-aquae in Lake Erie is more readily attributed
to decreased phosphorus concentration and the increasing N/P ratio (Smith
1983) than by Daphnia pulicaria cropping (Lynch 1980, Bergquist et al 1985).
A clearer water column, as observed in Lake Michigan and attributed to cascad-
ing effects (Scavia et al 1986), is difficult to evaluate in Lake Erie because
of storm induced events in the shallow waters of the Western Basin (Rockwell
1989). However, the reappearance and dominance of Asterionella formosa in
1984 may be related to the presence of D. pulicaria (e.g. Bergquist et al
1985).
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In an aquatic ecosystem dominated by large and efficient herbivores,
such as D. pulicaria and D. galeata mentodae, a grazing effect on phytoplank-
ton would be expected. Each year in the annual succession of the zooplank-
ton, the plankton community of Lake Erie changes from one dominated by
rotifers and copepods in the spring to rotifers, copepods and cladocerans,
including large Daphnia species, in the summer. In Lake Erie in 1985, phyto-
plankton biomass during the summer was inversely correlated with crustacean
size (r0.81), Daphnia biomass (r--0.63) and Calanoida biomass (r0.67)(Fig.
79). However, biomass of filamentous algae (mostly blue-greens) was posi-
tively correlated with Daphnia (r-0.98) and Calanoida biomass (r-0.92); i.e.,
biomass of potentially inedible filamentous algae increased to 17% of the
total algal biomass during the summer compared to <1.5% in the spring and
autumn (Fig.79). Similarly, the dominance of the large diatom Asterionella
formosa in 1984 and its decline in 1985 may be related to the presence and
dominance of D. pulicaria in 1984 and its decrease in importance within the
ecosystem in 1985 (Bergquist et al 1985). Biomass of large unicells, such as
PedLastrum, and colonial algae either did not change or decreased. Not all
changes were attributable to top-down control, however. The decrease in Apha-
nizomenon flos-aquae in Lake Erie is more readily attributed to decreased
phosphorus concentration and the increasing N/P ratio (> 30 to 1)(Smith 1983)
than by Daphnia cropping (Lynch 1980, Hawkins and Lampert 1989, Scavia et al
1986).
The size (greatest linear axial dimension) of the algal community in 1985
(minus the filaments and colonials) was inversely related to the abundance of
Crustacea and Daphnia (r - -0.787) and to the size of the Crustacea (Fig. 79).
That is, the weighted mean cell size of the edible portion of the algal commu-
nity decreased during the summer when the larger Cladocera, such as D. pulica-
ria and D. galeata mendotae, were abundant and grazing. These results agree
93
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well with models (Carpenter and Kitchell 1984), experimentally verified
(Bergquist et al 1985) of size-structured plankton communities, that predict
shifts to small algae at low biomass of small grazers and shifts to larger
algae as grazer size or biomass increase. However, the shifts in algal size
and biomass reported here in Lake Erie are changes that occur each summer and
do not necessarily represent permanent shifts in size structure of the algal
community. The mechanism for the decrease in algal biomass may be similar to
that for the spring "clear-water" phase described in some temperate lakes and
experimentally shown to be caused by high Daphnia biomass (Lampert et al
1986).
Top-down and bottom-up control of phytoplankton can be inferred from data on a
short-term basis. Correlation coefficients of phytoplankton abundance versus
total phosphorus and zooplankton abundance for each cruise on Lake Erie in
1985 are presented in Table 61. For each cruise, 11 stations were sampled
covering the entire length of the lake over a two-day period in 1985. Inter-
pretation of the correlations is as follows: A negative correlation between a
zooplankton group and phytoplankton implies grazing pressure on phytoplankton,
while a positive correlation between total phosphorus and phytoplankton abun-
dance suggests an enhancement of phytoplankton abundance due to phosphorus.
All correlations were positive in April suggesting that bottom-up effects were
influencing the food web. A different situation was evident by August. Phy-
toplankton were blooming, and all zooplankton groups had increased in abun-
dance. High negative correlations existed for Daphnia spp. and the Calanoida
suggesting a top-down influence on phytoplankton abundance. When D.
pulicaria became dominant in August, a negative fairly high correlation
existed between D. pulicaria and phytoplankton. By November, other species
of Daphnia and Calanoida exerted some influence on phytoplankton abundance.
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Calanoids were also negatively correlated with phytoplankton abundance
throughout the year, except April, suggesting a constant baseline effect on
phytoplankton.
At least two factors appear to regulate phytoplankton abundance. In Lake
Erie, phosphorus control was evident during the summer, but there were also
fairly high negative correlations between phytoplankton and Daphnia pulicaria,
Daphnia spp. and calanoids. Thus top down and bottom up control of the
trophic web of lake ecosystems exist simultaneously and either of the two
mechanisms of control can vary with season. This support for the bottom up :
top down theory of regulation of trophic biomass suggests a stronger coupling
of the zooplankton-phytoplankton link in Lake Erie than might be expected for
a eutrophic lake (McQueen et al 1989).
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Comparison of Lakes Michigan. Huron and Erie
A comparison of the phytoplankton assemblage between Lakes Michigan,
Huron and Erie reveals lake-specific differences superimposed on a common
base. Bacillariophyta comprised 63% to 67% of the average biomass in all
three lakes (Fig. 80), with varying percentages of the other Divisions in each
lake. Cryptophyta were more common in Lake Michigan (16.1% of biomass) than
in the other lakes, Chrysophyta were best represented in Lake Huron (8.7% of
biomass), and both Chlorophyta and Pyrrophyta were most abundant in Lake Erie
(8.8% and 10.7% of biomass, respectively.
The phytoplankton assemblange from the Western basin of Lake Erie was
different from that of the other two basins, and thereby influenced the lake-
wide average biovolume statistics for Lake Erie (Fig. 81). For example, Cya-
nophyta represented 13.13% of the common species biomass in the Western basin
but only 1.2% and 0.6% in the Central and Eastern basins, respectively.
Likewise, Pyrrophyta comprised 16.9% and 12.1% of the common biomass in the
Central and Eastern basins, respectively, but only 2.2% in the Western basin.
The number of common phytoplankton species shared between lake basin pairs
ranged from 18 for Lake Michigan and Lake Erie Central Basin to 30 for the
Central and Eastern basins of Lake Erie (Table 62). In general, the greatest
number of shared species occurred between the three basins of Lake Erie, and
the fewest number occurred between Lake Michigan and the Central and Eastern
basins of Lake Erie.
A Percentage of Similarity Index (Southwood 1966) was calculated between
basin pairs as the sum of the lesser of the percent of total biomass contrib-
uted by each shared common species (Table 62; Fig. 82). By this index, the
greatest similarity in phytoplankton community structure occurred between the
Central and Eastern basins of Lake Erie (70.42%), followed by the phytoplank-
ton in Lakes Michigan and Huron (51.36%), and in Lake Michigan and the Western
96
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basin of Lake Erie (42.77%). The least similar phytoplankton communities were
between Lake Huron and the Central and Eastern basins of Lake Erie (18.26% and
19.19%, respectively).
The relative contribution to the total biomass of common species was not
always similar between lake basins, however. The Relative Percent Difference
between biovolumes of each common shared species in each basin pair was calcu-
lated as the difference in percent biovolume of each shared species between
two lake basins dividied by the average percent biovolume for that species,
i.e., RPD - (|a - b|)/[(a + b)/2], where a and b are percent biovolume of a
species in lake basin a and b, respectively. An index was then constructed as
the percent of shared common species between lake basins with RPD > 1. (An
RPD of 1 equates to a difference of magnitude 3). By this index, lower
percentages imply more similar plankton communities, and the least different
communities were found between Lakes Michigan and Huron (17%), and between the
Central and Eastern basins of Lake Erie (17%)(Table 63). The greatest differ-
ences in shared species biovolumes were between the Central basin of Lake Erie
and Lake Michigan (50%) and between the Central and Western basins of Lake
Erie (41%).
Taken together, these analyses indicate that the phytoplankton assem-
blages were most similar between Lakes Michigan and Huron and between the
Central and Eastern basins of Lake Erie. The assemblage from the Western
basin was different in many ways from that of the rest of Lake Erie. It
appeared to be more similar to that from Lakes Michigan and Huron than from
the other two basins of Lake Erie.
Results of a comparison of the zooplankton community structure between
lakes are consistent with those of the phytoplankton data. The distribution
of biomass among major zooplankton taxa was similar between Lakes Michigan and
Huron, except that Lake Huron had about twice the Cladoceran biomass at the
97
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expense of the Calanoid copepod biomass (Fig. 83). In Lake Erie, a much lower
biomass of calanoid copepods was observed relative to the increases in cyclo-
poid copepods, cladocerans and rotifers. The Percentage of Similarity Index
between lake basins based on zooplankton biomass was, for Lakes Michigan and
Huron -59.21%, for Lakes Huron and Erie - 41.95%, and for Lakes Michigan and
Erie - 35.42%.
The zooplankton ratio (abundance of calanoid copepods/cyclopoid copepods
+ cladocerans) for 1983-1985 was similar for Lakes Michigan and Huron, and for
the Central and Eastern basins of Lake Erie (Fig. 84), although the Lake
Michigan and Lake Huron ratios were about three times greater than those for
the Lake Erie basins. Lowest ratios were always associated with the Western
basin of Lake Erie, implying more eutrophic conditions there.
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109
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Table 1. Latitude and longitude of plankton sampling stations, 1985,
Station Number
LAKE ERIE
LE60
LE57
LE55
LE43
LE42
LE73
LE38
LE37
LE36
LE78
LE30
LE31
LE32
LE15
LE63
LE10
LE09
Latitude
41°53'30"
41 49 54
41 44 18
41 47 18
41 57 54
41 58 40
42 16 54
42 06 36
41 56 06
42 07 00
42 25 48
42 15' 12
42 04 54
42 31 00
42 25 00
42 40 48
42 32 18
Longitude
83°11'48"
83 01 06
82 44 00
81 56 42
82 02 30
81 45 25
81 40 18
81 34 30
81 28 42
81 15 00
81 12 18
81 06 24
81 00 42
79 53 36
79 48 00
79 41 30
79 37 00
LAKE HURON
LH93
LH92
LH91
LH90
LH61
LH57
LH54
LH53
LH48
LH45
LH43
LH38
LH37
LH32
LH29
LH27
LH15
LH12
LH09
LH06
44°06'00"
43 48 30
43 42 00
43 24 00
45 45 00
45 40 00
45 31 00
45 27 00
45 16 42
45 08 12
45 00 48
44 44 24
44 45 42
44 27 12
44 22 00
44 11 54
44 00 00
43 53 24
43 38 00
43 28 00
82°07'00'
82 22 00
82 01 00
82 18 00
83 55
83 43
00
36
83 25 00
82 54 54
82 27 06
82 59 00
82 00 30
82 03 36
82 47 00
82 20 30
81 50 00
82 30 12
82 21 00
82 03 24
82 13 00
82 00 00
LAKE MICHIGAN
LM11
LM17
LM18
LM19
LM23
LM27
LM32
LM34
LM40
LM41
LM47
42°23'00'
42 44 00
42 44 00
42 44 00
43 08 00
43 36 00
44 08 24
44 05 24
44 45 36
44 44 12
45 10 42
87°00'00"
87 25 00
87 00 00
86 35 00
87 00 00
86 55 00
87 14 00
86 46 00
86 58 00
86 43 18
86 22 30
110
-------
Table 2. Plankton sampling dates for Lakes Michigan, Huron and Erie
in 1985.
Cruise
1
2
3
4
5
6
7
Lake
Michigan
4/15-22
5/1-2
6/5-6a
8/17-20
8/21-23
11/14-16
11/29-12/4
Lake
Huron
4/22-23
4/29-30
6/9-10
8/15-16
8/23-25
11/18-19
11/27-28
Lake
Erie
4/24-26
4/27-28
-
8/6-8
8/12-14
11/21-22
11/23-25
aphytoplankton collections only
Table 3. Sample dates and stations for Lake Erie, 1985. NS-not sampled.
Station
Number
60
57
55
43
42
73
36
37
38
78
32
31
30
63
15
10
09
4/24-26 4/27-29 8/6-8 8/12-14 11/21-22 11/23-25
x
x
X
X
X
X
X
X
X
X
ns
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
ns
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
111
-------
Table 4. Sample dates and stations for Lake Huron, 1985.
Station 4/22-23 4/29-30 6/9-10 8/15-16 8/23-25 11/18-19 11/27-28
Number
61
57
54
53
48
45
43
37
38
32
29
27
93
15
12
92
9
91
6
90
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
112
-------
Table 5. Sample dates and stations for Lake Michigan, 1985.
Station 4/15-22 5/1-2 6/5-6 8/17-20 8/21-23 11/14-16 11/29-
Number 12/4
11 XXXXX X X
17 XXXXX X X
18 XXXXX X X
19 XXXXX X X
23 XXXXX X X
27 XXXXX X X
32 XXXXX X X
34 XXXXX X X
40 XXXXX X X
41 XXXXX X X
47 XXXXX X X
113
-------
Table 6. Statistical comparison of zooplankton abundance and biomass from
north-south transects, Lake Erie. Average values for all cruises are compared
by ANOVA. Listed are probability values. In all cases P>0.05.
Station
42,47
Total
Calanoida
Cyclopoida
Copepoda
nauplii
Cladocera
Rotifera
Abundance
.771
.834
.606
.906
.487
.533
Biomass
.490
.880
.607
.906
.451
.080
Station
36,37,38
Abundance
.835
.794
.155
.671
.446
.848
Biomass
.588
.807
.374
.671
.615
.269
Station
30,31,32
Abundance Biomass
.518
.895
.099
.524
.966
.590
.875
.840
.539
.524
.956
.714
Table 7. Statistical comparison of phytoplankton abundance and biomass from
north-south transects, Lake Erie. Average values for all cruises are compared
by ANOVA. Listed are probability values. In all cases P>0.05.
Station
42,47
Station
36,37,38
Station
30,31,32
Total
BAG
CHL
CHR
CRY
COL
CYA
PIC
UNI
PYR
Abundance Biomass
.616 .875
.827 .529
.425 .355
.162 .097
.552 .236
.330 .774
.938 .582
.456 .337
.896 .494
.887 .378
Abundance Biomass Abundance Biomass
.965 .620 .731 .453
.650 .367 .959 .300
.431 .374 .798 .790
.989 .758 .315 .319
.184 .315 .174 .329
.490 .180 .269 .251
.317 .485 .845 .742
.773 .782 .453 .310
.422 .541 .114 .167
.643 .479 .150 .193
114
-------
Table 8. Average biological and chemical parameters (April-November) from a
1-m depth for Lakes Erie, Michigan and Huron, 1985. The trophic ratio and
zooplankton ratio are discussed in the text.
Turbidity (FTU)
Total phosphorus (ug/L)
Soluble Reactive
Phosphorus (ug/L)
Nitrite + Nitrate
(mg/L)
Chlorophyll a (ug/L)
Phytoplankton
(1000x#/mL)
(g/m3)
Zooplankton
(1000x#/m3)
(mg/m3)
Trophic Ratio
Zooplankton Ratio
Erie
(n-100)
2.64±.32
14.84±.82
2.20±.19
0.23±.015
Michigan
(n-64)
0.35±.02
4.28±.24
0.50±.06
0.23+.008
Huron
(n-58)
0.31±.01
3.09±.29
0.33±.06
0.29±.004
3.06+.32
4.48±.57
1.22±.ll
222±27
105.8±9.9
2.0
0.41
0.79+.06
2.84±.24
0.45+.043
34.9±4.1
47.9+5.2
8.0
1.53
0.79±.06
2.02±.ll
0.34±.021
67.7±9.4
59.2±7.0
2.7
2.9
115
-------
Table 9. Relative abundance of major phytoplankton divisions in Lake Michi-
gan, 1983, 1984 and 1985. Picoplankton are not included. Bac-Bacillariophyta,
Cat-Chloromanophyta, Chl-Chlorophyta, Chr-Chrysophyta, Col-Colorless
flagellates, Cry-Cryptophyta, Cya-Cyanophyta, Eug-Euglenophyta, Pyr-Pyrro-
phyta, Uni-Unidentified.
Biovolume/mL
Division
Bac
Cat
Chi
Chr
Col
Cry
Cya
Eug
Pyr
Uni
1983
57.79
0.02
5.38
6.70
1.04
13.76
3.24
0.04
7.50
4.52
1984
69.72
0.00
2.05
5.13
0.16
12.53
1.85
0.07
2.66
5.83
1985
63.95
0.00
2.16,
3.31
0.28
17.22
3.26
0.01
3.91
5.90
1983
10.08
0.01
6.10
14.12
1.61
11.67
26.40
<0.01
0.12
19.90
Cells/mL
1984
2.04
0.00
0.67
2.18
0.30
1.50
3.54
<0.01
0.02
6.89
1985
7.38
0.00
5.95
8.58
1.74
10.74
34.36
<0.01
0.15
31.10
116
-------
Table 10. Number of species and genera observed in each algal division or
grouping in Lake Michigan, 1983 to 1985. Results are for the non-winter
period.
