Uncoupling of bacteria and phytoplankton during the austral spring bloom in Gerlache Strait, Antarctic Peninsula

The response of the bacterial (Bacteria and Archaea) community to vernal ph ytoplankton blooms was examined over a grid of stations in Gerlache Strait, Antarctic Peninsula, during the RACER II program (29 October to 26 Novembe r 1989). Total bacterial production (0.13 to 10.6 mg C m(-3) d(-1)). based on the incorporation of H-3-leucine into protein, increased with increasing chlorophyll a (chl a) concentration. Bacterial cell-specific growth rate a lso increased with increasing primary production among stations. Neverthele ss, bacterial cell abundance was greatest at the sites that had the lowest chi a concentrations, and declined wherever phytoplankton bloomed. Early bl oom communities had few nanoprotist grazers; grazing was undetectable by th e Landry-Hassett dilution method during this period. Fully developed bloom communities (chl a > 10 mg m(-3)) had a profusion of nanoprotist grazers (m edian 3000 cells ml(-1)). Despite relatively low ingestion rates per indivi dual (0.9 bacteria cell(-1) h(-1)), the abundant grazing community kept bac terial biomass very low in Gerlache Strait, to the point that the metabolis m of the pelagic bacterial surface community was only a minor fraction of t otal ecosystem metabolism. Grazing was the apparent cause, although biomass limitation of the bacteria due to lack of resources (e.g. bioavailable dis solved organic matter) may be the ultimate cause of the uncoupling of bacte rial and phytoplanktonic communities in these habitats.