EPA-R3-73-044
A oust 1973 Ecological Research Series
Biological Investigations
of Lake Wingra
Office of Research and Monitoring
U.S. Environmental Protection Agency
Washington, D.C. 20460
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EPA-R3-73-044
August 1973
BIOLOGICAL INVESTIGATIONS OF LAKE WINGRA
By
Paul C. Baumann
Arthur D. Hasler
Joseph F. Koonce
Mitsuo Teraguchi
University of Wisconsin
Madison, Wisconsin 53706
Project 16010 EHR
Program Element 1B1031
Project Officer
Dr. A. F. Bartsch
Pacific Northwest Environmental Research Laboratory
National Environmental Research Center
Corvallis, Oregon 97330
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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EPA Review Notice
This report has been reviewed by the Environmental Protection Agency and
approved for publication. Approval does not signify that the contents
necessarily reflect the views and policies of the Environmental Protection
Agency, nor does mention of trade names or commercial products constitute
endorsement or recommendation for use.
11
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ABSTRACT
An investigation of seasonal changes in species diversity and. "biomass
of phytoplankton, zooplankton, benthos, and fish in Lake Wingra, Madison,
Wisconsin, was conducted during 1970 and 1971. The objective of this
study was to obtain ecological data on the biological components of an
aquatic ecosystem and to utilize these data along with concurrent chemi-
cal data to aid the development of systems models of nutrient and energy
fluxes in lake drainage basins.
Interpretations of data gathered during this study reveal several impor-
tant considerations for models of lake systems and future studies of
Lake Wingra. Phytoplankton associations, for example, appear to be
adaptive, self-organizing systems. Such behavior suggests the possibility
to apply optimization principles to phytoplankton models. The data
suggest, furthermore, that optimization analysis can be based on size
particle distributions of the phytoplankton, which, rather than species,
appears to be the basis of phytoplankton categories. Zooplankton and
benthos analyses, on the other hand, indicate that energy and nutrient
fluxes may be adequately approximated by simulating only a few species.
Finally, results of fish studies imply that models of whole lake eco-
systems must account for the mobility of predators in estimating their
impact on prey populations, which should be characterized by differing
spatial and temporal susceptibility to predation.
This report was submitted in fulfillment of EPA omnibus grant 16010 EHR
administered through the University of Wisconsin Eutrophication Research
Program.
111
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CONTENTS
Secti_on
I
II
III
IV
VI
VII
VIII
IX
Conclusions
Recommendations
Introduction
Observations of Natural Phytoplankton Associations
in Lake Wingra
Seasonal Changes in the Abundance of Pelagic-
Zooplankton Species in Lake Wingra
Seasonal Change in the Abundance of Oligochaetes
and Chironomids in Lake Wingra
Diel Patterns of Distribution and Feeding
of Selected Fish Species in Lake Wingra
Acknowledgements
References
3
5
7
31
6l
83
111
113
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FIGURES
PAGE,
1 HYDROGRAPHIC MAP OF LAKE WINGRA 9
2 ANNUAL TEMPERATURE DISTRIBUTION OF AVERAGE WATER
COLUMN TEMPERATURE IN LAKE WINGRA 13
3 ANNUAL DISTRIBUTION OF AVERAGE WATER COLUMN, pH AND
ALKALINITY IN LAKE WINGRA 1^
h AVERAGE AMMONIUM AND NITRATE CONCENTRATIONS FOR ONE
YEAR IN LAKE WINGRA ' 15
5 AVERAGE TOTAL AND DISSOLVED ORTHO-PHOSPHORUS CONCEN-
TRATIONS FOR ONE YEAR IN LAKE WINGRA l6
6 AVERAGE CONCENTRATIONS OF SILICATE (AS Si) AND IRON
(AS Fe) FOR PARTS OF ONE YEAR IN LAKE WINGRA 1?
7 AVERAGE DAILY PRODUCTIVITY AND FRESHWEIGHT BIOMASS
OF PHYTOPLANKTON IN LAKE WINGRA FOR ONE YEAR 19
8 CLASS COMPOSITION PATTERN OF PHYTOPLANKTON IN
LAKE WINGRA FOR ONE YEAR 20
9 SIZE DISTRIBUTION OF PHYTOPLANKTON IN LAKE WINGRA
FOR ONE YEAR 21
10 RELATIVE BIOMASS OF MOTILE AND NONMOTILE PHYTO-
PLANKTON IN LAKE WINGRA FOR ONE YEAR 22
11 RELATIVE BIOMASS OF COLONIAL AND UNICELLULAR PHYTO-
PLANKTON IN LAKE WINGRA FOR ONE YEAR 23
12 ANNUAL DISTRIBUTION OF TOTAL INCIDENT RADIATION AND
RELATIVE CARBON ASSIMILATION RATE BY PHYTOPLANKTON
IN LAKE WINGRA 2\\
13 CORRELATION OF TOTAL INCIDENT RADIATION AND RELATIVE
CARBON ASSIMILATION RATE BY PHYTOPLANKTON ON EACH
OBSERVATION DATE FOR ONE YEAR IN LAKE WINGRA 25
14 CONTOUR MAP OF LAKE WINGRA 32
15 SEASONAL CHANGES IN THE ABUNDANCE OF ALONA
QUADRANGULARIS IN LAKE WINGRA 36
16 SEASONAL CHANGES IN THE ABUNDANCE OF BOSMINA
LONGIROSTRIS IN LAKE WINGRA 37
vi
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PAGE
17 SEASONAL CHANGES IN THE ABUNDANCE OF CERlODAPHNIA
QUADRANGULA IN LAKE WINGRA 39
18 SEASONAL CHANGES IN THE ABUNDANCE OF CHYDORUS hO
SPHAERICUS IN LAKE WINGRA
19 SEASONAL CHANGES IN THE ABUNDANCE OF DAPHNIA
GALEATA IN LAKE WINGRA Ul
20 SEASONAL CHANGES IN THE ABUNDANCE OF DAPHNIA
RETROCURVA IN LAKE WINGRA ^3
21 SEASONAL CHANGES IN THE ABUNDANCE OF DIAPHANOSOMA
BRACHYURUM IN LAKE WINGRA hk
22 SEASONAL CHANGES IN THE ABUNDANCE OF LEPTODORA
KINDTII IN LAKE WINGRA 1*5
23 SEASONAL CHANGES IN THE ABUNDANCE OF CYCLOPS
BICUSFIDATUS THOMAS I IN LAKE WINGRA 1*7
2U SEASONAL CHANGES IN THE ABUNDANCE OF DIAPTOMUS
SICILOIDES IN LAKE WINGRA 1*8
25 SEASONAL CHANGES IN THE ABUNDANCE OF MESOCYCLOFS
EDAX IN LAKE WINGRA 1*9
26 SEASONAL CHANGES IN THE ABUNDANCE OF ASPLANCHNA
PRIODONTA, BRACHIONUS ANGULARIS. AND BRACHIONUS
CALYCIFLORUS IN LAKE WINGRA 51
27 SEASONAL CHANGES IN THE ABUNDANCE OF KERATELLA
COCHLEARIS IN LAKE WINGRA 53
28 SEASONAL CHANGES IN THE ABUNDANCE OF POLYARTHRA EURY-
PTERUS, POLYARTHRA VULGARIS, AND TETRAMASTIX
OPOLIENSIS IN LAKE WINGRA 5U
29 SEASONAL CHANGES IN THE STANDING CROP OF PELAGIC-
ZOOPLANKTON IN LAKE WINGRA 56
30 RELATIONSHIP BETWEEN STANDING CROP OF PELAGIC-
ZOOPLANKTON AND TEMPERATURE OF THE LAKE 57
31 CONTOUR MAP OF LAKE WINGRA AND LOCATIONS OF THE
SAMPLING STATIONS 62
32 LIGHT PENETRATION, AVERAGE TEMPERATURE AND AVERAGE
OXYGEN CONCENTRATION AT STATION 2 (c) IN LAKE WINGRA 65
VI1
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FAGE_
33 SEASONAL CHANGES IN THE ABUNDANCE OF LIMNODRILUS
HOFFMEISTERI (INCLUDES L_. UDEKEMIANUS") 67
3k SEASONAL CHANGES IN THE ABUNDANCE OF EUILYDRILUS
HAMMOIENSIS AT THE FIVE SAMPLING STATIONS 69
35 SEASONAL CHANGES IN THE ABUNDANCE OF CHIRONOMQUS
PLUMOSUS AT THE FIVE STATIONS 71
S
36 SEASONAL CHANGES IN THE ABUNDANCE OF PROCLADIUS SP.
AND TANYPUS SP- AT THE FIVE SAMPLING STATIONS 72
37 GRADIENTS IN THE ABUNDANCE OF LIMNODRILUS HOFF-
MEISTERI (INCLUDES L_. UDEKEMIANSUS) ALONG THE LONG
AND SHORT AXIS OF LAKE WINGRA AT DIFFERENT SEASONS 7^
38 GRADIENTS IN THE ABUNDANCE OF EUILYDRILUS
HAMMOIENSIS ALONG THE LONG AND SHORT AXIS OF LAKE
WINGRA AT DIFFERENT SEASONS 75
39 GRADIENTS IN THE ABUNDANCE OF CHIRONOMUS FLUMOSUS
ALONG THE LONG AND SHORT AXIS OF LAKE WINGRA AT
DIFFERENT SEASONS 77
kd GRADIENTS IN THE ABUNDANCE OF PROCLADIUS SP. AND
TANYPUS SP- ALONG THE LONG AND SHORT AXIS OF LAKE
WINGRA 78
kl CATCH PER TRAWL RUN DAY AND NIGHT FOR THE BLUEGILL
(LEFOMIS MACROCHIRUS) 86
1*2 PERCENT COMPOSITION BY NUMBER FOR SIZE CLASSES OF
THE BLUEGILL POPULATION IN LIMNETIC AND LITTORAL
ZONES ON SEPTEMBER 17-18, 1970 87
k3 PERCENT COMPOSITION BY BIOMASS OF THE BLUEGILL
POPULATION IN LIMNETIC AND LITTORAL ZONES ON
SEPTEMBER 17-18, 1970 88
hh DAILY FEEDING PERIODICITY OF TWO SIZE CLASSES OF
BLUEGILL IN THE LIMNETIC ZONE (SEPTEMBER 17-18,
1970) 89
>+5 DAILY FEEDING PERIODICITY OF 135mm OR LARGER BLUEGILLS
FROM THE LIMNETIC AND LITTORAL ZONES (SEPTEMBER 17-18,
1970) 90
U6 MEAN AMOUNTS (g) OF FOOD CONSUMED BETWEEN SAMPLING
PERIODS FOR TWO SIZE CLASSES OF BLUEGILL IN THE
LIMNETIC ZONE (SEPTEMBER 17-18, 1970) 9!*
viii
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PAGE,
U7 NUMBER OF ZOOPLANKTON AND MACROFOOD ORGANISMS PER
STOMACH FOR THREE SIZE CLASSES OF BLUEGILL 96
U8 PERCENT COMPOSITION BY NUMBER OF SPECIES OF ZOO-
PLANKTERS IN STOMACHS OF THREE SIZE CLASSES OF
BLUEGILLS 98
^9 CATCH PER TRAWL RUN DAY, AND CATCH PER TRAWL RUN
NIGHT OF YELLOW BASS (MORONE MISSISSIPPIENSIS)
TAKEN FROM A U8-HOUR SERIES 100
50 CATCH PER TRAWL RUN DAY AND CATCH PER TRAWL RUN
NIGHT FOR TWO SPECIES TAKEN FROM A 48-HOUR SERIES 102
51 PERCENT WEIGHT (g) OF STOMACH CONTENT PER WEIGHT
(g) OF FISH 103
IX
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TABLES
No.
1 Summary of Chemical Analysis Methods 11
2 Species of Cladocerans, Copepods, and Rotifers Found
in the Samples Taken from the Open-Water Eegion of
Lake Wingra during 1968 and 1969 35
3 Species and Abundance of Oligochaetes and Chironomids
in the Sediment of the Open Water Region of Lake Wingra 66
^ Mean Weight of Food (g) per Fish Present in the
Stomach for Two Length Classes of Bluegill at Different
Hours during the Sampling Period (September 17-18,
1970) 92
5 Mean Percent Numerical Composition of Macrofood
Species per Subsample (Two Fish) for Three Species
Classes of Bluegill 99
6 Mean Percent Numerical Composition of Macrofood
or Zooplankton Species per Subsample (Two Fish)
for Three Species 105
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SECTION I
CONCLUSIONS
Data from this project are useful to development of lake ecosystem models.
Principal finds are:
1. Seasonal succession of phytoplankton is an example of an optimization
process. The assemblage may, therefore, "be treated as one category
or perhaps several categories of different sized particles without in-
formation loss.
2. Low nutrient levels coupled with high phytoplankton production
rates indicate that nutrient recycling is the chief source of nutrients
sustaining production.
3. Only a few macrozooplankton dominate transfer and transformation
of energy and nutrients at the primary consumer trophic level.
k. Microzooplankton, predominantly rotifers, are not major components
in energy and nutrient cycling and may, therefore, be neglected entirely-
5. Benthos is dominated by one species that may also be the chief open
water food source for fish.
6. Fish diurnal movements must be considered in any attempt to des-
cribe their effect on prey populations.
7. Some attempt should be made to allow for spatial and temporal segre-
gation of predator and prey organisms for models to capture the dynamic
qualities of whole lake ecosystems.
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SECTION II
RECOMMENDATIONS
Three recommendations concerning the scope of whole lake system models
can be made:
1. Lake systems tend to be tightly structured communities. Nutrient
recycling must, therefore, be an integral part of any model.
2. Temporal and spatial variations of the biota vill present problems
to simulation models. The only boundaries really applicable to the
lake are limits of the water system. Habitat variability within the
lake must, therefore, be accounted for in models.
3. Species may be aggregated into larger functional categories and
may be categorized either as a group (e.g. nannoplankton) or by studies
of representative species (e.g. bluegill sunfish for pan fish).
Future work could concentrate, on some interesting problems. Because
Lake Wirigra is only a single lake, the generality of the conclusions
reached here should be tested against other lakes. Furthermore, the
data suggest that temperature and light are the most significant variables
in the system. Such a situation indicates that energy constraints
may play a decisive role in the structure of the lake ecosystem. Such
a possibility deserves more consideration. Finally, the tightly linked
trophic structure of the lake suggests some interesting experimental
manipulations to determine causal relationships in the development
of various noxious conditions associated with eutrophication.
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SECTION III
INTRODUCTION
Ecological data on biological components of aquatic ecosystems are
vital to the development and implementation; of systems models of nutrient
and energy flows in lake drainage basins. Such data serve to identify
key nutrient pathways and guide the formulation of realistic process
submodels. Two separate but interrelated systems modeling programs have
selected Lake Wingra as a study area. One, also funded by this EPA
grant, (Huff ^t_ al_.) is concerned with nitrogen and phosphorus move-
ment through the Lake Wingra Basin. The other is the US/IBP Eastern
Deciduous Forest Biome Project, which is studying and modeling physical,
biological and chemical processes in the Lake Wingra Drainage Basin.
Both of these modeling efforts rely on ecological baseline data and
insight into the processes controlling energy and nutrient flow through
ecosystems. Upon this foundation of interacting data gathering and model-
ing, refinements in systems models may evolve and not only enhance under-
standing of ecosystem functioning, but also provide insight into the most
sensitive parameters in the system. As a tool in modeling the Lake
Wingra drainage basin, therefore, the present project deals with charac-
terization of seasonal changes in species-diversity and biomass of phyto-
plankton, zooplankton, benthos, and fishes in Lake Wingra.
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SECTION IV
OBSERVATIONS OF NATURAL PHYTOPLANKTON ASSOCIATIONS
Introduction
An interesting aspect of phytoplankton ecology is seasonal change
in the pattern of species composition. This periodicity of phytoplank-
ton populations has "been observed in every aquatic ecosystem studied
and has been documented thoroughly in many studies (e.g., International
Association of Limnology, 1971). Despite years of research effort,
however, the explanation of the, complex interrelationships existing within
a phytoplankton community remains an unfulfilled goal. To be sure,
physiological mechanisms and population dynamics have been related to
environmental and biological factors in aquatic ecosystems. Literature
reviews (e.g., Hutchinson, 1967), for example, reveal correlations of
temperature, light, nutrient concentration, zooplankton grazing, and
parasitism with the appearance and disappearance of both individual
and groups of phytoplankton species.
Changing patterns of species composition indicate that phytoplankton
associations are dynamic systems (cf. Lund, 196U). Individual species
may vary in their tolerance to environmental fluctuations, but the
overall diversity and composition of the association ultimately reflect
all of the selective pressures in their ecosystem. Sager (1967) has
discussed the importance of measures of phytoplankton diversity as an
indicator of the "condition" of a lake ecosystem. Such measures when
compared among lakes emphasize response differences of phytoplankton
associations. Within a single lake, multivariate analysis techniques
(e.g., Allen and Koonce, in prep.) indicate that changing species com-
position pattern actually reflects varying dominance strategies. Such
analyses, for example, identify major algal stratagems (i.e., slow
growth rate, but wide tolerance to environmental fluctuations or rapid
growth rate, but restriction to well-defined regimes of light and tempera-
ture) and indicate when these various stratagems result in species pre-
dominance. Of themselves, however, observations of the dynamic nature
of environmental fluctuations and the correlated response of species
in an association shed little light on the exact mechanisms operating,
but form a foundation from which to evaluate the important principles
involved.
In order to study the underlying principles governing the mechanisms
which cause phytoplankton periodicity, an investigation of the phyto-
plankton in Lake Wingra was initiated.
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Study Site
Lake Wingra (Fig. l) is a small shallow lake within the City of Madison,
Wisconsin. The lake has a surface area of 136 hectares, a maximum natural
depth of IK 2 meters, and an average open water depth of 2.5 to 3.0 meters.
The lake is primarily spring fed, but five storm sewers provide inter-
mittent water supply to the lake. Much of the southern shore of the lake
belongs to the University of Wisconsin Arboretum and is an undisturbed
forest. The northern shore is dominated by recreational and residential
areas.
