Development of a New Technique for Quantifying Selective Ingestion of Diatoms by Deposit Feeders

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9314338 MAYER Deposit feeders typically dominate benthic communities in soft bottom sediments. Because they feed on the organically dilute mixture (typically 5% organic matter) of mineral grains, micro- organisms, and detritus, they process large volumes of sediment to obtain sufficient nutrition. Selective ingestion of the more nutritious components of sediment (e.g., diatoms) is a potentially important part of their feeding behavior. It also has profound ramifications for decomposition of organic matter, sediment stratigraphy, and the transport of organic matter and pollutants in sediment. However, quantification of selective ingestion by de- posit feeders is hampered by methodological problems. The goal of this research project is the development of a new technique for quantifying the degree to which deposit feeders selectively ingest diatoms, an important nutritional component of sediments. The technique to be developed by this project involves labeling an essentially inert component of diatoms (the frustule) with the radioactive isotope 68Ge(a metabolic analog of Si) such that incorporated 68Ge becomes a conservative radiotracer for diatoms. Consequently, selective ingestion of diatoms can be quantified by comparing the concentration of the radiolabel in fecal material with that in test sediment. This project will develop protocols for labelling diatoms and preparing samples for scintillation counting. Also, the degree to which the 68Ge activity of diatoms acts as a conservative radiotracer and the sensitivity of the technique will be evaluated. Finally, the developed method will be applied to quantify the selective ingestion of diatoms by one species of deposit feeder. ***