Plankton community structure and carbon cycling off the western coast of Greenland, with emphasis on sources of DOM for the bacterial community

The plankton community was investigated in Disko Bay, West Greenland, in August 1998, and the importance of phytoplankton versus zooplankton in providing substrates for the bacterial community was evaluated. Two distinct plankton communities were observed. In the stratified north side of the bay the surface water was nutrient depleted and high biomasses of phyto-, zoo- and bacterioplankton were observed; in contrast, the south side had less pronounced stratification, higher concentrations of nutrients and lower plankton biomass levels. Accompanying differences in the relative importance of the different sources of substrates for the bacteria were indicated from carbon flow scenarios and correlations between bacterial production and plankton biomass. These showed that the protozooplankton were most important in the north, while in the south the contributions from phytoplankton and zooplankton to the bacteria substrate pool were equal. Overall, the ciliates and heterotrophic dinoflagellates played a key role as grazers and in providing substrates for the bacteria in this arctic ecosystem.