Methods
At weekly intervals from 3 March 1970 until 23 February 1971 and periodi-
cally thereafter until mid-April 1971 » water samples were collected at
one station (Fig. l) for- estimation of primary production, phytoplankton
identification and enumeration, and chemical analyses. Water samples
were collected with a 2-liter nonmetallic Van Dorn sampler at three depths
(0, 1, and 2 meters) in the water column.
Estimation of primary production were based on standard in situ four
hour incubations of duplicate light and dark bottles containing 125 ml
of sample water to which 2 yci of WaH-^COg were added. Sample bottles
were suspended horizontally on specially constructed racks from a clear
plexiglas float. During collection and inoculation, samples were pro-
tected from light shock by conducting both procedures under a canvas
tarp. After the four hour incubation period, phytoplankton samples were
fixed with 0.5 ml of Lugol's solution, returned to the laboratory and fil-
tered through O.U7 y, membrane filters under a vacuum of 0.17 atm. The
filters were dried for at least two hours in a dessicator over silica
gel, exposed to concentrated HC1 fumes for ten minutes, and redried in
a dessicator for at least 30 minutes. Radioactivity of the filters
was then measured with a thin window, gas flow, planchet counter in
the Geiger-Miiller range. C fixation was calculated from the following
formula: 12 _ 12 _ . C_. . .
C,,. , = C •-,,-, fixed . k. . k0 . k_
fixed available .r-r - 123
C
available
where k, = counter efficiency
^. = isotope discrimination factor
k_ = bottle factor
Integral production over depth was determined planimetrically , and the
day rate was calculated from: P = P
o
where P is total production/m /day, PT is measured production/U hr, R
8
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LAKE WINGRA
DANE COUNTY, WISCONSIN
200 0 400 800
. . i i i i
Figure 1. Hydrographic map of Lake Wingra. (To convert scale in feet to meters,
multiply by 0.305.)
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is total incident radiation, and RT is the incident radiation during the
incubation period. Such a direct proportion seemed reasonable in Lake
Wingra from 2 hour incubations conducted over an entire day. Incident
solar radiation data were obtained from the U. S. Weather Bureau at
Truax Field, Madison, Wisconsin.
Following the start of the C incubation period, approximately three
liters of water were collected from each sampling depth and returned
to the laboratory for chemical analysis. Water analysis was conducted,
by routine procedures outlined in Table 1. Conductivity, pH, alkalinity,
and free C0_ were measured shortly after return from the field. Nitrate
and ammonia analyses were run on the same day samples were collected,
but phosphorus, iron, and silica, although prepared for analysis, were
not run until the following day. Samples for iron and phosphorus analy-
ses were transported in 300-ml glass bottles and all other samples in
1-liter polyethylene bottles. Prior to sampling, all sample collection
bottles were acid washed with 1:1 HC1 and rinsed repeatedly with tap
then distilled water. As a final precaution, all sample bottles were
rinsed with sample water before filling.
After water sample collection, light and temperature profiles were taken.
Temperature was measured with a Whitney Underwater Thermistor Thermometer
that was calibrated biweekly. White light intensity was measured with
a G-M Underwater Light Meter at half meter'intervals to the bottom of
the lake., The extinction coefficient for white light was calculated
from a linear regression of the natural logarithm of relative light
intensity versus depth:
In z= -ez
o
where e is the extinction coefficient, z the depth, and I and I the
light intensity at depth z and the surface, respectively.
Biomass estimates are based on species identification and enumeration
of sedimented samples (Utermohl, 1958). Separate 125-ml aliquots of
the incubation samples were fixed with Lugol's solution and preserved
for analysis. Depending on the biomass present, either 10 or 25 ml
duplicate subsamples of each aliquot were allowed to settle for 12
hours in specially constructed sedimentation chambers. The chambers
were then"placed on a mechanical stage of an inverted phase contrast
compound microscope, and phytoplankton species were identified and
counted at 625x. Enough transects (lOmm x 0.13mm) were processed to
encounter at least 100 individuals of the major species and at least
15 of the minor or rare species. Cell counts were converted to bio-
mass from cell volume calculations (e.g., Pechlaner, 1967). The cell
volume of each species was determined by approximating the shape of the
species with a solid geometrical formula. In making the conversion from
cell volume to biomass, a density of 1 g/ml was assumed for all species.
10
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TABLE 1
SUMMARY OF CHEMICAL ANALYSIS METHODS
Analysis
B3-»
NO — N
NO — N
PVP
Si03-Si
Iron
Alkalinity
co2
Method
Distillation
Cadmium Reduction
Brucine
Pho s pho-molyb dat e
Complexation
Silic o-molyb date
Complexation
Penanthroline
Acid Titration
Sodium Carbonate
Titration
Sensitivity
0.02 mg/1
0.7 yg/1
0.1 mg/1
1.0 yg/1
3.0 yg/1
20.0 yg/1
10.0 mg/1
*
Reference
1
2
1
3
2
1
1
1
References:
1. Standard Methods, 1965
2. Strickland and Parsons, 1968
3. Murphy and Riley, 1962
11
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Results
For a great part of the year, there was little or no thermal stratifica-
tion. As a result, both chemical and biological stratification was
limited. The following data, therefore, contain only average or total
water column values.
The average temperature of the water column in Lake Wingra varied from
0.5 C to 26.2 C (Fig. 2). The highest temperatures occurred from mid-
July to early August. The maximum open water temperature observed was
27.1*°C at the surface in late July.
Alkalinity and pH also demonstrated seasonal fluctuations (Fig. 3).
Alkalinity ranged from 194 mgCaCO_/liter under ice to 12^ mg CaCO /
liter in October. During the same time period, pH values varied
inversely with alkalinity from 7-^ to 9-1^. The highest pH values
occurred in late August and early September. Fluctuations in pH and
alkalinity indicate an equivalent fluctuation in total dissolved in-
organic carbon from 52 to 28 mg C/liter.
Nitrate concentrations fluctuated from 1 yg N/liter to 6lO yg N/liter
(Fig. H). It should be noted that a new analytical procedure was
initiated on 1 September 1970 and the sensitivity of the previous
nitrate method may not accurately reflect the low nitrate levels prior
to that time. Ammonia concentration followed a pattern similar to ni-
trate (Fig. JO. Both in 1970 and 19715 the highest values were observed
a month before ice out. During the ice-free period, however, the con-
centrations quickly fell below detectable limits (0.02 mg/l).
Concentration of dissolved ortho-phosphorus is low all year (Fig. 5).
Only during the winter does the concentration rise to 30 yg P/liter.
Much of the year phosphorus concentration is below 10 yg P/liter.
Total phosphorus analyses, on the other hand, reveal higher concentra-
tions (Fig. 5)> but even at the maximum concentration during July and
August, it never exceeded 70 yg P/liter.
Iron and silicate analyses were not run as often as the other analyses,
but for the most part, indicate uniformly low levels of iron and season-
ally varying silicate concentration (Fig. 6). Silicate concentrations,
for example, appear to be greater than 8 mg Si/liter toward the end of
the ice-free period, but drop precipitously during the spring diatom
bloom. Unfortunately, the iron analytical technique was not sensitive
enough for the low levels encountered, but seldom were concentrations
in excess of 0.05 mg/liter observed and no seasonal pattern in the data
can be detected.
Considering the relatively low levels of nitrogen and phosphorus during
the ice-free period, the phytoplankton biomass and productivity in Lake
12
-------
ICE COVER
24-
H
u>
U
o
Of,
UJ
o.
6H
p
I
I
I
I
M
I
\ *
\/\
M
M J
1970
S O
DATE
N
F
1971
M
Figure 2. Annual temperature distribution of average water column temperature in Lake Wingra.
Bars represent the observed range of temperatures on each measurement day.
-------
9
8
a.
7
6
ICE COVER
.O
-D-D-
_D-D'
P--0
..a
PH-n
ALKALI NITY -•
PO- --D
200^
u
D
u
O)
M5O
MA'M'J JASON D J F M AM
197O DATE 1971
Figure 3. Annual distribution of average water column pH and alkalinity in Lake Wingra.
-------
ICE COVER
M • A • M ' J ' J ' A ' S ' O
DATE
Figure k. Average ammonium and nitrate concentrations for one year in Lake Wingra.
-------
ICE COVER
TOTAL-P /ug/l A
DISS. ORTHO-P /ug/l •
Figure 5. Average total and dissolved ortho-phosphorus concentrations for one year in
Lake Wingra.
-------
8
6
<
U
4
M
SILICATE-O
IRON-*
ICE COVER
\ -a--
br''' ~'T>—-a'' X.Q
A M
1970
A S O
DATE
N
F M
1971
.10
.05
TO
O
z
(Q
M
Figure 6. Average concentrations of silicate (as Si) and iron (as Fe) for parts of one year
in Lake Wingra.
-------
Wingra are high (Fig. 7). The phytoplankton demonstrates only one pulse
in biomass (and that due primarily to one diatom species). The remainder
of the ice-free period, biomass is relatively constajijt (averaging about
20 g freshweight/m ). Productivity, as measured b^y C uptake, varied
from less than 10 mg C/m /day to over 7000 mg C/m /day, with an annual
mean daily productivity of 2^00 mg C/m /day. These productivity levels
are greater than those reported in the literature from any other lake
(Wetzel, unpublished summary). Furthermore, productivity in general
peaks with maximum light intensity in June and not with temperature in
mid-July to August.
An analysis of the taxonomic composition during the course of the study
reveals a typical pattern (Fig. 8). Winter associations are dominated
by cryptomonads and chrysomonads, spring associations by diatoms, early
summer associations are characterized by green coccoid algae and dino-
flagellates, midsummer and fall associations are dominated by blue-green
algae, and with the beginning of ice cover the association changes to
cryptomonads and diatoms. In general, however, the associations at
all times of the year are dominated by nannoplankton and ultraplankton
(Fig. 9)- Flagellated forms are dominant during the ice cover period
(Fig. 10), and colonial forms constitute the bulk of the phytoplankton
biomass during late summer and fall (Fig. 11).
Discussion
The phytoplankton's temporal pattern and the water chemistry fluctuations
reflect to varying degrees the cyclical temperature and light regimes
imposed on a temperate lake. In reflecting the cyclical nature of light
and temperature, therefore, phytoplankton periodicity in Lake Wingra is
similar to a wide variety of other lakes. As indicated in Figure 7, the
phytoplankton demonstrates a spring peak in biomass and a poorly defined
peak in fall. Although the morphology of Lake Wingra may impose some
moderating effect on the "boom-and-bust" cycles observed on other lakes,
this basic spring and fall bloom is common to a great many lakes (Pearsall,
1932; McCombie, 1953; Round, 1971).
18
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PRODUCTIVITY
FRESHWEIGHT C—O
M
J F M
1971
Figure J. Average daily productivity and fresh-weight biomass of phytoplankton in Lake
Wingra for one year.
-------
ICE -COVER
100
ro
o
CRYPTOPHYCEAE I |
CHLOROPHYCEAE I I I
CHRYSOPHYCEAE l±±J
BACILIARIOPHYCEAE LZJ
MYXOPHYCEAE IVsi
DINOPHYCEAE IQl
EUGLENOPHYCEAE •
J F ' M ' A
1971
Figure 8. Class composition pattern of phytoplankton in Lake Wingra for one year.
-------
ICE COVER
ro
H
100
NETPLANKTON-
NANNOPLANKTON-
Figure 9- Size distribution of phytoplankton in Lake Wingra for one year.
Size categories are netplankton (maximum dimension of cell greater than 50 urn) ,
nannoplankton (maximum dimension of cell less than or equal to 50 urn, but
greater than 10 ym), and ultraplankton (maximum cell dimension less than or
equal to 10 ym).
-------
ICE COVER
to
CO
O
CO
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<
»—
O
80
60
40
U
Of.
20
MOTILE ALGAE
NONMOTILE ALGAE
M
A M J J A SON D J FMA
1970 DATE 1971
Figure 10. Relative "biomass of motile and nomnotile phytoplarikton in Lake Wingra for one year,
-------
80-
<
O
60-
ro
40-
z
UJ
U
20-
COLONIAL ALGAE
UNICELLULAR ALGAE
ICE COVER
M A M J J
1970
A S ON D
DATE
J F M AM
1971
Figure 11. Relative biomass of colonial and unicellular phytoplankton in Lake Wingra for
one year.
-------
8-
X
o
O>
c
_D
O
O
6-
i 4H
<
o
<
O
2-
RELATIVE ASSIMILATION o—o
TOTAL RADIATION •—•
M ' A ^^M ' J
1970
S ' O
DATE
N
J ' F
1971
M ' A
-500 5
m
-400 >
C/l
-300 -
^
-200 §
-100 ^
(Q^
Q
Figure 12. Annual distribution of total incident radiation and relative carbon assimilation
rate by phytoplankton in Lake Wingra.
-------
500
CD
\
(J
OS
E
g
h-
<
_!
r, 1
300-
200-
100-
50
• ICE FREE PERIOD
O ICE COVER PERIOD
o o
o
o
o o
150
250 350 450 550 650
LIGHT INTENSITY (LANGLEYS/DAY )
750
Figure 13. Correlation of total incident radiation and relative carbon assimilation
rate by phytoplankton on each observation date &r one year in Lake Wingra.
-------
Productivity like standing crop fluctuates seasonally, "but its maximum
appears to be more associated with longest day lengths and highest tern- .
peratures. Again this observation is in accord with those of other in-
vestigators (Wetzel, 1966; Goldman and Wetzel, 1963). Of interest, how-
ever, is the relationship between incident light and relative assimilation
(Figs. 12 and 13). During parts of the year, there appear to be close
correlations between light and relative assimilation (Fig. 13), but during
other parts of the year, the relationship appears to be'obscure at best.
The reason for this lack of correlation is not clear. Certainly, other
environmental factors are changing during periods of poor correlation,
and there are some fairly obvious changes in the composition of the
phytoplankton (cf. Fig. 8). Taken as a whole-, therefore, the lack of •
a strong correlation with light may indicate shifting physiological
capabilities of the phytoplankton association.
Perhaps the best indication of changing adaptations Is the .progression
of algal Classes during the course of the year. Although the sequence
of algal Classes may vary, the succession can be demonstrated in lakes
from a wide variety of climatic regimes. In Lake Kinneret (Serruya
and Pollingher, 1971), for example, Dinophyceae and Cryptopyceae dominate
the plankton from January through June. Subsequently, the Chlorophyceae
become more important from July through November. The Myxophyceae do
not constitute major fractions of the biomass, but occur primarily in
July and August. A somewhat different success pattern has been reproted
for Lough Neagh, United Kingdom (Gibson, Wood, Dickson, and Jewson, 1971)»
but a changing pattern of dominance is still preserved. Alpine lakes,
covered by ice for long periods of the year, also reveal changing Class
composition patterns with the Myxophyceae assuming far less importance
(Pechlaner, 1967 and 1971). The apparent success of algal Classes in
the above lakes, and to some extent in Lake Wingra, are due mainly to
changes in abundance of a few species. Because of the nature of the
species' preadaptations, it is not unreasonable to envisage a changing
set of environmental and biological variables selecting out those species
or groups of species that'will grow most rapidly.
Observations of Lake Wingra phytoplankton indicate some adaptive char-
acteristics of the various algal Classes represented in the lake. Diatoms,
for example, appear to grow best during the low temperature periods of
spring and fall. Green algae (Chlorophyceae) appear-to be best adapted
to a 10° to 20°C-temperature range with the greatest day length. Blue-
greens (Myxophyceae), on the other hand, grow best during the warmest
part of the year and persist until temperature starts to drop off.
Finally, the flagellated Cryptophyceae and Chrysophyceae attain their
greatest biomass under ice cover.
Class succession patterns, however, are not ideal criteria upon which
to analyze the adaptive nature of phytoplankton associations. While
26
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to some extent members of a given algal Class share a common evolutionary
history—that to some degree limits the adaptive range of a species-,-
there are notable examples of wide-ranging adaptive characteristics of
some Classes. Blue-green algae, for example, have been reported in
dense concentration from hot springs to small ponds (Castenholz, 1967).
A more fruitful approach might entail an examination of the morphological
aspects of the changing species composition patterns.
For the purpose of discussion planktonic algae, their morphology can be
divided into five groups: coccoid (unicellular forms), monad (motile,
unicellular forms), colonial coccoid, colonial monad, and filamentous
algae. In Lake Wingra, the principal groups are coccoid, monad, and
colonial coccoid algae. The other two groups occur but not great enough
to warrant a separation from the colonial coccoid classification.
Within each of these categories, a further subdivision of size can
be made. The classification of net plankton, nannoplankton, and ultra-
plankton has been a traditional one for the plankton as a whole
(Strickland, I960). Under these criteria, all organisms are classi-
fied by the maximum dimension of their particular morphology. Those
cells or colony of cells whose maximum dimension exceeds 50 urn are
placed in the net plankton category, those with maximum dimensions be- '
tween 50 and 10 urn in the nannoplankton category, and those with maxi-
mum dimensions less than 10 um in the ultraplankton category. In this
study, I wish to depart from the traditional definitions of these
categories and modify them to restrict the maximum dimension argument
to cell size only and not to size of colony in which the cell resides.
The morphological variation of Lake Wingra phytoplankton has been
summarized in Figures 95 10, and 11. From these data and the associ-
ated environmental and biological data, some interesting conclusions
can be drawn. The size distribution of phytoplankton species, for
example (Fig. 9), indicates a shifting pattern of abundance of the
three size class categories. In general, nannoplankton and ultra-
plankton dominate the phytoplankton during much of the year, es-
pecially during periods of nutrient depletion. The advantage of such
a shift seems to be related to an adjustment, of surface to volume ratios
that allows for more efficient nutrient utilization at low concentra-
tions (e.g., Munk and Riley, 1952; Eppley et_ al., 19^9; and Corner and
Davies, 1971). In those cases where net plankton is a large proportion
of the phytoplankton in periods of nutrient deficiency (i.e., May to
June), the species of net plankton are the large flagellates Ceratium
hinundinella and Diplosalis acuta. These species of flagellates may
be able to compensate for their large surface to volume ratio by their
ability to move through the water—thus reducing the boundary layer
limiting nutrient uptake. The importance of nannoplankton and ultra-
plankton, therefore, appears to be an adaptation to low nutrient levels
encountered in the lake. When concentrations of nutrients are higher,
net plankton organisms appear to grow better (cf. Wetzel, 1.966; Maney,
1972).
