Collaborative Research: Interactions Among Deposit-Feeding, Organic Matter Diagenesis andAnimal Nutrition

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The global effects of deposit feeding on carbon burial are profound. Even though they consume only a small fraction of sedimentary organic matter (OM), deposit feeders influence the rate and extent of OM diagenesis by increasing oxygen penetration into sediments, redistributing particles, and stimulating diagenetic activity throughout the mixed layer. Sedimentary organic resources simultaneously determine, and are determined by, the activities of the benthic infauna. Understanding how deposit feeding and OM diagenesis interact is critical to developing realistically coupled biological/chemical models of carbon cycling in marine sediments. In this study, investigators at the Skidaway Institute of Oceanography and the University of Texas at Austin will study linkages and feedbacks between OM diagenesis and deposit-feeder ecology by examining the foraging behavior of a conveyor-belt feeding orbiniid polychaetes (Haploscoloplos robustus) in experimental microcosms. Effects of sedimentary OM concentrations on individual feeding rates, patch density, and rate x density interactions will be examined from an optimal foraging perspective. Documenting the dynamic balance among individual functional responses, sediment mixing, microbially-mediated organic transformations, and nutrient assimilation is a major focus of the proposed study. To study the coupled organism-microbe-sediment system, a novel isotopomer-based 13C tracer experiment is proposed. Bacterial co-metabolism of sedimentary carbon and labeled OM additions will lead to the formation of bacterially-synthesized OM having molecular 13C isotopic signatures that are distinct from both the (12C) sedimentary carbon and the added (13C) OM. Measurement of the incorporation of added label into a bacterial amino acid and fatty acid pools and subsequently deposit feeder biomass will be used to trace the fate of carbon as a function of H. robustus feeding rate and population density. Feedbacks among OM diagenesis, microbial production, and worm foraging behavior and growth will be quantified by independently manipulating organic supply, population density, and sediment mixing rate. In terms of broader impacts, this research project will feature several inter-institutional collaborations and will involve the training one graduate student (at UT) and two undergraduate students from the SkIO/Savannah State CIRE internship program.