MEPS 132:47-56 (1996)  -  doi:10.3354/meps132047

Size-specific grazing by the coastal zooplankton community in the northern Baltic was studied during the summer. Experiments on grazing by mesozooplankton and metazoan microplankton, fractionated by filtration through 140 and 40 um mesh, were carried out in the laboratory with two ^(14)C-labelled algae cultures, Brachiomonas submarina (size 10 to 15 um) and Pavlova lutheri (size 4 to 6 um). Zooplankton grazing on 2 size groups (>10 um and 2 to 10 um) of naturally occurring phytoplankton was also estimated. Mesozooplankton was composed of copepods Acartia spp. and Eurytemora affinis, the cladoceran Bosmina longispina maritima, rotifers Synchaeta spp. and meroplankton; metazoan microplankton consisted mostly of copepod nauplii and rotifers. Mesozooplankton had greater biomass and higher community clearance rate (CCR) when feeding on B. submarina than had metazoan microplankton. For mesozooplankton, the CCR on B. submarina was dependent on successional changes of total biomass of copepods and cladocerans, whereas the CCR on P. lutheri was variable, probably because of less efficient grazing by copepods. The CCR of metazoan microplankton on the test algae was variable and unpredictable, possibly because of the varying biomass specific clearance rates (BSCR) of rotifers and different naupliar stages of copepods. The mean CCR on P. lutheri did not differ between mesozooplankton and metazoan microplankton, because of the higher mean BSCR of the latter. The daily grazing of mesozooplankton on naturally occurring phytoplankton was estimated to average 9% of the daily primary production when rotifers, meroplankton or copepods were predominant, but 42% when B. longispina maritima was predominant. The integrated grazing of the mesozooplankton and metazoan microzooplankton was estimated to account for 13 and 6%, respectively, of primary production during summer.

Zooplankton grazing . Northern Baltic Sea . Tracer feeding technique