27
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Other than the period from May to June, there also appears to be a
rather definite separation of motile and nonmotile phytoplankton species
(Fig. 10). Although the reasons are not obvious for this temporal
segregation, the general abundance of flagellated organisms during ice
cover periods of the year appears to be a general rule (Wetzel, 1966;
and Pechlaner, 1967). Motility is certainly an adaptive advantage
in periods of ice cover when light intensity is low, and such an adapta-
tion may explain the abundance of motile organisms during the winter
months. Whatever the explanation, however, the apparent separation of
motile and nonmotile phytoplankton species is a further confirmation
of the adaptive nature of phytoplankton associations.
Perhaps the clearest indication of this adaptive nature is revealed
in a colonial versus unicellular analysis of phytoplankton with time
(Fig. 11). Colonial phytoplankton forms become most abundant from
August to October, and the onset of their abundance corresponds to
the maximum zooplankton standing crop observed in the lake (Teraguchi,
1969). This development of colonial biomass illustrates the optimiza-
tion aspects of pattern formation in phytoplankton associations.
A rational interpretation of the abundance of colonial algal biomass
might involve two basic processes—nutrient uptake and grazing by
zooplankton. As previously stated, phytoplankton species with larger
surface to volume ratios are at a competitive advantage during periods
of low nutrient concentration (Dugdale, 1967). These same species,
however, would also be subject to the most intense grazing pressure
(Burns and Rigler, 1967; Nauwerck, 1963). It would appear reasonable,
therefore, for those species with lower susceptibility to predation to
accumulate more rapidly. Within the sheltered confines of a colony,
however, low nutrient concentrations may yet exert an influence on
the species-, and the colonial species that do predominate are species
with the smallest cells. Microcystis incerta, for example, is more
abundant than Microcystis aeruginosa. In summary, the selection of
species best adapted to particular'nutrient supply and grazing regimes
appears to be a real process. Similar patterns have been observed for
a variety of other organisms (e.g., Lund, 1971; Dodson, 1970). Further-
more, the adaptive patterns observed appear to represent an optimization
process within the phytoplankton association. Expressed through fecundity,
this optimization process selects those species whose species' charac-
teristics maximize growth rate against grazing losses.
The concept of optimality in biological processes is well established
and finds expression in a wide variety of problems (cf. Rosen, 1967;
Waterman and Morowitz, 1965). As Rosen indicates, the "Principle of
Optimal Design" operates at two levels in biological systems: intrinsic
and extrinsic. Intrinsic optimization is concerned with metabolic effic-
iencies. Ecological examples of intrinsic optimization would include
observations on light and shade adapted species of planktonic diatoms
(Tailing, 1966; Jorgensen, 1969) and adaptations to temperature by
planktonic diatoms (Jorgensen, 1968). Extrinsic optimizations relate
28
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populations to specific environmental and biological variables—that is,
to natural selection in an ecosystem.
Although such selection pressures have obvious implications for evolu-
tion of species, on a shorter time scale they also determine the species
that become dominant in a given system. Rosen (1967) has summarized
the qualitative effects of extrinsic optimization on the process of
natural selection:
The fundamental point to notice with regard to
natural selection is that all types of competitive
advantage, regardless of their initial nature, are
ultimately translated into differences in fecun-
dity . . . and it is these differences in fecundity
which ultimately result in the predominance of the
advantageous forms after a sufficient time has
elapsed (p. 6).
He further qualifies these remarks to indicate a necessary assumption
that the environment is held constant for a sufficient time. Because
algal fecundity is directly translated into population biomass incre-
ments , Rosen's arguments concerning natural selection may easily be
adapted to shorter time intervals in which species succession is the
dominant mode of response. Under these conditions, extrinsic optimi-
zations in an ecological unit result in the predominance of the species
best adapted to the prevailing array of environmental and biological
variables.
Application of optimization principles to phytoplankton associations
is not without inherent difficulties. The chief obstacle to such
applications may be the absence of sufficiently constant environmental
conditions. Indeed, the bewildering diversity of planktonic organisms
has been tied to the absence of equilibrium conditions (Hutchinson,
196l), and models incorporating the lack of equilibrium conditions have
had some measure of success in simulating natural phytoplankton associ-
ations (Richerson, Armstrong, and Goldman, 1970). The absence of equili-
brium conditions, however, only obscure optimization patterns and do
not eliminate this process as a functional reality in natural phyto-
plankton associations. The appearance of optimization patterns in
Lake Wingra, therefore, tend to support the validity of intrinsic and
extrinsic optimization as functional concepts in this system.
Although the "Principle of Optimal Design" is useful in a qualitative
evaluation of temporal and spatial variations in natural phytoplankton
associations, its greatest value lies in its potential for quantifying
these patterns. The application of optimality principles to phytoplank-
ton associations is comparable to their use in engineering. Engineering
applications traditionally include: (l) defining a set of competing
solutions to a problem, (2) assigning a cost in mutually compatible
29
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units to each of the solutions, and (3) selection of the optimal solution
on a criterion of least cost (Rosen, 1967). In some cases the decision
may be a bit more complex. Designing a bridge, for example, one would
want to find an optimal design that would include maximum structural
stability for the least expense.
In contrast to engineering applications, optimization analysis of phyto-
plankton would provide a framework within which to determine physiological
capabilities most likely to yield the greatest biomass within a defined
regime of biological and environmental variables. Each set of physio-
logical capabilities available, as represented by an individual species,
would have a, growth rate associated with it. Physiological capabilities
dealing with nutrient uptake, for example, would include variations
in surface to volume ratios, colony formation, or motility. Extrinsic
properties of the system, i.e., zooplankton density, turbulence, light,
temperature, and nutrient availability, would enter the growth rate
function variables. The species with the highest growth rate would then
be considered to be the one that will produce the greatest biomass.
Although the preceding example is simplistic in some ways, utilization
of the principle in a dynamic model would allow one to deal explicitly
with short term environmental fluctuations, which would affect the optimal
physiological capabilities. Systematically employing realistic fluxes
of nutrients, light, and other important variables, such a model would
then provide a basis from which to forecast seasonal succession patterns.
The ability to predict seasonal succession patterns, therefore, would
directly aid management decisions regarding nutrient loading on or
development of lake ecosystems.
In conclusion, application of optimization principles to studies of
natural phytoplankton associations has potential to contribute both
basic understanding and also to the development of sound management
strategies to regulate nuisance phytoplankton communities. The
current level of understanding of the factors that regulate phytoplankton
succession patterns is largely based on results" of correlation analyses
between species appearance and various environmental variables (Wetzel,
1971). To be sure, there are more direct indications of controls and
control mechanisms from sophisticated experimentation, but, in general,
there exists no coherent body of theory that pulls all of the experi-
mental and correlation data together. Such a body of theory, if developed,
would significantly enhance our ability to deal with nuisance algal blooms,
and thereby strengthen our management capability. Although this dis-
cussion may be short of developing such a body of theory, I do feel
that significant advancement of our understanding of the complexity
of natural phytoplankton associations will require the conceptual or-
ganization that optimization principles provide.
30
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SECTION V
SEASONAL CHANGES IN THE ABUNDANCE OF
PELAGIC-ZOOPLANKTON SPECIES IN LAKE WINGRA
Introduction
One of the major objectives to be carried out in this study is the quanti-
fication of the role of pelagic-zooplankton population in the transporta-
tion and transformation of energy and nutrients in Lake Wingra. Design-
ing a study for this purpose requires certain strategy. Useful to the
development of the strategy are previously acquired data on the abun-
dance of pelagic-zooplankton species in Lake Wingra. These data can
be used to determine which species, from a multitude of species, one
must study in order to obtain a reasonable estimate of the role of the
zooplankton population in nutrient and energy flows in Lake Wingra.
This kind of determination is necessary, as it is practically impossible
to study individually populations of all existing species. Also, these
data can be used to select certain species populations so that the
feeding spectra (herbivores or predators) ascribable to the total
population are realistically represented by the selected few species.
Finally, the information from these data can be used to develop a
more optimal sampling design for future studies.
A literature review revealed that there is a lack of suitable, previously
acquired data on the abundance of pelagic-zooplankton species in Lake
Wingra. Tressler and Domogalla (1931) obtained data on seasonal changes
in the abundance of various genera of pelagic zooplankton. Since their
data were old and applicable only to genera, they would be of little
use for the development of the necessary strategy.
We initiated, therefore, a study to characterize the seasonal changes
in the abundance of pelagic-zooplankton species in Lake Wingra. Sam-
ples were collected systematically from July, 1968 to July, 1969. Analy-
sis of the samples was completed in the spring of 19TO.
Materials and Methods
Three sampling stations were established in Lake Wingra for the purpose
of monitoring the seasonal change in the abundance of the pelagic-zooplankton
species. These were located at the northeast, central, and southwest
portions of the lake. Samples were taken at these stations (Fig. lU)
at about two-week intervals during the ice-free period, about a week
interval during the early part of the ice-cover period, and about four-
week intervals during the latter part of the ice-cover period.
The cladocerans and copepods were sampled with a Clarke-Bumpus sampler
(No. 10 netting) during the ice-free period and with a large Wisconsin
31
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u>
ro
LAKE WINGRA
DANE COUNTY, WISCONSIN
200 0 400 800
Figure ~lk. Contour map of Lake Wingra. The stations are indicated
by crosses enclosed in circles.
-------
net (No. 10 netting) during the ice-cover period. The C-B sampler was
towed diagonally from near the bottom to the surface of lake in order
to obtain a sample, whereas the Wisconsin net was towed vertically from
near the bottom to the surface in order to collect a sample. Prelim-
inary investigation indicated that the volume of water sampled during
a two-minute diagonal tow with the C-B sampler was comparable to that
sieved during a total vertical tow with the other net. • During the
ice-cover period, a large rectangular hole was cut in the ice so as to
permit sampling. Triplicate samples were, collected from each of the
three stations at each sampling date. The samples were preserved in
5$ formalin solution.
The rotifers were usually sampled with a 2 liter Van Dorn water bottle.
On each sampling date, a sample was taken from 1, 2, and 2.75 m depths
at each station. Each 2 liter sample was filtered through a No. 35
net to concentrate the organisms which were preserved in 5% formalin
solution.
The cladoceran, copepod, and rotifer keys presented in the book edited
by Edmondson (1959) were used for the identifications.
¥e used a subsampling technique to estimate the number of individuals
of the various cladoceran and copepod species in each of the 'samples.
Only 1 ml aliquot taken from each sample was used for the estimation.
Statistical analysis (Ricker, 1938) revealed that .random subsamples
were usually taken from the samples under the imposed conditions of
stirring of the samples. The estimates (number of individuals of
the_various species) of each set of triplicate samples was expressed
at x +_ residual (E(x-x)/N).
We made total counts of the individuals of the various species of
rotifers in each of the samples. The organisms in each sample were con-
centrated with a small funnel (No. 35 netting), having a small opening
at the apex which was closed. The organisms were then placed in a small
chamber, and the total numbers of individuals of the various species
were counted. As the counts of the individuals of the various species
in the samples taken from 1,2, and 2.75 m were fairly comparable on
many sampling dates, we pooled the three sets of counts to derive the
mean value and residuals for each sampling date.
A settling technique was used to determine the volume (or standing crop)
of the pelagic zooplankters in each of the three samples taken on each
of the sampling dates. A mean volume was computed for each set of
s amples.
Light penetration and vertical temperature profiles were determined
on each sampling date, whereas the oxygen profile was usually deter-
mined on every other sampling date of the ice-free period and on every
sampling date of. the ice-cover period. Light penetration was determined
with a Secchi disc, while temperature profile was determined with a
33
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thermistor. A modified Winkler Method was used to measure oxygen content
of the water samples.
Results
CLADOCERAWS
Eighteen species of cladocerans were identified from plankton samples
taken from the open-region of Lake Wingra (Table 2). On the.basis of
our method of estimation (involving subsampling of the samples), the
numbers of individuals of ten of these species could not be quantified
from the samples taken throughout the one-year period. These ten species
were Acroperus harpae, Camptocercus macrurus, Ceriodaphnia megalops,
Ceriodaphnia reticula, Chydorus ovalis, Eurycerus lamellatus , Macrothrix
rosea, Pleuroxus denticulatus, Scapholeberis kingi, and Simocephalus
serrulatus. The individuals of the other seven species occurred in ade-
quate numbers for at least certain times of the year.
Alona quadrangularis
This species was present for only a very short period during the year
(Fig. 15). During the period of occurrence (primarily the month of
November), the estimated mean number of individuals of Alona quadrangularis
never exceeded about 1500 per 660 liters. For any given date of occur-
rence, the number of individuals at the three stations differed somewhat;
this was probably an artifact resulting from the use of subsampling
technique for estimation when very few individuals of this species
were present in the samples.
Bosmina longirostris
The seasonal trends in the abundance of this species at the three sam-
pling stations were very similar (Fig. 16). The density of Bosmina
longirostris was lowest during the summer (estimated mean counts ranged
from zero to about 1300 individuals per 660 liters), intermediate for
sampling dates during autumn and spring (estimated mean counts ranged
from about 5000 to about 16,000 individuals per 660 liters) and maxi-
mum during autumn and spring (estimated mean counts ranged from about
^5,000 to about 100,000 individuals per 660 liters during the period
which included sampling dates of 10 October, 2k October, and 7 November
1968, and ranged from about 50,000 to 220,000 individuals per 660 liters
during the period which included sampling dates of 22 April, 6 May, 23
May, and 6 June 1969). The periods of maximum density were preceded
by a sharp increase in numbers and followed by a sharp decrease in numbers.
On many of the sampling dates, the mean estimated densities of this species
at the three stations were fairly comparable (Fig. 16).
-------
Table 2. Species of cladocerans, copepods, and rotifers found in the
samples taken from the open-water region of Lake Wingra
during 1968 and 1969.
Cladocera
Acroperus harpae
Alona quadrangulari s
Bosmina longirostris
Camptocercus macrurus
Ceriodaphnia megalops
Ceriodaphnia quadrangula
Ceriodaphnia reticula
Cydorus sphaericus
Cydorus ovalis
Daphnia galeata
Daphnia retrocurva
Diaphanosoma brachyurum
Eurycerus lamellatus
Leptodora kindtii
Macrothrix rosea
Pleuroxus denticulatus
Scapholeberis kingi
Simocephalus serrulatus
Copepods
Cyclops bicuspidatus thomasi
Diaptomus siciloides
Eucyclops agilus
Mesocyclops edax
Rotifera
Asplanchna priodonta
Brachionus angularis
Brachionus calyciflorus
Filinia opoliensis
Keratella cochlearis
Keratella quadrata
Monostyla quadrindentata
Notholca acuminata
Polyarthra suryptern
Polyarthra vulguris
Synchaeta oblonga
Voronkowia mirabilis
35
-------
U)
CTN
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ID
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CO O
UJ O
CC 0
CO
o
(D
U3
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6 o
H
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. 0
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A NORTH-EAST (1)
• CENTRAL (2)
T SOUTH-WEST (3) .
'
(
'- A.. A.. A.. A., A., A., A., A
1 1 1 1 1 1 1 1 1 1
1
ALONA QUADRANGULARIS
L
1
.
*
i
ICE-COVER
1 1
- A., ^ A., 1
-
i i i i i i i i i ^ -i
16 30 12 27 II 24 10 24 7 26 i 1 1 18 22 6 23 6 20 8 23
JUL AUG SEP OCT NOV ' FEB MAR APR MAY JUN JUL
1968
1969
Figure 15. Seasonal changes in the abundance of Alona quadrangularis in Lake Wingra.
-------
CO
-q
en
DU
LJ
ct
to
LJ
tr
LJ
0
0
o
o
o
o
o
o
o
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A NORTH-EAST (1) BOSMINA LONGIROSTRIS
• CENTRAL (2) ^ t
* SOUTH-WEST (3) \ *
t .'* t .*» * f H
- I,
-
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1 I
1 Jr' t '
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. T
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1 I
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t t T ... ... :
i i . i § § i i i i i i i ii 11 i i . . i i . . i i i i i
16 30 12 27 1 24 10 24 7 26 j II 18 22 6 23 6 20 8 23
JUL AUG SEP OCT NOV ' FEB MAR APR MAY JUN JUL
1968 1969
Figure 16. Seasonal changes in the abundance of Bosmina longirostris in Lake Wingra.
-------
Ceriodaphnia quadrangula
This cladoceran species was present in the open-water region of Lake
Wingra only during late spring, summer, and autumn (Fig. 17). From '.
16 July to 7 November 1968, there was a steady decline in the number of
individuals. The mean number of individuals ranged from about 6,000
to 13,000 per 660 liters on 16 July and from about 500 to 3,500 on 7
November. This gradual decline in mean numbers was followed by a sharp
decrease in numbers. The estimated mean count of this species per 660
liters was zero at all stations on 26 November 1968, 11 February 1969,
18 March 1969, and 22 April 1969. From 6 May to 20 June, there was a
sharp increase in the number of individuals. This period of rapid
increase in numbers of individuals was followed by a peripd (includes
sampling dates of 20 June, 8 July, 25 July 1969) during which the average
density of this species ranged from about 70,000 to 150,000 individuals
per 660 liters.
The average densities of this species at the three stations were quite
different on many of the sampling dates in 1968, but were quite similar
on many of the sampling dates in 1969.
Chydorus sphaericus
This species was most abundant during spring, summer, and autumn
(Fig. 18). The maximum average density observed during these periods
was about 30,000 individuals per 660 liters, and the minimum density
was about 2,500 individuals per 660 liters. There was a sharp decline
in the numbers of individuals prior to ice-cover and a sharp increase
in numbers shortly after termination of ice-cover.
The mean densities of Chydorus at the three stations were similar only
for some sampling dates.
Daphnia galeata
The estimated mean numbers of this species per 660 liters was highest
during the summer (up to about 150,000 per 660 liters), intermediate
(up to about 70,000 per 660 liters) during the autumn, and lowest
(up to about 1*0,000 per 660 liters) during the winter and early spring
(Fig. 19). Most of the estimated mean values for summer sampling dates
were within the range of about 50,000 to about 130,000 individuals
per 660 liters. Most of the estimated mean values for the autumn sampl-
ing dates were within the range of about 20,000 to about 50,000 individ-
uals per 660 liters. Most of the estimated mean values for the winter
and early spring sampling dates were within the range of about 2,000 to
3,000 individuals per 660 liters.
