United States
Environmental Protection
Agency
Region 5
77 West Jackson Boulevard
Chicago, Illinois 60604
EPA 905-R-00-006
September 2000
EPA Results From The Great Lakes National
Program Office's Biological Open Water
Surveillance Program Of The
Laurentian Great Lakes for 1998
Richard P. Barbiero1 and Marc L. Tuchman2
1Dyncorp I & ET Inc.
6101 Stevenson Avenue
Alexandria, VA 22304
2U.S. EPA
Great Lakes National Program Office
77 W. Jackson, Boulevard - G-17J
Chicago, IL 60604
September 2000
U.S. Environmental Protection Agency
Great Lakes National Program Office
Jackson, Boulevard - G-17J, Chicago, IL 60604
Michigan Minnesota New York Ohio Pennsylvania Wisconsin
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INTRODUCTION
The Laurentian Great Lakes constitute the largest continuous body of fresh water
on earth, and with a volume of 24,620 km2(Wetzel, 1983), contain nearly 20% of
the world's unfrozen fresh water. These lakes represent an enormous cultural
and economic resource for both the United States and Canada. Increasing
population and industrial growth in recent history, however, has produced a trend
of increasing eutrophication and raised concerns about declining water quality in
the lakes. As a result of these concerns, in 1972 the United States and Canada
signed the Great Lakes Water Quality Agreement as an expression of each
country's commitment to restore and maintain the chemical, physical and
biological integrity of the Great Lakes Basin Ecosystem.
The Great Lakes National Program Office (GLNPO) of the United States
Environmental Protection Agency (USEPA) has primary responsibility within the
US for conducting surveillance monitoring of the offshore waters of the Great
Lakes. This monitoring is intended to fulfill the provisions of the Great Lakes
Water Quality Agreement (International Joint Commission, 1978) calling for
periodic monitoring of the lakes to: 1) assess compliance with jurisdictional control
requirements; 2) provide information on non-achievement of agreed upon water
quality objectives; 3) evaluate water quality trends over time; and 4) identify
emerging problems in the Great Lakes Basin Ecosystem. The monitoring effort is
focused on whole lake responses to changes in loadings of anthropogenic
substances, so sampling is largely restricted to the relatively homogeneous
offshore waters of each lake. Because of the daunting logistical exigencies of
sampling such a large area, temporal resolution is currently limited to two well-
defined periods during the year: the spring isothermal period and the stable,
stratified summer period.
GtNPO's monitoring of the Great Lakes began in 1983, with coverage at that
time including Lakes Michigan, Huron and Erie. Initially Lakes Ontario and
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Superior were excluded from monitoring because the former was already
monitored annually by Canada, and the latter was not felt to be susceptible to
eutrophication. In 1986 sampling was extended to include Lake Ontario, and in
1992 sampling of Lake Superior was added. In addition to a wide range of
physical and chemical parameters, the lakes have been sampled for
phytoplankton and zooplankton, including crustaceans and rotifers, since the
inception of the program. In 1997, a benthic invertebrate biomonitoring program
was added to complement the existing open water surveillance sampling. This
sampling program is unique in that all five lakes are sampled by one agency, and
samples are analyzed by one primary lab. Consequently, analytical methods, and
most importantly taxonomy, remain consistent both over time and across all five
lakes.
In this report we will present, for the first time, results of GLNPO's biological
surveillance sampling program from all five Laurentian Great Lakes. Our goal
here is to provide a brief general description of the offshore planktonic and the
benthic communities of all five Great Lakes from GLNPO's 1998 surveys.
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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METHODS
Field Methods
In 1998, samples were taken from all five lakes
aboard the R/V Lake Guardian during both a spring
and a summer survey. The spring survey ran from
29 March to 14 May, while the summer sampling was
conducted between 2 August and 5 September.
Between 13 and 22 stations were sampled on each
lake for plankton, benthos, or both (Figure 1). Two or
At each station, water column profiles for
temperature, conductivity, turbidity, pH, and in vivo
chlorophyll a fluorescence were taken using a
Seabird STE-911 CTD multi-sensor unit. Integrated
samples for soluble nutrients, in vitro chlorophyll a,
and phytoplankton enumeration were created from a
composite of water samples taken at discrete depths
(spring: surface, 5M, 10M, and 20M; summer:
Figure 1. Stations sampled during GLNPO 1998 surveys.
Plankton & Benthos Sites
Plankton Only Sites
Benthos Only
three stations per lake are designated master
stations, at which additional samples are taken in the
upper fifty meters of the water column.
surface, 5M, 10M, and upper metalimnion) with
Niskin bottles mounted on a SeaBird Carousel Water
Sampler. Samples for total soluble phosphorus
(TSP) were filtered in the field through 0.45 |j.m
Sartorius filters and preserved with H2SO4 for later
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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analysis in the lab. Samples for soluble silica (Si)
were stored at 4° C. Samples for phytoplankton
analysis were preserved in the field with Lugol's
solution, and with formalin upon return to the
laboratory.
Two net tows were performed at each site for
zooplankton sample collection, using a 0.5 m
diameter conical net (D:L = 1:3). The first tow was
taken from 20 meters below the water surface or 1
meter above the bottom, whichever was less, using a
64 urn mesh net, and the second tow from 2 meters
above the bottom or 100 m, whichever was less,
using a 153 urn mesh net. If the station depth was
less than 20 m, both tows were taken from one meter
above the bottom. Triplicate tows of each depth
were taken at the master stations. After collection,
zooplankton were immediately narcotized with soda
water, and were preserved with sucrose formalin
solution (Haney and Hall, 1973) approximately twenty
minutes later.
During the summer survey, quantitative samples for
benthic invertebrate analysis were collected from
selected sites using a Ponargrab sampler. Samples
were taken in triplicate, and material sieved through
a 500 urn mesh net. Samples were preserved with
buffered formaldehyde with Rose Bengal to a final
concentration of 5-10 % formaldehyde. In addition, a
fourth Ponar sample was collected at each site for
grain size determination and chemical analysis for
particulate carbon, nitrogen and phosphorus.
