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99
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TABLE 10. CORRELATIONS BETWEEN ROTIFERS AND SELECTED PHYSICOCHEMICAL VARIA-
BLES. VALUES EXCEEDING .228 ARE SIGNIFICANT AT THE .01 PROBABILITY LEVEL
AND ARE DESIGNATED BY AN ASTERISK ..(*)_
c.
p.
p.
s.
G.
K.
K.
T.
P.
S.
N.
N.
N.
S.
un-ieornis
pemata
vulgaris
stylata
sty lifer1
aoahlearis
longispina
popeellus
dolichoptera
kitina
squcanu la
fo liaeea.
lauTentiae
asymmetrica +
S. lakowitziana
Total Rotifers
Temp.
.488*
.390*
.456*
.329*
.313*
.196
-.174
.032
-.121
-.267*
-.253*
-.456*
-.512*
-.352*
.293*
Chloro. a
-.237*
-.229*
-.208
-.079
-.138
-.075
-.013
.003
.183
.093
.631*
.523*
.441*
.567*
-.065
Conduct .
-.036
.088
.040
.146
.140
.133
.113
-.024
.091
-.040
.085
.098
.336*
.118
.129
N03
.013
-.073
-.104
-.063
-.153
-.105
-.029
-.083
.026
.203
.224
.399*
.378*
.104
-.064
TPO.
4
-.005
-.065
.026
.111
.104
.102
.050
.001
-.062
.286*
.213
.155
.200
.113
.130-
Secchi
.005
-.193
-.099
-.216
-.125
-.120
.149
.061
-.070
.006
-.300*
-.218
-.154
-.229*
-.173
100
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101
-------
SECTION 5
DISCUSSION
HORIZONTAL DISTRIBUTION
A striking difference existed in species compostion and abundance between
Saginaw Bay and the open waters of Lake Huron. Eutrophic indicator species
occurred persistently in Saginaw Bay and occasionally along the western shore
of. Lake Huron. The rotifer community of the central basin had much lower
standing crops and was well-represented by cold stenothermal species. These
differences in composition and abundance can be largely attributed to the
trophic differences between the two areas of the lake and to differences in
depth. Cold stenotherms of the central basin were present in the hypolimnion
during thermal stratification. In Saginaw Bay, no hypolimnion was present so
cold stenotherms were absent.
Littoral genera such as Brachionus r Euchlanis, P^atyias f Lecane.
Monostvla. Lophocharisr and Trj.chotrj.af as well as some members of the Class
Digononta occurred in Saginaw Bay. These littoral species are able to inhabit
the limnetic zone because of morphological structures and behavioral patterns
having preadaptive value to planktonic existence (Pejler 1957s.) Voigt (1901)
and Green (1967, 1972) have observed similar instances where littoral or
benthic species inhabited the limnetic zone in response to algal blooms which
may serve as food or substrate for attachment.
The lower abundance of rotifers in the highly enriched Saginaw River as
compared to nearshore Saginaw 3fy stations may reflect an unfavorable
environment for growth and reproduction caused by the high flushing rate. The
predominance of eutrophic indicator species in the Saginaw River suggests that
these species may be more tolerant of industrial and municipal toxicants (and
possibly algal metabolites) than most open lake forms.
Pronounced horizontal patchiness was evident for some species such as
Svnchaeta kitina and £. stylata (Figures A-35, and A-42). However, during all
cruises, definite spatial or seasonal abundance of species occurred (see
Appendix A). Nearly all .species displayed greatest abundances in Saginaw Bay
and along the coastal area immediately below the mouth of the Bay, indicating
the strong influence of Saginaw Bay on southern Lake Huron waters. This
distribution resembles major circulation features between Saginaw Bay and
southern Lake Huron (Ayers et al. 1956).
The differences in seasonal species composition and abundance suggests
that ths -UtftLnction between inshore and offshore species composition is most
102
-------
highly developed during thermal stratification. In the upper Great Lakes,
stratification usually coincides with maximum rotifer abundance during July.
No sampling occurred during winter months, but Stemberger (197U) found that no
clear distinction existed during winter between nearshore and offshore species
composition in Lake Michigan waters adjacent to Milwaukee Harbor. A more
homogenous species composition probably also occurs between the Saginaw
embayment and Lake Huron waters during winter. This homogeneity in comosition
is probably brought about by more thorough mixing as well as a general
reduction in the number of species that occur in cold water.
