New Zealand Journal of Marine and Freshwater Research abstracts
Short-term impacts of nutrients, Daphnia, and copepods on microbial
food-webs of an oligotrophic and eutrophic lake
CAROLYN W. BURNS
MARC SCHALLENBERG
Department of Zoology
University of Otago
P. O. Box 56, Dunedin
New Zealand
email (Burns): carolyn.burns@stonebow.otago.ac.nz
Abstract Metazooplankton are potentially
important
links between classical food chains and pelagic microbial food-webs of lakes.
We determined the short-term effects of nutrient enrichment and predation on
the microbial food-webs of oligotrophic Lake Manapouri and eutrophic Lake
Hayes, New Zealand, in summer, by adding calanoid copepods (
Boeckella
hamata Brehm) and cladocerans (
Daphnia carinata King) to
in situ enclosures in the presence and absence of added nutrients
(nitrogen, phosphorus). In Lake Manapouri, bacteria and phytoplankton, but not
picocyanobacteria, increased in response to nutrients;
Daphnia reduced
the densities of phytoplankton, bacteria, heterotrophic nanoflagellates (HNF),
and ciliates; and
Boeckella lowered the densities of HNF and ciliates.
In Lake Hayes, the growth of bacteria, HNF, and phytoplankton, including
eukaryotic picoautotrophs, was enhanced by enrichment;
Daphnia depressed
the concentrations of picoautotrophs and HNF, whereas
Boeckella
decreased the density of ciliates. In both lakes,
Boeckella removed
ciliates at higher rates per unit biomass than
Daphnia. Our study
provides clear evidence of stimulation and inhibition of picoplankton by
nutrients, and of potential consumer-mediated control of microbial food-webs by
crustacean zooplankton.
Keywords microbial food-web; picoplankton; protozoa;
copepods; Daphnia; Boeckella; Lake Manapouri; Lake Hayes; trophic
interactions
M01015
Received 1 February 2001; accepted 23 April 2001
PDF file of entire paper: medium quality (1115K); (scanned from paper original: notes about this process)
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