Laboratory methods
Laboratory Methods
After acid persulfate digestion, TSP and PP were
measured on a Lachat QuikChem AE autoanalyzer
by the ascorbic acid method (APHA, 1985). Si was
determined by the molybdate method on a Lachat
QuikChem AE autoanalyzer (APHA, 1985). POC
was determined by the combustion-infrared method
on a Carlo Erba carbon analyzer (APHA, 1985).
Chlorophyll a, uncorrected for pheophytin, was
determined on a Turner Designs 10-AU fluorometer
following the method of Welschmeyer (1994).
Phytoplankton were identified and abundances were
estimated using the Utermb'hl technique (Lund et al.
1958) at a magnification of 500x, with diatoms other
than Rhizosolenia identified as either Gentries or
pennates. Diatoms were identified, and relative
abundances determined/from permanent slide
mounts at 1250x. Relative proportions of each taxon
of Gentries and pennates were then multiplied by the
appropriate Utermohl counts. At least 10 individuals
of each taxon were measured per sample, and cell
volumes computed using appropriate geometrical
formulae. Primary taxonomic keys used were
Prescott (1962), Kramer and Lange-Bertalot (1986,
1991, 1997), Patrick and Reimer(1966, 1975) and
Germain (1981).
Samples for zooplankton analysis were split in the
lab using a Folsom plankton splitter, and four
stratified aliquots examined per sample using a
stereoscopic (crustaceans) or compound (rotifers)
microscope. Adult calanoids were identified
according to Balcer et al. (1984). Adult cyclopoids
and harpacticoids were identified according to
Hudson et al. (1998). Immature calanoids and
cyclopoids are identified to the lowest taxonomic
level possible, usually suborder or genus. Nauplii
were counted with rotifers. The following
cladocerans were identified according to Balcer et al
(1984): Leptodora kindti, Polyphemus pediculus,
Holopedium gibberum, and Diaphanosoma birgei.
Brooks (1957) and Evans (1985) were used for all
Daphnidae. The remaining cladocerans
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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(Chydoridae, Bosminidae, and Macrothricidae) were
identified according to Edmundson (1959). Members
of Cercopagidae (i.e. Bythotrephes cedarstroemii,
Cercopagis pengoi) were identified according to
Rivier (1998). Length measurements were made on
the first twenty individuals of each species
encountered per sample (crustaceans) or per lake
(rotifers). Crustacean biovolumes were computed
using length-weight relationships found in the
literature, while rotifer biomass was calculated
according to A. Ruttner-Kolisko (in Bottrell et al.,
1976).
Organisms were picked out of benthos samples
under low magnification using a dissecting
microscope. Oligochaetes and chironomids were
mounted on slides and identified under a compound
scope at 63x; other organisms were identified under
a dissecting scope. Taxonomy followed Kathman
and Brinkhurst, 1998 (oligochaetes); Holsinger, 1972
(amphipods); Wiederholm, 1983 (chironomids) and
Merritt and Cummins, 1996 (all else).
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-B
RESULTS
Physical Chemical
Temperatures across the lakes during the spring
survey were between 2-4° C, with the exception of
the shallow western basin of Lake Erie, where
temperatures reached 7.6° C (Figure 2).
showed a general trend of increase from upstream to
downstream, i.e. along the sequence Superior,
Michigan, Huron, Erie and Ontario. Lake Michigan
was often an exception to this sequence, however,
exhibiting relatively elevated levels of alkalinity,
Alkalinity (mg/l)
100
«£>
-80
-60
-40 =
Chloride (mg/l)
-20 ^
-i. ?
-10
- 5
. 0
TSP Qig/l)
-a- **
=^
Temperature (°C)
-8
-6
4 i **
T
PH
-9
s _^_-L.
,=r~,
-7
Silica (mg/l)
-2
-1
i^-
E
-o Z
_350 Conductivity (nmhos)
-300 __
-250
-200
-150
-100
Chlorophyll Qig/l)
I
N02-N03(^g/l)
-750
-500
^^li^
-250
ON ER HU Ml SU ON ER HU Ml SU ON ER HU Ml SU
Figure 2. Box plots of physical and chemical data for the
Great Lakes, spring 1998. Boxes represent 25th, 50th
and 75th percentiles; whiskers indicate 10th and 90th
percentiles.
Concentrations of most chemical constituents
chloride, ph and conductivity. In the case of both
CJREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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-B
chlorophyll and dissolved phosphorus, Lake Erie
exhibited the highest average concentrations.
Dissolved silica showed a reverse trend, generally
decreasing from upstream to downstream. Nitrate
showed very little variation across the lakes.
During the summer survey, stable stratification had
difference per meter) ranged from 5.5 m in western
Ontario to 23.5 m in northern Lake Superior,
averaging between 14 and 17 for the upper lakes
and 19 and 11 for Lakes Erie and Ontario,
respectively. Epilimnetic temperatures at most sites
were generally between 21 and 24° C, with the
ped at nearly all open water sites in all lakes exception of Lake Superior, where temper,
Alkalinity (mg/l)
-100
"" "₯"
-80 - ^
-60
-40 -*=-
Chloride (mg/l)
-20 "*
-l\c\ i -i-
-10
-5
-0
TSP (jig/l)
- 12
-10
-8
-6
-4 ^
T i-=H
-2 ' r-gzj'S*
__
Temperature (°C)
-25
-20
-15
-10 ^3
-5
-10 -M PH *
-T-
-9
-8 =^=
-7
Silica (mg/l)
-2
-1 ^
<,-*"-
-350 Conductivity ((imhos)
-300
-250
-200
-150
-100
Chlorophyll (jig/l)
-4
-3
*""
_ ,
rt.*1-^
N02 - N03 (ng/l)
-750
-500
-T- ,
-2SO~ -±q-4-
ON ER HU Ml SU ON ER HU Ml SU ON ER HU Ml SU
Figure 3. Box plots of physical and chemical data for the
Great Lakes, summer 1998. Boxes represent 25th, 50th
and 75th percentiles; whiskers indicate 10th and 90th
percentiles.
except for Lake Erie, where stratification was only
evident in the deeper eastern basin. The depth of
were only about 10° C.
pH values across the lakes were higher than in
spring, and differences between the lakes were
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-D
somewhat more pronounced with Superior
substantially lower than the other lakes, and
Michigan and Ontario somewhat higher (Figure 3).