All cluster analyses grouped Saginaw Bay .stations along the southeast
coast to southern Lake Huron stations immediately below the mouth of the bay,
reflecting the dominant current. In addition, cluster analyses showed a
distinct inshore community on the east and west coasts of Lake Huron. The
existence of these groups suggests that internal wave dynamics, particularly
Kelvin waves, may cause entrainment of inshore waters. Mortimer (1971)
reported that Kelvin waves may have effects as far as 20 km offshore and that
the currents generated by these waves in Lakes Michigan and Ontario move
parallel to the shore in a counter-clockwise direction. Ayers et al. (1956)
showed that near-shore surface currents in Lake Huron often move in a
counter-clockwise direction, moving to the south along the western shore below
Saginaw Bay, and to the north along the eastern shore.
On the majority of cruises, cluster analyses identified an isolated group
on the western shore of southern Lake Huron.which consisted of only one or two
stations. In most instances, the station(s) comprising these groups were
closely related in Euclidean distance to Saginaw Bay groups, and may represent
remnants of water which may have originated from the Bay.
Clusters based on physicochemical variables revealed station groups with
strong similarities to those obtained from rotifer data. These results may be
indicative of a tight coupling of rotifers to their physicochemical environment.
The Shannon-Wiener diversity index provided no useful information to help
interpret the rotifer data. In fact, index numbers for southern Lake Huron
stations were similar to Saginaw Bay stations for all cruises, even though
great differences in species composition existed between these areas. These
indices were presented to demonstrate their ineffectiveness in dealing with
quantitative rotifer data.
VERTICAL DISTRIBUTION
Discrete depth samples taken throughout the water column appear to
adequately reflect the vertical distribution of rotifers, providing that
metalimnetic collections are made. Rotifers show a distinct maximum in the
metalimnion during thermal stratification. Rotifer stratification was most
strongly developed at deep stations during late June, July, and August (Cruises
5, 6, and 7). In remaining cruises pronounced species stratification was not
evident.
The cold stenothermal species which occur in the hypolimnion may also
affect cluster analysis of distribution data. The abrupt decline in total
103
-------
abundance in the hypolimnion, when averaged for the entire column, effectively
decreases the calculated mean standing crop. This effect is a function of
depth and varies with the number of samples taken in the hypolimnion. If
samples had been taken only from the epilimnion and metalimnion, the
differences in abundance between inshore and offshore stations during the
thermal stratification period might not have been as pronounced. However,
Stemberger (197*0 was able to show strong inshore-offshore differences in
abundance with samples collected at a single depth (2 m).
Abundance at 2 m was also strongly influenced by weather conditions
(Stemberger 197*0. Wave turbulence usually distributed rotifers more evenly
throughout the epilimnion, whereas during calm weather, rotifers usually
avoided near-surface waters. Thus, multiple depth samples avoid problems
associated with wind-generated turbulence.
4
In addition to thermal stratification and wind-generated turbulence,
vertical stratification of species may be influenced by a variety of other
factors. These factors include food, temperature, light, oxygen, and
predator-prey relationships with other plankters (Fairchild et al. 1977).
Peak abundance of Polvarthra vulgaris was usually above the peak of
Keratella cochlearis. Discrete sampling may have missed these peaks on some
occasions where the distribution of these species was not distinct during
thermal stratification. Stemberger (197*0 reported similar findings for Lake
Michigan. Pejler (1957J2.) suggested that differences in light preferences
between these two species may account for this distribution.
Conochilus unicornis showed a strong tendency to predominate in the
epilimnion and near-surface waters. However, during isothermal conditions, the
species occurred from the surface to the bottom. Stemberger (197*0 noted
similar near-surface distribution for the species. Fairchild et al. (1977)
reported that a population of £.. unicornis in Lancaster Lake, Michigan was
concentrated near the surface at night, but was more uniformly distributed in
the water column in the daytime. Shindler and Noven (1971) found that the
species had a maximum both at the surface and at a depth of *» m in Lake 122,
Ontario. Distribution of £.. unicornis. £. vulgaris. £_. remata. Synchaeta
stvlata. and Gastroous stvlifer correlated significantly with water
temperature. Distribution of these species was also strongly intercorrelated.