On most of the sampling dates, the estimated mean values for the three
stations were remarkably similar.
38
-------
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CO
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NOV ' FEB MAR APR MAY JUN JUL
1969
Figure IT. Seasonal changes in the abundance of Ceriodaphnia quadrangula in Lake Wingra.
-------
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18. Seasonal changes in the abundance of Chydoi~us sphaericus in Lalc
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16 30 12 27 II 24 10 24 7 26 ! I I 18 22 6 23 6 20 8 23
JUL AUG SEP OCT NOV ' FEB MAR APR MAY JUN JUL
1968 1969
Figure 19• Seasonal changes in the abundance of Daphnia galeata in Lake Wingra.
-------
Daphnia retrocurva
The seasonal trend in the abundance of this species was very similar
to the seasonal trend in the abundance of Daphnia galeata (Figs. 19 and
20). Daphnia galeata was most abundant during the summer, intermediately
abundant in the autumn, and least abundant in the winter and early spring
(Fig. 20). Generally, the ranges within which most of estimated values
for the summer and autumn sampling dates occurred were about 50,000
to about 150,000 individuals per 660 liters and about 5,000 to about
hO ,000 individuals per 660 liters. Estimated numbers of individuals
per 660 liters for winter and early spring sampling dates were usually
zero.
On many of the sampling dates, the estimated values for the three stations
were quite similar.
Diaphanosoma brachyarum
This species occurred only during the summer and early autumn (Fig. 21).
During the early summer, there was a rapid increase in the numbers of
these organisms. From 20 June 1969 to 25 July 1969, the estimated
values changed from zero to about 50,000 to 100,000 individuals per
660 liters. Maximum abundance occurred during July and August; most
of the values observed were within the range of about 30,000 to 80,000
individuals per 660 liters. From 11 September 1968 to 2k October 1968,
the estimated values changed from about 35,000 - 60,000 to zero indi-
viduals per 660 liters.
On most of the sampling dates, the estimated mean values for the three
stations were very similar.
Leptodora kindtii
This species occurred only for a short period (July to early part of
August) (Fig. 22). Most of the estimated mean values were in the range
of about 500 to 1,000 individuals per 660 liters for 30 July and 12
August 1969 and in the range of about 2,000 to 5,000 for 8 July and 25
July 1969.
On most of the sampling dates on which this species was present, the
values for the three stations were reasonably comparable.
COPEPODS
Four species of copepods (three cyclopoids and one calanoid) were identi-
fied from samples collected from the open-water region of Lake Wingra
during 1968 and 1969 (Table 2). Cyclops bicuspidatus thomasi, Diaptomus
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16 30 12 27
JUL AUG
I I 24
SEP
1968
10 24 7 26 | II 18
OCT NOV ' FEB MAR
22 6 23
APR MAY
1969
6 _20
JUN
8 23
JUL
Figure 20. Seasonal changes in the abundance of Daphnia retrocurva in Lake Wingra.
-------
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ICE-COVER
A»T
16 30 12 27 II 24 10 24 7 26
JUL AUG SEP OCT NOV
1968
II 18 22 6 23 6 20 8 23
FEB MAR APR MAY JUN JUL
1969
Figure 21. Seasonal changes in the abundance of Piaphanosoma "brachyurum in Lake Wingra.
-------
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16 30 12 27 II 24 10 24 7 26 i 1 1 18 22 6 23 6 20 8 25
JUL
i
AUG SEP OCT NOV i FEB MAR APR MAY JUN JUL
1968 1969
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Figure 22, Seasonal changes in the abundance of Leptodora kindtii in Lake Wingra,
-------
siciloides, and Mesocyclops edax were abundant enough throughout
the year so that the seasonal change in their abundance could be
characterized reasonably well.
Cyclops bicuspidatus thomasi
This species was present in adequate numbers throughout the year
(Fig. 23). Throughout the summer, their abundance seemed to remain
about 10,000 to 30,000 individuals per 660 liters. There was a
fairly sharp decline in the mean estimated abundance during the
autumn of 1968; during this period the mean abundance changed from
15,000 - 25,000 individuals per 660 liters to 1,300 - 3,000 indi-
viduals per 660 liters. Maximum mean abundance occurred during the
winter and early spring; most of the values were within the range
of 30,000 to 100,000 individuals per 660 liters. There was a
sharp decline in numbers during the late spring as the mean estimated
numbers changed from a range of 30,000 to 100,000 individuals per
660 liters,to a range of about 3,000 to 5,000 individuals per 660 liters.
From 20 June to 8 July 1969, there appeared to be another sharp increase in
abundance.
On most of the sampling dates, the mean estimated abundance for the
three stations were very similar.
Diaptomus siciloides
The seasonal trend in the abundance of this species involved only
minor fluctuations in abundance throughout the year (Fig. 2k). Through-
out the summer and autumn of 1968 and winter of 1969, the density of
this species appeared to fluctuate within the range of about 20,000
to 70,000 individuals per 660 liters. From 22 April to 6 June, there
seemed to be a gradual increase in the numbers of this organism. During
the period including 20 June, 8 July, and 25 July 1969, the density
of this species was in the range of about 50,000 to 100,000 individuals
per 660 liters.
Again, on most of the sampling dates, the numbers of this species at
the three stations were very comparable.
Mesocyclops edax
This cyclopoid copepod appeared to occur only during the summer (Fig. 25).
Its abundance on the various sampling dates in the summer of 1968 ranged
for the most part from 3,000 to 10,000 individuals per 660 liters. Its
abundance on the various sampling dates in the early summer of 1969
ranged generally, however, from 15,000 to 30,000 individuals per 660
liters.
Only on some of the sampling dates on which this species occurred did
the numbers of this organism at the three stations appear comparable.
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I6 30 12 27 II 24 10 24 7 26 | II 18 22 6 23 6 20 8 25
JUL AUG SEP OCT NOV ' FEB MAR APR MAY JUN JUL
I968 I969
Figure 2k. Seasonal changes in the abundance of Diaptomus siciloides in Lake Wingra.
-------
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16 30 12 27
JUL AUG
II 24 10 24 7 26 | I I 18 22 6 23 6 20 8 23
SEP OCT NOV ' FEB MAR APR MAY JUN JUL
1968 1969
Figure 25. Seasonal changes in the abundance of Mesocyclops edax in Lake Wingra.
-------
ROTIFERS
Twelve species of rotifers were identified from the samples collected
from the open-water region of Lake Wingra during 1968 and 1969 (Table
2). Since Keratella quadrata, Monostyla quadridenta, Kothplca acuminata,
Synchaeta oblonga, and Voronkowia mirabilis did not occur in adequate
numbers on most of the sampling dates, we were not able to characterize
reliably the seasonal change in their abundances.
Asplanchna priodonta
This species had only one major peak of abundance during the year
(Fig. 2.6). From 11 February to 6 May 1969, the average density of this
organism changed from virtually no individuals per 2 liters to at least
20 individuals per 2 liters. From 6 May to 6 June 1969, there was a
very rapid decline in the density of this species. On most of the other
sampling dates, this species was not present.
The variation in the average densities of this species at the three
stations for most of the sampling dates did not appear to be signi-
ficant .
Brachionus angularis
This species was most abundant during the summer and late spring (Fig.
26). From 16 July to 27 August 1968, the average density of this species
changed from practically no individuals per 2 liters to at least 20
individuals per 2 liters. From 27 August to 2k September 1968, the
average density changed from at least 20 individuals per 2 liters to
no individuals. Between 24 September to 26 November 1968, this species
was absent except on one sampling date. There appeared to be an in-
crease in the numbers of individuals from 26 November to 18 March
1969 and a decrease in the numbers of individuals from 18 March to 22
April 1969. Only on one sampling date (8 July) in the spring and summer
of 1969 did this species occur in reasonable numbers.
The densities of this organism at the three stations were similar on many
of the sampling dates.
Brachionus calyciflorus
This species was present only during late winter and early spring (Fig.
26). However, the average numbers of individuals of this species never
exceeded 18 individuals per 2 liters.
Keratella cochlearis
This species was present on all the sampling dates at least at two of the
50
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16 30 12 27 1 1 24 10 24 7 26 j 1 1 18 22 6 23 6 20 8 23
JUL AUG SEP OCT NOV i FEB MAR APR MAY
1968 1969
JUN
JUL
Figure 26. Seasonal changes in the abundance of Asplanchna priodonta, Brachionus
angularis, and Brachionus calyciflorus in Lake Wingra.
-------
three sampling stations (Fig. 27). A large increase in abundance occurred
during the period from l6 July to 30 July 1968; the average numbers of
individuals per 2 liters ranged from 22 to 25 on the former sampling
date and from 55 to 108 on the latter. A large decrease in abundance
took place during the period from 30 July to 27 August 1968; the average
number of individuals per 2 liter ranged from 55 to 108 on the former date
and from 3 to lU on the latter date. On the subsequent three sampling
dates, the density never exceeded 10 individuals per 2 liters. A moderate
increase in abundance occurred in October 1968; as the average number of
individuals per 2 liters changed from a maximum of 9 on 10 October to a
minimum of 21 on 2U October. The average density ranged from 20 - 25
individuals per 2 liters on the sampling dates of November 1968. From
18 March to 23 May 1969, the average density changed from a minimum
of 71 individuals per 2 liters to a maximum of 2 individuals per 2 liters.
'On the sampling dates of June and July 1969, the average density never
exceeded 17 individuals per 2 liters.
On most of the sampling dates, the average densities at the three stations
were remarkably similar.
Polyarthra eurypterus
This species vas present in low numbers mostly during the late summer
and autumn (Fig. 28). The density never exceeded 9 individuals per 2
liters.
Polyarthra vulgaris
This species occurred in varying numbers throughout the year (Fig. 28).
From 12 August to 7 November 1968, there appeared to be a gradual increase
in the numbers of individuals of ttiis species. During this period the
average density changed from about 1 to a maximum of 39 individuals per
2 liters. There was a decrease in the numbers of individuals from 7
November 1968 to 11 February 1969. On most of the sampling dates in the
spring and early summer of 1969, the average density rarely exceeded 10
individuals per 2 liters.
Tetra mastix (= Filinia) opoliensis
The seasonal trend In the abundance of this species consisted of high
density during the early part of the summer and very low density during the
other seasons (Fig. 28). Maximum average density was 32 individuals per
2 liters on 30 July 1968 and 57 individuals per 2 liters on 8 July 1969.
On most of the other sampling dates, the average density at the three
stations rarely exceeded 5 individuals per 2 liters.
52
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1969
Figure 27. Seasonal changes in the abundance of Keratella cochlearis in Lake Wingra.
-------
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'til 10
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POLYARTHRA EURYPTERUS
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POLYARTHRA VUL-GARIS
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TETRAM'ABTIX (=FILI-N(A) OPOLIEWSIS
ICE-COVER
I 1
i i i i i u
*'t *„. *- lit
16 30 12 27 tl 24 10 24 7 26 i I r 18 22 6 23 6 20 8 23
JUL At)G. SEP OCT NOY '< FEB MAR APR MAY JUN J UL
1968 1969
Figure 2Q. Seasonal changes in the abundance of Polyarthra
eurypterus , Polyarthra vulgaris . and Te-tramastix
opoliens-is in Lake Wingra.
-------
Standing Crop pf Pelagic Zooplankton
Not more than a 2.5 fold change in the volume of pelagic zooplankton
occurred during the sampling period (Fig. 29). Greatest average volume
wa,s recorded during the summer (32 to 3^ cc per 660 liters on 12 August
1968 and 33- 36 cc per 660 liters on 8 July 1969), whereas the feast
average volume was observed during the ice-cover period (6-9 cc per 660
liters on 11 February 1969 and 1+.5 - 12 cc per 660 liters on 8 March
1969). The seasonal trend ;Ln the volume of pelagic zooplankton seemed
to consist of a sharp increase from 16 July to 12 August 1969, a sharp
decrease from 12 August to 11 September 1968, a very gradual decrease
from 11 September to at lea.st 26 November, an increase from 8 March to
6 May 1969, a slight decrease from 6 May to 6 June 1969, and a pronounced
increase from 6 June to 8 July 1969.
There seemed to be a reasonable correlation between the average volume
of zooplankton and average water temperature (Fig, 30). The only sets
of data which did not fit reasonably well were those obtained for 12
August 1968 and 20 June 1969. Nevertheless, it seems that temperature
might be a good characteristic to use for the prediction of the volume
of pelagic zooplankton up to about 30 cc per 66,0 liters.
Discussion
CLADOCERANS
Of the cladoceran species, Acroperus harpae, Camptocercus macrurus,
Ceriodaphnia megalops, Ceriodaphnia. reticula, Cydorus ovalis, Eurycercus
lamellatus, Macrothrix rosea, Pleuroxus denticulatus, Scapholeberis
kingi, and Simocephalus serrulatus are present in such low numbers that
they are definitely not worth consideration in subsequent, detailed
studies.
Alona quadrangularis and Leptodora kindtii are probably not worth con-
sideration. Alona occurs only for a short time and never exceeds densities
of about 1500 per 660 liters (Fig. 15)- Leptodora kindtii occurs for
a short time (probably not more than a month period), but can reach
densities as h;Lgh a,s 50,000 per 660 liters (Fig. 22). In spite of this
fairly high density, Leptodora kindtii does not seem to have an obvious
effect on the various cladoceran species (also copepod species). During
the period when Leptodora is most abundant, there is no corresponding
decrease in density of the various cladoceran and copepod species (See
Figs. 15 to 25). Wright (1965), studying the population dynamics and
production of Daphnia in Canyon Ferry Reservoir, observed density de-
crease of Daphnia during peak abundance of Leptodora. This correspondence
is not obvious in Lake Wingra because Leptodora feeds probably on several
55
-------
vn
LL>
0
< 40
cr
Q
< 30
o
S 20
o
o
i I0
LU
« 0
^J. >— '
a NORTH-EAST (1) PELAGIC ZOOPLANKTON
• CENTRAL (2)
h- * SOUTH-WEST (3)
-
—
V
—
i
li tl
IT! {* , j
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ICE-COVER
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i 1
i i i i i i i i i i i i i i i i i i i ii ii i i i i i i i i i i i i i i
16 30 12 27 II 24 10 24 6 26 ] II 18 22 6 23 6 20 8 23
JUL AUG SEP OCT NOV i FEB MAR APR MAY JUN JUL
1968 1969
Figure 29. Seasonal changes in the standing crop of pelagic-zooplankton in Lake Wingra.
-------
40
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(D
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30
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1
1
0 10 20
AVERAGE TEMPERATURE IN °C
30
Figure 30. Relationship between standing crop of pelagic-
zooplankton and temperature of the lake.
57
-------
species and does not, therefore, affect greatly the population size
of any one species.
Bosmina longirostris, Ceriodaphnia quadrangula, Chydorus sphaericus,
Daphnia galeata, Daphnia retrocurva, and Diaphanosoma brachyurum must
be seriously considered for future studies, quantifying the role of
zooplankton population on the transformation and transportation of
energy and nutrients in Lake Wingra. These species are generally most
abundant during the summer and autumn when their average densities
may be as high as 100,000 per 660 liters (Figs. 16 to 21. Although
Bosmina retrocurva and Daphnia galeata are relatively not abundant
during the winter, their average densities are still at least 10,000
per 660 liters during this period. Thus, the populations of these two
species may have to be studied in the winter as well as in the summer
and autumn. Chydorus sphaericus, Daphnia retrocurva, Ceriodaphnia
quadrangula, and Diaphanosoma brachyurum need to be studied only during
the summer and winter -
The latter six species are known to be herbivores. Furthermore, the
adult individuals of these species are of similar small size; thus
it would not be unreasonable to assume that the biomass per adult
individual of these different species is fairly comparable.
COPEPODS
Cyclops bicuspidatus thomasi, Diaptomus siciloides, and Mesocyclops
edax must be considered in the future studies. Cyclops bicuspidatus
thomasi and Diaptomus siciloides must be 'considered throughout the
year. However, of these two species, Diaptomus siciloides is more
abundant than cyclops in summer and autumn and less abundant than this
species in the winter and early spring. Mesocyclops edax occurs in
fairly high densities generally only during the summer and is absent
during the autumn, winter, and spring.
The feeding habit of only one of these species is known with any
certainty. Cyclops bicuspidatus thomasi is primarily a predator.
ROTIFERS
On the basis of data obtained in 1968 and 1969, it does not seem
worthwhile to consider the rotifer populations in future studies
(quantifying the role of pelagic-zooplankton population of the trans-
formation and transportation of energy and chemicals in Lake Wingra).
Species such as Keratella quadrata, Monostyla quadridentata, Notholca
acuminata, Synchaeta oblonga, and Voronkowia mirabilis occurred in
very low numbers (less than 2 per 2 liters) once or twice during our
sampling schedule. Others such as Asplanchna priodonta, Brachionus
calyciflorus, Polyarthra eurypterus, and Polyarthra vulgaris
occurred for only short periods and never exceeded 30 individuals per 2
58
-------
per 2 liters (Figs. 26 and 28). Brachionus angularis, Keratella coch-
learis, and Tetramastix opoliensis occurred at densities exceeding 30
individuals per 2 liters only on a couple of occasions of very short
duration (Figs. 26, 27, and 28). Generally, the density values for
the various species were much lower than those recorded in the literature
(for example, Hutchinson, 1967).
Most of the species in Lake Vingra (exception is Asplanchna priodonta)
are known to feed on algae and bacteria (Hutchinson, 1967). Asplanchna
feeds to some degree on other rotifers and small crustaceans. Thus,
this species may have to be considered in the studies dealing with
population dynamics of certain cladoceran and copepod species.
Seasonal Change in Standing Crop of Pelagic Zooplankton
The seasonal trend in the standing crop of pelagic zooplankton reflects
generally the seasonal trends in the abundance (individuals per 660
liters) of most of cladoceran and copepod species (see Figs. 15 to 25
and Fig. 29). Thus, the volume of pelagic zooplankton was greatest during
the summer, intermediate during the autumn and spring, andJeast during
the winter. This seasonal trend may be a result of a lack of thermal
stratification-cycle in Lake ¥ingra, absence of heavy predation on
the zooplankton during the summer, and no food limitation during the
summer.