Values for chloride, alkalinity and conductivity were
essentially identical to spring. Both total soluble
phosphorus and chlorophyll were higher in the lower
lakes compared to the upper lakes, with Lake
Ontario on average exhibiting the highest values for
both parameters. Available nitrogen fluctuated within
a very narrow range for all lakes, while dissolved
silica was highest in Lake Superior and Lake Huron.
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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-B
Phytoplankton
Spring
During spring, a total of 261 phytoplankton taxa were
identified in the 72 samples examined. All lakes
site for the lakes ranged from 42 in Lake Erie to 73 in
Lake Huron. Diatoms, overwhelmingly the most
diverse group across all lakes, contributed between
40 and 50% of the species found in each lake (Figure
4b). Chlorophytes and chrysophytes each
cc
X
TO
250
200
150
100
50
200
B
Diatoms
Chlorophytes
Chrysophytes
Cryptophytes
Cyanophytes
OTHER
Figure 4. A.) Phytoplankton species richness, spring cruise,
1998. Boxes represent minimum, mean, and maximum
numbers of taxa per station at each lake; circles represent
total numbers of taxa found in each lake; B.) Contribution of
major taxonomic groups to species richness.
supported over one hundred taxa, with Lakes
Superior and Huron having the greatest number of
species (Figure 4a). Average numbers of taxa per
contributed between about 20 and 40 species per
lake, while between 10 and 12 species of
Cryptophyte were found in each lake. Other groups,
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while occasionally responsible for high numbers of
individuals, were considerably less diverse.
Total phytoplankton biovolumes across the lakes
ranged from 2.6- 104(o.m3mr1 at a site in Lake
Superior to 6.0- 106(im3mr1 at a site in Lake Erie
(Figure 5), with the most spatial heterogeneity
apparent in Lake Erie. Median biovolumes for each
lake, however, ranged only between 2.6- 105|o.m3mr1
Diatoms were the dominant phytoplankters at most
sites, making up between 70 and 80% of
phytoplankton biovolume, on a lake-wide basis, in all
lakes except Superior (Figure 6; Table 1).
Cryptophytes were second in importance,
contributing between 6% (Lake Erie) and 27% (Lake
Superior) of phytoplankton biovolume. Cyanophytes
contributed a relatively minor amount of biovolume to
Figure 5. Biovolume of the total phytoplankton community in the Great Lakes,
spring 1998. Inset shows box plots of phytoplankton biovolumes for each lake.
Ml HU ER ON
in Lake Michigan to 5.2- 105nm3mr1 in lakes Erie
and Ontario, with the exception of Lake Superior
(Median = 8.5- lOV3!"1).
most sites, although substantial populations were
found at some sites in Lake Superior and in southern
Lake Huron. Biovolumes of chlorophytes were
uniformly low throughout the lakes in spring.
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Figure 6. Relative biovolumes of major phytoplankton groups in the
Great Lakes, spring cruise, 1998. Inset shows whole-lake averages.
| | Centric Diatoms
^] Pennate Diatoms
| Chlorophytes
| Chrysophytes
^] Cryptophytes
| Cyanophytes
I Euglenophytes
| Dinoflagellates
| | Unidentified flagellates
100
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Summer
A total of 285 phytoplankton taxa were identified
from epilimnetic samples taken during the summer
survey, a number similar to that found in the spring.
Numbers of taxa found at each lake, and numbers of
phytoplankton divisions to species diversity was
similar to that of spring, although diatoms contributed
somewhat fewer species and chlorophytes and
chrysophytes slightly more (Figure 7b). Again, the
contribution of cryptophytes and cyanophytes to
.0
E
3
2
250
200
150
100
50
:
o
Diatoms
Chlorophytes
Chrysophytes
Cryptophytes
Cyanophytes
OTHER
Ml
HU
ER
ON
Figure 7. A.) Phytoplankton species richness, summer cruise,
1998. Boxes represent minimum, mean, and maximum
numbers of taxa per station at each lake; circles represent
total numbers of taxa found in each lake; B.) Contribution of
major taxonomic groups to species richness.
taxa found at sites within lakes, were also similar to
those in spring, although Lake Erie had slightly
greater species richness in summer compared to
spring (Figure 7a). The contribution of different
species richness was 10% or less.
There was considerably less site to site variability in
phytoplankton biovolumes in the summer, compared
to spring, varying from 6.96- 104|im3mr1 at a site in
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Lake Michigan to 2.54- 106(im3mr1 at a site in Lake
Erie (Figure 8). Lake-wide median biovolumes were
also more similar in summer compared to spring,
Populations of cyanophytes showed notable
increases only in Lake Erie. Dinoflagellate
populations also increased at many sites, with Lake
Figure 8. Biovolume of the total phytoplankton community in the Great Lakes,
summer 1998. Inset shows box plots of phytoplankton biovolumes for each lake.
Ml HU ER ON
1*10-Vm3/ml
5*105um3/ml
due mostly to larger biovolumes in Lake Superior.
As in spring, though, a high degree of spatial
heterogeneity in phytoplankton biovolumes was seen
in Lake Erie.
The most notable change in summer phytoplankton
communities was a shift away from diatoms (Figure
9; Table 2). Proportions of chrysophytes increased in
the upper lakes, and proportions of chlorophytes
increased substantially in Lakes Erie and Ontario.
Ontario in particular supporting particularly large
populations. These, however, were most often the
result of single large individuals of Ceratium
hirundinella or Peridinium being found in a sample,
so biovolume estimates of this division should be
interpreted with caution.