Svnchaeta kitina occurred in the hypolimnion during July and August but
was present throughout the water column in June. Larsson (1971) reported .£.
kitina in the epilimnion of Lake Blankvatn, Norway during the summer. In Lake
Huron the species displayed a significantly negative correlation with
temperature, indicating a cold water preference.
The cold stenotherms Notholca foliacea. Ji- laurentiae. Q. souamula.
Svnchaeta asvmmetrica. and .£. lakowitziana were more uniformly distributed
throughout the water column during spring prior to thermal stratification.
During thermal stratification, these species occurred in the lower depths of
the metalimnion and hypolimnion, indicating their cold water preference. Their
distribution was positively correlated with chlorophyll .a. Chlorophyll .a
biomass displayed a maximum in the hypolimnion, thus accounting for the high
104
-------
correlation coefficient. These cold forms were not as strongly intercorrelated
as the warm water species.
INDICATOR VALUE OF ROTIFERS
Consistent presence of certain species in waters of extreme trophic
conditions suggests they have some value in lake bioraonitoring studies. The
species most consistent as eutrophic indicators in Lake Huron were the warm
stenotherms A"Waec-psis fissar Brachionus spp., Conochi^oides dossuarius, and
Keratella cochlearis f. tecta. In addition, littoral genera, mainly warm
stenotherms, which occur in the limnetic environment may be considered as
indicators of eutrophy (Gannon and Stemberger 1978).
Cold stenothermal species which have potential as oligotrophic indicators
were Notholca laurentiae and Synchaeta asymmetrica. However, the presence of
these species may be more indicative of their preference for the cold waters of
the hypolimnion than a reflection of actual trophic conditions. During winter
months, these species occur in nutrient-enriched embayments (Stemberger 197*0 >
thus precluding their designation as oligotrophic indicators. Only after we
acquire further knowledge of the ecology of indicator species can we
realistically evaluate their importance in lake monitoring studies.
Certain species which exhibited limited distribution in Lake Huron were
related empirically to the physicochemical environment through cluster
analysis. However, such correlative data based on distributional inferences
did not explain the presence of indicator species. Reasons for their
occurrence were undoubtedly complex and related not only to physicochemical
conditions but also to seasonal distribution, diet, and competition or
predation with other zooplankters. Complications may have also resulted from
relative differences in tolerance of various species to toxic industrial or
municipal pollutants and algal metabolites.
Qualitative presence-absence data on indicator species is not always
useful in Lake Huron and other large water bodies. Massive water movements can
transport species to environmentally different areas of the lake where they
normally do not actively reproduce. Their presence in such waters may be
without indicator value. A judgement can be made on the significance of the
indicator's presence by comparing its abundance and composition percentage to
stations with similar physicochemical conditions. If the indicator is absent
from similar stations and its abundance and composition percentage is low,
occurrence at a single station or a few stations is probably accidental.
However, if the species is present at most stations with similar
physicochemical conditions, its presence may be of indicator value even though
it displays low abundance and composition percentage.
A major advantage of cluster analysis was that it eliminated the need to
make subjective decisions on the presence of indicator species. With cluster
analysis the entire rotifer community was evaluated, not merely one or two of
its components.
105
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REFERENCES
Ahlstrom, E. H. 19*10. A Revision of the Rotatorien Genera Brachionus and
Platyias with Descriptions of One New Species and Two New Varieties.
Bull. Amer. Mus. Nat. Hist. 77:143-184.
Ahlstrom, E.H. 1943- A Revision of the Rotatorien Genus KerateJ.la with
Descriptions of Three New Species and Five New Varieties. Bull. Amer.
Mus. Nat. Hist. 80:411-457.
Ayers, J. C., D. V. Anderson, D. C. Chandler, and G. H. Lauff. 1956.
Currents and Water Masses of Lake Huron. Univ. Michigan, Great Lakes
Res. Inst., Tech. Paper No. 1. 99 p.
Davis, C. C. 1966. Plankton Studies in the Largest Great Lakes of the
World, with Special Reference to the St. Lawrence Great Lakes of North
America. Univ. Michigan, Great Lakes Res. Div., Publ. No. 14:1-36.
Fairchild, G. W., R. S. Stemberger, L. C. Escamp, and H. A. Debaugh. 1977.
