SS3.18 Habitat Coupling in Lakes
Date: Thursday, June 13, 2002
Time: 11:30:00 AM
Location: Esquimalt
 
MehnerT, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, mehner@igb-berlin.de
Schulz, M, , Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany, michael.schulz@igb-berlin.de
Kasprzak, P, , Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Neuglobsow, Germany, daphnia@igb-berlin.de
Koschel, R, , Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Neuglobsow, Germany, rko@igb-berlin.de
 
SPATIO-TEMPORAL COUPLING IN A HOMOGENEOUS ENVIRONMENT: VARIABILITY OF TROPHIC IMPACT OF FISH IN THE PELAGIC ZONE OF A DEEP OLIGOTROPHIC LAKE
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The use of appropriate scales is crucial to the evaluation of trophic impact of fish populations. Lake-wide studies on predation and nutrient excretion often suffer from inadequate spatial and temporal resolution of fish density estimates. Even in a homogeneous environment like the pelagic area of a lake, fish migrations can couple different basins or depth strata. Here we determined density, biomass and growth of the dominant pelagic planktivore, vendace, by monthly hydroacoustic surveys in an oligotrophic lake. In combination with bioenergetics modelling, we calculated zooplankton predation and phosphorus excretion by the vendace population. Fish density and growth differed between the four basins of the lake such that the trophic impact of vendace showed similar spatial variability. In addition, we observed heterogeneity in the use of hypolimnetic depth strata by vendace during the season. Zooplankton biomass and SRP-concentration measured in one of the basins indicated that vendace may have suppressed their prey during late summer and autumn. By contrast, the calculated P-excretion by the fish was negligible compared with the lake-internal SRP-concentration and the external P load to the lake.