DYNAMICS OF BACTERIOPLANKTON DURING A PHYTOPLANKTON BLOOM IN THE HIGHARCTIC 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 degree s to 82 degrees N, 45 degrees to 65 degrees E), in July 1995. At the b eginning of July the sea was entirely covered by ice; at the end of Ju ly 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 ad aption 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 bacteri al abundance was 3.6 x 10(5) ml(-1). Mean bacterial production as meas ured by thymidine incorporation was 2.46 pg C l(-1) d(-1) while for le ucine incorporation it was 5.46 mu g C l(-1) d(-1). Total organic carb on varied over a narrow range (0.81 to 1.12 mg l(-1)). Pronounced spat ial variations in microbial parameters between waters surrounding diff erent islands were detectable. At Hayes Island phytoplankton biomass a nd production decreased within 3 wk while bacterial abundance and acti vity measured as thymidine and leucine incorporation increased. During this period the percentage of bacterial (as measured by leucine incor poration) to primary production increased from about 3% to more than 9 5% and the calculated total organic carbon turnover decreased from 258 to 28 d.