Environmental Variables Affecting Small Scale Distribution of Five
Rotifer Species in Lancaster Lake, Michigan. Int. Revue ges. Hydrobiol.
62:511-521.
Gannon, J. E. and S. A. Gannon. 1975. Observations on the Narcotization of
Crustacean Zooplankton. Crustaceana. 28:220-224.
Gannon, J. E. and R. S. Stemberger. 1978. . Crustacean and Rotifer Plankton
as Water Quality Indicators. Trans. Amer. Microsc. Soc. 97(1):16-35.
t
Green, J. 1967. Associations of Rotifers in the Zooplankton of Lake Sources
of the White Nile. J. Zool. Lond. 151:343-378.
Green, J. 1972. Latitudinal Variation in Associations of Planktonic
Rotifera. J. Zool. Lond. 167:31-39.
International Joint Commission. 1977. The Waters of Lake Huron and Lake
Superior, Vol. I. Summary and Recommendations. IJC, Upper Lakes
Reference Group, Windsor, Ontario. 236 p.
Larsson, P. 1971. Vertical Distribution of Planktonic Rotifers in a
Meromictic Lake; Blankvatn near Oslo, Norway. Norw. J. Zool. 19:47-75.
Mortimer, C. H. 1971. Large-scale Oscillatory Motions and Seasonal
Temperature Changes in Lake Michigan and Lake Ontario. Univ.
Wisconsin-Milwaukee, Center .Great Lakes Studies, Spec. Rept. No. 12,
Pt. 1 (text), 111 p., Pt. 2 (illustrations), 106 p.
106
-------
Nauwerck, A. 1972. Notes on the Planktonic Rotifers of Lake Ontario.
Canada Cent. Inland Waters, Great Lakes Biolimnol. Lab. 37 p.
(unpublished).
Pejler, B. 1957s.- Taxonomical and Ecological Studies on Plankton
Rotatoria from Central Sweden. K. Svenska Vetenskakad. Handl., No. 7-
52 p.
Pejler, B. 1957.b_- On Variation and Evolution in Planktonic Rotatoria.
Zool. Bidr. Uppsala. 32:1-66.
Pielou, E. 1975. Ecoloical Diversity. Wiley, New York. 165 pp.
Ruttner-Kolisko, A. 197*1. Plankton Rotifers, Biology and Taxonomy. Die
Binnengewasser. 26(1) suppl. 146 pp.
Schelske, C. L. and J. C. Roth. 1973. Limnological Survey of Lakes
Michigan, Superior, Huron and Erie. Univ. Michigan, Great Lakes Res.
Div., Publ. No. 17. 108 pp.
Schindler, D. W. and V. Noven. 1971. Vertical Distribution and Seasonal
Abundance of Zooplankton in Two Shallow Lakes of the Experimental Lakes
Area, Northeastern Ontario. J. Fish. Res. Board. Can. 28:245-256.
Sneath, P. H. A. and R. R. Sokal. 1973. Numerical Taxonomy: The Principles
and Practices of Numerical Classification. W. H. Freeman,
San Francisco.
Stemberger, R. S. 1973- Temporal and Spatial Distributions of Planktonic
Rotifers in Milwaukee Harbor and Adjacent Lake Michigan. Univ.
Wisconsin-Milwaukee, M.S. Thesis. 55 pp. (unpublished).
Stemberger, R. S. 1974. Spatial and Temporal Distribution of Rotifers in
Milwaukee Harbor and Adjacent Lake Michigan. Proc. 17th Conf. Great
Lakes Res., Internat. Assoc. Great Lakes Res. pp. 120-134.
Stemberger, R. S. 1976. NothoJ.ca laurentiae and £. michiaanens j.sf New
Rotifers from the Laurentian Great Lakes Region. J. Fish. Res. Board
Can. 33:2814-2818.
Voigt, M. 1904. Die Rotatorien und Gastrotrichen der Ungebung von Plon,
Plon Forsch.-Ber. 11:1-180.
Voigt, M. 1957- Rotatoria. Die Radertiere Mitteleuropas, 2 vols.,
Borntraeger, Berlin. 508 pp.
Watson, N. H. F. 1974. Zooplankton of the St. Lawrence Great Lakes-Species
Composition, Distribution, and Abundance. J. Fish. Res. Board Can.
31:783-794.