Division
Bacillariophyta
Chlorophyta
Chrysophyta
Cryptophyta
Cyanophyta
Picoplankton
Colorless
flagellates
Pyrrophyta
Euglenophyta
Unidentified
Chloromanophyta
Total
1 Picoplankton were grouped with the Cyanophyta
Species
1983 1984
168
86
49
23
21
(2)1
16
9
1
5
1
379
166
63
33
20
13
3
15
7
1
5
0
327
1985
90
41
36
21
12
3
10
5
1
3
0
222
Genera
1983 1984
33
36
13
4
10
(2)1
6
4
1
-
1
108
29
26
11
4
8
3
5
3
1
-
0
91
1985
23
21
11
4
7
3
4
5
1
-
0
79
117
-------
Table 11. Abundance of Rhizosolenia eriensis in Lake Michigan in 1983, 1984
and 1985. Values in parentheses represent R. eriensis+R. longiseta.
1983
cells %
mL'l biovolume
April
May
June
July
August
October
November
December
February
0.0
0.0
0.2
-
0.0
0.0
0.0
10.9
7.1
-
-
-
0.0
0.0
0.1
-
0.0
0.0(0.5)
0.0
9.1(9.2)
2.1(10.7)
-
-
-
cells
mL-1
10.3
9.3
-
52.4
22.6
17.5
21.9
-
3.2
8.3
4.8
1984
%
biovolume
17.5(30.5)
8.6(17.4)
-
33.4(36.1)
23.2(30.1)
26.9(30.1)
39.2(44.6)
-
7.9(8.3)
16.4(5.2)
4.6(5.2)
1985
cells %
mL~l biovolume
6.5
6.7
8.0
-
0.4
0.0
-
0.8
0.7
-
10.7(15.9)
7.7(11.0)
5.4(30.2)
-
0.8(1.2)
0.0(1.9)
-
1.6(3.5)
3.8(7.4)
-
118
-------
Table 12. Sunmary of conmon phytoplankton species occurrence in Lake Michigan during 1983. Sunmary is
based on all samples analyzed with picoplankton removed. Summary includes the maximum population density
encountered, the average population density and biovolume, and the relative abundance 0.5X of the total biovolume.
TAXON
BACILLARIOPHYTA
Asterionella formosa
Cyclotella comensis v. 1
Cyclotella court a
Cyclotella michiganiana
Cymatopleura solea
Entomoneis ornata
Fragilaria crotonensis
Fragilaria vaucheriae
Melosira islandica
Melosira italics subsp. subarctica
Rhizosolenia eriensis
Rhizosolenia sp.
Stephanodiscus alpinus
Stephanodiscus niagarae
Stephanodiscus transiIvanicus
Tabellaria fenestrata
Tabellaria flocculosa
Total
CHLOROPHYTA
Cosmarium sp.
Green coccoid - bacilliform
Monoraphidium contortum
Stichococcus sp.
CHRYSOPHYTA
Dinobryon bavaricum
Dinobryon cylindrical)
Dinobryon divergens
Dinobryon sociale v. americanum
Haptophyte sp.
Unidentified coccoids
COLORLESS FLAGELLATES
Colorless flagellates
Stylotheca aurea
Total
Total
Total
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas erosa v. reflexa
Cryptomonas marssonii
Cryptomonas pyrenoidifera
Rhodomonas mi nuta v. nannoplanktica
MAXIMUM
CELLS/ML
206
834
158
117
5
4
755
115
137
357
53
133
22
18
6
79
202
8
376
201
761
262
311
258
802
785
540
810
172
202
25
11
25
49
777
ERAGE X OF
LS/ML
12.6
56.4
6.8
12.9
0.3
0.2
63.5
10.7
12.9
39.1
2.8
1.8
3.2
0.8
0.3
4.4
18.0
0.4
42.3
40.8
24.6
20.4
19.0
16.5
51.0
197.9
49.7
30.9
7.2
30.8
7.1
1.3
2.6
6.5
287.5
TOTAL
CELLS
0.40
1.78
0.21
0.41
0.01
0.00
2.01
0.34
0.41
1.24
0.09
0.06
0.10
0.03
0.01
0.14
0.57
7.81
0.01
1.34
1.29
0.78
3.42
0.64
0.60
0.52
1.62
6.26
1.57
11.22
0.98
0.23
1.21
0.97
0.23
0.04
0.08
0.21
9.10
MEAN
BIOVOLUME
CU.uM/mL
3,787
2,094
16.734
2,849
6,407
3,578
45,316
4,889
11,679
7,130
6,593
7,705
20,720
10,562
6,765
7,751
52,393
7,470
889
332
2,106
1,636
6,130
2,478
6,659
2,466
512
1,457
2,291
699
15,341
2.635
2,405
2,976
23,929
X OF TOTAL
BIOVOLUME
0.93
0.51
4.11
0.70
1.57
0.88
11.12
1.20
2.87
1.75
1.62
1.89
5.09
2.59
1.66
1.90
12.86
53.26
1.83
0.22
0.08
0.52
2.65
0.40
1.50
0.61
1.63
0.61
0.13
4.88
0.36
0.56
0.92
0.17
3.77
0.65
0.59
0.73
5.87
Total
10.63
11.78
119
-------
Table 12(cont.). Sunnary of comnon phytopiankton species occurrence in Lake Michigan during 1983. Summary
is based on all samples analyzed with picoplankton removed. Summary includes the maximum population density
encountered, the average population density and biovolume, and the relative abundance (X of total cells and
X of total biovolume). Common species were arbitrarily defined as having an abundance of i 0.5X of the
total cells or >0.5X of the total biovolume.
CYANOPHYTA
Anacystis montana v. minor 3,289 482.5 15.27 3,201 0.79
Coccochloris elabans 694 22.6 0.71 392 0.10
Coelosphaerium naegelianum 1,227 42.0 1.33 176 0.04
Gomphosphaeria lacustris 818 40.6 1.28 283 0.07
Oscillatoria agardhii 344 15.2 0.48 2,985 0.73
Oscillator*a limnetica 2,266 149.0 4.72 1,104 0.27
Oscillatoria minima 399 23.4 0.74 315 0.08
Oscillatoria subbrevis 736 15.9 0.50 625 0.15
Total 25.04 2.23
PYRROPHYTA
Ceratium hirundinella 8 0.2 0.01 22,349 5.49
Gymnodinium sp. #2 16 0.3 0.01 4,026 0.99
Peridinium sp. 8 0.4 0.01 2,764 0.68
Total 0.03 7.15
UNIDENTIFIED
Unidentified flagellate - ovoid 1,630 409.5 12.96 9,287 2.28
Unidentified flagellate - spherical 1,859 533.8 16.90 8,999 2.21
29.86 4.49
VBSSSSXSSS S=SSSSSS==
Total 89.22 87.36
120
-------
Table 13. Summary of common phytoplankton species occurrence in Lake Michigan during 1984. Summary is
based on all samples analyzed with picoplankton removed. Summary includes the maximum population density
encountered, the average population density and biovolume, and the relative abundance (X of total cells and
% of total biovolume}. Common species were arbitrarily defined as having an abundance of > 0.5X of the
total cells or >0.5X of the total biovolume.
TAXON
BACILLARIOPHYTA
Asterionella formosa
Cyclotella comensis v. 1
Cyclotella comta
Cyclotella ocellata
F rag iIar i a capuci na
Fragilaria crotonensis
Melosira islandica
Melosira italica subsp. subarctica
Nitzschia lauenburgiana
Rhizosolenia eriensis
Rhizosolenia longiseta
Stephanodiscus alpinus
Stephanodiscus alpinus?
Stephanodiscus niagarae
Stephanodiscus transiIvanicus
Synedra filiformis
Synedra ulna v. chaseana
Tabellaria flocculosa
CHLOROPHYTA
Dictyosphaerium ehrenbergianum
Monoraphidium contortum
Oocystis submarine
CHRYSOPHYTA
Chrysophycean coccoids
Dinobpyon divergens
Dinobryon sociale v. americanum
Haptophyceae
Monosiga ovata
Total
Total
Total
COLORLESS FLAGELLATES
Colorless flagellates
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas marssonii
Cryptomonas rostratiformis
Rhodomonas minuta v. nannoplanktica
Total
CYANOPHYTA
Anacystis montana v. minor
Coelosphaerium naegelianum
Gomphosphaeria lacustris
Oscillatoria limnetica
Oscillatoria minima
MAXIMUM
CELLS/ML
184
2,568
96
265
161
376
96
74
10
110
162
18
11
14
7
118
23
82
278
344
254
630
303
1,743
1,456
352
311
270
65
25
25
965
2,790
982
655
2,070
4,132
ERASE X OF
LS/ML
21.2
105.0
4.0
21.5
11.2
68.7
12.1
10.5
0.7
17.0
19.4
2.3
0.6
1.1
0.8
10.4
2.1
13.7
23.6
38.5
23.4
75.4
24.0
101.4
169.3
22.2
25.7
44.9
10.5
3.8
1.4
225.5
277.8
28.9
20.7
198.9
166.0
TOTAL
CELLS
0.59
2.91
0.11
0.60
0.31
1.91
0.34
0.29
0.02
0.47
0.54
0.06
0.02
0.03
0.02
0.29
0.06
0.38
8.94
0.65
1.07
0.65
2.37
2.09
0.67
2.81
4.70
0.62
10.89
0.71
1.25
0.29
0.11
0.04
6.26
7.94
7.71
0.80
0.57
5.52
4.61
MEAN
BIOVOLUME
CU.uM/mL
5,865
3,212
10,488
1,905
3,688
44.659
12,959
2,693
4,418
118,337
21,867
9,303
3,871
17,126
15,111
3,953
16,754
40,391
178
401
378
291
4,938
10,032
1,666
281
443
1,365
24,275
4,995
4,986
17,924
1,215
138
97
2,109
3,532
X OF TOTAL
BIOVOLUME
1.14
0.62
2.04
0.37
0.72
8.67
2.52
0.52
0.86
22.98
4.25
1.81
0.75
3.33
2.93
0.77
3.25
7.84
65.36
0.03
0.08
0.07
0.19
0.06
0.96
1.95
0.32
0.05
3.34
0.09
0.27
4.71
0.97
0.97
3.48
10.40
0.24
0.03
0.02
0.41
0.69
Total
19.22
1.38
121
-------
Table 13(cont.). Sumary of common phytoplankton species occurrence in Lake Michigan during 1984. Sumary
is based on all samples analyzed with picoplankton removed. Summary includes the maximum population density
encountered, the average population density and biovolurne, and the relative abundance (X of total cells and
X of total biovolume). Common species were arbitrarily defined as having an abundance of i 0.5X of the
total cells or >0.5X of the total biovolume.
PYRROPHYTA
Gymnodinium sp. 16 0.6 0.02 5,151 1.00
Peridinium sp. 16 1.6 0.04 4,218 0.82
Total 0.06 1.82
UNIDENTIFIED
Unidentified flagellate - ovoid 4.287 985.0 27.55 23,202 4.51
Unidentified flagellate - spherical 1,350 465.0 12.91 6,471 1.26
40.26 5.76
K==SS===SS sssssa==ss
Total 90.40 88.33
122
-------
Table U. Sunmary of comnon phytoplankton species occurrence in Lake Michigan during 1985. Summary is
based on all samples analyzed with picoplankton removed. Sunmary includes the maximum population density
encountered, the average population density and biovolume, and the relative abundance (X of total cells and
X of total biovolume). Comnon species were arbitrarily defined as having an abundance of & 0.5X of the
total cells or >0.5X of the total biovolume.
TAXON
BACILLARIOPHYTA
Asterionella formosa
Cymatopleura solea
Cymatopleura solea v. apiculata
Fragilaria crotonensis
Melosira islandica
Melosira italica subsp. subarctica
Rhizosolenia eriensis
Rhizosolenia longiseta
Stephanodiscus alpinus
Stephanodiscus niagarae
Stephanodiscus sp. #09
Stephanodiscus transilvanicus
Synedra filiformis
Synedra ulna v. chaseana
labellaria flocculosa
Total
CHLOROPHYTA
Dictyosphaerium ehrenbergianum
Green coccoid - bacilliform
Monoraphidium contortum
Total
CHRYSOPHYTA
Haptophyceae
COLORLESS FLAGELLATES
Colorless flagellate - ovoid
CRYPTOPHYTA
Chroomonas acuta
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas marssonii
Cryptomonas ovata
Cryptomonas pyrenoidifera
Cryptomonas rostratiformis
Cryptomonas sp.
Rhodomonas lens
Rhodomonas mi nuta v. nannoplanktica
Total
CYANOPHYTA
Anabaena sp.
Anacystis montana
Anacystis montana v. minor
Gomphosphaeria lacustris
Oscillatoria limnetica
Oscillatoria minima
Oscillatoria subbrevis
MAXIMUM
CELLS/ML
221
4
2
157
208
146
41
503
52
17
17
8
95
33
133
565
1,145
352
524
393
155
295
65
25
25
82
12
65
139
466
1,309
4.639
5,285
3,066
1,530
843
744
Total
ERAGE X OF
LS/ML
16.1
0.1
0.0
20.3
30.2
27.0
3.3
31.8
4.4
2.2
0.2
1.2
5.0
1.8
7.5
30.7
44.6
47.3
125.8
25.0
16.3
30.8
10.9
2.2
1.7
8.9
1.2
6.1
25.1
193.5
21.8
60.2
446.0
181.7
139.5
90.2
16.8
TOTAL
CELLS
0.57
0.00
0.00
0.71
1.06
0.95
0.12
1.12
0.15
0.08
0.01
0.04
0.18
0.06
0.26
5.32
1.08
1.57
1.66
4.32
4.43
0.88
0.57
1.08
0.38
0.08
0.06
0.31
0.04
0.22
0.88
6.81
10.45
0.77
2.12
15.70
6.40
4.91
3.17
0.59
33.66
MEAN
BIOVOLUME
CU.uM/mL
5,181
5,889
2.954
16,274
34,830
6,624
23.593
30,333
30,205
48,153
6,881
18,292
2,521
15,363
24,291
242
1,156
546
2,807
610
531
1.241
27,597
2,976
3,474
4,767
4,867
2,464
4,711
19,335
2,418
106
5,363
908
713
1,580
821
X OF TOTAL
BIOVOLUME
1.16
1.32
0.66
3.64
7.80
1.48
5.28
6.79
6.76
10.78
1.54
4.10
0.56
3.44
5.44
60.77
0.05
0.26
0.12
0.44
0.63
0.14
0.12
0.28
6.18
0.67
0.78
1.07
1.09
0.55
1.06
4.33
16.11
0.54
0.02
1.20
0.20
0.16
0.35
0.18
2.67
123
-------
Table 14(cont.). Summary of common phytoplankton species occurrence in Lake Michigan during 1985. Sum-
mary is based on all samples analyzed with picoplankton removed. Summary includes the maximum population
density encountered, the average population density and biovolume, and the relative abundance (X of total
cells and X of total biovolume). Common species were arbitrarily defined as having an abundance of > 0.5X
of the total cells or S0.5X of the total biovolume.
PYRROPHYTA
Ceratium hirundinella
Gymnodinium helveticum f. achroum
Gymnodinium sp.
Peridinium sp.
Total
UNIDENTIFIED
Unidentified flagellate - ovoid
Unidentified flagellate - spherical
8
8
8
16
2,675
638
Total
Total
0.2
0.2
0.6
1.5
691.2
190.0
0.01
0.01
0.02
0.05
0.09
24.33
6.69
31.02
90.15
4,119
2,543
2,770
5,760
19,974
6.045
0.92
0.57
0.62
1.29
3.40
4.47
1.35
5.83
89.98
Table 15. Comparison of abundance of Cyclotella species at offshore sites in
August of 1970, 1983, 1984 and 1985, Lake Michigan. Data from Holland and
Beeton (1972), Makarewicz (1987, 1988) and this study. Stations 22, 23 and 27
are geographically comparable to Holland and Beeton's offshore sites. Values
are in cells/mL.
Cyclotella
michiganiana
Cyclotella
stelligera
11/8/70
Offshore
Stations
71-182
300-613
17/8/83
Stations
22&27
0.44-6.8
0.17-2.2
15/8/84
Stations
22&27
0.38-4.5
1.7-2.8
20-21/8/85
Stations
23&27
1.4-16.4
0.9-6.4
124
-------
Table 16. Distribution of indicator diatom species in Lake Michigan. The
classification scheme followed Tarapchak and Stoermer (1976). MI- mesotrophic
but intolerant of nutrient enrichment, Mo- mesotrophic and tolerant of moder-
ate nutrient enrichment, E- eutrophic. 1970-71, 1977, 1983 and 1984 data are
from Holland and Beeton (1972), Stoermer and Tuchman (1979), Makarewicz (1987,
1988) and this study.
MI M2 E
19772 (Nearshore) 6 5 7 1.6
1970-713 454 2.3
19831 531 8
19841 452 4.5
19851 441 8
1 Only diatoms contributing >0.5% of the total biomass or > 0.1% of
the total abundance are classified.
2 Only diatoms contributing >0.1% of the abundance are classified.
3 Only "predominant" species are classified.
125
-------
Table 17. Relative abundance of zooplankton in Lake Michigan.
