Pelagic microbial heterotrophy in response to a highly productive bloom of the marine haptophyte Phaeocystis antarctica in the Amundsen Sea Polynya
Williams, Colin Malcolm
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Bacteria play a significant role in elemental cycling in the ocean. The Amundsen Sea Polynya International Research Expedition (ASPIRE) sought to better understand how heterotrophic bacteria respond to intense austral summer blooms, dominated by the haptophyte Phaeocystis antarctica. Bacterial production (BP) rates were measured using 3H-leucine incorporation and bacterial respiration (BR) was estimated with carbon dioxide changes in dark-bottle 48-hr incubations. When combined, BP and BR yield average bacterial growth efficiencies (9.6% ± 0.6 with a range from 5 to > 20%, depending on assumptions and conversion factors). One explanation for low BGE is low macro- and micro-zooplankton abundances in the upper 100 m compared to oligotrophic systems, resulting in reduced DOM flux to the bacteria from minimal grazing of organic rich P. antarctica. Bacterial production correlates with particulate organic matter concentration (R2=0.76), and size fractionation experiments show 70% of BP is particle-associated. Exoenzyme hydrolysis also correlates with high POM concentrations, suggesting strong particle-association of bacterial activity in the Amundsen Sea Polynya.