In lake with thermal stratification-cycle, the typical seasonal trend
in the abundance of Daphnia consists of maximum density during late
spring and early autumn and low density during the summer (Hall, 196U;
McWaught, 196U). This type of seasonal trend is thought to be a result
of optimal food availability during late spring and early autumn
(when nutrient conditions are ideal for algal growth) and of heavy
predation of zooplankton (Hall, 196*1; Wright, 1965) or limited food
during the summer.
There is a reasonable correlation between volume of pelagic zooplankton
and temperature (Fig. 30). Thus, temperature may be used to predict
the biomass of pelagic zooplankton in Lake Wingra. This correlation
is what one might expect if other conditions (seasonal thermal stratifi-
cation cycle in the lake, heavy predation on zooplankton during the
summer, no food limitation during the summer) did not prevail.
Density and Standing Crop of Zooplankton at the Three Stations
On most of the sampling dates, the variation in the density and standing
crops (of most of the species) between the three stations did not seem
large (Figs. 15 to 30). This means that it is not necessary to sample
more than one small area of the lake (its location is not critical)
59
-------
to get density values from which population estimates of the species
in the lake. Of course, since we are interested in population estimates
of the pelagic-zooplankton species, it may be necessary to determine
the extent to which these species are distributed shore-ward. This
determination would improve the population estimates as volume of water
occupied by these species will be better known.
60
-------
SECTION VI
SEASONAL CHANGE IN THE ABUNDANCE OF
OLIGOCHAETES AND CHIRONOMIDS IN LAKE WINGRA
Introduction
The benthos constitutes an important component of a lake ecosystem.
Larger insect larvae, for example, may serve as a major fish food
organism. The benthic organisms thus serve ,as a key link to convert
detrital sediment material to harvestable food biomass. In this paper,
seasonal changes in the abundance of various species of oligochaetes
and chironomids during the period from 6 July 1968 to 25 July 1969
are described.
Methods
Five sampling stations were established on Lake Wingra (Fig. 3l).
Stations 1, 2, and 3 were located on the northeast, central, and south-
west portions of the lake, respectively. Station h was situated between
Station 2 and the south shore, whereas Station 5 was located between
Station 2 and the north shore. All five stations had depths of about
3 m. The characteristics of the bottom sediments at Stations 1, 2, 3,
and 5 appeared to be very similar. Only at Station 5 did we find marl
in the bottom samples.
Two samples were collected from each station at about two-week intervals
during the ice-free period, about a six-week interval during the early
period of ice cover, and about four-week intervals during the latter
part of the ice-cover period. A standard Ekman dredge (15.2 x 15-2 cm)
was used to collect the samples, while a bucket with the bottom made
of fine wire gauze (mesh diameter of 0.22 mm) was used to concentrate
the bottom samples. Wide-mouth bottles (32 oz.) were used for temporary
storage of the concentrated samples.
On each sampling date of the ice-free period, we followed "the same
procedural sequence for obtaining the bottom organisms. The boat was
first anchored at the station. This was followed by lowering the opened
dredge gently into the bottom sediment. After the sampler was closed,
it was hauled rapidly to the surface and placed in the sieving bucket.
The sampler was opened inside the bucket to release the bulk of the
sediment contained in the sampler. We then lowered the bucket into
the lake to allow water to enter it through the gauze bottom. This
61
-------
ON
ro
LAKE WINGRA
DANE COUNTY, WISCONSIN
200 0 400 800
/ STATION 3
STATION I NE
STATION 2 C
STATION 3 SW
STATION 4 SE
STATION 5 EDGE
Figure 31. Contour map of Lake Wingra and locations of the sampling stations.
-------
water was used to remove the sediment stuck to the inside of the dredge.
The bottom sediment in the bucket was agitated, sifted, and washed to
remove most of the sediment and debris. We then washed the remaining
content into the bottle.
A slightly different procedural sequence was followed to obtain bottom
organisms on sampling dates of the ice-cover period. We made a large
opening (2 x 2 m) in the ice at each station. The dredge was handled
in the manner described previously. After hauling the closed dredge
to the surface, we immediately released the bulk of the bottom sediment
into a large plastic bag. With the opened dredge still positioned over
the opening of the bag, the sediment still left in the dredge was washed
into the bag. The bags containing the samples were taken to the labora-
tory. All the sediment in each bag was put into the sieving bucket
arid was subjected to agitation, sifting, and washing. The content
remaining in the bucket was washed into the bottle.
A chemical preservative was not added to the bottles containing these
reduced samples. Preliminary analysis revealed that live organisms,
because of their movement and usually contrasting coloration, could be
detected more readily from the debris and sediment present even in these
reduced samples. These samples were therefore refrigerated at 2 to h C
prior to being analyzed for bottom organisms.
Collecting the organisms from each of these reduced samples involved
a repetition of the following set of procedures. The content (sediment,
debris, organisms, and some water) of the bottle was agitated by a
strong stream of water released from a tap. A portion of this content
was poured into a steel tray coated with porcelain, and some water was
subsequently added to the tray. The organisms in the tray were removed
with the use of a fine pair of forceps and a small suction pipette, and
were then put into 15% alcohol solution contained in a small vial.
When all the organisms were removed, the sediment and debris left in the
tray were discarded. These procedures were repeated in the same sequence
until the entire sample was analyzed for the organisms.
The chironomids and oligochaetes were identified to species whenever
possible. Identification of the genus and/or species of chironomids
was based on the labial appendages of type specimens prepared by Dr.
William Hilsenhoff, Department of Entomology, University of Wisconsin.
To identify the chironomids in our samples, we mounted their heads on
slides and examined the labial appendage with a dissecting scope (Bausch
and Lomb) set at a magnification of 120X. Identification of the species
of oligochaetes was based on the keys developed by Brinkhurst (19 6b and
1965) and on type specimens prepared by us with the assistance of Dr.
Ralph Brinkhurst, Department of Zoology, University of Toronto. Relatively
few chironomids and oligochaetes could not be identified confidently to species,
63
-------
In the presentation of our results, the density of various species of
oligochaete and chironomid is expressed as number per 2 samples, or
as average number per 2 samples plus or minus the residual. The first
expression of density (#/two samples) was used to examine the change
in the abundance of oligochaetes and chironomids at the various sampling
stations during the study period. The second expression, _ n
x + E
r.
i
(where x = mean; n = sample size; andjr. = x - x = absolute value
of the i residual) was used to obtainHepresentative density values
for different stations for the four seasonal periods of the year.
Some physical and chemical variables were monitored at Station 2 during
this study. Temperature, light penetration, and oxygen concentration
were measured with a thermistor, secchi disc, and modified Winkler Method,
respectively. Temperature was measured at depth intervals of 0.5 m>
whereas oxygen was monitored at an interval of 1.0 m. We obtained
temperature data on every sampling day and light-penetration data on every
sampling day of only the ice-free period. Oxygen profile was determined
at l|-6 week intervals. These data are presented in Fig. 32.
Results
OLIGOCHAETES
Five species of oligochaetes were found in the bottom samples collected
during our study period. These were Limnodrilus hoffmeisteri (Claparede),
Limnodrilus udekemianus (Claparede), Euilydrilus hammoiensis (Mich. ) ,
Ilyodrilus templitoni ( Southern), and Stylaria lacustris (Linnaeus).
Of the 21Ul oligochaete specimens collected, 1069 (k9.9%) belonged to
our combined grouping of Limnodrilus hoffmeisteri and L_. udekemianus.
Since the latter of these two species was very rare, virtually all
the organisms assigned to this combined grouping can be considered to
be Limnodrilus hoffmeisteri. Almost equally numerous was Euilydrilus
hammoiensis as 92k (1*3.2$) of the total belonged to this species.
Only 122 (5-7%) of the specimens were Ilyodrilus templitoni. Stylaria
lacustris was indeed rare as only 7 (0.3$) individuals of this species
were encountered during the study. Nineteen specimens could not be
identified to genera or species (Table 3).
Limnodrilus hoffmeisteri - hammoiensis
Seasonal pattern in the abundance of these individuals (mainly L.
hoffmeisteri) was not consistent between stations (Fig. 33). The
density of these oligochaetes at Station 3 (southwest) did not change
-------
1968 1969
JULY AUG. SEPT. OCT. NOV. FEB.MAR.APR. MAY JUNE JULY
6 16 30 12 27 24 10 24 7 26 18 19 22 13 22 6 20 8 25
Si i
a
2 j_ LIGHT PENETRATION
~i i i r
ICE
COVER
~l I T
O O
o o
o o
0
e
UJ
* 20
tr
UJ
a.
2
UJ 10
0
20
CL
o; is
4 A A
A A
z
X
o
10
Fieure 32 Light penetration, average temperature and average
oxygen concentration at Station 2 (c) in Lake Wingra.
65
-------
Table 3. Species and abundance of oligochaetes and chironomids in the
sediment of the open-water region of Lake Wingra. From July
1968 to August 1969.
Oligochaetes
Limnodrilus hoffmeisteri
and L_. udekemianus combined
Euilydrilus hammoiensis
Ilyodrilus templitoni
Stylaria lacustris
Unknowns
Chironomids
Chironomus plumosus
Chironomus attenuatus
Procladius sp.
Tanypus sp.
Unknowns
Total Number
1069
924
122
7
19
Total Number
1091
10U
170
7_
Percent of
Total
^9-9
43.2
5-7
0.3
100
Percent of
Total
76.9
3.3
11.9
100
66
-------
STATIONS
NE C SW EDGE C SE
30
20
^ '°
D
0
— r>
CO °
UJ
cr
3O
UJ 0(3)
L i
_
0
i
_
_
i
-
-
• (5)
i
1
1
SUMMER
(5) 1968
J(5)
1
I
'(5)
-
1(5) |
AUTUMN
1968
>(2)
1(3)
1(2}
WINTER -T
1969
1(2)
T,_.
f(2)
_L
SPRING
1969
'(5)
f(5)
4
(2)
'(4)
i
-
(5)
[(2) <
i
_
_
-
1(2)
-
• 12)
-
-
1(5)
'(4)
' '
LIMNODRILUS HOFFMEISTERI
- L. UDEKEMIANUS
Figure 33. Seasonal changes in the abundance of Limnodrilus
hoffmeisteri (includes L_. udekemianus). Solid bar
indicates abundance based on 2 samples, whereas clear
bar represents abundance based on 1 sample. L indicates
no data as a result of samples drying during storage,
while 0 represents zero abundance on the basis of one
sample.
-------
significantly during the year; it rarely exceeded 5 per two samples.
Although the density ranged from about 5 to 39 per two samples at
Station 3 (central), a seasonal pattern in abundance was not clearly
evident. With the exception of four sampling dates (6 July 1968, 12
August 1968, 13 May 1969), the density never exceeded 20 per two samples
at this centrally located station. At Station 1 (northeast), the number
of individuals per two samples ranged from about 1 to 77, but the seasonal
trend in abundance was not clear except for a sharp increase and sub-
sequent rapid decrease in abundance during the spring of 1969. The change
in abundance of these oligochaetes at Station k (northeast) during
spring of 1969 was similar to that at Station 1. Unique to Station k
was, however, the lack of individuals on many of the sampling dates.
There appeared to be a distinct seasonal trend in abundance at Station
5 (edgewood); density increased gradually from about 5 per two samples
to about 30 per two samples during the period from 6 July 1968 to
18 February 1969, and it decreased quite sharply to about 1 per two
samples from 18 February to 25 July 1969.
Euilydrilus hammoiensis
Seasonal trend in the abundance of this species was fairly consistent
between stations (Fig. 3U). Although the density at Station 3 remained
within a narrow range of 0-6 per two samples, there appeared to be a
seasonal trend consisting of a progressive increase in density to maxi-
mum from winter to late spring, progressive decrease in abundance from
late spring to the end of autumn. Seasonal trends in abundance at
Stations 2, 1, and k were reasonably similar and consisted of relatively
low density during the summer, autumn and winter, abrupt increase in
density to maximum during early spring, and fairly pronounced decrease
in abundance during late spring. The initiation of the abrupt increase
in density observed at these 3 stations seemed to coincide with the time
at which the lake became open. Seasonal pattern in abundance at Station
5 differed slightly from those at Stations 2, 1, and k; no organisms
were present on many of the sampling dates of summer and early autumn,
and there was a pronounced increase in density in late autumn.
Ilyodrilus templitoni and Stylaria lacustris
These two species did not occur in adequate numbers to describe reliably
their seasonal trend in abundance. Of 122 specimens of Ilyodrilus
templitoni which were collected during our study, 50% of them were
recorded on one sampling date (6 July 1968). Only seven individuals
of Stylaria lacustris were found during our investigation, and all of
them occurred on one sampling date (6 July 1968) at Station 2.
CHIRONOMIDS
Only three genera of chironomids!were present in the bottom sediments
68
-------
10
0
20
_i
< 10
D
O
co 0
UJ
cr
UJ 40
o
<
(V
£ 30
>
+, 20
CO
UJ 10
1
_J
Q.
1 o
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g 90
I—
cr 80
LJ
Q.
cr 70
UJ
CD
5 go
_j 60
Z
UJ 50
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£ 40
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30
20
10
0
STATIONS
NE C SW EDGE C SE
1 I 1
T SUM
4(4) I9€
w(5) w(4)
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AUTl
I9(
o
WIN
19
o
-
• (2) m(2)
-
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1 1 1
MER
58
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JMN T
58
<
TER
B9
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,(2) (2)
r SPRING
1969
|(5)
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L d(5)
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$M
j
j
d(5)
i(5) <'(5)
. » "^ _„
1 1 J
EUILYDRILUS HAMMOIENSIS
Figure 3U. Seasonal changes in the abundance of Euilydrilus
hammoiensis at the five sampling stations.
69
-------
of the open-water region of Lake Wingra. These were Chironomus , Frocladius ,
and Tanypus. The species of Chironomus were C_. plumosus and £. attenuatus ,
but the species of the other two genera were not known. Of 1^17 chirono-
mids collected during the study, 1091 (76.9/0, ^5 (3.3$), IpU (7-W,
170 (11. 9%), and 7 (0.5$) were £. plumosus , £. attenuatus , Frocladius sp. ,
Tanypus sp. , and unknowns , respectively.
Chironomus plumosus
Seasonal trend in the abundance of this species was fairly consistent
between stations (Fig. 35)- The density rarely exceeded- 10 per two
samples at all stations during the summer of 1968. An abrupt increase
in numbers was observed in early autumn at most of the stations , and
relatively high density ranging from 20 to about ^0 per two samples
was maintained during early autumn and winter. A sharp decrease in
numbers shortly prior to or shortly after the end of the ice-cover
period was obvious at all stations. This sharp decrease in density was
generally followed by further decrease in abundance until an obvious
minimum density of less than U per two samples was reached. At all sta-
tions, there was an ebrupt increase in density between 6 and 20 June 1969.
Procladius sp.
Although the density of this species was less than 10 per two samples
throughout the study, there was a noticeable seasonal pattern in abun-
dance which appeared similar at all stations (Pig. 36). Few individuals
of Frocladius were present on at least half of the sampling dates during
the summer of 1968. In contrast, no individuals were present on most
of the sampling dates during the autumn and winter- Typifying the
sampling dates of the spring and summer of 1969 was the consistent
presence of few to several individuals.
Tanypus sp.
The density of this form never exceeded 10 per two samples during the
study period, and the seasonal trend in the abundance of this organism
was not noticeably clear (Fig. 36). Only in the spring was the density
maintained relatively high at all stations.
GRADIENT IN THE ABUNDANCE OF BENTHIC ORGANISMS
Benthos gradients in Lake Wingra were determined for the four seasons,
summer of 1968, autumn of 1968, winter of 1968-1969, and spring of 1969.
Data collected from 6 July through 27 August 1968 were "pooled" to obtain
average number per two samples and residual at each station for this
summer period. Data taken from 24 September through 26 November 1968
70
-------
STATIONS
=>
O
oo
UJ
O
<
cr
uj
>
•H
UJ
_l
Q.
cr
UJ
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cr
UJ
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UJ
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CE
UJ
10
0
30
20
10
0
40
30
20
10
0
20
10
NE C SW EDGE C SE
T~
-
<
-
-
-
ft" i
>(3)
<
surv
r(5) j "9
AUT
1
MER T
68 1(5)
UMN _,0.
1968 Ivt'
'(2)
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'(3)
WIN
19
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-
- 3
3
• 15) ,
L _—
K2)
<
4
'(5)
>(2)
SPR
19
i(5)
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TER T
59 1
3
ING
69
T <
1
j,5, I'""
'(2)
l
-
'(3)
-
;<2)
<
'(5)
_
(2)
'(4)
CHIRONOMUS PLOMOSUS
Figure 35. Seasonal changes in the abundance of Chironomus
plumosus at the five stations.
71
-------
NE
STATIONS
SW EDGE
C
~T
SE
~T~
•D
Q
co 4
UJ
cr
uj 3
tr
UJ
UJ
CL
<
oo
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UJ
CL
cn 4
UJ
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PROCLADIUS SP.
T
I
SPRING
! 1969
<>(4)
T
4)
TANYPUS SP
<'(5)
T
SPRING
1969
<>(4)
(4)
Figure 36. Seasonal changes in the abundance of Procladius sp,
and Tanypus sp. at the five sampling stations.
-------
•were used to derive average numbers per two samples and residual at
each station for the autumn period. Only the density measurements ob-
tained on 18 February and 19 March 1969 were used to calculate average
abundance and residual for the winter period. Results obtained on 22
April, 13 May, 22 May, 6 June, and 20 June were used to obtain statis-
tics representative of the spring period. For any seasonal period with
two sampling dates having one sample each, the counts were "lumped"
and expressed as number per two samples. For any season with three
sampling dates having one sample each, two samples were randomly selected
from the three and the counts expressed on the basis of these two samples.
No representative statistics were computed for the summer of 1969 be-
cause two sets of counts based on two samples were rare due to one
of the pair of samples being lost as a result of drying.
OLIGOCHAETES
Limnodrilus hoffmeisteri (+L. udekemianus)
The seasonal average density of these organisms at Stations 3, 2, and
1 were calculated to characterize their density pattern along the long
axis of the lake (Fig. 37). Low, intermediate, and high densities were
consistently associated with Stations 35 2, and 1, respectively, during
the autumn, winter, and spring. These results suggested a fairly linear
increase in average density from Station 3 to Station 1.. Density re-
lationship between stations for the summer was an exception as the
highest density was at Station 2. Even for the summer, Station 3 had
the lowest density.