Rotifera
Cladocera
Copepoda nauplii
Cyclopoida
Calanoida
Mysidacea
Harpacticoida
Percent
Biomass
1983
N
0
T
C
A
L
C
U
L
A
T
E
D
1984
2.
39.
11.
15.
30.
0.
<
6
8
2
8
4
2
1
1985
1.
14
10
7
67
0
<
1
.2
.2
.0
.4
.1
.1
Percent
Abundance
1983
59.
3.
21.
5.
10.
<
<.
7
2
3
7
1
1
1
1984
67.
4.
15.
6.
6.
<
<.
5
1
6
2
6
1
1
1985
39.
2.
34.
8.
15.
<
<.
9
1
8
1
1
1
1
126
-------
Table 18. Summary of common zooptankton species occurrence in Lake Michigan during 1985. Species were
arbitrarily classified as common if they accounted for >0.1X of the total abundance or >1.0X of the total
biomass, with the exception of rotifers. Rotifer species were considered common if they accounted for >1.0X
of the total abundance.
TAXON
MAXIMUM
DENSITY
AVERAGE
DENSITY
X OF TOTAL
ABUNDANCE
MEAN
BIOMASS
(ug/m*)
X OF TOTAL
BIOMASS
COPEPODA
Copepoda - nauplii
Cyclopoida
Cyclopoid - copepodite
Cyclops bicuspidatus thomasi
Tropocyclops prasinus mexicanus
Calanoida
Diaptomus - copepodite
Diaptomus ash I andi
Diaptomus mi nutus
Diaptomus oregonensis
Diaptomus sicilis
Limnocalanus - copepodite
Limnocalanus macrurus
CLADOCERA
Daphnia galaeta tnendotae
Daphnia pulicaria
Daphnia retrocurva
ROTIFERA
Collotheca sp.
Conochilus unicornis
Gastropus stytifer
Kellicottia longispina
Keratella cochlearis
Keratella crassa
Ploesoma truncatum
Polyarthra major
Polyarthra vulgar is
Synchaeta sp.
62,951 12,162.6
Total
Total
34.80
57.74
1.88
4,865
10.16
12,808
2,772
858
18,704
9,352
1,105
375
2,009
1,030
438
2,289.2
417.2
' 66.4
3,242.7
1,004.5
252.2
52.1
494.6
146.3
53.1
6.55
1.19
0.19
9.28
2.87
0.72
0.15
1.42
0.42
0.15
1,488
1,640
89
23,510
2,461
588
253
3,235
565
1,432
3.11
3.42
0.19
49.08
5.14
1.23
0.53
6.75
1.18
2.99
83.76
6,402
2,467
1,266
447.9
161.3
47.3
1.28
0.46
0.14
3,664
2,654
169
7.65
5.54
0.35
13.54
5,484
10,091
12.970
11,945
25,683
18,208
31,589
19.048
63,902
25,581
Total
Total
604.5
976.6
743.6
1.166.3
1.747.7
524.4
493.1
833.8
3,913.5
1,819.0
1.73
2.79
2.13
3.34
5.00
1.50
1.41
2.39
11.20
5.20
36.69
==========
96.31
2
15
22
15
7
23
10
111
193
44
0.00
0.03
0.05
0.03
0.01
0.05
0.02
0.23
0.40
0.09
0.92
==========
98.23
127
-------
Table 19. Early August Cladocera abundance in 1954, 1966, 1968, 1983, 1984
and 1985 in Lake Michigan. Data from Wells (1970), Makarewicz (1987, 1988)
and this study. Values represent the mean station number/nH. Values in
parentheses do not include Stations 6, 56, 64 and 77 and are directly compara-
ble to the 1985 data.
1954 1966 1968 1983 1984 1985
Leptodora
kindtii
Daphnia
gal eat a
Daphnia
retrocurva
Diaphanosoma
brachyurum
29
1200
1400
2
4
0
79
0
16
0.4
2100
0
34
(42)
514
(883)
82
(87)
1
98
(66)
3508
(4650)
1061
(1061)
0
43
2150
266
1
Daphnia
longiremis
Daphnia
pulicaria
Holopedium
gibberum
Polyphemus
pediculus
Bosmina
longirostris
Eubosmina
coregoni
Ceriodaphnia
quadrangula
0
0
0
16
0 0
0 2
2 15
26 98
1
4
14 47
0 1011 248 694
(2447) (303)
5
10
16
16
456 536 8
(23) (66)
13
0
342 5231 33
(318) (169)
159
(80)
0
208 66
(202)
0 0
128
-------
Table 20. Early August Copepoda abundance in 1954, 1966, 1968, 1983, 1984
and 1985 in Lake Michigan. Data from Wells (1970), Makarewicz (1987, 1988)
and this study. Values represent the mean station number/m-*. Values in
parentheses do not include Stations 6, 56, 64 and 77 and are directly compara-
ble to the 1985 data.
1954 1966 1968 1983 1984 1985
Liwnocalanus
macrurus
Epischura
lacustris
Diaptomus
sicilis
Mesocyclops
edax
Senecella
calanoides
Cyclops
bicuspidatus
Diaptomus
ashlandi
Cyclops
vernalis
Eurytemora
affinis
Diaptomus
oregonensis
Diaptomus
minutus
91
41
3
200
0.2
310
140
0
0
63
39
34
7
1
0
0.2
1000
220
0
33
58
25
270
21
3
0
0.1
860
13
0
3
100
1500
18
(13)
19
(17)
79
(85)
13
(7)
1.4
1457
(2118)
1256
(2185)
0
0
138
(92)
151
(245)
64
(55)
14
(16)
155
(73)
31
(48)
0
2807
(2737)
1733
(2363)
16
0
58
(29)
183
(254)
9
43
12
107
0
1074
1148
0
3
78
342
129
-------
Table 21. Average crustacean zooplankton biomass (dry weight) for 1976, 1984
and 1985, Lake Michigan. Values are the mean+ S.E. The 1976 data (Bartone
and Schelske 1982) were converted to dry weight assuming carbon content was
50% of dry weight.
1976 50.0±14.8 mg/m3
1984 33.6±14.7 mg/m3
1985 47.9±5.2 mg/m3
130
-------
Table 22. The ratio of calanoids to cyclopoids plus cladocerans geographi-
cally in Lake Michigan, 1983, 1984 and 1985. ns-no sample.
Calanoida
Station
77
64
57
47
41
34
27
23
18
11
6
(North)
Cyclopoida + Cladocera
1983 1984 1985
(South)
0.37
0.41
1.74
1.52
1.10
1.03
1.53
1.15
3.01
1.71
0.87
0.23
0.20
0.69
0.57
0.57
0.80
0.84
1.32
1.93
1.09
0.75
ns
ns
ns
1.01
1.22
1.29
1.76
1.36
1.92
2.12
ns
131
-------
Table 23. Correlation (r) of phytoplankton abundance with total phosphorus
concentrations and zooplankton abundance within individual cruises (11 sta-
tions) in Lake Michigan, 1985. NO - observed.
Daphnia Daphnia Rotifera Calanoida Total
pulicaria spp. Phosphorus
4/15-22 NO .021 -.136 -.682 -.118
5/1-2 NO .104 -.014 -.600 .043
6/5-6 NO .162 .292 .458 .025
8/17-20 -.247 -.599 -.186 -.348 .390
11/14-16 .131 -.040 -.336 -.157 .666
11/29-12/4 .462 .465 .093 .093 .401
132
-------
Table 24. Number of species and genera observed in each algal division or
grouping, Lake Huron, 1983, 1984 and 1985.
Division
BAG
CHL
CHR
CRY
CYA
PIC
COL
PYR
EUG
UNI
CAT
Total
Species
1983
1984
1985
158
73
36
22
13
(2)*
13
10
4
3
1
156
64
35
17
13
3
13
9
1
4
0
120
32
25
14
9
3
3
3
,0
3
1
Genera
1983
1984
1985
329
315
213
29
28
10
3
6
(2)*
4
4
3
1
88
28
28
12
4
7
3
5
4
1
0
92
26
16
10
3
6
3
2
3
0
1
70
* Included in Cyanophyta in 1982
Table 25. Relative abundance of major phytoplankton divisions in Lake Huron,
1983, 1984 and 1985. The picoplankton are not included. BAC-Bacillariophyta,
CAT-Chloromanophyta, CHL-Chlorophyta, CHR-Chrysophyta, COL-Colorless Flagel-
lates, CRY-Cryptophyta, CYA-Cyanophyta, EUG-Euglenophyta, PYR-Pyrrophyta, UNI-
-Unidentified.
Division
BAG
CAT
CHL
CHR
COL
CRY
CYA
EUG
PYR
UNI
%
Biovolume/mL
1983
1984
1985
70.05
.02
3.55
7.30
.15
8.51
1.72
.12
3.33
62.90
0.00
2.77
9.67
.13
9.25
1.44
.06
7.27
67.37
.02
3.70
10.03
.74
9.26
2.02
.00
1.27
%
Cells/mL
5.24
6.52
5.89
1983
8.65
<0.01
3.11
11.92
.42
8.41
21.92
.01
.11
45.43
1984
1985
17.26
0.00
3.56
13.01
.77
7.68
25.72
.01
.15
31.83
18.18
<.01
4.56
14.31
6.02
11.24
19.48
.00
.11
26.08
133
-------
Table 26. Abundance of Rhizosolenia eriensis in Lake Huron, 1983, 1984 and
1985. Values in parentheses in 1983 represent Rhizosolenia sp. and in 1984 R.
longiseta.
1985
1983
1984
Date
April
May
June
July
August
October
cells/mL biomass cells/mL
0
0
0
0
0
0
0
.1
.2
-
.0
.0
.0
.4
.0
0.01
0.01(38.3)
-
0.0(59.2)
0.0(11.3)
0.0(12.1)
1.0(6.1)
0.0(8.7)
6
5
51
26
33
9
5
.3(0
.4(0
-
.0(0
.7(0
.1(0
.9(0
.8(0
biomass
.43)
.46)
,81)
.92)
.15)
.51)
.39)
9
6
18
30
35
29
16
.0
.3
-
.1
.4
.1
.1
.1
cells/mL
106
40
200
86
24
.4
.9
-
.4
-
.4
.5
-
biomass
16(4)
4(4)
-
15(7)
-
14(9)
3(8)
-
November
December
January
February
2.9(0.44) 10.3
2.4(0.0) 4.4
10.7(0.17) 12.4
151.4
175.5
29(1)
33(0)
134
-------
Table 27. Summary of common phytoplankton species occurrence in Lake Huron
during 1983. Summary is based on all samples analyzed with picoplankton removed.
Summary includes the maximum population density encountered, the average pop-
ulation density and biovolume, and the relative abundance (% of total cells and
% of total biovolume). Common species were arbitrarily defined as having an
abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
TAXON
BACILLARIOPHYTA
Asterionella formosa
Cyclotella comensis v. 1
Cyclotella comta
Cyclotella kuetzingiana v. planetophora
Cyclotella ocellata
Cymatopleura solea v. apiculata
Fragilaria crotonensis
Fragilaria intermedia v. fallax
Helosira islandica
Rhizosolenia sp.
Stephanodiscus niagarae
Stephanodiscus transiIvanicus
Tabellaria flocculosa
Tabellaria flocculosa v. linearis
MAXIMUM AVERAGE X OF TOTAL MEAN X OF TOTAL
CELLS/ML CELLS/ML CELLS BIOVOLUME BIOVOLUME
CU.uM/mL
Total
CHRYSOPHYTA
Chrysosphaerella longispina
Dinobryon bavan'cum
Dinobryon cylindricum
Dinobryon divergens
Dinobryon sociale v. americanum
Haptophyte sp.
Total
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas erosa v. reflexa
Cryptomonas pyrenoidifera
Rhodomonas mi nuta v. nannoplanktica
Total
CYANOPHYTA
Anacystis montana v. minor
Anacystis thermal is
Coccochloris elabans
Coelosphaerium naegelianum
Gomphosphaeria lacustris
Oscillatoria limnetica
PYRROPHYTA
Ceratium hirundinella
Gymnodinium sp.
Gymnodinium sp. #2
Total
Total
UNIDENTIFIED
Unidentified flagellate - ovoid
Unidentified flagellate - spherical
Total
Total
103
385
51
80
254
3
123
60
90
143
3
8
133
21
8.3
42.2
5.5
14.2
25.6
0.1
23.7
7.0
10.9
14.7
0.3
0.8
17.4
1.2
0.32
1.64
0.21
0.55
1.00
0.01
0.92
0.27
0.42
0.57
0.01
0.03
0.68
0.05
2,534
1,456
15,136
4,265
1,997
11,525
19,619
4,302
14,559
109,236
4,932
7,575
51,945
2,189
0.68
0.39
4.05
1.14
0.53
3.08
5.25
1.15
3.89
29.20
1.32
2.03
13.89
0.59
1,135
5,211
0.1
0.3
0.2
419.4
746.1
6.69
9.47
7.82
21.15
0.00
0.01
0.01
0.02
16.34
29.06
45.40
==s=r=
90.55
4,791
2,344
2,892
8,944
10,573
67.18
74
155
164
141
524
859
11.5
13.1
13.8
18.5
42.1
144.0
0.45
0.51
0.54
0.72
1.64
5.61
4,523
1,675
5,014
4,032
5,140
1,346
1.21
0.45
1.34
1.08
1.37
0.36
5.81
65
16
8
33
311
14.7
4.6
1.1
5.3
175.2
0.57
0.18
0.04
0.20
6.82
295
8,754
2,119
2,997
13,005
0.08
2.34
0.57
0.80
3.48
7.26
2,556
115
434
900
920
974
325.7
14.8
32.3
63.2
32.2
74.8
12.69
0.58
1.26
2.46
1.25
2.91
1,429
2,079
361
285
175
241
0.38
0.56
0.10
0.08
0.05
0.06
1.22
1.28
0.63
0.77
2.68
2.39
2.83
5.22
89.37
135
-------
Table 28. Summary of common phytoplankton species occurrence in Lake Huron
during 1984. Summary is based on all samples analyzed with picoplankton removed.
Summary includes the maximum population density encountered, the average pop-
ulation density and biovolume, and the relative abundance (% of total cells and
% of total biovolume). Common species were arbitrarily defined as having an
abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
TAXON
BACILLARIOPHYTRA
Asterionella formosa
Cyclotella comensis v. 1
Cyclotella comens is v. 2
Cyclotella comta
Cyclotella kuetzingiana v. planetophora?
Cyclotella ocellata
Cyclotella sp.
Cyclotella stelligera
Fragilaria crotonensis
Fragilaria intermedia v. fallax
Melosira islandica
Rhizosolenia eriensis
Rhizosolenia longiseta
Stephanodiscus alpinus
Stephanodiscus mi nutus
Stephanodiscus niagarae
Tabellaria flocculosa
CHLOROPHYTA
Cosmarium sp.
Oocystis pusilla
CHRYSOPHYTA
Chrysophycean coccoids
Chrysosphaerella longispina
Dinobryon cylindricum
Dinobryon divergens
Dinobryon sociale
Dinobryon sociale v. americanum
Haptophyceae
Total
Total
Total
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas pyrenoidifera
Cryptomonas rostratiformis
Rhodomonas minuta v. nannoplanktica
Total
CYANOPHYTA
Anacystis montana v. minor
Coelosphaerium naegelianum
Gomphosphaeria lacustris
Oscillatoria limnetica
Oscillatoria minima
MAXIMUM
CELLS/ML
168
1,367
101
35
135
1,000
U3
267
375
25
43
131
33
19
85
2
181
16
198
160
1,325
196
254
589
540
589
115
31
33
8
360
4,606
1,047
851
942
335
ERAGE X OF
LS/ML
27.5
94.2
20.9
2.3
13.2
113.2
15.1
25.3
44.7
2.6
6.5
17.2
2.9
1.5
19.4
0.2
25.0
0.7
15.2
36.2
31.4
13.3
32.0
65.6
27.8
110.1
22.8
4.5
4.2
0.8
155.1
445.4
77.6
79.0
45.9
17.3
TOTAL
CELLS
0.99
3.40
0.75
0.08
0.48
4.08
0.54
0.91
1.61
0.09
0.23
0.62
0.10
0.05
0.70
0.01
0.90
15.57
0.03
0.55
0.57
1.31
1.13
0.48
1.16
2.37
1.00
3.97
11.41
0.82
0.16
0.15
0.03
5.59
6.76
16.07
2.80
2.85
1.66
0.62
MEAN
BIOVOLUME
CU.uM/mL
8,545
3,382
578
7,576
3,615
9,063
684
568
36,435
2.068
8,107
75,628
2,181
3,659
788
3.300
64,228
2,013
1,166
175
7,701
3.981
6,062
9,978
4,368
1,353
670
9,572
2,269
3.049
12.757
2,042
310
352
203
419
X OF TOTAL
BIOVOLUME
2.17
0.86
0.15
1.92
0.92
2.30
0.17
0.14
9.24
0.52
2.06
19.17
0.55
0.93
0.20
0.84
16.28
58.41
0.51
0.30
0.81
0.04
1.95
1.01
1.54
2.53
1.11
0.34
8.52
0.17
2.43
0.58
0.77
3.23
7.18
0.52
0.08
0.09
0.05
0.11
Total
24.00
0.84
136
-------
Table 28(cont.). Summary of common phytoplankton species occurrence in Lake
Huron during 1984. Summary is based on all samples analyzed with picoplankton
removed. Summary includes the maximum population density encountered, the average
population density and biovolume, and the relative abundance (% of total cells
and % of total biovolume). Common species were arbitrarily defined as having
an abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
PYRROPHYTA
Ceratium hirundinella
Gymnodinium helveticum f. achroum
Gymnodinium sp.
