Structure of plankton communities in the Dogger Bank area (North Sea) during a stratified situation

Abstract

In May 1990 greatest phytoplankton biomass and production rates were observed within a subsurface maximum around the pycnocline. Fluorescence maxima were found at depths >15 m and often >30 m. Small flagellates dominated the phytoplankton. The vertical distributions of the smaller heterotrophs (bacteria, heterotrophic nanoflagellates and ciliates) were closely related to the fluorescence distribution. Carbon budgets suggest that c15% of phytoplankton production was channelled directly into the larger zooplankton (copepods), while north of the Dogger Bank, c30% was ingested by copepods. Carbon budgets suggest that ciliates could potentially have been of nutritional importance to the copepod population. Copepods possessed the ability to clear a substantial fraction of ciliate production. The high biomass of bacteria, heterotrophic flagellates and ciliates, as well as the fact that primary production of the larger (grazable) phytoplankton did not appear to be sufficient to meet copepod energy requirements, suggest the importance of the microbial loop in carbon cycling in the North Sea during the stratified period. -from Authors