CS35 Trophic Dynamics
Date: Friday, June 14, 2002
Time: 9:15:00 AM
Location: Carson A
 
KairesaloT, University of Helsinki, Lahti, Finland, timo.kairesalo@helsinki.fi
Kornijow, R, , University of Agriculture, Lublin, Poland, rkorn@ursus.ar.lublin.pl
Vakkilainen, K, , University of Helsinki, Lahti, Finland, kirsi.m.vakkilainen@helsinki.fi
Horppila, J, , University of Helsinki, Helsinki, Finland, jukka.horppila@helsinki.fi
Luokkanen, E, , University of Helsinki, Lahti, Finland, eira.luokkanen@vyh.fi
 
MECHANISMS BEHIND THE STABILITY OF CLEAR-WATER STATE IN LAKES: INTERACTIONS BETWEEN ELODEA, ROACH AND ITS PREY COMMUNITIES
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We tested experimentally (using 5 m2 field mesocosms) two hypotheses: (1) that trophic cascade caused by planktivorous fish via predation on crustacean zooplankton can be hampered by submerged macrophytes (Elodea canadensis); and (2) that zoobenthos and epiphytic macroinvertebrates as alternative prey can soften the predation pressure of fish on zooplankton, which mechanism should stabilize the system. Elodea-beds provided a favourable and safe habitat for small cladocerans and epiphytic macroinvertebrates but not for Daphnia or benthic animals. Filter-feeding crustaceans were able to control phytoplankton even though their grazing rate among macrophytes was reduced. Roach (Rutilus rutilus) increased phytoplankton biomass. When fish faced shortage of cladoceran food, or had difficulties in finding them within dense Elodea-beds, they switched their diet to detritus, epiphytic algae, macrophytes and macroinvertebrates. In conclusion, our first hypothesis was supported while the second one only partly. Epiphytic macroinvertebrates turned out to be of minor importance for fish and hence also for the trophic cascade impact on water clarity.