Experimental study of size‐selective phytoplankton grazing by a filter‐feeding cichlid and the cichlid's effects on plankton community structure1

Abstract

In laboratory experiments, feeding rates of small (40–61‐mm standard length, SL) and large (98–143‐mm SL) Galilee Saint Peter’s fish ( Tilapia galilaea ) on phytoplankton and zooplankton increased as a function of particle size, leveling off when particle size exceeded 6–10 µ m. Fish had high feeding rates on zooplankton, the large dinoflagellates Peridinium cinctum and Peridinium elpatiewsky, and a few nanoplankton, but most species of nanoplankton were consumed at lower rates. To examine community‐level effects of the fish, we conducted two 7‐d outdoor tank experiments with six fish‐density treatments ranging from 0 to 400 g m −3 . Crustaceans, rotifers, and Peridinium spp. declined as functions of fish density, but nanoplankton abundance was highest at intermediate fish densities. Suppression of Peridinium spp. by fish resulted in a reduction of total chlorophyll and gross primary production.