JGOFS: Carbon Flow Through The Microbial Loop in the Arabian Sea: Heterotrophic Nanoplankton Growth Rates and Picoplankton Grazing

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9310693 Caron Pico-sized organisms (organisms 0.2 - 2.0um) constitute a very significant portion of the production and living biomass of oceanic plankton communities. Primary production by photosynthetic microorganisms in these size classes (cyanobacteria, prochlorophytes, some small eukaryotic algae) are major contributors to total primary production in the plankton. Likewise, recent evidence suggests that bacteria may be the largest single repository of living biomass in many pelagic ecosystems. Collectively, the activities and fates of these assemblages strongly influence the flow of energy and biologically reactive elements in the ocean. Because these assemblages are generally smaller than the particles captured efficiently by metazoan zooplankton, the repackaging of these microorganisms into larger consumers is a fundamental step for their incorporation into pelagic food webs. Protistan consumers in the nanoplankton size range (largely flagellated protozoa ~20 um in size) play a pivotal role in plankton communities as the primary consumers of picoplankton assemblages (both bacteria and phototrophs). Yet, there is still little information on the rates of consumption of bacteria and small phytoplankton in oceanic environments, or on the growth and production rates of protistan consumers. As a part of the U.S. Joint Global Ocean Flux Study in the Arabian Sea, Dr. Caron will perform experiments to investigate the grazing rates and production of nanoplanktonic consumers from the surface waters and O2 minimum layer of this oceanic environment. The overall goal in this work is to quantify carbon flow through the first trophic interaction in the microbial plankton.