RUI: Influences of Benthic Boundary-Layer Flow on Distributions and Feeding Rates of Protists in Subtidal Near-Bottom Water and Surficial Sediments

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Microbial processes at the sediment-water interface (SWI) and in near-bottom water are critical for benthic productivity, nutrient cycling, and benthic-pelagic coupling in numerous subtidal marine environments, including coastal waters, continental shelves, and the deep sea. The roles of protists in the microbial food webs of the benthic-planktonic transition zone, however, are poorly understood. This proposal describes a study of combined field sampling and laboratory experiments to elucidate influences of benthic boundary-layer (BBL) flow on protistan ecology. The project is designed to answer the following questions: (1) what are the vertical distributions and abundances of protists at the SWI and in near-bottom water, (2) to what extent, and by what mechanisms, does BBL flow influence these distributions, and (3) to what extent, and by what mechanisms, do variations in BBL flow affect feeding rates of heterotrophic protists at the SWI and in near-bottom water? To answer these questions, the objectives of the research are: (1) to characterize the vertical distributions of protists in the near-bottom water and surficial sediment of a coastal subtidal habitat, Buzzards Bay, MA, and to relate these distributions to tidal variations in flow speed; (2) to investigate in a laboratory flume the mechanisms by which flow influences vertical distributions of cells as seen in the field; and (3) to measure in a flume the influences of BBL flow on feeding rates of heterotrophic protists under conditions similar to the field. The results of this work will provide novel insights into physical-biological interactions in benthic microbial ecology and benthic-pelagic coupling in coastal habitats. Through these processes, the physical energy level of flow in subtidal coastal habitats may have far-reaching influences on microbial trophic dynamics, secondary production, and biogeochemical processes in the near-bottom and surficial-sedimentary zone.