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 9. Relative biovolumes of major phytoplankton groups in the
Great Lakes, summer cruise, 1998. Inset shows whole-lake averages.
^j Centric Diatoms
^ Pennate Diatoms
| Chlorophytes
| Chrysophytes
^ Cryptophytes
| Cyanophytes
I Euglenophytes
| Dinoflagellates
|J Unidentified flagellates
100
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-H
Zooplankton
Spring
Diversity of the crustacean communities on a site by
site basis was relatively low across the lakes, with
most sites supporting between 6 and 17 species,
with the exception of Superior, where no more than 7
taxa were found at any site (Figure 10a). Total
numbers of taxa found in each lake varied from 9
(Superior) to 20 (Erie).
Total crustacean abundances (excluding nauplii)
varied from 39 animals m"3 at ER 10 to over 12,000
at stations in Erie and Huron (Figure 11). Overall,
however, within lake differences in abundances were
-3
30 -
25
I *>-
| 15-
a
Z 10
5
0
20
| 15-
0
| 10 -
D
2
5
0
A
0
0
B
_
o
__
SU Ml HU ER ON
Figure 10. Minimum, maximum and mean number
of taxa per site, and total number of taxa per lake,
for A:) crustaceans and B:) rotifers, spring 1998.
relatively minor, with the dramatic exception of Lake
Erie, where abundances varied over two orders of
magnitude. Most sites supported similar numbers of
organisms; lake-wide median abundances for Lakes
Michigan, Huron and Ontario were between 4,034
and 5,716 animals m'3. Abundances in Lake
Superior were substantially lower (median=935
animals m ), while abundances in Lake Erie ranged
from 35 to over 8,000 animals m'3. The high degree
of spatial variability in Lake Erie was not solely a
result of inter-basin differences. While abundances
in the eastern basin were uniformly low, both the
central and western basins supported communities
that varied in size by several orders of magnitude.
During spring, crustacean communities across all
five lakes were overwhelmingly dominated by
copepods, although the relative importance of
calanoids and cyclopoids varied from lake to lake.
Immature copepods made up a substantial portion of
the individuals found at all site. Lakes Michigan and
Huron were dominated by calanoids, while Lake
Ontario was dominated by cyclopoid copepods.
Dominance varied from site to site in Lake Erie, with
calanoids more prevalent in the western basin, and
cyclopoids in the central basin. Sites in the eastern
basin were composed almost entirely of very small
populations of immature cyclopoids. In Lake
Superior, calanoids and cyclopoids were often co-
dominant. Overall most sites in the spring were
dominated by a very small number of species,
usually belonging to one or a few genera (Table 3).
Comparing the relative contribution of rotifers and
nauplii to zooplankton community biomass is
problematic, since the former are only enumerated
from shallow tows, which have been shown to
provide highly misleading estimates of adult
crustacean biomass, particularly if taken during the
day. On the other hand, deep tows in many cases
probably underestimate crustacean biomass, since
the deeper portion of the water column is probably
devoid of most species; thus there is a dilution effect
when calculating volumetric biomass. However, it
was felt that the best estimate of the relative
contribution of nauplii and rotifer biomass was to
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 11. Abundances of major crustacean groups in the Great Lakes,
spring 1998. Inset shows whole lake averages.
| Bosmina spp.
J Daphnia spp.
1 Other Cladocerans
I Calanoida
I imm Calanoida
£ Cyclopoida
] Imm Cyclopoida
SU Ml HU ER ON
6,000/m3
3,000/m3
< 600/m3
Figure 12. Total zooplankton biomass by major group in the Great Lakes, spring, 1998.
Inset represents whole lake averages.
SU Ml HU ER ON
| Bosmina spp.
J Daphnia spp.
^ Cladoceran
^| Calanoida
| Immature Calanoida
I Cyclopoida
J Immature Cyclopoida
] Nauplii
I Rotifers
<^ 25mg/m3
12.5 mg/m3
< 2.5 mg/m3
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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combine estimates of the former from shallow tows
with estimates of the latter from deep tows, bearing
in mind that at deeper (>40 m) sites, the latter might
community composition were apparent, although
communities tended to be fairly consistent over
broad geographic areas (Figure 13). Synchaeta was
Figure 13. Relative abundance of rotifer genera, spring cruise, 1998.
Inset shows whole-lake averages.
] Notholca
I Synchaeta
] Kellicottia
] Keratella
| Po/yarthra
I Asplanchna
J Gastropus
| Ascomorpha
I Conochilus
J Trichocerca
| Filinia
I Co/loth&ca
be underestimated.
In spite of their relatively small size, nauplii
contributed, on a lake-wide basis, about 20-30% of
total estimated zooplankton biomass in all lakes
except Ontario, where they contributed only 6%
(Figure 12). Rotifers, on the other hand, were always
less than 5% of zooplankton biomass, with the
exception of a few sites in Lake Erie. Species
richness of rotifers was similar to that of crustaceans,
averaging between 6 and 12 species per site for the
five lakes (Figure 10b). In all betweenIO and 19
species were found in each lake. In spite of this low
species richness, some lake to lake differences in
present at most sites, while Kellicottia, and to a
lesser extent Keratella, were more abundant in the
upper lakes, particularly in Superior. The relative
contribution of Notholca to rotifer abundance was
greater in southern Lake Huron and the lower lakes.
Summer
Species richness of the crustacean community was
substantially higher during the summer, compared to
spring, with most sites supporting between 9-15
species (Figure 14a). Total numbers of taxa found in
each lake varied from 16-27. Again, Lake Erie had
the greatest number of species overall, with nearly
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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every species that was found in the other four lakes
also found in Lake Erie.
Total crustacean abundances (excluding nauplii)
were substantially higher during the summer than in
spring in most lakes (Figure 15). Lake-wide median
abundances in Erie and Ontario were over twelve
I!)