Gymnodinium sp. #2
Total
UNIDENTIFIED
Unidentified flagellate - ovoid
Unidentified flagellate - spherical
8
6
8
8
1.481
2,193
0.1
0.2
0.5
0.3
615.9
264.7
0.00
0.01
0.02
0.01
0.04
22.21
9.55
13,887
3,303
3,068
5,388
16,433
9,047
Total
Total
31.76
3.52
0.84
0.78
1.37
6.50
4.17
2.29
90.11
6.46
ESSXXS
88.72
137
-------
Table 29. Summary of common phytoplankton species occurrence in Lake Huron
during 1985. Summary is based on all samples analyzed with picoplankton removed.
Summary includes the maximum population density encountered, the average pop-
ulation density and biovolume, and the relative abundance (% of total cells and
% of total biovolume). Common species were arbitrarily defined as having an
abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
TAXON
BACILLAR10PHYTA
Asterionella formosa
Cyclotella comensis
Cyclotella comensis v. 1
Cyclotella comensis v. 2
Cyclotella comta
Cyclotella kuetzingiana v. planetophora
Cyclotella ocellata
Cyclotella sp.
Cyclotella stelligera
Cymatopleura solea v. apiculata
Diatoma tenue v. elongatum
Fragilaria crotonensis
Fragilaria intermedia v. fallax
Melosira islandica
Rhizosolenia eriensis
Rhizosolenia longiseta
Stephanodiscus alpinus
Stephanodiscus mi nutus
Stephanodiscus niagarae
Stephanodiscus transiIvanicus
Synedra ulna v. chaseana
Tabellaria flocculosa
CHLOROPHYTA
Cosmarium sp.
Green coccoid - ovoid
Monoraphidium setiformae
CHRYSOPHYTA
Chrysophycean coccoids
Chrysosphaerella longispina
Dinobryon divergens
Dinobryon sociale
Haptophyceae
COLORLESS FLAGELLATES
Colorless flagellates
Stelexmonas dichotoma
Total
Total
Total
Total
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Rhodomonas lens
Rhodomonas mi nuta v. nannoplanktica
MAXIMUM
CELLS/ML
99
260
779
95
72
446
264
148
255
1
23
153
25
122
57
295
14
102
5
8
4
68
8
123
164
106
1,317
80
319
630
387
237
98
25
90
360
ERAGE X OF
LS/ML
23.8
10.9
42.9
18.4
4.9
48.7
34.2
25.1
13.4
0.0
2.2
30.7
2.6
20.6
11.2
24.0
0.7
12.2
0.2
0.5
0.2
12.5
0.3
21.8
22.6
U.8
66.9
6.9
27.6
138.6
99.5
21.7
22.3
7.3
24.2
164.9
TOTAL
CELLS
1.18
0.54
2.12
0.91
0.24
2.41
1.69
1.24
0.66
0.00
0.11
1.52
0.13
1.02
0.56
1.19
0.03
0.60
0.01
0.03
0.01
0.62
16.83
0.02
1.08
1.12
2.22
0.73
3.31
0.34
1.37
6.86
12.62
4.93
1.07
6.00
1.10
0.36
1.20
8.16
MEAN
BIOVOLUME
CU.uM/mL
8,603
1,488
1,239
562
15,636
7,393
2,224
1,035
226
2,907
1,810
24,552
2,466
26,636
50,115
18,131
2.823
452
6,771
9,194
1,833
33,315
4,406
691
792
87
18,985
2,725
5,238
2,834
1,972
526
688
13,000
3,126
11,901
X OF TOTAL
BIOVOLUME
2.51
0.43
0.36
0.16
4.56
2.15
0.65
0.30
0.07
0.85
0.53
7.16
0.72
7.76
14.61
5.28
0.82
0.13
1.97
2.68
0.53
9.71
63.95
1.28
0.20
0.23
1.72
0.03
5.53
0.79
1.53
0.83
8.71
0.57
0.15
0.73
0.20
3.79
0.91
3.47
Total
10.82
8.37
138
-------
Table 29(cont.). Summary of common phytoplankton species occurrence in Lake
Huron during 1985. Summary is based on all samples analyzed with picoplankton
removed. Summary includes the maximum population density encountered, the average
population density and biovolume, and the relative abundance (% of total cells
and % of total biovolume). Common species were arbitrarily defined as having
an abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
CYANOPHYTA
Agmenellum quadruplicatum
Anabaena sp.
Anacystis montana v. minor
Anacystis thermalis
Gomphosphaeria lacustris
Oscillatoria limnetica
Oscillatoria minima
Oscillatoria subbrevis
1
145
483
1,407
245
1,554
1,080
548
644
Total
PYRROPHYTA
Gymnodinium helveticum f. achroum
UNIDENTIFIED
Unidentified flagellate - ovoid
Unidentified flagellate - spherical
29.9
12.0
138.8
14.7
81.5
63.1
33.7
19.3
0.4
1.48
0.59
6.87
0.73
4.03
3.12
1.67
0.95
19.45
0.02
1,587
679
400.6
123.4
Total
Total
19.83
6.11
25.95
16
1,667
785
1,460
341
930
410
1,315
0.00
0.49
0.23
0.43
0.10
0.27
0.12
0.38
2,731
15,712
3,167
2.02
0.80
4.58
0.92
93.90
5.50
91.79
139
-------
Table 30. Phytoplankton common (abundance >0.1% of the total cells or >0.5%
of the total biovolume) in 1985 but not in 1983 and 1984, Lake Huron.
Bacillariophyta
Diatoma tenue var. elongatum
Synedra ulna var. chaseana
Chlorophyta
Green coccoid - ovoid
Monoraphidium setiformae
Cryptophyta
Rhodomonas lens
Cyanophyta
Agmenellum quadruplicatum
Anabaena sp.
Oscillatoria subbrevis
Colorless Flagellates
Stelexmonas dichotoma
140
-------
Table 31. Distribution of indicator diatom species in Lake Huron. The clas-
sification scheme of Tarapchak and Stoermer (1976) was utilized. Ml-meso-
trophic but intolerant of nutrient enrichment, M2-mesotrophic and tolerant of
moderate nutrient enrichment, E-eutrophic. 1971, 1975-76 and 1983 data are
from Munawar and Munawar (1979), Lin and Schelske (1978) and Makarewicz
(1987).
19711
1975-762
19833
19843
19853
l()nly diatoms cantributing >5% of the seasonal biomass are classified.
?0nly "abundant" diatom species are classified.
30nly diatoms contributing >0.5% of the biomass for the study period are
classified.
Ml
6
2
7
6
5
M2
3
4
2
3
3
E
3
2
2
3
3
M1+M2/E
3.0
3.0
4.5
3.0
2.7
Table 32. Relative abundance of zooplankton in Lake Huron.
Percent Biomass Percent Abundance
Rotifera
Cladocera
Copepoda nauplii
Cyclopoida
Calanoida
Amphipoda
Mysidacea
1983
N
0
T
C
A
L
C
U
L
A
T
E
D
1984
2
27
14
13
42
<
0
.5
.5
.7
.3
.0
.1
.0
1985
1
26
13
9
48
0
<
.5
.3
.9
.8
.5
.0
.1
1983
41.
4.
23.
11.
19.
0.
<.
1
8
1
2
8
0
1
1984
56
2
18
7
15
<
0
.0
.9
.6
.3
.3
.1
.0
1985
40
1
30
7
20
0
<
.3
.4
.4
.6
.3
.0
.1
141
-------
Table 33. Summary of common zooplankton species occurrence in Lake Huron
during 1985. Species were arbitrarily classified as common if they accounted
for >0.1% of the total abundance or >1.0% of the total biomass, with the
exception of rotifers. Rotifer species were considered common if they
accounted for >1.0% of the total abundance.
TAXON
MAXIMUM
DENSITY
AVERAGE
DENSITY
X OF TOTAL
ABUNDANCE
MEAN
BIOMASS
-------
Table 34. Comparison of mean crustacean abundance for the sampling period in
1971 (April-November), 1974/75 (April-November), 1983 (August-October), 1984
(April-December) and 1985 (April-November). 1971 data modified from Watson
and Carpenter (1974), 1974/75 data from McNaught et al (1980), 1983 and 1984
data from Makarewicz (1987, 1988). NF - not found. Values are in number/m3.
1971
Cladocera
Bosmina longirostris 553 (1047)*
Eubosmina coregoni 330 (765)*
Daphnia retrocurva
Daphnia galeata mendotae 339 (852)*
Daphnia pulicaria 0 (0)
Chydorus sphaericus 18
Holopedium gibberum 229 (580)*
Cyclopoida
Cyclops bicuspidatus
thomasi 3764 (3274)*
Cyclops vernalis 7.5 (5)*
Tropocyclops prasinus
mexicanus 63 (61)*
Mesocyclops edax 5 (6.7)*
Calanoida
Diaptomus ashlandi 246 (37)*
Diaptomus minutus 462 (322)*
Diaptomus sicilis 117 (77)*
Diaptomus oregonensis 109 (92)*
Limnocalanus macrurus 64 (44)*
1974/75** 1983*** 1984 1985
4109
2084
361
692
0
391
576
1271
117
310
91
745
966
496
192
34
518
229
74
1029
363
NF
58
2346
.5
577
115
206
465
145
140
9.3
338
326
36
586
71
NF
158
316
1.5
21
40
1071
369
502
93
20
100
55
42
514
39
<.l
145
482
NF
72
22
2264
1006
1134
222
37
*
**
August, September and October average
Includes Saginaw Bay
*** August and October average
143
-------
Table 35. Abundance of Bythotrephes cederstroemL by season and geography in
1985, Lake Huron. y
Station
61
54
43
32
93
15
12
9
6
4/22
0
0
0
0
0
0
0
0
0
4/29
0
0
0
0
0
0
0
0
0
6/9
0
0
0
0
0
0
0
0
0
8/15
0
0
36
0
0
0
0
0
8
8/23
0
0
0
8
0
23
34
11
11
11/18
72
0
0
0
24
0
0
0
0
11/27
11
6
0
0
0
0
4
0
6
mean
11.9
0.9
5.1
1.1
3.4
3.3
5.4
1.6
3.6
Table 36. Mean abundance of rotifers in Lake Huron in 1974, 1983, 1984 and
1985. Data from Stemberger et al (1979), Evans (1986), Makarewicz (1987,
1988) and this study. NF - not found in short tow.
Colletheca
sp.
Conochilus
unicornis
Filinia
longiseta
Gastropus
stylifer
KellicottLa
longiseta
Keratella
cochlearis
Keratella
earlinae
Notholca
squamula
Polyarthra
dolichoptera
Polyarthra
remata
Polyarthra
vulgaris
Synchaeta
kitina
Synchaeta
stylata
Synchaeta sp.
1974
1980
1983
1984
1985
April -Nov.
#/L
0.8
15.0
3.4
5.2
6.8
41.9
10.9
7.4
3.0
6.8
17.6
8.1
7.1
2.4
April -July
#/L
0.0
0.79
<0.1
0.27
1.15
1.86
<.01
1.8
0.12
0.12
0.05
NF
NF
1.03
Aug. -Oct.
#/L
0.90
7.10
0.004
1.10
2.10
2.00
0.08
NF
0.07
0.01
3.00
NF
NF
0.10
April-Dec.
#/L
0.67
10.87
0.007
1.09
3.78
6.65
0.10
0.57
0.43
0.65
2.92
NF
NF
1.5
April-Nov
#/L
1.16
11.30
0.01
1.60
3.12
4.47
0.03
0.94
0.58
0.17
1.61
NF
Nf
1.02
144
-------
Table 37. Ratio of Calanoida to Cladocera plus Cyclopoida in Lake Huron, 1983,
1984 and 1985.
Station
61
54
45
37
32
27
12
09
06
(North)
Calanoida
Cyclopoida + Cladocera
1983 1984 1985
(South)
0.67
1.11
1.19
1.57
2.13
1.37
1.98
1.31
1.23
0.90
36
84
33
46
16
83
00
1.
2.
2,
.53
.38
,80
2.32
2.93
.10
.64
.19
1.89
2,
2,
3,
2.67
Table 38. Comparison of the plankton ratio (Calanoida/Cyclopoida+Cladocera)
between the northern stations of Lake Huron and Lake Michigan.
Lake Michigan
Station 77
Lake Huron
Station 61
Lake Mean
1983
0.37
0.67
1.49
1984
0.23
0.90
1.61
mean
0.32
0.78
1.55
Table 39. Abundance of selected zooplankton species in northern and southern
Lake Huron in 1984. Values are number/m^. Southern Lake Huron is defined as
south of Station 27.
Conochilus
unicornis
Kellicottia
longispina
Diaptotnus
minutus
1984
1985
Northern
Southern
12,526
4,729
14,183
7,869
1984
3,897
2,449
1985 1984 1985
Holopedium
gibberum
1984 1985
3,624
2,514
298
383
1,079
920
239
29
162
123
145
-------
Table 40. Correlation (r) of phytoplankton abundance with total phosphorus
concentrations and zooplankton abundance within individual cruises (10 sta-
tions) in Lake Huron, 1985. NO - observed.
Daphnia Daphnia Rotifera Calanoida Total
pulicaria spp. Phosphorus
4/22-23 NO .772 .800 .198 .180
4/29-30 -.148 .016 .207 -.154 -.669
6/9-10 -.215 .038 -.215 -.386 -.344
8/15-16 .232 -.156 .061 -.354 -.112
8/23-25 -.030 .003 -.167 -.198 .088
11/18-19 NO .093 -.113 -.156 .001
11/27-28 -.465 -.020 .222 -.407 -.476
146
-------
Table 41. Number of species and genera observed in each algal division or
grouping, Lake Erie, 1983, 1984 and 1985. Bac-Bacillariophyta, Cat-Chloroma-
nophyta, Chl-Chlorophyta, Chr-Chrysophyta, Col-Colorless flagellates,
Cry-Cryptophyta, Cya-Cyanophyta, Pic-Picoplankton, Eug-Euglenophyta,
Pyr-Pyrropnyta, Uni-Unidentified.
1983
176
108
29
14
16
.
15
8
2
3
1
Species
1984
171
96
28
15
18
3*
11
9
0
4
1
1985
162
115
29
19
20
3
8
6
2
4
1
Division
BAG
CHL
CHR
CRY
CYA
PIC
COL
PYR
EUG
UNI
CAT
TOTAL 372 356 369
* Included in Cyanophyta in 1983.
1983
30
38
11
3
9
.
6
4
2
0
0
Genera
1984
30
38
14
4
10
0
4
4
0
0
0
1985
29
37
14
3
9
0
3
4
2
0
0
103
104
101
Table 42. Number of species identified and percentage of species belonging to
various taxonomic groups. 1970 data represent the mean for the Central, West-
ern and Eastern Basins [modified from Munawar and Munawar (1976)].
Number of Species
Division
BAG
CHL
CHR
CYA
CRY
EUG
PYR
PIC
UNI
COL
1970
134.3
16.3
58.0
6.3
11.2
3.3
0.7
4.0
1983
372
1984
356
Percent Composition
47.3
29.0
7.8
4.3
3.8
0.5
2.2
0.8
4.0
48.0
27.0
7.9
5.1
4.2
0.0
0.0
0.8
1.1
3.1
1985
369
43.9
31.2
7.9
5.4
5.1
0.5
1.6
0.8
1.1
2.2
147
-------
Table 43. Relative abundance of major phytoplankton divisions in Lake Erie,
1983 - 1985. Picoplankton are not included. BAC-Bacillariophyta, CAT-Chloro-
manophyta, CHL-Chlorophyta, CHR-Chrysophyta, COL-Colorless Flagellates,
CRY-Cryptophyta, CYA-Cyanophyta, EUG-Euglenophyta, PYR-Pyrrophyta,
UNI-Unidentified.
Division
%
Biovolume/mL
%
Cells/mL
1983
BAG
CAT
CHL
CHR
COL
CRY
CYA
EUG
PYR
UNI
60
<0
15
0
0
9
3
<
8
2
.4
.1
.0
.9
.1
.1
.4
.1
.5
.5
1984
48
0
11
1
0
13
3
0
12
8
.1
.0
.6
.6
.6
.2
.8
.0
.9
.0
1985
63
<0
8
1
0
7
4
<0
10
2
.2
.1
.8
.4
.7
.8
.3
.1
.7
.9
1983
8.
<0.
12.
4.
0.
11.
32.
<0.
0.
30.
