Production of bacterial substrate by marine copepods: Effect of phytoplankton biomass and cell size

Abstract

Laboratory experiments were performed to evaluate the importance of grazing activity of the marine copepod Acartia tonsa for production of substrate for bacteria. Acartia tonsa were fed a range of concentrations of the nanoflagellate Rhodomonas baltica, the diatom Ditylum brightwelli and the dino-flagellate Ceratium lineatum. Regardless of the concentration of R. baltica, no detectable response in bacterial biomass was observed due to grazing. However, when A. tonsa grazed the larger phytoplankton cells of D. brightwelli and C. lineatum, responses in bacterioplankton were observed. It was estimated that approximate 54-69% of the grazed carbon was lost to the surroundings when A. tonsa was feeding on these large phytoplankton species. The laboratory results were applied to a dataset from a coastal temperate ecosystem. This analysis showed that the copepod contribution to the DOC pool was as important as the leakage from the primary producers. It is concluded, that the DOM contribution from copepods will be largest when grazing plankton communities are composed of large species.