25
20
15 -
10
0
20
15
5 -
su
Ml
HU
ER
ON
Figure 14. Minimum, maximum and mean number
of taxa per site, and total number of taxa per lake,
for A:) crustaceans and B:) rotifers, summer 1998.
and four times greater, respectively, than spring
abundances, while lesser, but still substantial,
increases were seen in Lakes Huron and Superior.
In contrast, the median abundance in Lake Michigan
decreased slightly from spring to summer.
As in spring, copepods, and in particular immature
copepods, contributed significant numbers to all
sites. On a lake-wide basis, diaptomid copepodites
were among the dominant individuals in all lakes but
Ontario, accounting for 21-55% of total individuals.
Cyclopoid copepodites also contributed a substantial
number of individuals to all lakes, contributing 12-
26% of individuals on a whole-lake basis.
Cladocerans, largely from the genera Daphnia,
Bosmina and Eubosmina, contributed a larger share
of individuals during the summer in all lakes except
for Superior (Table 4). As in spring, a high degree of
spatial heterogeneity was found in Lake Erie;
dramatic differences in species composition were
also found between different sites in Lake Ontario.
Bosmina longirostris, present in all five lakes,
achieved very large populations in the western and
eastern basins of Lake Erie and the western basin of
Lake Ontario. Its numbers were greatly reduced in
the eastern basin of Lake Ontario, apparently being
replaced by Daphnia retrocurva, an organism
otherwise found in substantial numbers only in
western Lake Erie.
Three major predatory cladocerans were found in
the lakes: the native Leptodora kindtii, a recent
invader Bythotrephes cederstroemi, and Cercopagis
pengoi, which appeared in the lakes for the first time
in 1998 (Figure 16). Of the three, Bythotrephes was
the most widely distributed, being recorded from 42
of the 72 sites sampled. It was present in all lakes
with the exception of Lake Ontario, and attained its
highest populations in the central basin of Lake Erie.
The distribution of Leptodora was much more
restricted, although it achieved a maximum
abundance more than double that of Bythotrephes.
Interestingly, its distribution showed little overlap with
that of Bythotrephes, with substantial numbers of
individuals found in the western basin of Lake Erie
and Lake Ontario, areas where Bythotrephes was
rare or absent. Cercopagis pengoi was first noted in
Lake Ontario in late July of 1998, and by August
appeared to be restricted to four sites in the eastern
basin of the lake. The maximum abundance of
Cercopagis was somewhat higher than that of
Bythotrephes (465 individuals m"3 compared to 317
individuals m"3, respectively, as estimated from 20 m
tows).
OREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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-B
Individuals of Bythotrephes were not noted at sites
where Cercopagis occurred; in contrast, sizable
populations of Leptodora were found at sites
containing Cercopagis. Perhaps most interesting
was the distinct decrease in Bosmina populations at
notably higher than at stations on the eastern side of
the lake, again showing a negative relationship with
the predator Cercopagis. Rotifer biomass, on the
other hand, was substantially greater in the summer
than in the spring and, as with nauplii, made up a
Figure 15. Abundances of major crustacean groups in the Great Lakes,
summer 1998. Inset shows whole lake averages.
Ml HU ER ON
| Bosmina spp.
1 Daphnia spp.
| Other Cladocerans
I Calanoida
I Immature Calanoida
| Cyclopoida
J Immature Cyclopoida
50,000/mJ
20,000/m
< 5,000/m'
sites containing Cercopagis, which, as noted above,
appeared to be replaced by the larger-bodied D.
retrocurva. This could have been the result of direct
predation of Cercopagis on Bosmina.
Nauplii made up a much smaller percentage of total
biomass in summer compared to spring, with the
upper lakes averaging 4-7% and Lakes Erie and
Ontario 15 and 23%, respectively (Figure 17). In the
latter lake, biomass of nauplii at western sites was
greater percentage of total biomass in the lower
lakes (10-21%), compared to the upper lakes (5-8%).
Rotifer species richness during the summer was
similar to spring values for the lower lakes, but most
sites in the upper lakes exhibited an increase in
numbers of rotifer species (Figure 14b). Rotifer
community dominance by and large shifted away
from Notholca, Synchaeta and Kellicottia to
Polyarthra, Ascomorpha, and Conochilus (Figure 18).
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Figure 16. Abundances of predatory cladocerans in the Great Lakes,
summer, 1998, as estimated from 20 m tows
Substantial populations of Synchaeta still existed in
Lake Superior in summer, and Keratella, which was
moderately abundant in all lakes except Erie in the
spring, comprised a similar or somewhat higher
percentage of rotifer communities in the summer.
The increase in species richness in summer resulted
in stronger lake to lake, and in some cases within
lake, differences in the distribution of rotifer species
compared to spring. The upper lakes all supported
distinct rotifer communities, while notable differences
in community composition were seen between the
western basin and the central and eastern basins of
Lake Erie, as well as between the eastern and
western basins of Lake Ontario.
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 17. Total zooplankton biomass by major group in the Great Lakes, summer, 1998.
Inset represents whole lake averages.
I Bosmina spp.
I | Daphnia spp.
| | Cladoceran
jjj^l Calanoida
| Immature Calanoida
| Cyclopoida
[ | Immature Cyclopoida
| | Nauplii
| Rotifers
-150 mg m"3
75 mg m"
< 15 mg m"'
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 18. Relative abundance of rotifer genera, summer cruise, 1998.
Inset shows whole-lake averages.
Notholca
I Synchaeta
| | Kellicottia
J Kerate/la
| Polyarthra
| Asplanchna
] Gastropus
J Ascomorpha
| Conochilus
J Trichocerca
| Ploesoma
I Collotheca
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Benthos
Figure 19. Sediment composition at benthic sites in the Great Lakes,
summer 1998. Inset shows whole lake averages.
J Fine Gravel
| Medium Sand
J Fine Sand
] Silt
I Clay
O Superior Michigan Huron O Erie O Ontario
100
200 0 100
Depth (m)
200
Figure 20. Relationship between depth and substrate characteristics.
Lines indicate least squares regressions.
