Dynamics of bacterioplankton during a phytoplankton bloom in the high Arctic waters of the Franz-Joseph Land archipelago

Bacterial abundance and activity were followed during a phytoplankton bloom in the high Arctic, the Franz-Joseph Land archipelago (80 degrees to 82 degrees N, 45 degrees to 65 degrees E), in July 1995. At the beginning of July the sea was entirely covered by ice; at the end of July the ice coverage was about 50 %. Water temperature varied between -1 and -0.6 degrees C and salinity between 32 and 35 parts per thousand. Phytoplankton cells exhibited photoinhibition even during incubation periods when maximum radiation was <400 mu E m(-2) s-1, indicating adaption to a low radiation level. Phytoplankton biomass, averaged over all 5 sampling sites, was 2.2 mu g chl a l(-1); primary production, at the 50% radiation level, was 27.3 mu g C l(-1) d(-1) and mean bacterial abundance was 3.6 x 10(5) ml(-1). Mean bacterial production as measured by thymidine incorporation was 2.46 pg C l(-1) d(-1) while for leucine incorporation it was 5.46 mu g C l(-1) d(-1). Total organic carbon varied over a narrow range (0.81 to 1.12 mg l(-1)). Pronounced spatial variations in microbial parameters between waters surrounding different islands were detectable. At Hayes Island phytoplankton biomass and production decreased within 3 wk while bacterial abundance and activity measured as thymidine and leucine incorporation increased. During this period the percentage of bacterial (as measured by leucine incorporation) to primary production increased from about 3% to more than 95% and the calculated total organic carbon turnover decreased from 258 to 28 d.