The average density at Stations 5, 2, and k was determined to assess
the density pattern along the short axis of the lake (Fig. 38). Den-
sity relationship between stations differed with seasons. For the
summer, the highest density was at Station 2, and the lowest at Stations
5 and h (densities at these two stations were similar). For the autumn,
the densities at Stations 5> 2, and k were similar.
The density pattern for the winter consisted of the highest value,at •
Station 5, intermediate at Station 2, and lowest at Station k. For the
spring, the density relationship was just the opposite to that of win-
ter, with highest abundance at Station U and lowest at Station 5.
Euilydrilus hammoiensis
For the species, the density relationship between stations situated
along the long axis of the lake was similar only for summer and winter
(Fig. 38). Relatively high density at Station 1 and virtually identical
low density (less than 2 per two samples in all cases) at Stations 2 and
3 were characteristic of these two seasons. In contrast, relatively high
73
-------
1968 1969
JULY AUG SEPT OCT NOV FEBMARAPR MAY JUNE JULY
6 16 30 12 27 24 10 24 7 26 18 19 22 13 22 6 20 8 25
r—I I I I 1 1 1 1 1 1 I I I I
SOUTHWEST
LIMNODRILUS HOFFMEISTERI
SOUTHWEST
_ EDGEWOOD
Figure 37. Gradients in the abundance of Limnodrilus hoffmeisteri
(includes Jj. udekemianus) along the long and short axis
of Lake Wingra at different seasons. Number enclosed
in brackets represent sample size used to calculate the
statistics. Open circle does not represent an average
as only one pair of samples was available.
-------
1968 |969
JULY AUG SEPT OCT NOV FEB MAR APR MAY JUNE JULY
6 16 30 12 27 24 10 24 7 26 18 19 22 13 22 6 20 8 25
EUILYDRILUS HAMMOIENSIS
Figure 38. Gradients in the abundance of Euilydrilus
along the long and short axis of
Lake Wingra at different seasons.
75
-------
and similar density at Station 2 and 1 and low abundance at the other
station were observed for autumn. For the spring, the high density vas
at Station 1, intermediate at Station 2, and lowest at Station 3.
The density relationship between stations located along the short axis
of the lake was similar only for summer and autumn (Fig. 38). Stations
5, 2, and k had comparable average density during these seasons; however,
the average density values ranged from 0 to about 2 for the summer, and
from 9 to 11 for the autumn. Seasonal average density at Stations 2
and U was similarly low (less than 2 samples) and that at Station 5
was high (about 26 per two samples) for winter. For spring, the highest
average density was at Station U, and lowest, but identical density
(23.7 per two samples) at the other two stations.
CHIRONOMIDS
Chironomus plumosus
Only for autumn and winter was there a similarity in the density .re-
lationships between Stations 3, 2, and 1 (Fig. 39)- For these seasons,
there appeared to be an association of highest density with Station 1,
intermediate with Station 2, and lowest with Station 3. For the summer,
Station 1 had a comparatively high abundance, and Station 2 and 1 had
similar, low density. The density relationship between stations for
spring was opposite to that of autumn, with highest average density at
Station 3 and comparable values at the other two stations.
Stations 5, 2, and k have a similar density relationship for summer
and winter and an opposing relationship between autumn and spring
(Fig. Uo) • For the former two seasons, Stations 2 and U had a comparable
average density which was less than that of Station 5. The difference
between the density at Station 5 and that at the other two stations was
small for the summer and large for the winter. Highest, intermediate,
and lowest densities were associated with Stations 5, 2, and U, respectively
in the autumn and with Stations U, 2, and 5» respectively, in the spring.
Procladius sp.
Only for the spring were there adequate data to compute average density
of this organism at Stations 1, 2, 3, k, and 5 (Fig. 1|0). Density re-
lationship between stations established along the long axis of the lake
consisted of a relatively high abundance at Station 3, and low, but
similar, density at Stations 2 and 1. Average density at Stations 5,
2, and k, situated along the short axis, was, however, similar for the
same seasonal period.
Tanypus sp.
Adequate amount of data was also restricted to the spring for this
76
-------
1968 1969
JULY AUG SEPT OCT NOV FEBMARAPR MAY JUNE
6 16 30 12 27 24 10 24 7 26 18 19 22 13 22 6 20
T
JULY
8 25
T
CHIRONOMUS PLUMOSUS
Figure 39. Gradients in the abundance of Chironomous plumosus
along the long and short axis of Lake Wingra at
different seasons.
77
-------
1968 1969
- JULY AUG SEPT OCT NOV FEB MAR APR MAY
6 16 30 12 27 24 10 24 7 26 18 19 22 13 22
JUNE JULY
6 20 8 25
NORTHEAST
L
SOUTHEAST
r—i 1 1 \ 1 1
TANYPUS
SP.
Figure Uo. Gradients in the abundance of Procladius sp.
and Tanypus sp. along the long and short axis
of Lake Wingra. Spring, 1969.
78
-------
organism (Fig. 1*0). Highest, intermediate, and lowest densities were
at Stations 3, 2, and 1, respectively. For stations situated along
the short axis, highest, intermediate, and lowest abundance were associ-
ated with Stations 5, 2, and U, respectively.
Discussion
The predominant benthos of Lake Wingra are Limnodrilus hoffmeisteri,
Euilydrilus hammoiensis, and Chironomus plumosus. These species are
almost equally abundant as 1069 L_. hof fmeisteri, 92^ L_. hammoiensis ,
and 1091 C_. plumosus were collected during our sampling period from
early July 1968 to mid-July 1969.
Limnodrilus hoffmeisteri
Seasonal trend in the abundance of L_. hoffmeisteri is neither distinct
at all stations nor consistent between stations(Fig. 33). Lack of
discrete seasonal pattern in abundance may be due in part to the lack
or incompleteness of data on some of the sampling dates as a result of
losing samples through drying. However, since data are absent or in-
complete on many occasions for comparable dates for the different
stations, the consistency in the seasonal trend between stations should
not be affected by this aspect. There is, nevertheless, a lack of
similarity in the seasonal pattern at the different stations (Fig. 33):
this suggests the existence of local variations in the seasonal trend
of environmental factors influencing this species.
The highest density of L_. hoffmeisteri which has been encountered during
the study is 77 per two samples. This is roughly equivalent to l6l7
per square meter, a density far less than most recorded by Hiltunen
(1969) for the western basin of Lake Erie, by Brinkhurst (1967) for
Saginaw Bay, and by Brinkhurst (1970) for Toronto Harbour, Lake Ontario.
In spite of this comparatively low abundance of this oligochaete in
Lake Wingra, there are distinct gradations in its density along both
the long and short axis of the lake.
The most consistent density gradient for the long axis is a fairly linear
increase in density from Station 3 to Station 1, or from the southwest
portion to the northeast portion of the lake (Figs. 38 and 3l). Similar
results have been found by Brinkhurst (19&7) at the mouth of the Saginaw
River, and by Hiltunen (1969) at the mouth of the Detroit and Maumee
Rivers. Both investigators have observed a decreasing density with increaS'
ing distance from the mouth of the rivers. The trend in density along
the Jong axis of Lake Wingra is opposite to those observed by Brinkhurst
and by Hiltunen; the lowest density is at the inlet side of the lake,
and the highest at the outlet side of the lake. These results suggest
79
-------
that the bottom sediment of Lake Wingra may have increasing amounts of
organic material from the southwest to the northeast side of the Iake5
and that the inlet (or inlets) at the southwest side is not the major
source of organic material entering this lake.
Density relationship "between stations located along the short axis of
Lake Wingra is not as seasonally consistent as that between stations
situated along the Jong axis (Figs. 37 and 31). It is different for
every season (Fig. 37). We do not have any plausible explanation for
this seasonal variation in density relationship.
Euilydrilus hamTnoiensis
Seasonal trend in the abundance of Euilydrilus hammoiensis is fairly
distinct at all, stations and also consistent between stations (Fig. 3*0-
For all stations, low abundance is associated most frequently with summer,
autumn, and winter, whereas high density is associated most often with
spring. These results suggest that this species has one generation per
year in Lake Wingra.
Density relationship between stations along the long axis of the lake
indicates not only a striking difference in density between the three
stations (3, 2, and l), but also an increasing density of this organism
with increasing distance from the southwest portion of the lake (Figs.
39 and 3l). This density gradient is fairly similar for different
seasons, but is not as linear as that observed for L_. hoffmeisteri.
The availability of more organic material with increasing distance
from the southwest portion of the lake is also suggested from this
trend of E_. hammoiensis.
Densities of E_. ha.irmioiensis at the three stations positioned along the
short axis of the lake are not similar in all seasons (Figs. 38 and 31).
Only in spring and summer are there comparable density at the three
stations. The reasons for seasonal change in the density relationship
between the three stations are not known.
Chironomus plumosus
Seasonal pattern in the abundance of this species is not only fairly
distinct, but also remarkably consistent between stations (Fig. 35).
The decline in the abundance of this organism during the spring for
all stations probably reflects the loss of larvae (fourth-instar) from
the lake through emergence. Abrupt, increase in larval density from 6
June to 20 June 1969 may reflect the, hatching of another generation of
larvae.
Density relationship between stations along the long axis of the lake
indicates only a slight difference in density between the stations for
most of the seasons (Figs. 39 and 31). There is generally only a slight
80
-------
linear increase in density with increasing distance from the southwest
portion of the lake, and this density gradient is less pronounced than
those for the two oligochaete species. This gradient for C_. plumosus
may also reflect a gradient in the amount of organic material available
to them along the long axis of the lake.
Density relationship between stations along the short axis of the lake
is fairly consistent as there is a general tendency for density to in-
crease from Station h (southeast side of the lake) to Station 5 (edge-
wood or northwest side of the lake) (Figs. 39 and 31). The only
exception to this trend is in the spring. A fairly consistent density
relationship between stations along this axis for this species and
not for the two major oligochaete species suggests that the amount of
organic material is not necessarily the common factor per the abun-
dance of the three species.
General Remarks
From the" standpoint of numbers, Limnodrilus hoffmeisteri, Euilydrilus
hammoiensis, and Chironomus plumosus are most prominent. However,
numerical prominence does not necessarily mean that these benthic
organisms are the most important of the benthos in terms of their
contribution to energetics and nutrient cycling in Lake Wingra. Until
acceptable data on the turnover rates of these organisms are available,
the true importance of these species cannot be assessed. Especially
important for the determination of turnover rates arfe the rates at which
these benthic organisms are being eaten by the fishes in this lake.
Studies on food preference and feeding rates of the fishes have not been
completed yet. Until such studies are completed, whether numerical pro-
minence reflects true importance of these species with respect to
energetics and nutrient cycling cannot be determined.
The role of benthic organisms in the transport and transformation of
energy and nutrient through lakes can best be studied with the con-
sideration of population dynamics. To investigate the population •
dynamics of these organisms, one can measure the total population or
concentration of individuals. Since population attributes based ori total
population are logistically impossible to measure, one is usually
forced to deal with concentration or density for these purposes. It
is usually assumed that the density monitored is quite representative.
However, for benthic organisms in Lake Wingra, the attainment of re-
presentative density is still a very difficult problem. Knowing that
the seasonal trend and density of the organisms varies with location,
one must establish one to several stations from which he can collect
representative samples. The establishment of these strategic stations
81
-------
will be difficult as they must reflect representative seasonal trend as
well as representative density. Thus, even to treat the dynamics of these
organisms on a density basis is a monumental task. If the stations are
not carefully selected, the results from the study will have no meaning
to Lake Wingra, the energetic and nutrient dynamics of which one wishes
to describe.
82
-------
SECTION VII
DIEL PATTERNS OF DISTRIBUTION AND
FEEDING OF SELECTED FISH SPECIES IN LAKE WINGRA
Introduction
An important objective of this study is understanding the community
structure and energy dynamics of fish populations in the lake. A
previous thesis completed on the ecology of the panfish in the lake (Helm,
1958) raised questions and indicated areas in which greater study was
needed. Helm's data supported a theory of spatial segregation of po-
tentially competitive species. Also present in Helm's work was evidence
for diel migrations "by certain species.
With the research reported, we have tried to clarify these points.
Four species most abundant in open water were chosen for study: blue-
gill (Lepomis macrochirus), pumpkinseed (Lepomis gibbosus), white
crappie (Pomoxis annularis), and yellow bass(Morone mississippiensis).
Bluegill were sufficiently numerous that separate limnetic and littoral
feeding habits could be studied as well as competition among size
classes. Food resources of the various species were studied along
with predator prey relations. Revealing energy flow patterns and inter-
action among the dominant panfish species was the main goal of the in-
vestigation.
Sampling Techniques
Fish were sampled by trawling in the limnetic zone and by electric
shocking in the littoral zone. The otter trawl, a shrimp try net,
measured five meters across and had a maximum vertical gape of approxi-
mately one meter during the tows. In the open water series, a complete
circuit of the lake was made with the trawl. This series consisted
of samples every four hours over a US-hour period once every month from
April through November, 1970. On September 17-18, 1970, additional
tows were run in straight lines down the long axis of the lake. These
were taken at three hour intervals over a 24-hour period. All hauls
within a series were consistent in speed, length, and location in the
lake.
Only in September was shocking in the littoral zone used in conjunction
with trawling in open water. A transect was shocked both preceding and
following each trawl haul. Transects, one at each end of the lake,
extended from open water to the shore (approximately 50 meters). The
generator was a three phase AC type rectified for a DC output of ap-
proximately sixteen amps. Two sections of pipe suspended under the barge
and one meter lengths of spring hung from these by eyebolts formed a
83
-------
large cathode, which enabled us to maximize the usable current. The anodes
were 75 cm circles of .2.5 cm diameter copper tubing. The tubing was
attached to an insulated handle containing wires tleading to the anode.
An individual electrode had an effective range of approximately 1 lA
meters. The gear was mounted on a 5 1/2-meter pontoon barge powered
by a thirty-five horsepower outboard motor. Two electrodes were used
on every run. Fish swimming towards the electrodes were dipnetted from
the water.
Up to one hundred individuals of each species captured during the open
water trawls were measured and any remaining were counted. Total length
was measured by punching the length on acetate sheets. These measure-
ments were later grouped at 5mm intervals. All fish were released alive
in the center of the lake.
During September all fish taken by both sampling methods were frozen
on dry ice in the field. We later measured and counted all fish taken
in September and subsampled for stomach analysis. Only pumpkinseed, yellow
bass, white crappie, and bluegill ,(three size classes) were numerous enough
to permit analysis of food. Ten fish from each species or size class
were dissected for each time period and method of capture. For bluegills
ten small (75-95mm), ten medium (I05-125mm) , and ten large (l35min and
above) were analyzed. These three size classes were chosen to include
the three maxima in September size frequency distributions. The inter-
vening intervals were omitted to eliminate borderline individuals which
might have had intermediate characteristics. The intestine was clamped
at the pyloric sphincter and the esophagus was cut at the entrance to
the stomach. With a forceps the stomach contents were squeezed into a
weighing pan. Contents (wet weights) were weighed to O.OOOlg and ex-
pressed as a percent of body weight. The mean and standard deviation
from the mean were computed for each subsample.
Stomach contents were preserved with a ten percent formaldehyde solu-
tion for qualitative analysis. Bluegill (three size classes), pumpkin-
seed, white crappie, and yellow bass were analyzed qualitatively for the
1600 hour series open water trawls, and the 135mm and above group was
also analyzed for the 1600 hour series in the littoral zone. For the
most efficient use of the available equipment, stomach contents were
combined in five groups of two fish each for analysis. With those
stomachs containing few zooplankters, we counted all organisms in the
sample. When large numbers of zooplankters occurred, subsamples, were
taken. Organisms were strained from the sample through plankton netting
and then washed into a flask with 100ml of water.' The flask was agitated
on a Genie Mixer to distribute the zooplankton. evenly throughout the
solution. A one ml sample was removed from the flask for counting after
each mixing, ten such subsamples being taken in all.
Bluegill Distribution
Bluegill were the dominant species in the lake numerically. Our gear
-------
("bottom trawl) appeared to be most effective for sampling this population,
which^Helm's (1958) studies have- indicated are present near the bottom-
when in open water. Catch per unit effort during the day was relatively-
constant from April through July at approximately1 300 fish per haul
(Figure 1*1). ' From August through October, greater numbers were taken
with a maximum of 860 fish per haul in September. In November the catch
per unit effort dropped to 50 fish per haul, the lowest of any month.
Wight catches remained low (usually less than 100 per haul), except
during October, -when bluegills were approximately equally abundant
in the open vater during day and at night.
During the September trawling and shocking series, all fish captured
were measured. A sample size of over 1,000 fish for each zone was used
to compare the size class distribution in the open water and the littoral
zone (Figure 1*2). Young-of-the-year fish formed a large percentage of
the littoral population (88$). However, if only the adult population
is considered, the 130mm and over size class formed the greatest per-
centage of the littoral population ("50%), while in the limnetic zone,
the two intermediate size classes occur in far greater numbers (32%
and 5^$)- Young-of-the-year were apparently not migrating to the epilim-
nion of the limnetic zone at this time, as Werner (1969) reported for
Crane Lake, Indiana. Surface and mid-water trawls also used in the sampling
did not catch any bluegill young-of-the-year.
Converting the numbers to biomass by multiplying by the mean weight of the
individuals in a length class had the effect of reducing the importance
of the 70-99™n fish and increasing the importance of the 135™n and over
fish (Figure 1*3). In the limnetic zone the 100-129mm length class domi-
nated the biomass (56$), while young-of-the-year were of no significance.
Young-of-the-year were significant in the littoral zone, however, com-
prising 16$ of the biomass. The 130mm and above fish dominated this
region, comprising 63% of the entire population and 13% of the adult
population. Both intermediate length classes were of less importance
in the littoral than the limnetic zone.
