Dynamics of bacterioplankton during a phytoplankton bloom in the high arctic waters of the Franz-Joseph land archipelago

Abstract

Bacterial abundance and activity were followed during a phytoplankton bloom in the high Arctic, the Franz-Joseph Land archipelago (80° to 82° N, 45° to 65° 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°C and salinity between 32 and 35 ‰. Phytoplankton cells exhibited photoinhibition even during incubation periods when maximum radiation was <400 μE m-2 s-1, indicating adaption to a low radiation level. Phytoplankton biomass, averaged over all 5 sampling sites, was 2.2 μg chl a l-1; primary production, at the 50 % radiation level, was 27.3 μg C l-1 d-1 and mean bacterial abundance was 3.6 × 105 ml-1 Mean bacterial production as measured by thymidine incorporation was 2.46 μg C l-1 d-1 while for leucine incorporation it was 5.46 μg 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.