107
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Williams, L. G. 1962. Plankton Population Dynamics. Nat. Water Qual.
Netwk., U.S. Publ. Health Serv., Publ. No. 663, Suppl. 2, 90 pp.
Williams, L. G. 1966. Planktonic Rotifers of Major Waterways of the United
States. Limnol. Oceanogr. 11:83-91.
108
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APPENDIX A
COMPUTER-PLOTTED HORIZONTAL DISTRIBUTION OF ROTIFER ABUNDANCE
109
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110
-------
Ill
-------
112
-------
113
-------
114
-------
115
-------
116
-------
117
-------
118
-------
119
-------
120
-------
121
-------
122
-------
123
-------
124
-------
125
-------
126
-------
127
-------
128
-------
129
-------
130
-------
131
-------
132
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3
£
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cr
TO
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fe:
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134
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135
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138
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139
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140
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141
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0)
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147
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148
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149
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150
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151
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152
-------
153
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154
-------
155
-------
156
-------
APPENDIX B
STATION BEARINGS
Southern Lake Huron Stations
Station
no.
01
02
03
OM
05
06
07
08
09
10
11
12
13
14
15
16
17
Lat. N. Long. W.
M3°09.8' 82°27.9'
M3014.6' 82°30.0'
i^lM.e* 82°25.4'
U3°14.6' 82°17.V
43°1M.6' 82°09.2'
43°14.6' 82°04.V
43°21.0* 81°57.3'
43°27.V 81°50.3'
43°33.8' 81°M3.2'
M3°33.9' 81°48.2'
H3°33.9« 82°00.2'
U3°33.9' 82°1M.8'
43°33.9f 82°22.0'
43°33.9' 82°33-3'
H3°^2.^ 82°3M.8»
M3°57.6' 82°36.6«
44°OM.5' . 82°36.6'
Station
no.
18
19
20
^ 21
22
23
2M
25
26
27
28
29
30
31.
32
33
3M
Lat. N. Lona. M.
M4°05.6« 82°23.5'
4M°06.7' 82°10.4«
MU°07.8' 81°57.0'
44°12.0' 82°13.0'
MU°13.0' 82°27.0'
4M°14.0' 82°39.0'
4«t°l6.3' 82°55.0'
44°20.1' 83°05.7'
4n°23.9' 83°16.2'
M4°30.0' 83°15.8'
4H°28.7' 83°02.6'
4M°27.5' 82°U9.1»t
44°26.5' 82°tO.O'
4402l».9' 82°26.0.'
W°23.0' 82°16.0'
14°22.5' 82°29.9'
MM°21.0' 82°52.5'
157
-------
Station
no.
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
Saginaw
Station
no.
01
02
03
04
05
Lat. N,
44°20.1'
44°10.9'
44°08.5'
44°06.0»
44°03.6»
44°01.2'
44°03.3'
44°06.2»
44°09.0»
44°11.7'
44°14.7'
44°19.7f
44°16.5'
44°13.2'
44°09.9'
Bay Stations
Lat. N.
43°38.0'
43°43.0''
43°51.4'
44°06.5'
43°40.3'
Lone. Wt
83°05.7'
83°31.2-
83°25.8-
83°20.6'
83°15.3'
83°09.9'
83°02.9'
83°08.9'
83°14.6»
83°20.6'
83°26.3'
83°18.8'
83°12.0'
83°05.4'
82°58.9f"
Lone . W*.
83°51.0'
83°53.3'
83°54.0'
83°31.8'
83°51.8'
Station
no.
50
51
52
«
53
54
55
56
57
58
59
60
60 A
61
62
Station
no.
06
07
08
09
10
Lat. N.
44°06.7'
44°01.4'
43°50.7'
43°50.7'
43°50.7'
43°50.7'
43°50.7»
43°50.7'
43°42.3f
43°33.9'
43°24.3'
43°20.0f
43°14.6'
43°10.0'
Lat. N.
^3°39.7'
43°40.3'
43°39.8-
43°39.1'
43°41.4'
T /"*IKI rr U
LiUn^ i W .
82°52.2»
82°40.2'
82°35.6-
82°30.0'
82°16.5'
82°03.1'
81°50.0'
81°45.0«
81°52.5'
82°00.2f
82°08.6'
82°15.5'
82°17.4'
82°21.5f
*
T f^v\ ft U
j-tOn^ | w .