Bluegill Feeding Periodicity
Stomach contents reached a maximum of over 1.2.% of the body weight for
the 75-95mm length class in the limnetic zone, this occurring at 1900
(Figure 1*1*). Maximum fullness occurred earlier for 105-125mm fish (l600)
at a level about one-half as high (0.7$). Large fish from the limnetic
zone maintained the same stomach content to body weight ratio as the
previous size class through 1000, after which their percentage decreased,
leaving the 1000 figure as a maximum (Figure 1*5). Large bluegill in the
littoral zone contained more food than those from the open water, reach-
ing a maximum at 1300 and maintaining a relatively full stomach through
1900. Keast and Welsh (1968) recorded the stomach content maxima for
bluegill at 1500. Since they used bluegill ranging from 90-ll*0mm, these
data appeared to be fairly consistent with ours. However, their findings
that bluegill recommenced feeding at 2030 did not agree with the data on
85
-------
APR
Figure 1+1
MAY JUN JUL AUG SEP OCT NOV
Catch per trawl run day and night for the "bluegill
(Lepomis macrochirus)- Open circles are the mean of
the day values with vertical lines for the standard
deviation from the mean, and solid circles are the
average of the night values with vertical lines for
the range. (The sampling consisted of two 2U-hour
series! with day samples' at 0800, 1200, arid 1600 and
with night samples at 0000).
86
-------
TOTAL POPULATION
60
40
UJ
o
cc
0«
o. 20
LIMNETIC
60
40
20
BLUEGILL > 70mm
LIMNETIC
I-
z
UJ
u
a:
UJ
P-
80
60
40
20
LITTORAL
<69 70-99 100- 130
129
80
60
40
20
LITTORAL
70-99 100- I30>
129
LENGTH IN mm
Figure U2. Percent composition by number for size classes of
the bluegill population in limnetic and littoral
zones on September 17-.18, 1970. Percentages were
calculated separately for the entire population
and for fish 70mm or larger.
87
-------
TOTAL POPULATION
60i- LIMNETIC
I- 40
2
UJ
o
01
CL 20
BLUEGILL > 70mm
60r- LIMNETIC
40
20
80-
60
liJ
O
OL
20
LITTORAL
n
80
60
40
20
LITTORAL
<69 70-99 100- I30>
129
70-99 100- I30>
129
LENGTH IN mm
Figure ^3. Percent composition by biomass of the "bluegill
population in limnetic and littoral zones on
September 17-18, 1970. Percentages were cal-
culated separately for the entire population
and for fish 70 mm or larger.
-------
0400
1000
1600
2200
0400
1.2
I05-I25mm
i.O
.8
UJ
o
cc
LJ
Q.
_L
_L
_L
_L
0400 1000 1600 2200 0400
TIME OF DAY IN HOURS
Figure kk. Daily feeding periodicity of two size classes
of bluegill in the limnetic zone (September
17-18, 1970). Solid points are percent mean
weight's (g) of stomach content per gram of fish;
vertical lines" are standard deviation from the
mean.
89
-------
1.2
LIMNETIC
LJ
LJ
1.0
.8
.41
I
_L
_L
0400
1000
1600
2200
0400
1.2
1.0
-B\
LITTORAL
LU
£
LJ
_L
I
I
I
I
I
0400
Figure
1000 1600 2200
TIME OF DAY IN HOURS
0400
Daily feeding periodicity of 135mm or larger
bluegills from the limnetic and littoral zones
(September 17-18, 1970). Solid points are per-
cent mean weights (g) of stomach content per
gram of fish; vertical lines are standard
deviation from the mean.
90
-------
Figures kk and h$. This lack of any night feeding in LakeWingra differed
from the results of both Keast and Welch (1968) and Seaburg and Moyle( 196*0,
whose field data indicated fairly constant feeding throughout the 2k hours.
Although ^ a lack of night data precludes calculations, the large bluegill
in the littoral zone appeared to have a significantly higher daily ration
than those in the limnetic zone. Considering only bluegill caught in
open water, the percent of the body weight represented by the stomach
contents declines with an increase in size. Smaller fish also reached
their maximum values later in the day, indicating a longer feeding period.
If several conditions have been met, the average amount of food consumed
between sampling periods can be determined from the average weights of
food present in the stomach (Table k). First, no feeding should have
occurred between those sampling periods from which the digestive rate
was calculated. Secondly, all the fish sampled must have belonged to
the same population. Finally, an assumption must be made concerning the
nature of the digestive rate and how it varied with meal size.
We assumed the first two conditions were fulfilled, the second of these
being supported by our distribution data. The third assumption created
more of a problem. Digestive rates have been under intensive study in
recent years, and the literature supports three different points of
view. Pandian (1967) stated that the percent body weight per hour
digested increased as digestion proceeds, and that the digestive rate
was a direct function of time. The results of other investigators,
however, demonstrated that the amount of food digested per unit time
increased as the meal size increased. Many of these same investigators,
though, assumed that once this amount per unit time was determined,
it remained constant throughout the period of digestion (Hunt, I960;
Kitchell and Windell, 1968; Windell et_ al., 1969).
Some recent research indicated that the amount of food digested per unit
time also decreased as the food mass remaining in the stomach decreased.
Seaburg and Moyle (196*0 used this assumption in their calculation of the
average daily meal for bluegill. Tyler (1970) fitted both a recti-
linear and curvilinear (exponential) equation to his data on digestion in
cod. The negative exponential gave the best fit, meaning that for equal
time intervals, equal percentages of the amount present in the stomach
would be passed into the intestine. A rectilinear fit would have indi-
cated that a constant quantity is passed per unit time. Thus, in Tyler's
study, greater quantities were removed from the stomach in the early hours
of digestion than later in the process. Conditioned regressions had also
been used to determine digestion rate (McKone, 1971)- Again, these in-
dicated that the digestive rate was proportional to the amount of food
remaining in the stomach, or that the grams per hour digested were larger
for larger stomach volumes.
Most of the literature, therefore, supported a digestion rate which varied
with meal size. We" assumed a curvilinear function for our data (using
91
-------
Table k. Mean weight of food (g) per fish present in the stomach for two length classes of
"bluegill at different hours during the sampling period (September 17-18, 1970).
Time
Weight
of
Food
Time
Weight
of
Food
Small Fish
0700 1000 1300 1600 1900
.0387 .0693 .0790 .1208 .1331
Medium Fish
0700 1000 1300 1600 1900
.0985 .1509 .1628 .1933 .1739
2200 0100 0^00
.1120 .OU89 .0159
2200 0100 OkOO
.11*96 .101U .0522
VQ
ro
-------
percent of remaining mass digested per unit time as a constant). If a
mechanism did exist (as it seemed to) which could adjust the digestive
rate according to the initial meal size, logically this.mechanism would
also adjust the digestive rate as the size of the initial meal changes.
The greatest percent of mass lost between two adjacent sampling periods
occurred between 0100 and OUOO for both small and medium-sized bluegill
(Table U). This was 67^5$ for the 75-95mm fish and k&.5% for the 105-
125mm fish. Although much of the literature stated that the digestive
rate was constant for all size classes, smaller individuals were found
to have a faster digestive rate by both Seaburg and Moyle (196*0 and
Pandian (1967).
The amount of food consumed between two sampling periods could be ex-
pressed by the equation:
At= (P/100)(St) + (St+1-St)
where: A = the amount of food eaten between times t and t+1
U
P = the greatest percent decrease of mass between any two adjacent
sampling periods
S = the average weight of food per stomach at the sampling period
at time t
S = the average weight of food per stomach at the sampling
period of time t+1 immediately following sampling period S
O
Solving this equation, a graph of food consumed plotted against time was
constructed (Figure ^6). The period of least feeding (assumed to be
zero feeding) occurred between 0100 and OhOO for both smaller length
classes of bluegill. Large bluegill consumption was not determined
because of lack of night data. Small (75-95mm) bluegill fed most
heavily throughout the afternoon and early evening (1300-1900).
Medium (l05-125mm) bluegill had feeding maxima extending from 0700 to
1600, with a light depression between 1000 and 1300. Feeding activity
seemed to both begin earlier in the day and to decline earlier in the
day for this latter length class.
Bluegill Daily Ration
Daily ration was derived from Hie expression:
(1/W) Z A
t=l *
where: W = the average weight of the fish being studied
n = the number of sampling periods within 2H hours.
Using this equation and Figure U6, the daily ration was calculated to be
3.9$ of the body weight for small bluegill, and 1.8$ of the body weight
for medium bluegill.
93
-------
FOOD CONSUMED, WEIGHT IN GRAMS
.IUUU
.0800
.0600
.0400
.0200
.0000
02
.1000
.0800
.0600
.0400
.0200
.0000
02
I
1
1
1
i
1
i
i
_ i
i
—
i i i i i i i i ii
00 0600 1000 1400 1800 2200 0200
|
i i ' I
i {
! i
i i
—
i i i i i i i i ii
00 0600 1000 1400 1800 2200 0200
TIME OF DAY IN HOURS
Ugure k6. Mean amounts (g) of food consumed between
sampling periods (position of dotted lines)
for two size classes of "bluegill in the
limnetic zone (September 17-18, 1970).
-------
Both the digestive rates and the daily rations were slightly higher than
most values found in the literature. Gerking (195*0 found that a daily
ration of 3% was about the maximum for bluegills held in aquaria at room
temperature and fed mealworms. Seaburg and Moyle (196*0 calculated that
the average summer daily ration for bluegill in Grove and Maple Lakes,
Minnesota, ranged from I.h% to 2.2%. Keast and Welsh (1968) reported
a daily ration of 2.5% for bluegill in June. Other data from Lake
Wingra placed the daily ration in September at 1.38% for small blue-
gills and 1.18% for medium bluegills (Magnuson and Kitchell, 1971).
Part of the difference between our values and those of Magnuson and
Kitchell were probably due to a different definition of the two length
classes. Especially in the small length class, fish used by them averaged
larger (l3.5g) than ours (l0.6g). There was also a difference in the
average stomach to body weight ratios for that month. Both studies
calculated 0.1*8 for the medium bluegills, but whereas the value of
Magnuson and Kitchell for small bluegills was 0.56, ours was 0.73.
This difference may have been due to the different sampling periods
within the month, or again have reflected the larger fish used by
Magnuson and Kitchell.
The rest of the discrepancy originated from a difference in digestive
rates. The above study estimated 35% digestion in 3 hours at 19 C.
Our field data calculated rate may be too high, especially considering
the small (ten fish per period) sample size, (if the first assumption
had been violated, i.e. , if fish had been feeding between 0100 and OUOO,
this would have increased not decreased the rate.) However, rates
calculated in the lab may be too low. ¥indell (1967) demonstrated
that starvation prior to feeding experiments decreased the rate of
digestion. Also, stress produced by handling and confinement might have
caused a decrease in digestive efficiency. Therefore, laboratory derived
digestive rates might have been lower than those actually occurring in
the field. Whether or not our own data were in error, the equations
presented should provide a viable method for the determination of daily
ration from field data, providing the three assumptions previously
mentioned have been met.
Food Organisms Utilized by Bluegill
Qualitative analysis of the stomach contents was carried out for those
fish captured by both boom shocker and trawl at 1600 hours September.
Bluegill in the littoral zone were selecting macrofood items (pre-
dominantly chironomid larvae) while those in the open water were selec-
tively feeding on zooplankton (Figure Vf). Ball (19^8) also noted that
fish feeding on zooplankton did not feed on macrofood items at the
same time. In limnetic samples, bluegill of the largest length class
contained fewer zooplankters per stomach than small and medium blue-
gill. Therefore, the large bluegill in this area appeared to be at a
disadvantage. Large bluegill did have a greater number of macrofood
items per stomach than the smaller length classes, especially in the
95
-------
3000
3000.-
Ct
LJ
GO
2
Z> 2000
2000
1000
1000
Q_
O
O
N
SMALL MED. LARGE
SMALL MED. LARGE
60.-
UJ
CO
Q
O
O
U.
O
(T
O
40
20
SMALL MED. LARGE
LIMNETIC
60
40
20
n
—
—
SMALL MED. LARGE
LITTORAL
Figure kl. Number of zooplankton and macrofood organisms
per stomach for three size classes of bluegill;
small (T5-95mm), medium (l05-125mm), and large
(135mm and larger) taken in the limnetic zone
September 17-18, 1970).
96
-------
littoral zone. Unfortunately, we only determined numbers of macro-
food items per stomach rather than weights or volumes. Macrofood animals
(especially the chironomids) found in large bluegill were bigger than
those found in the smaller individuals. Therefore, there would have
been an even greater difference between the amount of macrofood per
large bluegill compared with the amount per smaller bluegill if weight
or volume had been used.
Cladocerans, especially Daphnia retrocurva, were the most abundant
zooplankters found in bluegill stomachs (Figure U8). All three size
classes of bluegill had approximately the same percentage composition
of the various types of organisms. Bosmina sp. , however, were only taken
to any degree by the smallest size class, while Ceriodaphnia sp. were
more common in the two larger size classes. Copepods were scarce, making
up less than 1$ of the number of zooplanktors in each of the three
size classes. Cladocerans have been often reported as an important
item in the bluegill diet (Helm, 1958; Gerking, 1962; Seaburg and
Moyle, 196U; and Keast and Webb, 1966). Copepods were often also
present, although at low levels (Helm, 1958; Gerking, 1962; Keast
and Webb, 1966). In Leonard's (19^0) study, smaller bluegill• fed on
zooplankton while the larger fish fed on macrofood items. This was
not substantiated by our data from the limnetic zone. Werner (1969
demonstrated that bluegill young-of-the-year in Crane Lake, Indiana,
fed almost entirely on planktonic crustaceans, including Daphnia galeata,
Ceriodaphnia spp. , Bosmina spp., and copepods. Adult bluegill taken
during the summer by Ball (19^8) utilized Daphnia spp., Ceriodaphnia
spp., Diaptomus spp. , and Cyclops spp. An important point to notice
is the bluegill did not feed on chironomids in open water, even though
this organism is available here, as will be shown later by pumpkinseed
feeding habits.
Chironomid larvae were the most numerous food organisms for all three
size classes of bluegill in the littoral zone (Table 5). Chironomid
pupae were also numerous as were Odonata nymphs, other dipteran larvae,
and terrestrial insects. Hemipterans were found more often in large
fish and mollusks were found more often in 105-125mm fish. Only in the
largest size class did fish occur as a food item. Chironomid immatures
emerged as a major bluegill food in studies by Helm (1958), Seaburg
and Moyle (19610, and Etnier (l97l), and as the most important food item
in studies by Leonard (19^0), Ball (19^8), Gerking (1962), and Keast
and Webb (1966). Research also demonstrated that bluegill frequently
utilize Odonata nymphs (Leonard, 19^0; Ball, 19^8; Keast and Webb, 1966;
and Etnier, 1971), terrestrial insects (Ball, 19^8; Keast and Webb,
1966), and Etnier, 1971), mollusks (Ball, 19^8; and Keast and Webb, 1966),
and fish (Helm, 1958; and Keast and Webb, 1966).
Distribution of Other Panfish
Yellow bass distribution in the limnetic zone was quite different from
that of bluegills (Figure V?). From April through July, yellow bass
97
-------
60r
SMALL
£ 40
UJ
o
QC
S 20}
O1-
60,-
HL
n
MEDIUM
40
20
0
60.
LARGE
o
ct:
UJ
40
20i
n
o
QQ
O
o>
Ci
O
1
«»
•6
o
5
o.
-5
TJ
x
o
o
-------
Table 5. Mean percent numerical composition of macrofood species per
subsample (two fish) for three size classes of bluegill. Each
size class represents ten fish taken from the limnetic zone
on September 17-18, 1970. Only subsamples containing food
were used (two 105-125mm fish did not contain food, i.e..,
one subsample).
Food Organism
Chironomid Larvae
Chironomid Pupae
Other Dipterans
Odonata
Hemiptera
Terrestrial Insects
Heleidae
Mollusca
Fish
Other
Total Number of Food
Organisms
Percent of
Total Food
7 5-9 5mm
fish
66.7
5.9
3.3
12.6
0.1
8.7
0
2.1
0
0.5
U67
Percent of
Total Food
10 5-12 5mm
fish
1;8.6
11.8
5.fc
5.0
l.U
17. ^
O.U
5-5
0
k.h
139
Percent of
Total Food
135nnn+
fish
59.8
7-9
7-1
11.6
7.2
2.7
0.8
1.2
0.9
0.8
535
99
-------
10
9
8
6
-r!
et
Q_
u
o
APR MAY JMN JUL AUG SEP OCT NOV
Figure ^9. Catch per trawl run day (0800, 1200, and 1600) and
catch per trawl run night (0000) of yellow bass
,(Mo rone, mississippiensis) taken from a l*8-hour
series, dp.en circles are the mean of the six day
values and vertical lines the standard deviation from
this mean. The solid circles are the average of two
night values and vertical lines are the range.
100
-------
were always caught in small numbers. Although night catch per unit effort
was always higher, no significant differences between day and night
catches occurred during this period. Between August and October, the
difference between day and night became substantial. Either the species
was now more abundant in the limnetic zone at night or its catchability
at night had increased. Finally, in November there was some increase
in the day catch and an extremely large increase in the night catch.
Helm (1958) also caught more yellow bass at night than during the day.
He later electrified his trawl, however, and increased his catch per
unit effort of yellow bass by a factor of eight without increasing his
catch per unit effort of bluegill. This leads to the conclusion that
yellow bass were avoiding the unelectrified gear. The rise in
catch per unit effort for yellow bass in November, though, might have
indicated an actual increase in abundance. Whether or not this was
the case remains unknown.
White crappies reached a maximum abundance in open water in May
(Figure 50). After May, the catch per unit effort declined through-
out the rest of the sampling period. All samples reflected a greater
abundance during the day than at night. Helm (1958) captured white
crappie almost exclusively between 0500 and 1900 hours. This species
was taken in small numbers compared to bluegill and yellow bass.
Multilevel trawling by Helm (1958) showed that white crappie were midway
up in the water column rather than being on the bottom. Although we
also used a midwater trawl, we didn't obtain any conclusive data. The
major portion of the white crappie population could possibly have been
above the level at which our gear operated. Therefore, the white crappie
population may not have been adequately sampled.
Pumpkinseed distribution (Figure 50) was fairly consistent throughout
most of the sample period. Numbers never reached high levels in the open
water, since the majority of the population remained in the littoral
zone. Although more pumpkinseeds were usually cuaght during the day
than during the night, the difference was never great. A maximum abun-
dance seemed to occur in April and a general absence of the species
from the open waters occurred in November, coinciding with the disap-
pearance of bluegills from this same area (Figure 4l). Most of the
pumpkinseed population seemed to remain in the littoral zone throughout
the day. Therefore, it is probable that only a small proportion of
the population was available to our trawl.