9
1
6
0
5
2
6
1
2
1
1984
11
0
4
4
2
12
31
0
0
32
.2
.0
.8
.5
.9
.0
.5
.0
.3
.6
1985
14.9
<0.1
12.9
10.1
5.6
15.6
25.8
<0.1
0.4
14.6
148
-------
Table 44. Phytoplankton and zooplankton biomass, total phosphorus and chloro-
phyll a concentrations in the Western, Central and Eastern Basins of Lake
Erie, 1983, 1984 and 1985. Picoplankton are not included. To allow
comparisons between years, two samples from spring (April and May), summer
(August) and winter (late October through December) were averaged. Values are
in g/m-* unless noted otherwise. Total phosphorus and chlorophyll a are the
averages of the 3m samples.
Western
Central
Eastern
Phytoplankton
Abundance
(cells/mL)
1983
1984
1985
Biomass
1983
1984
1985
mean
Zooplankton
Biomass
1984
1985
Abundance
1984 (#/L)
1985
11,430
9,479
10,637
1.48
1.36
1.62
1.75
0.055
0.084
295.6
342.0
Total Phosphorus
1983(ug/L) 26.8
1984(ug/L) 23.9
1985(ug/L) 23.8
Chlorophyll a
1983(ug/L) 5.68
1984(ug/L) 5.10
1985(ug/L) 6.59
4,642
4,186
3,509
1.59
0.75
1.38
1.31
0.052
0.117
94.3
211.7
16.8
19.4
13.9
4.05
3.27
2.88
3,519
2,953
2,220
0.83
0.53
0.54
0.70
0.054
0.096
130.4
154.7
12.8
12.4
10.3
2.22
2.11
0.84
Entire
Lake
(mean±S.E.
6,187±750
5,331±462
4,483±568
1.35±.13
0.86±.08
1.22±.ll
0.053±.0062
0.106±.0098
159.6±25
221.6+27
149
-------
Table 45. Location of maximum abundance of selected common species in 1983,
1984 and 1985, Lake Erie.
1983
1984
1985
Actinocyclus normanii
f. subsalsa
Fragilaria crotonensis
Fragilaria capucina
Melosira granulata
Melosira islandica
Stephanodiscus sp.
Stephanodiscus binderanus
Tabellaria flocculosa
Oscillatoria tennis
Oscillatoria limnetica
Oscillatoria subbrevis
Anacystis montana
var. minor
Aphanizomenon flos-aquae
spheres
Cryptomonas erosa
Chroomonas norstedtii
Merismopedia tenuissima
Pediastrum simplex
var. duodenarium
Coelosphaerium naegelianum
Scenedesmus ecornis
Peridinium aciculiferum
Asterionella formosa
Gymnodinium sp.#2
Haptophyte
Western
Western
Western
Western
not common
not common
Western
Western
Western
Western
Western
not common
Western
Western
not common
Western
Western
Western
Western
not common
Western
not common
Western
Western
Central
not common
not common
Western
Western
Central
not common
Western
Western
not common
not common
Western
Western
not common
not common
Western
Western
Western
Western
Western
Western
Western
Western
Western
Western
Western
not common
Central
Central
Central
Central
not common
not common
not common
Western
Western
Western
Central
Central
Central
Central
Western
not common
not common
not common
not common
not common
not common
150
-------
Table 46. Summary of common phytoplankton species occurrence in western basin,
Lake Erie during 1983. Summary is based on all samples analyzed with picoplankton
removed. Summary includes the maximum population density encountered, the average
population density and biovolume, and the relative abundance (% of total cells
and % of total biovolume). Common species were arbitrarily defined as having
an abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
TAXON
BACILLAR10PHYTA
Actinocyclus normanii f. subsalsa
Cyclotella meneghiniana
Diatoma tenue v. elongatum
Fragilaria capucina
Fragilaria crotonensis
Fragilaria intermedia v. fallax
Melosira granulate
Helosira islandica
Rhizosolenia eriensis
Rhizosolenia sp.
Stephanodiscus alpinus
Stephanodiscus alpinus?
Stephanodiscus binderanus
Stephanodiscus niagarae
Synedra f iliformis
Tabellaria flocculosa
Tabellaria flocculosa v. linearis
Tabellaria sp.
CHLOROPHYTA
Cosmarium sp.
Mougeotia sp.
Oocystis borgei
Total
Total
CHRYSOPHYTA
Dinobryon cylindrical)
CRYPTOPHYTA
Cryptomonas erosa
Cryptomonas marssonii
Cryptomonas marssonii v.?
Rhodomonas mi nuta v. nannoplanktica
Total
CYANOPHYTA
Anabaena spirpides
Anacystis marina
Anacystis montana v. minor
Aphanizomenon flos-aquae
Coccochloris penipcystis
Merismopedia tenuissima
Oscillatoria limnetica
Oscillatoria subbrevis
Oscillatoria tenuis
MAXIMUM
CELLS/ML
88
181
209
603
554
85
555
104
671
507
78
38
234
20
482
316
49
111
25
352
115
255
286
65
139
1,890
687
141,208
5,072
2,561
1,227
15,544
1 1 , 266
27,399
5,081
AVERAGE X OF
CELLS/ML
11.8
19.3
19.7
92.5
173.3
18.2
81.5
9.9
40.9
25.7
13.8
4.7
50.8
3.4
29.4
39.8
9.0
8.0
2.3
36.2
14.4
28.0
73.2
16.9
18.7
701.5
64.7
52,613.9
560.8
189.3
474.7
1,221.7
1,561.1
1,421.6
291.4
TOTAL
CELLS
0.02
0.03
0.03
0.14
0.27
0.03
0.13
0.02
0.06
0.04
0.02
0.01
0.08
0.01
0.05
0.06
0.01
0.01
1.01
0.00
0.06
0.02
0.08
0.04
0.11
0.03
0.03
1.09
1.26
0.10
81.55
0.87
0.29
0.74
1.89
2.42
2.20
0.45
MEAN
BIOVOLUME
CU.uM/mL
80,734
7,759
11,164
21,406
89,972
7,974
36,996
10,453
17,568
191,069
18,270
8,913
26,409
61,310
8,980
103,387
18,269
17,419
76,094
24,055
9,634
10,533
163,058
14,964
9,811
35,741
8,455
14,105
5,004
14,962
1,320
382
11,499
55,610
16,374
X OF TOTAL
BIOVOLUME
5.40
0.52
0.75
1.43
6.02
0.53
2.47
0.70
1.17
12.77
1.22
0.60
1.77
4.10
0.60
6.91
1.22
1.16
49.34
5.09
1.61
0.64
7.34
0.70
10.90
1.00
0.66
2.39
14.95
0.57
0.94
0.33
1.00
0.09
0.03
0.77
3.72
1.09
Total
90.52
8.54
151
-------
Table 46(cont.)- Summary of common phytoplankton species occurrence in western
basin, Lake Erie during 1983. Summary is based on all samples analyzed with
picoplankton removed. Summary includes the maximum population density encoun-
tered, the average population density and biovolume, and the relative abundance
(% of total cells and % of total biovolume). Common species were arbitrarily
defined as having an abundance of > 0.5% of the total cells or >0.5% of the total
biovolume.
PYRROPHYTA
Gymnodinium sp. 16 0.8 0.00 7.721 0.52
Peridinium sp. 25 3.7 0.01 7,987 0.53
Total 0.01 1.05
UNIDENTIFIED
Unidentified flagellate - ovoid 3,960 1,422.2 2.20 24,807 1.66
Unidentified flagellate - spherical 1,252 517.1 0.80 9,904 0.66
Total 3.01 2.32
Total 95.92 84.24
152
-------
Table 47. Summary of common phytoplankton species occurrence in western basin,
Lake Erie during 1984. Summary is based on all samples analyzed with picoplankton
removed. Summary includes the maximum population density encountered, the average
population density and biovolume, and the relative abundance (% of total cells
and % of total biovolume). Common species were arbitrarily defined as having
an abundance of > 0.5% of the total cells or >0.5% of the total biovolume.
TAXON
BAC1LLARIOPHYTA
Actinocyctus normanii f. subsalsa
Asterionella formosa
Fragilaria capucina
Fragilaria crotonensis
Metosira granulate v. granulate
Melosira islandica
Stephanodiscus alpinus
Stephanodiscus binderanus
Stephanodiscus niagarae
Stephanodiscus parvus
Stephanodiscus sp.
labeltaria flocculosa
CHLOROPHYTA
Cosmarium sp.
Monoraphidi urn contortum
Oocystis borgei
Pediastrum simplex v. duodenarium
CHRYSOPHYTA
Chrysosphaerella longispina
Dinobryon cylindricum
Haptophyceae
COLORLESS FLAGELLATES
Colorless flagellates
Stelexmonas dichotoma
Total
Total
Total
Total
CRYPTOPHYTA
Chroomonas norstedtii
Cryptomonas erosa
Cryptomonas pyrenoidifera
Cryptomonas rostratiformis
Rhodomonas mi nuta v. nannoplanktica
MAXIMUM
CELLS/ML
16
143
407
826
247
1,564
77
2,506
120
512
776
207
25
386
180
393
1,088
360
1,317
376
1,186
425
295
344
33
2,348
'ERAGE X OF
.LS/ML
1.0
39.4
87.6
181.1
17.9
107.6
9.1
159.1
6.1
58.8
95.9
27.1
1.7
58.0
13.9
27.8
36.9
37.9
139.6
49.2
164.1
73.6
49.1
24.5
4.0
689.3
TOTAL
CELLS
0.01
0.42
0.92
1.91
0.19
1.13
0.10
1.68
0.06
0.62
1.01
0.29
8.34
0.02
0.61
0.15
0.29
1.07
0.39
0.40
1.47
2.26
0.52
1.73
2.25
0.78
0.52
0.26
0.04
7.27
MEAN
BIOVOLUME
CU.uM/mL
8,220
103,692
24,746
124,332
7,706
123,141
13,882
43,676
162,706
2,394
8,269
60,946
74,100
420
10,964
37,884
10.022
8,790
2,905
1,304
5,846
1,914
95,413
10,641
12.958
53.586
X OF TOTAL
BIOVOLUME
0.60
7.62
1.82
9.13
0.57
9.05
1.02
3.21
11.95
0.18
0.61
4.48
50.22
5.44
0.03
0.81
2.78
9.06
0.74
0.65
0.21
1.60
0.10
0.43
0.53
0.14
7.01
0.78
0.95
3.94
Total
8.87
12.82
153
-------
Table 47(cont.). Summary of common phytoplankton species occurrence in western basin, Lake Erie during 1984.
Summary is based on all samples analyzed with pi coptankton removed. Summary includes the maximum population
density encountered, the average population density and biovolume, and the relative abundance (X of total cells
and X of total biovolume). Common species were arbitrarily defined as having an abundance of t 0.5X of the
total cells or sO.5% of the total biovolume.
CYANOPHYTA
Agmenellum quadruplicatum 1,047 54.5 0.58 15 0.00
Anabaena sp. 1,162 90.7 0.96 15,300 1.12
Anacystis montana v. minor 22,253 1,939.2 20.46 9,738 0.72
Anacystis montana v. montana 6,954 234.3 2.47 16,456 1.21
Aphanizomenon flos-aquae 2,643 259.6 2.74 18,707 1.37
Coelosphaerium naegelianum 3,436 276.4 2.92 1,158 0.09
Gomphosphaeria lacustris 2,544 99.3 1.05 2,677 0.20
Merismopedia tenuissima 6,218 303.5 3.20 364 0.03
Oscillatoria limnetica 5,179 395.2 4.17 1,481 0.11
Spiralina subtilissima 3,788 114.8 1.21 307 0.02
Total 39.75 4.86
PYRROPHYTA
Peridinium sp. 41 5.0 0.05 9,773 0.72
UNIDENTIFIED
Unidentified flagellate - ovoid 4,303 1,600.5 16.88 50,524 3.71
Unidentified flagellate - spherical 2,479 806.2 8.51 27,835 2.04
Total 25.39 5.76
CSSSSZSSS3E KSSSSSSSSS
Total 87.98 85.56
154
-------
Table 48. Summary of comnon phytoplankton species occurrence in western basin, Lake Erie during 1985. Summary
is based on all samples analyzed with pfcoplankton removed. Summary includes the maximum population density
encountered, the average population density and biovolume, and the relative abundance (X of total cells and X
of total biovolume). Common species were arbitrarily defined as having an abundance of > 0.5X of the total
cells or >0.5X of the total biovolume.
TAXON
BACULARIOPHYTA
Actinocyclus normanii f. subsalsa
Asterionella formosa
Cyclotella comensis v. 1
Cyclotelia meneghiniana
Diatoma tenue v. elongatum
Fragjlaria capucina
Fragilaria crotonensis
Nelosira island)ca
Rhizosolenia eriensis
Rhizosolenia longiseta
Skeletonema potamos
Stephanodiscus alpinus
Stephanodiscus binderanus
Stephanodiscus niagarae
Stephanodiscus parvus
Stephanodiscus sp.
labellaria flocculosa
CHLOROPHYTA
Actinastrum hantzschii
Botryococcus sp.?
Cosmarium sp.
Green coccoid - ovoid
Green coccoid - sphere
MonorapMdium contortum
Scenedesmus acuminatus
Scenedesmus quadricauda
CHRYSOPHYTA
Chrysophycean coccoids
Dinobryon divergens
Haptophyceae
COLORLESS FLAGELLATES
Colorless flagellates
Stelexmonas dichotoma
Total
Total
Total
Total
CRYPTOPHYTA
Cryptomonas erosa
Rhodomonas minute v. nannoplanktica
MAXIMUM
CELLS/ML
137
173
612
498
335
598
556
202
104
168
671
120
167
40
1.051
335
199
393
1,841
16
794
540
303
65
311
1,014
254
1,530
777
614
131
4,712
AVERAGE X OF
CELLS/ML
19.5
34.4
82.6
50.2
27.3
78.4
124.6
31.1
33.2
16.6
125.8
31.7
36.0
8.0
118.0
94.6
37.4
53.6
220.4
3.2
112.3
88.6
110.9
11.4
83.6
176.8
24.1
372.3
212.3
113.6
49.1
1,019.5
TOTAL
CELLS
0.18
0.32
0.78
0.47
0.26
0.74
1.17
0.29
0.31
0.16
1.18
0.30
0.34
0.08
1.11
0.89
0.35
8.92
0.50
2.07
0.03
1.06
0.83
1.04
0.11
0.79
6.43
1.66
0.23
3.50
5.39
2.00
1.07
3.06
0.46
9.58
MEAN
BIOVOLUME
CU.uM/mL
195,513
13,835
3,216
15,104
18,681
21,506
79,571
24,829
86,595
16,678
7.415
37,412
15,982
154,628
5,153
8,482
65,255
1,590
7,001
108,819
5,699
9,424
1,299
12,057
3,627
2,015
11,806
8,632
6,577
4,868
64.679
69,555
X OF TOTAL
BIOVOLUME
12.05
0.85
0.20
0.93
1.15
1.33
4.90
1.53
5.34
1.03
0.46
2.31
0.99
9.53
0.32
0.52
4.02
47.45
0.10
0.43
6.71
0.35
0.58
0.08
0.74
0.22
9.21
0.12
0.73
0.53
1.38
0.41
0.30
0.71
3.99
4.29
Total
10.05
8.28
155
-------
Table 48(cont.). Summary of cormon phytoplankton species occurrence in western basin. Lake Erie during 19S5.
Summary is based on all samples analyzed with picoplankton removed. Summary includes the maximum population
density encountered, the average population density and biovolume, and the relative abundance (X of total cells
and X of total biovolume). Common species were arbitrarily defined as having an abundance of > 0.5X of the
total cells or >0.5X of the total biovolume.
CYANOPHYTA
Agmenellum quadruple caturn
Anabaena flos-aquae
Anabaena sp.
Anabaena spiroides
Anacystis montana v. minor
Aphanizomenon flos-aquae
Gomphosphaeria lacustris
Merismopedia tenuissima
Oscillatoria limnetica
Oscillatoria minima
Oscillatoria subbrevis
PYRROPHYTA
Gymnodinium helveticum
Gymnodinium sp.
Peridinium sp.
Total
Total
UNIDENTIFIED
Unidentified flagellate - ovoid
Unidentified flagellate - spherical
Total
2,806
3,199
4,761
6,823
1,661
9,228
1,064
1,636
8,271
974
4,140
8
25
8
1,808
556
404.5
177.7
360.0
379.1
323.2
1,047.7
98.2
127.3
1,139.9
98.6
' 437.7
0.5
3.2
1.4
703.6
181.8
3.80
1.67
3.38
3.56
3.04
9.85
0.92
1.20
10.72
0.93
4.11
43.19
0.00
0.03
0.01
0.05
6.61
1.71
8.32
85.41
212
4,341
13,773
33,022
3,657
128,727
813
67
12,552
1,311
14,644
10,708
8,958
15,480
38,539
8,650
0.01
0.27
0.85
2.04
0.23
7.93
0.05
0.00
0.77
0.08
0.90
13.13
0.66
0.55
0.95
2.17
2.38
0.53
2.91
85.23
156
-------
Table 49. Phytoplankton common (abundance >0.5% of the total cells or >0.5%
of the total biovolume) in 1985 but not in 1983 and 1984, Lake Erie.
Bacillariophyta
Rhizosolenia eriensis
SurLeila biseriata var. bifrons
Rhizosolenia eriensis
Chlorophyta
Botryococcus sp.?
