Mesozooplankton grazing under conditions of extreme eutrophication in Guanabara Bay, Brazil

Abstract

The objective of the present study was to quantify mesozooplankton grazing in the eutrophic waters of Guanabara Bay. Mesozooplankton (>200 μm) was dominated by the copepods Acartia lilljeborgi, Acartia tonsa, Parvocalanus crassirostris and Paracalanus furcatus. Dinoflagellates, specifically the species Prorocentrum triestinum, were an important group for mesozooplankton nutrition, being ingested in significant amounts during all experiments. On average, 12.3 ± 2.9 P. triestinum cells were ingested copepod -1 min-1 (other dinoflagellates: 11 ± 8 cells copepod-1 min-1). Filamentous cyanophyceae and nanoplankton were ingested in one experiment each, but the mesozooplankton community generally preferred dinoflagellates to these groups, which were always abundant in the water column. Euglenophyceae were not ingested, although they dominated in one experiment. Mesozooplankton ingested, on average, only 0.2% of the nano- and microplankton biomass per day. The results suggest that grazing was not a controlling process for the nano- and microplankton community in the study area. Addition of zoeae larvae of Chasmagnatus granulata (Decapoda: Brachyura: Grapsidae) in one experiment had a significant effect on the mortality of adult copepods, probably due to a predator-prey relationship.