Feeding Periodicity of Yellow Bass and Pumpkinseed
Pumpkinseed had a low percent stomach content to body weight (Figure
51). The pattern appeared to be bimodal, although the spread of the means
was not great. Keast and Welsh (1968) also recorded a bimodal feeding
periodicity curve for pumpkinseed with one peak at 0800 and another at
1800. Although this agreed well with Figure 51, our data did not show
the lower peak which they observed at 0300.
101
-------
in
a
O I
PUMPKINSEED
H
O
ro
2-
WHITE CRAPPIE
APR MAY JUN JUL AUG SEP OCT NOV
Figure 50. Catch per trawl run day (0800, 1200, 1600) and catch per trawl run night (OOOO)
for two species taken from a ^8-hour series. Open circles are the mean of the
six day values and vertical lines are the standard deviation from this mean.
The solid circles are the average of two night values and the vertical lines
are the range.
-------
0400
1
2.4
2.2
2.0
1.8
1.4
I- 1.2
Z
Id
<-> 1.0
o:
UJ
Q- .8
1000
—I—
1600
2200
1
0400
1
.6
.4
.2-
0400
Figure 51
1000 1600 2200 0400
TIME OF DAY IN HOURS
Percent weight (g) of stomach content per weight (g)
of fish. Open circles are individual yellow bass;
solid points are means for pumpkinseed, and vertical
lines are standard deviation from the mean.
103
-------
Yellow bass percentages were plotted separately for individual fish
instead of averaged, because of the great variability inherent in their
feeding behavior (Figure 5l)- The points which were significantly
higher than the basal grouping were for fish that had eaten either one
or two young-of-the-year Lepomis spp. Over 10$ of the sample had fish
remains in the stomach. No young-of-the-year were eaten at night, but
feeding seemed to continue throughout the day. Previous studies (Helm,
1958) also indicated continuous feeding throughout the day.
Food Organisms Utilized by Other Panfish
¥hite crappies relied heavily on zooplankton for their food supply in
open water. Macrofood items occurred only in trace amounts in these
stomachs. Over l/i| of the zooplankters present in white crappie stpmachs
were Mesocyclops spp. (Table 6). Both Daphnia galeata and Daphnia
retrocurva formed significant portions of the diet. Unfortunately, a
large number of cladocerans were unidentifiable because of their advanced
state of digestion. Zooplankters were also reported by Helm (1958)
as being important in the white crappie diet. Marcy (195^0 found a pre-
dominance of cladocerans in the crappie of Sanctuary Lake, Pennsylvania,
while those from the deeper Middle Lake, Pennsylvania, contained a pre-
dominance of copepods. First year white crappie studied by Mathur and
Robbins (1971) utilized copepods more intensively toward the fall and
winter, these organisms comprising 32$ of the food by September, lone
of the white crappie examined in our study contained fish remains. Helm
(1958) also failed to find any utilization of fish by the Lake Wingra white
crappie population.
Pumpkinseeds fed only on macrofood organisms. These were almost ex-
clusively chironomid larvae, with some chironomid pupae and Heleidae
also being utilized (Table 6). Chironomid larvae were frequently
reported in the literature as comprising a significant portion of the
pumpkinseed diet (Ball, 1958; Seaburg and Moyle, 1964; Keast and Welsh,
1968; and Etnier, 1971). All of these publications also found that
snails represented a major food item for pumpkinseed. Since these
feeding studies were based on fish captured mainly in the littoral
zone, a habitat difference exists which might explain the lack of
snails in pumpkinseeds captured for this study.
Yellow bass fed both on chironomid larvae and fish, with fish (young-
of-the-year Lepomis spp.) probably being the more important macrofood
item as weight or volume (Table 6). Even early researchers reported
that yellow bass fed on insects and fish (Burnham, 1910). Helm (1958)
found that chironomids and fish were of major importance, but that
zooplanktors were equally important. Recent research by Bulkley (1970)
indicated that the food preferences of yellow bass changed during the
year. Chironomids were utilized heavily from April to July, zooplankton
in April and in the winter, and young-of-the-year yellow bass from August
to October. Bulkley found that by September 27$ of the stomachs con-
tained fish, and these fish comprised 84$ of the volume in the stomachs.
10 it
-------
Table 6. Mean percent numerical composition of' macr'ofood or zooplahkton
species per subsample (two fish) for three spediesi Each
species represents ten adult fish taken from the limnetic zone
on September 17-18, 1970. Only subsamples containing food
were used.
Food Organism
Chironomid Larvae
Chironomid Pupae
Other Dipterans
Odonata
Hemiptera
Terrestrial Insects
Heleidae
Mollusc a
Fish
Other
Percent of
Total Food
Yellow Bass
62.5
0
0
0
0
0
0
0
37.5
0
Percent of Percent of
Total Food Total Food
Pumpkins eed White Crappie
92.9
3.U
0
0
0
0
2.9
0
d
0.8
Total Number of
Food Organisms
Bosmina sp.
Daphnia galeata
Daphnia retrocurva
.Ceriodaphnia sp.
Other Cladocerans
Mesocyclops sp.
Diaptomus sp.
Cyclops sp.
Total Number of
Food Organisms
202
0.2
17^
21,2
25, U
27.^
0.1
1:9
105
-------
Perhaps the greater use of zooplankton shown by Helm was due to the fact
that much of his sample was caught earlier in the year.
Migrations and Seasonal Distribution Patterns
Reports of diel migrations or movements of fish within lakes were common
in the literature. Some of these migrations were definitely associated
with a migrating or changing food source (McNaught and Easier, 196l) ,
and some appeared to be correlated with temperature changes (Grossman, 1959&
and Grossman, 1959b). Others, including bluegill migrations, appeared
to be a response to changing light intensities (Easier and Bardach, 19^-9;
John, 1959; Davis, 196U; and Werner, 1969).
Since several of the species in Lake Wingra apparently varied greatly
in abundance from month to month, changing effectiveness of the gear
must be considered. Catch per unit effort is based on a set of assump-
tions regarding the catchability of the populations being studied. If
any of these assumptions are incorrect, then the conclusions drawn from
the data will be invalid (Robson and Regier, 1971)• That the gear used
will be equally effective in capturing all of the species being studied
is one such assumption of major importance. Selectivity of the gear can
result from extrinsic factors (type of gear, methods of handling the gear,
etc.) or intrinsic factors (behavior differences among or within species,
differences due to sex or size, time of day sampled, season, etc.) or
an interaction between these factors (Lagler, 1971).
Extrinsic factors were reduced by the use of catch per unit effort as
only a relative measure of abundance. The limnetic and littoral zones
were sampled separately, and samples were taken every three or four hours
in a twenty-four hour series, eliminating time of day as a factor- Some
error in the trawling statistics was probably introduced, though, by
extrapolation from the population at the bottom of the lake to that of
the entire limnetic zone. White crappie, for instance, may have been
concentrated above the area effectively sampled by the trawl. Therefore,
the relative abundance estimated for white crappie may have been low.
Yellow bass could probably escape the trawl during the day thereby also
appearing to be fewer in number than was naturally the case.
For all the species other than yellow bass, a consistently greater catch
per unit effort occurred during the day than at night (when the fish
should have had more trouble avoiding the gear). This lent credence
to the effectiveness of the gear on those fish available to it. Another
concern was whether a consistent amount of effort was used each month.
This was supported by the greatest catch per unit effort of the different
species occurring in different months. The greatest catch per unit effort
of yellow bass occurred in November, when the smallest catches of blue-
gill occurred (Figures ^1 and 1$). Pumpkinseed and white crappie (Figure
50) had maxima in April and May, respectively.
Almost all the fish taken in the monthly trawl series were released. The
removal of the more vulnerable fish from the population, therefore,
should not have been a problem. During any one month, the same area
in the limnetic zone was, however, frequently sampled. A decrease
106
-------
in catch might, therefore, be expected in later runs due to the earlier
disturbances. The twenty-four hour series, though, vas spaced out over
a week, and this bias would also have been consistent for each month.
Boom shocking was selective for larger fish, smaller fish having less
voltage drop from head to tail. The crew members dipnetting fish may
also have been unconsciously selecting the larger specimens. However,
the^great numbers of young-of-the-year bluegill taken by this method
indicated that these biases were probably not very great. Certain
species also seemed better able to break free from the electric field due
to a faster swimming rate.
Intrinsic factors which might have influenced the data included varying
catchability with changing seasons of environmental conditions (Ricker,
1958;). The sudden increase in the catch per unit effort of yellow bass
in November (Figure V?) might have been caused by colder water tempera-
tures. This temperature decrease might have slowed the fish to the
point that they were then vulnerable to a gear (bottom trawl) which
they had been able to avoid previously. If so, however, this only em-
phasized the decrease in the limentic bluegill population at this time
(Figure Ul). A seasonal factor that would make a previously unobtainable
species easily catchable seems highly unlikely.
A change in environmental conditions could also affect a species' catch-
ability. Helm (1958) stated that white crappie may rise in the water
column on cloudy days. If this is true, a month in which the sampling
was done in cloudy weather might show a false drop in the limnetic crappie
population. The fish normally caught may simply have moved above the
level sampled by the gear. No serious decreases in the population size
were actually shown by the data however (Figure 50). Even considering
all of these possible biases, some actual changes in the distribution
patterns of fishes in the lake were pointed out by the data. Among
these were the differences in day as opposed to night catch per unit
effort and the different directions of change in the bluegill and yellow
bass population distributions in November.
Therefore, if our data accurately represent the situation in Lake Wingra,
a significant portion of the bluegill population was migrating into the
limnetic zone during the day and returning to the littoral zone at night
(Figure Ul). This movement seemed to intensify in late summer and then
disappear in November. Combining this information with the inshore
data (Figure k-2) led to the conclusion that the participants in the
migration were largely fromlhe two intermediate size classes. A
greater proportion of the young-of-the-year and large fish seemed to
remain in the littoral zone. This distribution for the young-of-the-
year could be expected, since the dense vegetation beds offered a great
deal of protection.
Yellow bass also engaged in diurnal onshore-offshore movements in certain
situations (Carlander and Cleery, 1968). Helm (1958) noted an evening
107
-------
onshore movement in Lake Wingra. The data from our study were not con-
clusive, since it appeared that most yellow bass were able to escape
the gear in the daytime (Figure ^9)-
Food Utilization among Different Size Classes of Bluegill
Bluegills of all three size classes utilize the same types of food when
they are present in the same habitat (Figures kj and U8, Table 5). All
bluegills in the limnetic zone fed on zooplankton, which the small and
medium sized fish obtained in much greater numbers. Conversely, all
adult bluegills in the littoral zone fed on macrofood organisms, largely
chironomid larvae. Here the largest bluegill appeared to be the most
successful feeders.
This was also demonstrated by the stomach to body weight ratios , higher
for those bluegill greater than 135nim caught in the littoral zone than
for the same size class caught in the limnetic zone. The ratio for this
group in open water was far lower than the ratios for the two smaller size
classes. Therefore, there appeared to be an advantage for bluegills of
large size to remain in the shallow water and not to participate in the
migration to the limnetic zone during the day. A large percentage of
this upper size class did appear to remain inshore (Figure ^2).
Food Utilization among Different Species
In the limnetic zone, adult white crappie fed almost exclusively on zoo-
plankton. Only bluegill, of the species studied, also utilized this food
source in open water. However, the white crappie appeared to select a
much greater proportion of copepods than did the bluegill (Figure U8,
Table 6), thereby minimizing the overlap of food organisms.
Pumpkinseeds utilized chironomid larvae as their main food, item in the
limnetic zone. Yellow bass fed on chironomids as well, but also preyed
on young-of-the-year Lepomis spp. (Table 6). Since the pumpkinseed
population was sparse in the limnetic zone, little if any competition
could be possible even with the similarity in diet. Except for yellow
bass, none of the fish studied, including the white crappie were pisci-
vorous in the limnetic zone.
The Effect of Interactions Between Lake Wingra's Fish Species on the
Ecosystem's Energy Flow
Some of the interactions of the Lake Wingra fishes in mid-September could
now be summarized. Most of the bluegills between 70mm and 135mm took
part in a diel migration to the limnetic zone each morning. While in the
open water, these fish concentrated near the bottom where they fed on
zooplankton. Here they were associated with yellow bass which may also
take part in at least a partial migration). The yellow bass preyed on both
young-of-the-year Lepomis spp. and chironomid larvae. Pumpkinseed were also
108
-------
present in this area in small numbers, feeding on chironomids. Dispersed
slightly above this level were the white crappie. These fish were feeding
on zooplankton, but due either to selection or a vertical distribution
of zooplankton species, they preyed far more heavily on Mesocyclops spp.
than did the bluegill.
Most young-of-the-year and large bluegill remained in the littoral zone.
Here the large bluegill cropped chironomids and other macrofood organisms.
Pumpkinseeds in the littoral zone probably fed on chironomids and snails
(Ball, 19^8; Seaburg and Moyle, 196k; Keast and Welsh, 1968; and Etnier,
1971)- According to Helm (1958), yellow bass also utilized the chironomids
in this area as part of a diet which again included small fish.
White crappie were largely replaced by black crappie in the littoral
zone. Fyke net catches of May, 1969, contained more black crappie than
any other species (2.3% of the total catch). White crappie composed only
1% of these littoral samples. In open water, black crappie were only
caught infrequently and in low numbers. A spatial segregation of these
two species appeared to be present in Lake Wingra. Food habits of both
these fish in the littoral area were not well known.
At dusk most bluegill returned to the littoral zone, but did very little
feeding during the night. Digestion did occur, however, and nutrients
from the limnetic zone were deposited by the bluegills in the littoral
area as feces and urine. Pumpkinseeds also fed almost entirely during
the day (Figure 51; Spencer, 1929). Yellow bass (some of which may have
also traveled to the littoral zone) continued to feed through the night,
although fish were then no longer part of the diet.
These relationships were obviously dependent upon seasonal changes. The
catches per unit effort indicated that the situation in early summer was
probably quite different from that in September. Changes of migration
patterns with the time of year have been recorded for perch (Hasler and
Bardach, 19^9) and for redside shinner (Grossman, 1959a). Changes of
food items from month to month have been reported for bluegill (Gerking,
1962; Seaburg and Moyle, 196*0 , yellow bass (Bulkley, 1970), and white
crappie (Mathur and Bobbins, 1971). Preliminary data from Lake Wingra
also indicated monthly changes in the food of all major panfish species
(Magnuson and Kitchell, 1971).
Conclusion
This study, therefore, points out the great complexity of interaction which
exists between units in the ecosystem. Data extrapolation and ecosystem
modeling should be done remembering the limitations indicated by our
study- Littoral zone and open water habitats should be studied separately
to get a good average of the feeding habits of those fish species which
occupy both areas. These feeding habits, as well as the population structure,
will also change from month to month, thereby requiring sampling over the
109
-------
entire year to obtain an accurate yearly average. Different size classes
of a species must also be studied separately to document the changes in
food preference and habitat which often occur with growth.
The implications of these data are that models of whole lake ecosystems
must account for the mobility of predators in estimating their impact
on prey populations characterized by differing spatial and temporal
susceptibilities to predation.
110
-------
SECTION VIII
ACKNOWLEDGEMENTS
Advice to the participants in this study was rendered by Dr. John J.
Magnuson and Dr. G. Fred Lee. Technical assistance was provided by Ms.
Elizabeth Gardella, Ms. An-Chein Sung, Mr. Hans Zoerb, Mr. Greg Bach,
Ms. Marita Roherty, and Ms. Margaret Henzler. Mssrs. David Carroll,
Gerald Chipman, James Bruins, John Gryskiewicz, and Tom Clark also
contributed their skills to this study. The help of all these people
is gratefully acknowledged. Special thanks should be given to the
students at the Laboratory of Limnology who donated their time to
this project.
In addition to funds from the EPA, this project received funds from the
Eastern Deciduous Forest Biome Project (US/IBP funded by NSF subcontract
3351 under Interagency Agreement AG-199, ^0-193-69 with AEC-ORNL).
Ill
-------
SECTION IX
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SELECTED WATER
RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
1, Report No.
w
4. Title
Biological Investigations of Lake Wingra
7. Author(s)
J. F. Koonce, M. Teraguchi, P. C. Baumann, A. D. Easier
Laboratory of Limnology
University of Wisconsin
i2, Sponsoring, Organization
15. Supplementary Notes
Environmental Protection Agency report number,
EPA-R3-73-044, August 1973.
Report 'Ko.
Organization
ifi 16010 EHE
of Report and
Covered
16 Abstract ft. .... _ n1 . . .,. ., .,. „
An investigation of seasonal changes in species diversity and biomass of
phytoplankton, zooplankton, benthos, and fish in Lake Wingra, Madison, Wisconsin,
was conducted during 1970 and 1971. The objective of this study was to obtain
ecological data on the biological components of an aquatic ecosystem and to utilize
these data along with concurrent chemical data to aid the development of systems
models of nutrient and energy fluxes in lake drainage basins.
Interpretations of data gathered during this study reveal several important
considerations for models of lake systems and future studies of Lake Wingra. Phyto-
plankton associations, for example, appear to be adaptive, self-organizing systems.
Such behavior suggests the possibility to apply optimization principles to phyto-
plankton models. The data suggest, fuitoermore, that optimization analysis can be
based on size particle distributions of the phytoplankton, which, rather than
species, appears to be the basis of phytoplankton categories. Zooplankton and benthos
analyses, on the other hand, indicate that energy and nutrient fluxes may be ade-
quately approximated by simulating only a few species. Finally, results of fish
studies imply that models of whole lake ecosystems must account for the mobility
of predators in estimating their impact on prey populations, which should be char-r
acterized by differing spatial and temporal susceptibility to predation.
*Aquatic Life, Aquatic Algae, Aquatic Crustaceans, Fish *Aquatic
Environment, *Biological Communities, *Theoretical Analysis,
*Succession, Lakes
U, A^-acy »- «-Cte"
7,0. Security C'ia\s;.
(Page)
A^tiuaos gjMgxxjfajafreH, .T. F. Koonce
23. No. (it
Pagfis
22. Price
Send To:
WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D.C. 20240
Universitv of Wisconsin
WHSIC 102 (H£V. JUNE 397ij
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