Chlamydocapsa planktonica
Green coccoid - ovoid
Green coccoid - sphere
Oedogonium sp.
Scenedesmus quadricauda
Cyanophyta
Anabaena flos-aquae
Anabaena spiroides
Chrysophyta
Chrysophycean coccoids
Cryptophyta
Rhodomonas lens
Pyrrophyta
Amphidinium sp.
Table 50. Average abundance and biomass of Rhizosolenia eriensis, Oedogonium
sp. and Amphidinium sp., Lake Erie, 1985.
cells/mL urn^/mL
1983 1984 1985 1983 1984 1985
(n-77) (n-117)(n-100) (n-77) (n-117)(n-100)
Rhizosolenia
eriensis 11.7 1.4 6.1 5,019 1,180 16,007
Oedogonium sp. 3.1 2.4 15.2 4,549 905 19,495
Amphidinium sp. 4.1 2.9 4.8 3,870 1,183 17,515
157
-------
Table 51. Importance of Asterionella formosa during the spring of 1984 and
1985, Lake Erie. 1984 sampling dates: 4/18, 4/20, 5/1. 1985 sampling dates:
4/24, 4/27.
Biovolume (g/m^) All Species
Rank 1984 1985
1 0.162 (Asterionella formosa) 0.406 (Stephanodiscus niagarae)
2 0.160 (Fragilaria crotonensis) 0.164 (Peridiium sp.)
3 0.123 (Melosira islandica) 0.072 (Ehodomonas minuta)
4 0.109 (Gymnodinium sp.) 0.066 (Tabellaria flocculosa)
Abundance (#/mL) Diatoms Only
1 238 (Stephanodiscus sp.) 88 (Fragillaria crotonensis)
2 224 (Asterionella formosa) 70 (Stephanodiscus parvus)
3 170 (Fragillaria crotonensis) 62 (Staphanodiscus hantzschii)
4 117 (Stephanodiscus parvus) 59 (Fragillaria capucina)
158
-------
Table 52. Mean maximum biomass of selected common phytoplankton species in
1970, 1983, 1984 and 1985, Lake Erie. Data from Munawar and Munawar (1976)
and this study. 1970 data - graphical accuracy. Percent reduction is from
1970 to the average of 1983 to 1985.
Actinocyclus
normanii
Stephanodiscus
niagarae
Stephanodiscus
tenuis
Stephanodiscus
binderanus
Fragilaria
crotonensis
Fragilaria
capucina
Peridinium
aciculiferum
Ceratium
hirundinella
Rhodomonas
minuta
Cryptomonas
erosa
Pediastrum
simplex
Staurastrum
paradoxum
Aphanizomenon
flos-aquae
BASIN
Western
Eastern
Central
Western
Western
Western
Eastern
Central
Western
Central
Eastern
Central
Eastern
Central
Eastern
Eastern
Central
Western
Central
Central
Western
1970
g/m3
4
1
2
0
1
0
1
3
7
2
0
0
1
1
2
1
0
2
0
0
2
.7
.4
.3
.6
.8
.5
.0
.4
.9
.4
.4
.2
.0
.8
.0
.6
.4
.0
.4
.4
.0
1983
g/m3
0
1
2
0
0.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.30
.05,
.19
.12
001
.11
.15
.11
.18
.02
.04
.06
.05
.35
.31
.04
.10
.63
.06
.07
.10
1984
g/m3
0
0
0
1
0.
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.05
.22
.53
.14
002
.04
.45
.16
.29
.03
.01
.18
.03
.13
.35
.05
.14
.40
.00
.00
.09
1985 Mean Percei
83-85 Reduct
g/m3 g/m3
0
0
1
0
0.
0
0
0
0
0
0
0
0
0
0
.68
.47
.60
.35
015
.07
.01
.09
.28
.33
.01
.00
.00
.22
.07
0.0002
0.0003
0.
0.
0.
0.
13
11
00
48
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.34
.58
.44
.54
006
.07
.19
.12
.25
.14
.02
.08
.03
.28
.24
.03
.08
.39
.06
.02
.22
93
59
37
11
99
85
81
96
97
94
95
60
97
84
88
98
80
81
86
94
89
159
-------
Table 53. Distribution of indicator species in the Western Basin of Lake
Erie. The classification scheme of Tarapchak and Stoermer (1976) was uti-
lized. Only diatoms contributing 5% or more of the biomass for a cruise are
classified. Mi - mesotrophic but intolerant of nutrient enrichment, M£ -
mesotrophic and tolerant of moderate nutrient enrichment, E - eutrophic. 1970
data are from Munawar and Munawar (1976). 1978 data are from Devault and
Rockwell (1986).
MI M2 E M1+M2/E
1970 0 1 5 0.2
1978 0 3 3 1.0
1983 1 2 3 1.0
1984 3 2 2 2.5
1985 2 2 2 2.0
Table 54. Trophic status of the Western, Central and Eastern basins of Lake
Erie in 1970, 1983/84 and 1985. The classification scheme of Munawar and
Munawar <1982) is u$ed, 1970 data is from Munawar and Munawar (1982). Based
on average biomass of basins in 1983, 1984 and 1985.
1970 1983 + 1984 1985
Eastern Basin mesoeutrophic oligotrophic oligotrophic
Central Basin mesoeutrophic mesotrophic mesotrophic
Western Basin eutrophic mesotrophic mesotrophic
160
-------
Table 55. Relative abundance of zooplankton in Lake Erie.
Rotifera
Cladocera
Copepoda nauplii
Cyclopoida
Calanoida
Harpacticoida
Amphipoda
Percent
Biomass
1983
N
0
T
C
A
L
C
U
L
A
T
E
D
1984
13
40
12
17
16
<0
.6
.5
.3
.1
.5
. 1
1985
5
35
12
23
23
<0 .
.5
.1
.8
.4
.2
1
1983
69.
6,
15.
5.
3.
<0.
2
0
8
4
7
1
Percent
Abundance
1984
80
3
10
3
2
<0
.1
.2
.4
.9
.5
. 1
1985
70
4
15
5
4
<0
.8
.2
.2
.3
.4
. 1
0.0
0.0
0.0
161
-------
Table 56. Summary of common zooplankton species occurrence in Lake Erie dur-
ing 1985. Species were arbitrarily classified as common if they accounted for
>0.1% of the total abundance or >1.0% of the total bioraass, with the exception
of rotifers. Rotifer species were considered common if they accounted for
>1.0% of the total abundance.
TAXON
COPEPODA
Copepoda - nauplii
Cyclopoida
Cyclopoid - copepodite
Cyclops bicuspidatus thomasi
Cyclops vernal is
Mesocy clops - copepodite
Hesocyclops edax
Tropocyclops prasinus mexicanus
Calanoida
Di apt onus - copepodite
Di apt onus oregonensis
CLADOCERA
Bosmina longirostris
Chydorus sphaericus
Daphnia galaeta mendotae
Daphnia retrocurva
Diaphanosoma sp.
Eubosmina coregoni
Eurycercus lamellatus
Leptodora kindtii
ROTIFERA
Ascomorpha oval is
Asplanchna priodonta
Conochilus unicornis
Kellicottia longispina
Keratella cochlearis
Keratella crassa
Keratella hiemalis
Keratella quadrats
Notholca squamula
Polyarthra dolichoptera
Polyarthra major
Polyarthra remata
Polyarthra vulgaris
Synchaeta sp.
MAXIMUM
DENSITY
(#/m3>
140,098
32,818
10,832
8,151
14,157
9,609
2,095
42,227
19,032
49,548
15,229
23,680
11.583
21,621
20,735
1.244
1,001
97,548
21,021
805,564
27,348
156,229
42,041
46,910
250,959
88,817
79,390
31,531
107,784
1215683
468,620
AVERAGE
DENSITY
(tf/m3)
33,761.3
6,137.1
1,670.1
220.0
1,925.0
1,075.7
528.3
6,091.8
3,013.9
1,834.0
639.6
2,030.6
1,459.0
1,194.7
2,072.2
37.2
42.3
5,048.9
797.9
39,199.1
4,048.2
17,431.4
2,315.4
5,315.6
5,443.4
10,191.3
5,908.5
3,847.8
3,223.2
27,294.5
16,262.1
% OF TOTAL
ABUNDANCE
15.24
2.77
0.75
0.10
0.87
0.49
0.24
2.75
1.36
TOTAL 24.56
0.83
0.29
0.92
0.66
0.54
0.94
0.02
0.02
TOTAL 4.20
2.28
0.36
17.69
1.83
7.87
1.05
2.40
2.46
4.60
2.67
1.74
1.45
12.32
7.34
TOTAL 66.04
=~=±S = E = = ZS
MEAN
BIOMASS
(ug/m5)
13,505
5,244
7,941
1,239
3,169
6,369
718
9,704
13,248
2,146
737
12.956
6,975
2,119
4,703
5,102
1,088
102
1,133
412
63
66
112
197
368
209
289
424
59
1,150
458
X OF TOTAL
BIOMASS
12.76
4.95.
7.50
1.17
2.99
6.02
0.68
9.17
12.52
57.77
2.03
0.70
12.24
6.59
2.00
4.44
4.82
1.03
33.85
0.10
1.07
0.39
0.06
0.06
0.11
0.19
0.35
0.20
0.27
0.40
0.06
1.09
0.43
4.76
TOTAL 94.80
96.38
162
-------
Table 57. Common zooplankton species observed in either 1983, 1984 or 1985
but not in all three years, Lake Erie. 1983 and 1984 data are from Makarewicz
(1987, 1989). Yes - common. No - not common.
1983 1984 1985
Calanoida
Diaptomus siciloides yes no no
Cladocera
Daphnia pulicaria no yes no
Diaphanosoma
leuchtenbergianum yes no yes
Eurycercus lamellatus no no yes
Leptodora kindtii no yes yes
Rotifera
Ascomorpha oval is no yes yes
Ascotnorpha ecaudis yes no no
Asplanchna priodonta no yes yes
Brachnionus sp. yes yes no
Kellicottia longispina yes no no
Keratella earlinae no yes no
Keratella hiemalis yes no yes
Keratella quadrata no no yes
Nolthoca folicea yes yes no
Nolthoca laurentiae yes yes no
Notholca squamala no yes yes
Polyarthra retnata no yes yes
163
-------
Table 58. Abundant (1967) and predominant (1983-1983) rotifer species in
1967, 1983 1984 and 1985, Lake Erie. Values in parentheses represent percent-
age of total abundance.
1967
Brachionus
angularis
Brachionus
calyciflorus
Conochilus
unicornis
Keratella
cochlearis
Keratella
quadrata
Kellicottia
longispina
Synchaeta
sp.
Polyarthra
vulgaris
1983
Polyarthra
vulgaris(18.4)
Synchaeta
sp. (9.5)
Keratella
cochlearis(7.3)
Conochilus
unicornis(5.3)
Keratella
hiemalis(3.5)
Brachionus
sp.(3.0)
1984
1985
Polyarthra Conochilus
vulgaris(22.5) unicornis(17.7)
Synchaeta
sp. (9.5)
Polyarthra
major(4.9)
Polyarthra
vulgaris (12.2)
Keratella
cochlearis(7.9)
Notholca Synchaeta
squamula(ll.1) sp. (7.4)
Keratella Notholca
cochlearis(4.9) squamula(4.6)
Polyarthra
dolichoptera(2.7)
164
-------
Table 59. Occurrence of eutrophic zooplankton indicator species in Lake Erie,
1984 and 1985. Values - mean number/nH
BASIN
Western
84 85
Brachionus angularis
B. budapestinen*
B. calyciflorus
B. caudatus
Filinia long Ls eta
Keratella cochlearis f.
Trichocerca cylindrica
T. elongata*
I. multicrinis
T. pusilla
177
92
97
81
459
tecta 2,062
397
907
477
36
1,156
445
72
0
563
5,359
2,823
0
2,297
0
Central
84 85
0
0
0
0
2.8
9.2
0
0
42
0
366
0
0
0
179
0
0
0
770
0
Eastern
84 85
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
36
0
* Not listed as a eutrophic species by Gannon and Stemberger (1978).
Table 60. Ratio of Calanoida abundance to Cladocera plus Cyclopoida abundance
in Lake Erie, 1983 to 1985. Nauplii are not included in the ratio.
1983
1984
1985
WESTERN
BASIN
0.19
0.27
0.16
CENTRAL
BASIN
0.31
0.42
0.49
EASTERN
BASIN
0.45
0.36
0.59
MEAN
0.32
0.35
0.41
165
-------
Table 61. Correlation (r) of phvtoplankton abundance with total phosphorus
concentrations and zooplankton abundance within individual cruises in Lake
Erie 1984. NO - observed.
Daphnia Daphnia Rotifera Calanoida Total
pulicaria spp. Phosphorus
4/18-19 NO .535 .714 .343 .801
5/1-2 NO -.941 -.771 -.992 -.811
8/5-6 -.509 -.079 .021 -.534 .756
8/19-20 -.548 .061 .929 -.383 .910
12/4-5 NO -.448 .097 -.345 .505
166
-------
Table 62. Number of common species shared by Lake Michigan^ Lake Huron and
three basins in Lake Erie3 and the Percentage of Similarity" between lake
basin pairs in 1985.
Lake Lake Lake Lake Lake
Michigan Huron Erie-W Erie-C Erie-E
Number of
Common Species 43 47 48 43 40
Number
Lake
Lake
Lake
Lake
Lake
Michigan
Huron
Erie-W
Erie-
Erie-
C
E
51
42
32
33
.36
.77
.33
.91
Percentage
24
35.
18.
19.
of
65
26
19
of Shared
22
27
33
36
.28
.03
Common
18
20
29
70.42
Similarity between
Species
18
19
27
30
lake basins
-W: Western Basin; Erie-C: Central Basin; Erie-E:Eastern Basin
^Percent of Similarity was calculated as the sum of the lesser biovolume for
all shared species between lake basins.
167
-------
Table 63. Number of shared species with Relative Percent Difference3 (RPD) >
1 (Upper) and percent of shared species with RPD > 1 (Lower) based on biovo-
lume of common phytoplankton species in Lakes Michigan, Huron and ErieD in
1985.
Lake
Michigan
Lake
Huron
Lake
Erie-W
Lake
Erie-C
Lake
Erie
-E
Number of
Common Species 43 47 48 43 40
Lake
Lake
Lake
Lake
Lake
Michigan
Huron
Erie-W
Erie-C
Erie-E
17
27
50
39
Number
4
22
30
37
of Shared
6
6
41
37
Species
9
6
12
17
with PPD >
7
7
10
5
1
Percentage of Shared Species with RPD > 1
aRPD - the difference in percent biovolume of each species between two lakes
basins divided by the average percent biovolume for that species i.e., (:a-
b:)/(a+b)/2, where a - percent biovolume in basin a, and b - percent biovolume
in basin b.
: Western Basin; Erie-C: Central Basin; Erie-E: Eastern Basin.
168
-------
10
Lake Erie
Main Lake Sampling Station
Lake Ontario
Lake
Huron
A
N
Michigan
ri_t__ji JLake
Detroit yst.clair
Erie New York
Pennsylvania
Cleveland
Ohio
United States
Figure 1. Lake Erie plankton sampling stations, 1985.
-------
Station Locations
Lake Michigan - Main Lake
Manistique
Traverse City
34 A Michigan
Ludington
Petosky
Muskegon
Benton Harbor
Figure 2. Lake Michigan sampling stations, 1985.
170
-------
Lake Huron
Main Lake
Sampling Locations
Figure 3. Lake Huron sampling stations, 1985.
-------
ro
PEA
on »
I?
VOI-*
00
rt
o
-
I
ft
§
I
rt
n
n
I
mm3/L
CELLSx1000/ML
p
b
o
xl
CD
-------
0)
Q_
0.9
o
5 0.6-
o
CD
8 0.3
0.0
LAKE MICHIGAN
BAG
CRT
M J J A S 0 N
v
3
m
o>
e
V
Q_
I CHL
CHR
A CYA
A PYR
D PIC
0.0
Figure 5. Seasonal distribution of Algal divisions in Lak* Michigan.
Bac-Bacillariophyta, Chl-Chlorophyta, Chr-Chrysophyta, Col-C.plorless flagel-
lates, Cry-Cryptophyta, Cya-Cyanophyta, Pic-picoplankton, fyr-Pytrophyta,
Uni-unidentified flagellates, 1985.
173
-------
i
I
Cryptomonas ovata
Figure 6. Seasonal distribution of Cryptomonas ovata, Lake Michigan, 1985.
-------
01
Rhodomonas lens
Figure 7. Seasonal distribution of Rhodomonas lens, Lake Michigan, 1985,
-------
Gymnodinlum helvetlcum f. achroum
Figure 8. Seasonal distribution of Gymnodinlum helvetlcum, Lake Michigan,
1985.
-------
IDU-
1
53 80-
Ld
O
i
i
>
Cyclotella comensis
1982
1984
1986
Figure 9. Average abundance of Cyclotella comensis In 1983, 1984 and 1985,
Lake Michigan.