Benthos sampling depths ranged from 12 m to 257
m, averaging just over 100 m, and substrates were
characterized by varying proportions of silt, clay and
fine sand (Figure 19). Sites in Lakes Erie and
Superior tended to have a slightly lower percentage
of fine sand; otherwise substantial differences did
not exist from lake to lake. There was a tendency
towards finer substrates with increasing depth, with
silt, clay and 3> (the inverse log of sediment grain
size) all tending to increase with depth, while sand
tended to decrease (Figure 20).
Sediment nutrient concentrations varied between
2.1-83.0 (x = 26.2) mg C gm DW1 for carbon; 0.05-
4.9 (x = 1.3) mg N gm DW"1 for nitrogen and 0.2-1.9
(x = 1.0) mg P gm DW"1 for phosphorus, and were
generally comparable to those found in 1997. High
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 21. Sediment concentration of carbon, nitrogen and
phosphorus at benthos sites in the Great Lakes, summer 1998.
r85
mgC/g dw
L 0
mgN/g dw r 5
mgP/g dw
values occurred at Green Bay, Lake Michigan and
Saginaw Bay, Lake Huron (Figure 21). In general,
though, large lake to lake differences were not found
in these parameters. Sediment nutrient content,
most notably phosphorus, and percent water
exhibited a tendency to increase with depth (Figure
22).
Most sites supported a very limited number of taxa,
with maximum numbers of taxa per site ranging from
4 -19 for the five lakes, and minimum numbers of
taxa per site between 2 and 6 (Figure 23). There
was a clear trend of greater species richness
associated with higher trophic state; numbers of taxa
increased along the sequence Superior-
>Huron/Michigan->Ontario->Erie. Lake Erie
supported the greatest number of taxa overall (35),
O Superior Michigan 0 HuronQ Erie O Ontario
o 100 200 o 100
Depth (m)
Figure 22. Relationship between depth and sediment chemistry.
Lines indicate least squares regressions.
while benthic invertebrate communities in Lake
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 25. Relative abundances of major benthic groups
in the Great Lakes, summer 1998. Inset shows whole lake averages.
SU Ml HU ER ON
^| Oligocheata
j Chironomidae
J Diporeia spp.
| Mysisrelicta
| Sphaeridae
I Other
Figure 26. Abundance of Diporeia spp. in the Great Lakes, summer 1998
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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Figure 25. Relative abundances of major benthic groups
in the Great Lakes, summer 1998. Inset shows whole lake averages.
SU Ml HU ER ON
Oligocheata
Chironomidae
Diporeia spp.
Mysis rellcta
Sphaeridae
Other
Figure 26. Abundance of Diporeia spp. in the Great Lakes, summer 1998
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The amphipod Diporeia was by far the dominant
benthic invertebrate in the upper three lakes,
although it was absent from Lake Erie, nearshore
sites in Lake Ontario, and Saginaw Bay in Lake
Huron (Figures 25, 26). Oligochaetes were the
second most dominant group, and made up a
majority of individuals at those sites where Diporeia
did not. They were the most diverse group, with a
total of 26 different species identified in 1998.
Members of the oligochaete family Tubificidae made
up at least 50% of the oligochaete communities in all
lakes except Lake Superior, where members of the
family Lumbriculidae were the most common (Figure
27). The proportion of lumbriculids increased along
the sequence Erie->Ontario->Huron/Michigan-
>Superior, which is in keeping with their preference
for lower productivity environments. Tubificids, on
the other hand, were more common in the lower
lakes and at shallower sites in Lakes Michigan and
Huron. Over a dozen genera of Chironomidae were
also found in the lakes (Figure 28). The oligotrophic
genus Heterotrissocladius was the only chironomid
found in Lake Superior, and also dominated the off-
shore sites of Lakes Michigan and Huron.
Communities in the lower lakes were more diverse,
supporting notable populations of Chironomus,
Procladius and Micropsectra, among other genera.
Figure 27. Relative abundances of oligochaete taxa in the Great Lakes, summer 1998.
Inset shows whole lake averages.
J Stylodrilus heringianus
f Imm. Lumbriculidae
f Enchytraeidae
| Naididae
J Aulodrilus americanus
f Limnodrilus hoftmeisteri
~J Potamothrix vejdovskyi
I Quistadrilus multisetosus
] Spirosperma ferox
I Tublfex tubifex
| Other Tubificidae
^ Imm. Tubificidae w/o hair
Imm. Tubificidae w/ hair
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Figure 28. Relative abundances of chironomid genera in the Great Lakes,
summer 1998. Inset shows whole lake averages.
SU Ml HU ER ON
Chironomus
Cryptochironomus
Parac/adope/ma
Paratendipes
Polypedilum
Micropsectra
Stempellinella
Tanytarsus
I Protanypus
I I Heterotrissocladius
J Ab/abesmyia
H Coe/otanypus
I Procladius
n
n
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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SUMMARY
Phytoplankton communities in the Great Lakes were highly diverse, with much of that diversity
contributed by diatoms, which dominated the plankton of all lakes in the spring, with the
exception of Lake Superior. Summer communities shifted away from diatoms, towards
chrysophytes in the upper lakes and chlorophytes in the lower lakes. Zooplankton communities
were considerably less diverse, and were composed in most cases of less than a dozen
species. Crustacean communities in all lakes except Lake Ontario were dominated by
diaptomid copepods in spring. During summer, both abundance and species richness
increased, the latter owing largely to the appearance of populations of cladocerans. In the
upper lakeSjfsummer communities were dominated by diaptomid copepods, cyclopoid
copepodites; and Daphnia galeata mendotae (co-dominant with Holopedium gibberum in Lake
Superior), and showed a high degree of spatial homogeneity. Communities in Lake Erie
exhibited both greater species richness and spatial heterogeneity. Lake Ontario was unusual in
its relative lack of calanoid copepods, being dominated instead by cyclopoid copepods, along
with Bosmina and Daphnia. A new predatory cladoceran in Lake Ontario, Cercopagis pengoi,
appeared to have already had an impact on zooplankton community structure. Rotifer
communities were a minor component of zooplankton biomass in the spring, but increased in
importance in the summer. The benthos was notably species-poor in the Great Lakes.
