Pulses of Productivity, Patches, and Pelagic Tunicates: Fine-scale aggregations influence trophic structure

              Pulses of productivity resulting from upwelling of deep, nutrient rich water occur periodically in boundary current systems. Pelagic tunicates (PT) are a filter-feeding group of gelatinous zooplankton that often form aggregations or blooms in response to boundary current upwelling, although the mechanisms driving upwelling differ among ecosystems. Aggregations of PT can have pronounced impacts on local trophic webs through consumption of small prey and production of detritus. While it has been established that oceanic-PT can serve as a mechanism of carbon export in upwelling zones through sinking of large detritus and carcasses, molecular and stable isotope techniques have suggested the roles of PT in coastal and shelf ecosystems involve greater feedback with the microbial loop. To better understand these dynamics, we conducted cruises in 3 sequential years in the South Atlantic Bight to capture cross-shelf gradients under different upwelling conditions. Using an in situ imaging vehicle, we observed PT populations which revealed aggregations over small (1-5 m) vertical spatial scales in response to upwelling. In layers with PT, we also found lowered bulk dissolved Oxygen concentrations despite elevated bulk Chl a. Finally, microbial respiration incubations from stations with PT aggregations revealed enhanced heterotrophic activity in the microbial loop. Our initial findings indicate that PT may be influential to the fate of primary productivity pulses on shelves, likely through aggregating labile carbon in the detrital pool.

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Primary Presenter: Patrick Duffy, University of Georgia (patrick.duffy@skio.uga.edu)

Authors:

Marc Frischer, University of Georgia  (marc.frischer@skio.uga.edu)

Laura Treible, Savannah State University  (treiblel@savannahstate.edu)

Emily Gipson, University of Georgia  (emily.gipson@uga.edu)

Adam Greer, University of Georgia  (atgreer@uga.edu)