-------
o
30 T
20-
10"
LAKE MICHGAN
OO Total
PIC
47 41 34 27
23
18
-H
11
O
O
O
o
1.5T
1.0--
0.5-
0.0
47
NORTH
o
-
A-
A-
D-
OBAC
CHL
ACHR
ACYA
DCRY
34 27
STATION
23 18
SOUTH
Figure 10. Annual geographical distribution of major algal divisions
(numerical) in Lake Michigan. Bac-Bacillariophyta, Chl-Chlorophyta, Chr-Chry-
sophyta, Col-colorless flagellates, Cry-Cryptophyta, Cya-Cyanophyta, Pic-pico-
plankton, Pyr-Pyrrophyta, Uni-unidentified flagellates, 1985.
178
-------
E
O.BT
0.4
0.0
LAKE MICHIGAN
oo TOTAL
47 41 34 27 23 18 11
I
0.6T
0.4
0.2
0.0
47 41 34 27 23 18 11
0.04T
0.02
0.00
47
NORTH
41 34 27 23
STATION
18 11
SOUTH
Figure -fl. Annual geographical distribution of major algal divisions
(biomass) in Lake Michigan. Bac-Bacillariophyta, Chl-Chlorophyta, Chr-Chryso-
phyta, Col-colorless flagellates, Cry-Cryptophyta, Cya-Cyanophyta, Pic-pico-
plankton, Pyr-Pyrrophyta, Uni-unidentified flagellates, 1985.
179
-------
O
8
OO Aug21-23
Nov 14-16
AA Nov 29-Dec 4
BT
o
o
o
4..
OO April 15-22
May 1-2
A June 56
A Aug 17-20
A-
A-
47
NORTH
41
I 1
34 27
STATION
-H 1 1
23 18 11
SOUTH
Figure 12. Geographical distribution of phytoplankton abundance on all
cruises, Lake Michigan, 1985.
180
-------
LAKE MICHIGAN
10r
CO
O
O
O
5--
Ld
O
..
0
1960 1965 1970 1975 1980 1985
Figure 13. Historical abundance of phytoplankton in Lake Michigan.
Horizontal bars are the mean. Wide vertical lines are the standard error.
Thin vertical lines are the range. Data are from Stoermer and Kopczynska
(1967a and b), Rockwell et al. (1980), Makarewicz (1987) and this study.
Picoplankton are not included.
-------
LAKE MICHIGAN
90 T
60-
30--
H 1 1 1 1 1
AMJJASON
801
B
40-
1 1 1
AMJJASON
Figure 14. Seasonal zooplankton abundance in Lake Michigan, 1985.
182
-------
12T
LAKE MICHIGAN
Calanoida
DD Cladocera
AA Cyclopolda
AMJJASON
75 T
50-
25--
Copcpoda
DD Rotlfera
AMJJASON
Figure 15. Seasonal flucuation (numerical) of zooplankton groups in Lake
Michigan, 1985. Copepoda refers to the nauplius stage of the Copepoda.
183
-------
12T
LAKE MICHIGAN
Copepoda
DD Cyclopolda
AA Rotifera
AMJJASON
60 T
Calanolda
DD Cladocera
N
Figure 16. Seasonal flucuation (biomass) of zooplankton groups in Lake
Michigan, 1985. Copepoda refers to the nauplius stage of the Copepoda.
184
-------
CD
tn
1.0T
0.5--
0.0
U\KE MICHIGAN
Diaptomus sicilis
oo 1983
1984
A A 1985
77 64 57 47 41 34 27 23 18 11 06
NORTH SOUTH
STATION
Figure T7. Geographical distribution of Diaptomus sicilis in-Lake Michigan,
1985.
-------
00
2T
1 +
O
-
A-
A-
LAKE MICHIGAN
O Bosmina longirostris
Eubosmina coregoni
A Conochilus unicomis
A Holopedium gibberum
47
NORTH
41
34 27
STATION
23
18 11
SOUTH
Figure 18. Geographical distribution of selected zooplankton in Lake
Michigan, 1985.
-------
00
8T
LAKE MICHIGAN
OO Notholca laurentiae
AA N. squamula
DD N. follacea
Polyarthra remata
AA P. vulgaris
47 41
NORTH
34 27 23
STATION
18 11
SOUTH
Figure 19. Geographical distribution of selected zooplankton in Lake
Michigan, 1985.
-------
UVKE MICHIGAN
BT
4+
OO Calanotda
Cladocera
AA Cyclopolda
50 T
25--
OO Total
Copepoda
AA Rotifera
47 41
NORTH
34 27
STATION
23 18 11
SOUTH
Figure 20. Geographical distribution (numerical) of major zooplankton groups
in Lake Michigan, 1985. Copepoda - Copepoda nauplius.
188
-------
LAKE MICHIGAN
00
vo
OT
OT
a
E
g
m
150 T Lakewide Offshore Average
O 100m Station
40m Station
100--
50--
Total
Daphnia spp.
1974
1978
1982
1986
Figure 21. Historical trends in zooplankton biomass during July and August,
Lake Michigan. The 1984 and 1985 data (Makarewicz 1988, This Study) are the
mean of all offshore stations. Modified from Scavia et &1 (1986).
-------
UKE MICHIGAN 1985
0.18T
1-1.2
a
AMJJASOND
Figure 22. (A) Seasonal total algal and filamentous algal biomass and mean
weighted edible algal size in 1985; (B) The seasonal mean crustacean size and
Daphnia spp. and adult Calanoida abundance, 1985, Lake Michigan.
190
-------
o
o
o
X
3
UJ
O
40 T
30
20
10
1.0T
E
E
0.5
0.0
Total
A Total minus
plcoplankton
AMJJASON
1 - 1
B
1 - 1 - 1 - 1
AMJJASON
Figure 23. Seasonal phytoplankton biovolume and abundance trends in Lake
Huron, 1985.
191
-------
vo
LU
i
m
LJ
o
a:
UJ
CL
0.9T
LAKE HURON
0.6-- sn
0.3-
o1
o-
A-
A-
D-
OBAC
CHL
ACYA
ACHR
DCRY
PYR
VPIC
Figure 24. Seasonal distribution of algal (% biovolume) divisions in Lake
Huron, 1985. Bac-Bacillariophyta, Chl-Chlorophyta, Chr-Chrysophyta, Cry-Cryp-
tophyta, Cya-Cyanophyta, Pic-Picoplankton, Pyr-Pyrrophyta.
-------
0.50T
0.25
0.00
LAKE HURON
ID TOTAL
H 1 1 1 1
0.09 T
OOCHL
ODCHR
A CRT
0.00-1 1 1 1
0.02T
OCYA
nnwc
A PVR
0.00
61 54 45 37 32 27 12 09 06
NORTH SOUTH
STATION
Figure 25. Annual geographical distribution of major algal divisions in
Lake Huron, 1985.
193
-------
1.0T
0.5
0.0
LAKE HURON
O O Nov IB-IB
Nev 27-28
H 1 1 1 1 K
E
E
1.0T
0.5
oo Aug 15-18
Aug 23-25
0.0-1 1 1 1 1 1 1 1 1 1
1.0T
0.5
Oo Apr 22-29
Apr 29-30
AA Jun 09-10
I 1 1 1 1 1
61
NORTH
54 45 37 32 27 12 09 06
STATION
SOUTH
Figure 26. Seasonal geographical distribution of phytoplankton biomass,
Lake Huron, 1985. Bac-Bacillariophyta, Chl-Chlorophyta, Chr-Chrysophyta,
Cry-Cryptophyta, Cya-Cyanophyta, Pic-Picoplankton, Pyr-Pyrrophyta.
194
-------
en
Diatoma tenue v. elongatum
i
Figure 27. Geographical and seasonal distribution of Diatoma tenue var.
elongatum, Lake Huron.
-------
IO
Synedra ulna v. chaseana
Figure 28. Geographical and seasonal distribution of Synedra ulna var.
chaseana, Lake Huron.
-------
vo
Rhodomonas lens
Figure 29. Geographical and seasonal distribution of Rhodomonas 'lens, Lake
Huron.
-------
Agmenellum quadruplicatum
00
Figure 30. Geographical and seasonal distribution of Agmenellum
quadruplicatum, Lake Huron.
-------
to
vo
ro
E
o>
1.5T
LAKE HURON
1.0-
0.5-
0.0
1970
1974
1978
1982
1986
Figure 31. Historical offshore algal biomass trends in Lake Huron. Values
are the mean±S.E. and the range. Data are from Munawar and Munawar (1979),
Makarewicz (1987, 1988) and this study. 1980 data are modified froma GLNPO
data base (1980).
-------
120T
BO-
40--
LAKE HURON
1 1 1 1 1
AMJJASON
150
100-
50
1 1 1 1-
B
_ |
AMJJASON
Figure 32. Seasonal zooplankton biomass (A) and abundance (B) in Lake
Huron, 1985.
200
-------
LAKE HURON
10T
oo Cladoc«ra
Cyclopolda
AMJJASON
75 T
50--
25-
oo Calanolda
Copapoda
«rw Rotlfero
B
AMJJASON
Figure 33. Seasonal fluctuation (numerical) of zooplankton groups in Lake
Huron, 1985. Copepoda refer to the nauplius stage of the Copepoda.
201
-------
LAKE HURON
oo Cyclopolda
RoWera
AMJJASON
90T
60-
B
30--
oo Calanotda
Ctadocera
AA Copepoda
AMJJASON
Figure 34. Seasonal flucuation (bionass) of zooplankton groups in Lake
Huron, 1985. Copepoda refers to the nauplius stage of the Copepoda.
202
-------
f\>
o
co
=tfc
1.0T
0.5--
LAKE HURON
Daphnia pulicaria
O O 1983
1984
A A 1985
61 54
NORTH
45 37 32 27 12
STATION
09 06
SOUTH
Figure 35. Geographical distribution of Daphnia pulicaria from 1983 to
1985, Lake Huron.
-------
40
30
20
10
0
o
A
A
LAKE HURON
O Calanolda
Cladoeera
A Copepoda
A Cyclopolda
54 45 37 32 27 12 09 06
Total
OO RotJfera
61
NORTH
45 37 32 27
STATION
12 09 06
SOUTH
Figure 36. Geographical distribution (abundance) of malor zooplankton
§roups in Lake Huron, 1985. Copepoda refers to the nauplius stage of the
opepoda.
204
-------
20
15
10
5
LAKE HURON
OO Copepoda
Cyclopolda
AA Rotffera
61 54 45 37 32 27 12 09 06
150T
100-
50-
OO Total
Colanolda
AA Cladocera
09 06
SOlfiH
Figure 37. Geographical distribution (biomass) of major zooplankton groups
in Lake Huron, 1985. Copepoda refers to the nauplius stage of the Copepoda.
205
-------
1.6T
0.8
LAKE HURON
Dlaptomus mlnutus
oo 1983
1984
AA 1985
54 45 37 32 27 12 09 06
4.2 T
2.1
0.0
Diaptomut ashland!
oo 1983
1984
AA 1985
O 5
61 54 45 37 32 27 12 09 06
2.4 T
Dlaptomui ilcllla
oo 1983
1.2+ « 1B84
AA 1985
61
NORTH
54 45 37 32 27 12 09 06
STATION
SOUTH
Figure 38. Geographical distribution of Diaptomis minutus, D. ashlandi and
D. sicilis in 1983, 1984 and 1985. Data are from Makarewicz (1987, 1988) and
this study.
206
-------
LAKE HURON
Holopedium gibberum
oo 1983
1984
AA 1985
61 54 45 37 32 27 12 09 06
2.0 T
1.0-
Daphnia galaeta mendotoe
oo 1963
54 45 37 32 27 12 09 06
1.0T
0.5
Daphnia pulicaria
o o 19B3
1984
A A 1985
61 54 45 37 32 27 12 09 06
N°RIH STATION
Figure 39. Geographical distribution of Holopedium gibberum, Daphnia
galaeta mendotae and Daphnia pulicaria in 1983, 1984 and 1985. Data are from
Makarewicz (1987, 1988) and this study.
207
-------
40 T
20
\
LAKE HURON
Conochllua unfcornis
oo 1983
1984
AA 1985
I I I 1 I 1 I 1 1
61 54 45 37 32 27 12 09 06
12T
6
Kellicottia longisplna
oo 1983
1984
A 1985
61 54 45 37 32 27 12 09 06
18T
Keratella cochlearis
oo 1983
1984
A A 1985
61
NORTH
54 45 37 32 27 12 09 06
STATION
SOUTH
Figure 40. Geographical distribution of Conochilus unlcornis, Kellicottia
longispina and Keratella cochlearis in 1983, 1984 and 1985, Lake Huron. Data
are from Makarewicz (1987, 1988) and this study.
208
-------
4T
2-
LAKE HURON
Nothoica aquamula
oo 1Q63
1984
AA 1985
61 54 45 37 32 27 12 09 06
Gastropus stylifer
-o 1983
» 1984
61 54 45 37 32 27 12 09 06
4T
2-
Synchaeta sp.
oo 1983
1984
AA 1985
61 54 45 37 32 27 12 09 06
STATION
Figure 41. Geographical distribution of Nothoica squaaula, Gastropus
stylifer and Synchaeta spp. in 1983, 1984 and 1985, Lake Huron. Data are from
Makarevicz (1987, 1988) and this study.
209
-------
30 T
20--
ro
»-»
o
10-
U\KE HURON
Crustacea (excluding nauplif)
o
1966
1971
1976
1981
1986
Figure 42. Crustacean abundance (excluding nauplii) of Lake Huron,
1970-1985. Values are the mean + S.E. Data are from Watson (1974), McNaught
(1980), Makarewlcz (1987, 1988). 1974 data represent oofshore sites only.
-------
ro
360T
270--
180--
90-
LAKE HURON
Rotifera
O 1974
O 1983
A 1984
A 1985
Figure 43. Abundance of Rotifera in Lake Huron in 1974, 1983 1985 and 1985,
1974 data are from offshore stations only (Stemberger et al 1979).
-------
U\KE HURON - 1983
W 'W
I
ro
ro
Q_
O
AMJJASOND
o
0)
o
o
n
o
a
i
I
a
Figure 44. Relationship between mean weighted edible phytoplankton size and
Crustacea and Daphnia abundance, 1983. Vertical bars represent Daphnia
abundance. Abundance values are the mean for a cruise. Picoplankton are not
included. Edible phytoplankton are defined as all species minus colonial and
filamentous forms.
-------
LAKE HURON - 1984
r _^
1
ro
_g
QL
I
0.
AMJJASOND
Figure 45. Relationship between mean weighted edible phytoplankton size, mean
weighted Crustacea size and Crustacea and Daphnia abundance, 1984. Vertical
bars represent Daphnia abundance. Abundance values are the mean for a cruise.
Picoplankton are not included. Edible phytoplankton are defined as all spe-
cies minus colonial and filamentous forms.
-------
ro
^ "«
1
c
o
.*-»
_*
c
£
CL
O
LAKE HURON - 1984
Daphnia (#/L)
T50
a.
o
o
0)
o
o
§
6
I
D
AMJJASOND
Figure 46. Relationship between mean weighted edible phytoplankton size and
Crustacea and Daphnia abundance, 1984. Vertical bars represent Daphnia abun-
dance . Abundance values are the mean for a cruise. Picoplankton are not
included. Edible phytoplankton are defined as all species minus colonial and
filamentous forms.
-------
ro
en
W^ "^
I
C
O
c
_g
o.
o
|>
Q.
O
LAKE HURON - 1985
Daphnia (#/!.)
T80
-40
o
0)
o
D
H
6
i
D
AMJJASOND
Figure 47 Relationship between mean weighted edible phytoplankton size, mean
weighted Crustacea size and Crustacea and Daphnia abundance, 1985. Vertical
bars represent Daphnia abundance. Abundance values are the mean for a cruise.
Picoplankton are not included. Edible phytoplankton are defined as all spe-
cies minus colonial and filamentous forms.
-------
LAKE ERIE
50
E 40--
o
o
o
(/) 20-
u ln
o iut
o o TOTAL
TOTAL MINUS
PICOPLANKTON
2T
1-
B
M
1 1
0 N
Figure 48. Seasonal phytoplankton abundance (A) and biomass (B) trends in
Lake Erie, 1985. Plotted are the means of all stations (17) for a given
cruise. Four samples were not completely counted due to high turbidity (Sta-
tion 60, April 24 and November 21; Station 55, April 25; Station 57, November
21) and are not included.
216
-------
0.9T
UJ
o
O
m
LU
o
o:
LJ
CL
OB AC
CHL
A CYA
ACHR
DCRY
PYR
VPIC
AMJ JASON
Figure 49. Seasonal distribution of algal divisions in Lake Erie, 1985. Bac
- Bacillariophyta, Chi - Chlorophyta, Chr - Chrysophyta, Cry - Cryptophyta,
Cya - Cyanophyta, Pic - Picoplankton, Pyr - Pyrrophyta.
217
-------
80-r
60-
40-
20-
LAKE ERIE
oo TOTAL
aa Pic
H - 1 - 1 - 1 - 1
1 - 1 - 1 - 1
O
O
O
X
CO
LU
O
oo BAG
na CYA
1-
oo CHL
Dn CHR
A CRY
WEST
-l-
EAST
-*
4-
-f-
60 57 55 42 73 37 78 31 15 09
STATION
Figure 50. Annual geographic distribution of major algal divisions in Lake
Erie, 1985. Plotted are the means of all seasonal samples for a given sta-
tion. Station 42 is the mean of Stations 42 and 43. Station 37 is the mean
of Stations 36, 37 and 38. Station 31 is the mean of Stations 30, 31 and 32.