Profundal communities were very similar in all lakes except Lake Erie, and were dominated by
an association consisting of the amphipod Diporeia, the oligochaete Stylodrilus heringianus,
and the chironomid Heterotrissocladius, along with unidentified members of the Sphaeriidae.
Communities in shallower regions varied greatly from site to site, but were usually characterized
by lesser abundances or the absence of Diporeia and the dominance of oligochaetes.
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ACKNOWLEDGMENTS
It is a pleasure to acknowledge the following individuals, who were largely responsible for the
production of data presented in this report: Jennifer L. Gronefeld, Larissa Granovski and
Joseph B. Volerman (phytoplankton), Linda A. Kuhns, Lori L. Schacht and Ruth E. Little
(zooplankton), and Ken K. Klubek (benthos). Their hard work and dedication is highly
appreciated. Excellent graphical and analytical support was provided by Mark A. DiMartino.
Chemical analyses were overseen by Michael Yusim. We would also like to express our great
appreciation to captain Dave Moser and the entire crew of the RA/ Lake Guardian for their
assistance throughout the course of this work.
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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B
LITERATURE CITED
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The Identification And Ecology Of The Common Crustacean Species. Madison, Wl:
University of Wisconsin Press.
Bottrell, H.H., Duncan, A., Gliwicz, Z.M., Grygierek, E., Herzig, A., Hillbricht-llkowska, A.,
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Evans, M. 1985. The morphology of Daphnia pulicaria, a species newly dominating the
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Germain, H. 1981. Flore des Diatomees Eaux Douces et Saumatres. Paris: Societe Nouvelle
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Haney, J.F. & Hall, J.D. 1973. Sugar coated Daphnia: a preservation technique for Cladocera.
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Kathman, RD and R.O. Brinkhurst. 1998. Guide to the Freshwater Oligochaetes of North
America. College Grove, TN: Aquatic Resources Center.
Krammer, K. and H. Lange-Bertalot. 1986, SuRwasserflora von Mitteleuropa, ll:2
Bacillariophyceae. 1 Teil: Naviculaceae. Gustav Fischer Verlag Jena: New York, NY.
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Bacillariophyceae. S.Teil: Centrales, Fragilariaceae, Eunotiaceae. Gustav Fischer Verlag:
NY, New York.
Krammer, K. and H. Lange-Bertalot. 1997. Siifcwasserflora von Mitteleuropa, ll:2
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GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM %
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Rivier, I.K. 1998. The Predatory Cladocera (Onychopoda: Podonidae, Polyphemidae,
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pheopigments. Limnol. Oceanogr. 39:1985-1992.
Wetzel, R.G. 1983. Limnology. Philadelphia, PA: Saunders.
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Larvae. Ent.Scand. Suppl. No. 19.
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9
Table 1. Ten most dominant phytoplankton species, by biovolume, in spring 1998. Numbers indicate lake-wide average biovolumes (nm3/ml).
Lake Superior
Species |nm3/ml
Rhodomonas minuta 9,327
Aulacoseira islandica 8,669
Cyclotella comta 4,739
Cryptomonas erosa 4,661
Haptophyceae 4,537
Gymnodinium sp. 3,977
Anacystis montana f. minor 3,750
Oscillatoria minima 3,709
Stephanodiscus subtransylvanicus 3,007
Stephanodiscus niagarae 2,488
Lake Michigan
Species nm3/ml
Aulacoseira islandica 86,441
Aulacoseira subarctica 73,867
Stephanodiscus subtransylvanicus 59,003
Stephanodiscus alpinus 17,273
Cryptomonas erosa 9,056
Cryptomonas ovata 5,854
Rhodomonas lens 5,403
Rhodomonas minuta 3,564
Gymnodinium helveticum f. achroum 3,527
Gymnodinium sp. 3,343
Lake Huron
Species |um3/ml
Aulacoseira islandica 149,213
Oscillatoria tenuis 35,682
Aulacoseira subarctica 34,486
Tabellaria flocculosa 28,456
Rhodomonas minuta 16,133
Rhodomonas lens 8,027
Tabellaria fenestrata 7,797
Haptophyceae 7,448
Stephanodiscus subtransylvanicus 5,775
Cryptomonas pyrenoidifera 4,902
Lake Erie
Species um3/ml
Aulacoseira islandica 786,555
Stephanodiscus hantzschii f. tenuis 70,265
Stephanodiscus niagarae 56,404
Rhodomonas minuta 40,481
Stephanodiscus binderanus 32,028
Stephanodiscus alpinus 22,608
Stephanodiscus pan/us 17,672
R. minuta v. nannoplanctica 14,304
Anacystis montana f. minor 10,718
Unidentified flagellate #5 9,779
Lake Ontario
Species |u.m3/ml
Aulacoseira islandica 242,768
Stephanodiscus niagarae 90,528
Stephanodiscus alpinus 64,429
Rhodomonas minuta 43,431
Thalassiosira baltica 41,246
Gymnodinium helveticum f. achroum 38,579
Cryptomonas erosa 19,535
Gymnodinium sp. 12,517-
Cryptomonas ovata 11,597
Nitzschia lauenburgiana 9,062
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Table 2. Ten most dominant phytoplankton species, by biovolume, in summer 1998. Numbers indicate lake-wide average biovolumes Oiim3/ml)
Lake Superior
Species n.m3/ml
Cyclotella comta 21,871
Dinobryon bavaricum 16,025
Cyclotella delicatula 8,637
Rhodomonas minuta 8,630
Dinobryon divergens 7,189
Dinobryon bavaricum var. vanhoeffenii 6,169
Cryptomonas erosa 4,748
Cryptomonas erosa var. reflexa 3,906
Fragilaria crotonensis 3,898
Dinobryon sociale 3,657
Lake Erie
Species um3/ml
Pediastrum simplex 87,160
Pediastrum sp. 63,732
Fragilaria crotonensis 61,089
Cyclotella ocellata 40,522
Microcystis sp. 39,437
Cyclotella comensis 30,850
Rhodomonas minuta var. nannoplanctica 29,602
Rhodomonas minuta 21,605
Ceratium hirundinella 20,337
Cryptomonas erosa 19,021
Lake Michigan
Species |iim3/ml
Cryptomonas erosa 23,515
Chrysosphaerella sp. 13,085
Aphanocapsa delicatissima 13,067
Planktonema lauterborni 12,933
Fragilaria crotonensis 11,932
Gymnodinium sp. 11,763
Peridinium sp. 11,010
Dinobryon divergens 8,724
Haptophyceae 7,129
Rhodomonas minuta 6,933
Lake Ontario
Species um3/ml
Ceratium hirundinella 161,822
Peridinium sp. 66,610
Cryptomonas erosa 44,073
Staurastrum gracile 42,877
Rhodomonas minuta 39,086
Fragilaria crotonensis 36,247
Rhodomonas minuta var. nannoplanctica 32,213
Oocystis borgei 25,723
-"*" Dinobryon divergens 25,374
Tetraedron minimum 23,912
. ..