83°50.3'
83°50.4'
83°48.3'
83°50.9'
83°49.0'
158
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Station
nOj
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
Lat, HL
43°39.8'
43°38.3'
43°41.0'
43°42.7'
43°44.8'
43°46.8'
43°42.0'
43°44.3'
43°46.9'
43°50.0»
43°39.9'
43°49.4'
43°48.4'
43°46.9'
43°42.0'
43°45.5f
43°48.9'
43°51.5'
'43°54.9'
43°58.0'
43°56.0'
43°54.5'
43°50.1'
43°53.0'
43°58.8'
Lone. W.
83°44.0'
83°39.5'
83°46.5f
83°38.8»
83°51.4'
83°54.8'
83°44.0'
83°46.3'
83°48.5'
83°51.8'
83°52.5'
83°38.4»
83°44.5f
83°39.V
83°37.0'
83°31-3'
83°36.8'
83°40.3'
83°44.6'
83°48.8»
83°40.4'
83°31.6'
83°29-8'
83°23.8'
83°34.8'
Station
no.
36
37
38
39
40
41
42
43
44
45
'46
47
48
49
50
51
*
52
53
54
55
56
57
58
59
Lat. N.
44°01.3'
44°00.9'
43°58.1'
43°55,7'
44°04.7'
43°38.8«
44°03-7'
44°01.2'
43°59.0'
44°11.0'
44°00.3'
44°16.5'
44°14.5'
44°12.4'
44°10.3f
44°07.4'
44°04.3'
44°03.3'
43°36.8-
43°36.1'
43°44.0'
44°08.0f
44°03.2f
43°40.4'
Lone. W.
83°39.5'
83°32.5'
83°24.9'
83°20.0'
83°34.8'
83°51.0'
83°26.3f
83°20.6'
83°16.5'
83°24.0'
83°08.6'
83°29-5f
83°28.3'
83°23.0'
83°17.7'
83°10.2'
83°05.0'
82°59.8'
83°51.4'
83°53.5'
83°37.5f
83°24.0'
83°13.0'
83°53-9'
159
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
1. REPORT NO.
EPA-600/3-79-085
2.
4. TITLE AND SUBTITLE
Spatial and Seasonal Structure of Rotifer Communities
in Lake Huron
7. AUTHOR(S)
Richard S. Stemberger, John
Bricker
E. Gannon, and F. James
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Biological Station
The University of Michigan
Pellston, Michigan 49769
*
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Duluth, Minnesota 55804
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
August 1979 issuing date
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
1BA769
11. CONTRACT/GRANT NO.
803086 and 803037
13. TYPE OF REPORT AND PERIOD COVERED
Final April 1974-Nov. 1977
14. SPONSORING AGENCY CODE
EPA-600/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report presents comprehensive data on species composition and distribution
of planktonic rotifers in Saginaw Bay and southern Lake Huron from April to November,
1974. Rotifer species composition and abundance differed greatly between Saginaw Bay
and open Lake Huron waters. Through cluster analyses, these differences were
empirically related to the physicochemical environment. The results of these analyses
suggest that rotifers are valuable organisms in water quality assessment studies.
Several species which displayed distribution limited to eutrophic Saginaw Bay stations
or to oligotrophic offshore Lake Huron stations were potentially useful as environ-
mental indicators. Based on rotifer data, the greatest impact of Saginaw Bay waters
on Lake Huron occurred along the western shore of southern Lake Huron below the mouth
of the bay. In general, inshore stations of southern Lake Huron displayed greater
rotifer abundances than mid-lake stations.
Certain rotifers displayed distinct epilimnetic of hypolimnetic vertical
distributions. However, maxima of total rotifer abundance usually occurred in the
vicinity of the metalimnion. Wind-generated turbulence often distributed rotifers
more evenly in the epilimnion.
17.
a. DESCRIPTORS
KEY WORDS AND DOCUMENT ANALYSIS
b.lDENTIFIERS/OPEN ENDED TERMS
.Plankton Bloom and Zooplankton Lake Huron
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
20. SECURITY CLASS (This page)
UNCLASSIFIED
c. COSATI Field/Group
57H
21. NO. OF PAGES
178
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
160
4II.S. GOVERNMFNT PRINTING OFFICE: 1979:657-060/5376
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