Station 15 is the mean of Stations 15 and 63 and Station 09 is the mean of
Stations 09 and 10. Graph A data points were calculated without four samples
that were not completely counted due to high turbidity (Station 60 on April 24
and November 21, Station 55 on April 25 and Station 57 on November 21). Graph
C and the CYA line on Graph B were calculated without two samples that were
not completely counted due to high turbidity (Station 60 and Station 57 on
November 21). Bac - fiacillariophyta, Chi - Chlorophyta, Chr - Chrysophyta,
Cry - Cryptophyta, Cya - Cyanophyta, Pic - Picoplankton.
218
-------
LAKE ERIE
oo TOTAL
oD BAG
OH 1 1 1 1 1 1 1 1
E
cn
0.500 T
0.250-
0.000
oo CYA
aa CHL
CRY
0.090 T
0.060
0.030-
0.000
oo CHR
a
i 1 1 1 1 1
EAST
60 57 55 42 73 37 78 31 15 09
Figure 51. Annual geographical distribution (biomass) of major algal
divisions in Lake Erie, 1985.
219
-------
120T
80-
40--
LAKE ERIE
oo April 24-26
aa April 27-28
O
O
O
X
CO
LJ
O
80
60
40
20
0
40
30
20-
10-
4f\ °° Augutt 8-8
y \ oD Auguit 12-14
N^C^i^x^-.
H 1 1 1 1 1 1 1 1 I
oo November 21-22
aa November 23-25
60 57 55 42 73 37 78 31
STATION
15 09
Figure 52. Geographical distribution of phytoplankton abundance, Lake Erie,
1985. Station 42 is the mean of Stations 42 and 43. Station 37 is the mean
of Stations 36, 37 and 38. Station 31 is the mean of Stations 30, 31 and 32.
Station 15 is the mean of Stations 15 and 63. Station 09 is the mean of
Stations 09 and 10.
220
-------
ro
ro
Rhizosolenia eriensis
Figure 53. Geographical and seasonal distribition of Rhizosolenia eriensis,
1985.
-------
ro
ro
ro
Amphidinium sp
Figure 54. Geographical and seasonal distribition of Amphidinium sp. , 1985,
-------
ro
ro
co
Oedogonium sp
Figure 55. Geographical and seasonal distribition of Oedogonlw* sp. , 1985.
-------
ro
ro
en
en
D
£
o
*m
LAKE ERIE
o 1970
O 1983
A 1984
A 1985
J A S 0 N D J
Figure 56. Seasonal flucuation of weighted mean phytoplankton biomass in
1970, 1983, 1984 and 1985, Lake Erie. 1970 data modified from Munawar and
Munawar (1976). 1983 and 1984 data from Makarewicz (1988, 1989). Values are
corrected by using the weighting factors of 15.6%, 59.6% and 24.6% for the
western, central and eastern basins (after Munawar and Munawar 1976).
-------
19.5
E
X
en
ro
ro
01
1954
1962
1970
1978
1986
Figure 57. Regression (r2-80.5) of phytoplankton biomass versus time in
western Lake Erie. Modified from Gladish and Munawar (1980). 1956-58 data
are from the Bass Island region. 1970 data from Point Pelee and near the
mouth of Detroit River. 1975-76 data are from northern portions of the west-
ern basin. 1978 data are from similar geographic areas as 1970 (Devault and
Rockwell 1986). 1979 data are not included because of a reduced sampling
regime and other technical difficulties (Devault and Rockwell 1986). 1983-85
data are from Stations 60, 57 and 55. Except for the 1956 and the 1957-58
data sets, all enumeration was by the Utermohl technique^ In 1956 and
1957-58, a settling technique was used, but counts were not made on an
inverted microscope. Thin vertical lines are the range. Wide vertical lines
are the standard error.
-------
8T
LAKE ERIE
ro
ro
en
4+
cn
oo Western
oo Central
aa Eastern
1968
» » i i i
1973
1978
1983
1988
Figure 5.8. Phytoplankton blomass versus time for the Western, Central and
Eastern Basins of Lake Erie. Data are from Munawar and Munawar (1976,
graphical accuracy) and Devault and Rockwell (1986).
-------
16T
12--
ro
ro
Q.
0
.c
o
LAKE ERIE
o Western
O Central
Eastern
1968
1974
1980
1986
Figure 59. Time trend in annual cruise mean concentration of corrected chlo-
rophyll a since 1970. Data from Rathke (1984) and Rockwell (1989).
-------
LAKE ERIE
60 T
ro
ro
00
0)
13
o
JC
0.
01
o
o
-t->
o
40--
on
20-
o-
o-
A-
-O Western
-O Central
-A Eastern
0
1968
1974
1980
1986
Figure 60. Time trend in annual cruise average of total phosphorus since
1970, Lake Erie. Data are from Depinto et al (1986) and Rockwell (1989).
-------
LAKE ERIE
250 n
125-
H 1 1 1 1 1 1
500 T
250--
B
H 1 1 1 1 1 1 1
AMJJASON
Figure 61. Seasonal zooplankton biomass (a) and abundance (b) in Lake Erie,
1985. Plotted are the means of all stations for a cruise date.
229
-------
UKE ERIE
400
300-
o-
V-
-O Copapoda
V Rottfera
30 T
20--
B
10-
OO Calanolda
Cladocera
AA Cyclopolda
AMJJASON
Figure 62. Seasonal abundance distribution of zooplankton groups in Lake
Erie, 1985. Copepoda refers to the nauplius stage of the Copepoda.
230
-------
ro
CO
CT>
U\KE ERIE
100T
75--
50-
A-
A-
D-
o Calanoida
Cladocera
A Copepoda
A Cyclopoida
n Rotifera
25-
0 N
Figure 63. Seasonal biomass distribution of zooplankton groups in Lake Erie,
1985. Copepoda refers to the nauplius stage of the Copepoda.
-------
LAKE ERIE
oo Total
aa Rotifera
AA Total Crustacea
i 1 1 1
o°
60 T
OO Calanolda
DD Cladocera
AA Copepoda
AA Cyclopolda
60 57 55 42 73 37 78 31
WEST
STATION
15 09
EAST
Figure 64. Geographical distribution (abundance) of zooplankton groups in
Lake Erie, 1985. Copepoda refers to the nauplius stage of the Copepoda.
232
-------
LAKE ERIE
160
120-
80-
40-
0
oo Total
aa Rotifera
AA Total Crustacea
75 T
50-
25
o
D
A
O Calanoida
D Cladocera
A Copepoda
A Cyclopoida
60 57 55 42 73 37 78
WEST STATION
15 09
EAST
Figure 65- Geographical distribution (biomass) of zooplankton groups in Lake
Erie, 1985. Copepoda refers to the nauplius stage of the Copepoda.
233
-------
6T
LAKE ERIE
3
O O MMOcydop* wtax
DD Cyclops bicuspMotm thomoai
AA Daphnle galovta m*ndota«
* Dkjptomui oragonensls
0.10T
0.05
0.00
Oo Cenodaphnia lacustris
Da Holopedium gibberum
AA Daphnia pulicaria
80 T
oo Dtaptomua - copepodite
oD Ascomorpha ovalis
A A Conochilus unicornis
40-
60 57 55 42 73 37 78 31 15 09
STATION ^ST
Figure 66. Geographical distribution of selected zooplankton species in Lake
Erie, 1985. Station 42 is the mean of Stations 42 and 43. Station 37 is the
mean of Stations 36, 37 and 38. Station 31 is the mean of Stations 30, 31 and
32. Station 15 is the mean of Stations 15 and 63. Station 09 is the mean of
Stations 09 and 10.
234
-------
120T
80-
40-
0
LAKE ERIE
OO Polyarthra rwnata
DD Synchoeta *p.
AA KerateUa Qrlino.
§a-
P i fl
OO Dlaphanotoma tp.
DD Chydoru* phoericua
AA Brochlonut budopMtlrwn
Notholca foliaeea
Kvratella arllno*
OO Cyclops vernolis
DD Diaptomus minutus
AA D. siciloides
^ Eurytemora copepodite
E. affinis
60 57 55 42 73 37 78 31 15 09
WEST STATION
Figure 67. Geographical distribution of selected zooplankton species in Lake
Erie, 1985. Station 42 is the mean of Stations 42 and 43. Station 37 is the
mean of Stations 36, 37 and 38. Station 31 is the mean of Stations 30, 31 and
32. Station 15 is the mean of Stations 15 and 63. Station 09 is the mean of
Stations 09 and 10.
235
-------
ro
OJ
Chydorus sphaericus
Figure 68. Geographical and seasonal distribition of Chydorus sphaericus,
1985.
-------
Bythotrephes cederstroemi
GO
Figure 69. Geographical and seasonal distribition of Bythotrephes ceder-
stroemi, 1985.
-------
Cyclops vernalis
rv>
CO
oo
Figure 70. Geographical and seasonal distribition of Cyclops vernalis, 1985.
-------
ro
co
10
100T
75-
50-
25- l
LAKE ERIE
OO Copepoda
OO Cladocera
AA Total Crustacea
1937 1947 1957 1967 1977 1987
Figure 71. Crustacean zooplankton abundance since 1939 in the Western Basin
of Lake Erie. Values are the mean ± Standard Error. 1939 data are from
Chandler (1940; April-October). 1949 data are from Bradshaw (1964; April-
October) . 1983 (April-November) and 1984 (April-December) data are from Maka-
rewicz (1987, 1988). 1985 (April-November) are from this study.
-------
ro
-p»
o
=*fc
LAKE ERIE
150T
O Cladocera
O Adult Copepoda
A Total Copepoda
100--
50-
1937 1947 1957 1967 1977 1987
Figure 72. July and August abundance of Cladocera and Copepoda in the Western
Basin of Lake Erie since 1939. Total Copepoda refers to adults plus the
nauplius stage. Data are from Chandler (1940), Bradshaw (1964), Hubschraan
(I960), Britt et al (1973), Davis 1969a, Makarewicz (1987, 1988) and this
study. The number of adults and total copepods in 1939 and 1959 follow Brad-
shaw 's (1964) calculations.
-------
LAKE ERIE
250 T
o-
o
A-
01970
01983
A 1984
A 1985
ro
125-
AMJ JASONDJ
Figure 73. Seasonal flucuation of weighted mean Crustacea (nauplii excluded)
abundance In 1970, 1983, 1984 and 1985, Lake Erie. 1970 data follow Watson
and Carpenter (1974). 1983 and 1984 data are from Makarewicz (1987, 1988).
1983-1985 values are corrected using the weighting factors of 15.6%, 59.6%
and24.6% for the Western Central and Eastern Basins (after Munawar and Munawar
1976).
-------
500 T
no
-t>
ro
250-
o
o
a
0
1982
LAKE ERIE
o Western
$ Central
n Eastern
1984
1986
Figure 74. Zooplankton biomass versus time for the Western, Central and
Eastern Basins of Lake Erie.
-------
ro
-t»
co
800 T
600 -
400 -
200--
LAKE ERIE
01939
01961
A1983
A1984
D1985
AMJJASOND
Figure 75. Seasonal fluctuation of Rotlfera In the Western Basin of Lake Erie
from 1939 - 1985. Sources: 1939 - Chandler (1940); 1961 - Britt et al (1973);
1983 and 1984 - Makarewicz (1987, 1988). The 1970 samples of Nalepa (1972)
are not included because they are from the far western end of the basin and
may not be representive of the entire basin.
-------
Ld
ro
35-
28-
21-
14-
7-
n.
*
.
^
^ ^
I
i
i
\
i
!
|
P
Cs
s
\
\
X
m
i
1972
1976
1980
1984
Figure 76. Projected abundance (millions of fish) of flshable walleye (age
2+) in western Lake Erie (Ohio waters). Data are from the Ohio Department of
Natural Resources (1989).
-------
1200T
ro
->
en
CO
LL.
Q
LJ
Of
Q
800--
400-
WALLEYE
1976 1979 1982 1985 1988
Figure 77. Sport angler harvest of walleye from the Central Basin (District
II and III of the Ohio Department of Natural Resources) of Lake Erie. Data
from the Ohio Department of Natural Resources (1989).
-------
75T
50
25-
AUEW1FE
Q4II+IIi
Ld
?2 120T
ID
m
<
L±J
1
LJ
o:
80
40
SPOTTAIL SHINER
H 1 1 1 1 1 1 14
1000
EMERALD SHINER
1976
1979 1982 1985 1988
Figure 78- Time trend of autumn emerald and apottail shiner (age 1 and older)
abundance in the Central Basin and alewife (young-of-the year) from the West-
ern Basin of Lake Erie. Data from the Ohio Department of Natural Resources
(1989). Data in 1986 and 1988 are from a limited number of stations due to
inclimate weather. Values represent the geometric mean of catch per trawling
hour. Abundance index values are different from Makarewicz (1988) due to
revisions in calculations by the Ohio Departmentof Natural Resources.
246
-------
0.20
0.00
100
E
o
0)
u
o
o
Calanoida
Daphnia spp
0.7
0.6
AMJJ ASON D
Figure 79. (A)Seasonal total algal and filamentous algal biomass and mean
weighted edible algal size in 1985; (B) the seasonal mean crustacean size and
Daphnia spp. and adult Calanoida abundance, 1985.
247
-------
100 -r
00
-------
100 T
ro
-t»
<£)
-------
n
093
I^ERCENT SIMILARITY
00
0>
l-t
o
3
rt
tfl
(-
S
-
OOOOOOOOO
O
o
I
rt
O
ft
o
(n
13
(D
O
H-
ro
in
oo
H
-------
100 T
ro
tn
CO
CO
o
E
o
O
-t
o
c
CD
o
L_
CD
Q_
75 --
50 --
25 --
0
2Z3CAL
S3CYC
Ukd^MQ
cm
COP
CLA
ROT
MICHIGAN
HURON
ERIE
Figure 83- Comparison of the zooplankton composition of Lakes Michigan
Huron and Erie, 1985. '
-------
ro
01
ro
o
I
-M
D
O
o +
o
s- <
o o
o
ISI
3 T
1 "
0
1983
1984
1985
MICHIGAN HURON
ERIE-W ERIE-C ERIE-E
Figure 84. Comparison of annual zooplankton ratios in Lakes Michigan, Huron
and Erie.
-------
TECHNICAL REPORT DATA
1. REPORT NO.
EPA-905/3-90-003
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
Phytoplankton and Zooplankton in Lakes Erie, Huron and
Michigan: 1985
5. REPORT DATE
December 1989
6. PERFORMING ORGANIZATION CODE
5GL
7. AUTHOR(S)
Joseph C. Makarewicz and Paul E. Bertram
8. PERFORMING ORGANIZATION REPORT NO.
GLNPO Report No. 01-91
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Biological Sciences
State University of New York
College at Brockport
Brockport, New York 14420
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
R005007-01
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
Great Lakes National Program Office
230 South Dearborn Street
Chicago, Illinois 60604
13. TYPE OF REPORT AND PERIOD COVERED
Final 1985
14. SPONSORING AGENCY CODE
GLNPO
15. SUPPLEMENTARY NOTES
Paul E. Bertram, EPA Project Officer
16. ABSTRACT
During the spring, summer and autumn of 1985, the structure of the phytoplankton and zooplankton communities in
the offshore waters of Lake Michigan, Lake Huron and Lake Erie was monitored. In Lake Michigan, the presence
of an oligotrophic rotifer association and the oligotrophic crustacean indicator species Diaptomus sicilis and
Limnocalanus macrurus, the predominance of mesotrophic diatom species, and the abundance and biomass of
plankton between that of Lake Huron and Lake Erie suggest that the offshore waters are currently in the
oligotrophic-mesotrophic range. In Lake Huron, the presence of an oligotrophic rotifer assemblage, the domination
of the calanoid copepods, the abundance of the oligotrophic Diaptomus sicilis, and relatively low zooplankton
abundance suggest that the offshore waters continue to be oligotrophic. In Lake Erie, phytoplankton and
zooplankton species composition and biomass suggest a more productive status than Lake Michigan and Lake
Huron. Data support the classification of the Western Basin as meso-eutrophic, the Central Basin as mesotrophic
and the Eastern Basin as oligo-mesotrophic. Significant changes in the composition of the zooplankton community
with the appearance of the large cladoceran Daphnia pulicaria in Lake Erie are attributed to a change in
planktivory. The planktivorous emerald and spottail shiners have dramatically declined in abundance, possibly due
to a resurgence of the walleye and the salmonine stocking programs.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTIONS
b.
IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field Group
Great Lakes, Lake Michigan, Lake Huron, Lake
Erie, Limnology, Eutrophication, Community
Structure, Plankton, Phytoplankton, Zooplankton,
Species
18. DISTRIBUTION STATEMENT
Document is available to the Public through the
National Technical Information Service (NTIS),
Springfield, VA 22161. Limited copies may be
available from GLNPO.
19. SECURITY CLASS (This Report)
21. NO. OF PAGES
252
20. SECURITY CLASS (This page)
22. PRICE
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