Lake Huron
Species u.m3/ml
Chrysosphaerella longispina 70,186
Ceratium hirundinella 18,740
Cyclotella comensis 14,190
Peridinium sp. 13,405
Dinobryon bavaricum , 12,081
Cryptomonas erosa 12,045
Rhodomonas minuta 8,316
Cyclotella comta 6,852
Cryptomonas erosa var. reflexa 6,501
Fragilaria crotonensis 6,408
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Table 3. Dominant crustacean zooplankton in the Great Lakes, spring, 1998. Numbers indicate lake-wide average apundances/m3.
Lake Superior
Species #/m3
Leptodiaptomus sicilis 474
Diacyclops thomasi 258
Limnocalanus copepodites 202
Cyclopoid copepodites 46
Limnocalanus macrurus 21
Diaptomid copepodites 18
Senecella copepodites 3
Mysis relicta 1
Senecella calanoides 1
Lake Erie
Species #/m3
Diacyclops thomasi 657
Cyclopoid copepodites 615
Leptodiaptomus ashlandi 333
Diaptomid copepodites 200
Leptodiaptomus minutus 134
Bosmina longirostris 133
Skistodiaptomus oregonensis 127
Leptodiaptomus sicilis 116
Limnocalanus copepodites 79
Daphnia galeata mendotae 49
Cake Michigan
Species #/m3
Diaptomid copepodites 2,265
Leptodiaptomus ashlandi 1,698
Leptodiaptomus sicilis 444
Leptodiaptomus minutus 394
Diacyclops thomasi 145
Cyclopoid copepodites 81
Limnocalanus macrurus 30
Limnocalanus copepodites 9
Tropocyclops prasinus mexicanus 9
Mysis relicta 3
Lake Ontario
Species - .. #/m3
Diacyclops thomasi '"' 2,098
Cyclopoid copepodites 1,230
Diaptomid copepodites 531
Limnocalanus copepodites 200
Leptodiaptomus sicilis 49
Skistodiaptomus oregonensis 23
Eubosmina coregoni 14
Tropocyclops prasinus mexicanus 11
Bosmina'longirostris 9
Limnocalanus macrurus 8
Lake Huron ife"
Species #/m3
Diaptomid copepodites 2,425
Leptodiaptomus ashlandi 2,000
Leptodiaptomus sicilis 737
Leptodiaptomus minutus 694
Diacyclops thomasi 306
Cyclopoid copepodites 240
Limnocalanus copepodites 130
Limnocalanus macrurus 70
Epischura copepodites 12
Diaptomus oregonensis 4
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Table 4. Dominant crustacean zooplankton in the Great Lakes, summer, 1998. Numbers indicate lake-wide average abundances/m3
Lake Superior
Species #/m3
Diaptomid copepodites 2,764
Cyclopoid copepodites 1,189
Holopedium gibberum 447
Diacyclops thomasi 385
Daphnia galeata mendotae 372
Limnocalanus macrurus 128
Leptodiaptomus sicilis < 114
Bosmina longirostris 44
Bythotrephes cedarstroemi 6
Senecella calanoides 6
Lake Erie
Species #/m3
Diaptomid copepodites 3,880
Cyclopoid copepodites 2,049
Eubosmina coregoni 1,766
Daphnia galeata mendotae 1,559
Diaptomus oregonensis 1,293
Bosmina longirostris 1,258
Mesocyclops copepodites 697
Epischura copepodites 693
Mesocyclops edax 642
Daphnia retrocurva 451
"Lake Michigan
Species #/m3
Daphnia galeata mendotae 2,666
Diaptomid copepodites 2,230
Cyclopoid copepodites 1,192
Leptodiaptomus sicilis 449
Diacyclops thomasi 341
Leptodiaptomus ashlandi 307
Bosmina longirostris 179
Leptodiaptomus minutus 161
Epischura copepodites 133
Limnocalanus macrurus 64
Lake Ontario
Species ' . #/m3
Bosmina longirostris 22,392
Cyclopoid copepodites 21,895
Daphnia retrocurva 14,206
Diacyclops thomasi 6,113
Eubosmina coregoni 1,330
Diaptomid copepodites 187
Limnocalanus macrurus 171
Leptodiaptomus sicilis 111
Cercopagis pengoi 90
Skistodiaptomus oregonensis 80
Lake Huron
Species #/m3
Daphnia galeata mendotae 3,768
Diaptomid copepodites 3,590
Cyclopoid copepodites 2,637
Bosmina longirostris 671
Diacyclops thomasi 617
Diaptomus minutus 557
Leptodiaptomus ashlandi 551
Leptodiaptomus sicilis 326
Epischura copepodites 187
Eubosmina coregoni 130
GREAT LAKES BIOLOGICAL OPEN WATER SURVEILLANCE PROGRAM
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