United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
Research and Development
EPA-600/S3-84-025 Mar. 1984
Project Summary
The Limnetic Zooplankton of
Lakes in Katmai National
Monument, Alaska
Kenneth E. Biesinger
The limnetic zooplankton in lakes of
the Naknek River system in south-
western Alaska were sampled exten-
sively during 1962-63. The numerically
dominant forms of limnetic zooplankton
were Diaptomus sp., Cyclops sp.,
Daphnia longiremis, Bosmina coregoni.
Kellicotia longispina. and Conochilus
unicornis. Some littoral and benthic
forms were also identified but not
studied in detail. Species composition
and the relative abundance of each
species differed considerably among the
four major lakes and also among basins
within the lakes. These differences were
consistent with limnological differences
in physical and chemical characteristics.
Iliuk Arm contains glacial flour from
glaciers and pumice from volcanic activ-
ity and had the lowest standing crop.
South Bay of Naknek Lake receives
turbid water from Iliuk Arm and clear
water from Brooks Lake and was more
productive than Iliuk Arm. but much
less than other basins in Naknek Lake
and the other lakes. The clear and
warmer waters of the North Arm of
Naknek Lake had the highest standing
crop. Seasonal pulses of zooplankton
occurred in mid-July and again, in late-
August. Annual changes were also
studied and in 9 out of 10 comparisons,
zooplankton were more abundant in
1963 than in 1962. Die! migrations of
groups of zooplankton and individual
dominant species were also examined.
Cladoceransand rotifers ascended near
the surface waters at night, but de-
scended to deeper depths during the
day.
This Project Summary was developed
by EPA's Environmental Research Labo-
ratory, Duluth, MN, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report order-
ing information at back).
Introduction
The sockeye salmon (Oncorhynchus
nerka) resource of Bristol Bay in south-
western Alaska is one of the most valu-
able in the world. These anadromous fish
spawn in lakes and rivers, then the young
spend from 1 to 3 years in the lakes before
migrating to the Pacific Ocean. While in
"nursery" lakes the young are pelagic
zooplankton feeders but relatively little is
known about the zooplankton of Alaskan
sockeye nursery lakes. This project re-
ports the occurrence, distribution and
abundance of zooplankton species during
the growing season of June to October
over a two-year period.
In 1962 and 1963 the limnetic zoo-
plankton were studied in four lakes of the
Naknek River drainage system in Katmai
National Monument on the Alaska Penin-
sula. The lakes were Coville, Grosvenor,
Brooks and Naknek. Naknek Lake hasfive
relatively distinct basins which were
studied individually. These lakes and
basins were formed or modified by glaci-
ation, and the watersheds are mainly
sedimentary rock with some igneous
outcrops and volcanic ash deposits.
Hardy Plankton Samplers were used
for sampling at six depths from 1 to 35
meters. Zooplankton collected were pre-
served in 3% formalin for counting and
identification. Identification was done
under magnification. Limnetic samples
from the four lakes and their basins
yielded five species of Copepoda, five
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species of Cladocera and ten species of
Rotifers. The dominant limnetic forms
common to all lakes were Diaptomus sp.,
Cyclops sp.,Daphn/a longiremis, Bosmina
coregoni, Kellicotia longispina and Con-
ochilus unicornis. Rotifers were more
abundant in the uppermost lake, Coville,
in July (nearly half the zooplankton).
Cladoceranswere most important numer-
ically in Grosvenor Lake in July and
August. In all other lakes and Naknek
basins, copepods dominated the zooplank-
ton.
Dominance of one species of copepod,
cladoceran or rotifer was evident in
almost all samples. Ordinarily one species
in each group constituted the bulk of the
sample. For "copepods it was usually
Cyclops sp.; for cladocerans, usually
Daphnia longiremis; and for rotifers, usu-
ally Kellicotia longispina or Conochilus
unicornis.
Differences in limnological conditions
were reflected in differences in zooplank-
ton. Northwest Basin of Naknek is a
shallow bay, which, sampled in July
during a heavy Anabaena sp. bloom,
yielded a very low standing .crop of
zooplankton dominated by Bosmina cor-
egoni. Iliuk Arm receives glacial flour,
pumice and silt with an average secchi
disc reading of about 0.5 meters. Standing
crops were low at all readings, and were
dominated by copepods. South Bay re-
ceives turbid water from Iliuk Arm and
clear water from Brooks. Zooplankton
were moreabundantthan in Iliuk Arm but
less abundant than in any other area
sampled. North Arm water was clear and
warm, and had the largest standing crops
of zooplankton in the lakes and basins
sampled. Copepods dominated at most
stations, although cladocerans and roti-
fers were also important. Coville Lake is
warm and shallow. The standing crop
was abundant, and was dominated by
Cyclops, although Diaptomus sp., and
rotifers were well represented. Grosvenor
Lake is deep and slightly colder than the
other lakes and basins. It is fed from both
ends and standing crop varied throughout,
from very abundant to low where turbid
water was received. Seasonal variations
in standing crop were noted in some of
the lakes. The highest number of zoo-
plankton occurred in July, and a second
less abundant pulse was seen at the
beginning of September. Seasonal
changes in species composition were
seen in the same lakes Copepods com-
prised a large percent of the total plankton
at all times. Cyclops sp. decreased and
Diaptomus sp. increased from July to
October. Cladocerans and rotifers exhib-
ited vertical diel migrations. Large propor-
tions of these zooplankton ascended near
the surface waters at night and descended
to depths of 5 to 1 5 meters during the day.
The diurnal descent went deeper in clear
Brooks Lake than in turbid Naknek Lake.
Zooplankton abundance and species com-
position differed between basins within
lakes, between lakes within seasons, and
between seasons.
Conclusions
Relatively clear lakes or basins were
the most productive of zooplankton. Water
turbid from glacial flour and pumice
yielded low standing crops. The domi-
nance of one species of copepod, clado-
ceran or rotifer was evident in nearly all
areas studied. Copepods were usually
more numerous than any other group.
Diel vertical migrations were observed in
cladocerans and rotifers.
The EPA author Kennetth E. Biesinger is with the Environmental Research
Laboratory, Duluth, MN 55804.
The complete report, entitled "The Limnetic Zooplankton of Lakes in Katmai
National Monument, Alaska," (Order No. PB 84-153 758; Cost: $8.50, subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA author can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
6201 Congdon Blvd.,
Duluth, MN 55804
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