OBJECTIVES: Our overall objective is to quantify how suspension-feeding organisms living attached to the hard substrate formed by oyster reefs serve to remove phytoplankton from the water column and thereby help improve water quality. Specifically, for hooked mussels and tunicates, two of the most abundant (by biomass) organisms on oyster reefs, we will: • Determine biomass-specific, temperature-dependent, and seston concentration-dependent rates of water filtration and biodeposition • Assess filtration efficiency for particles between 1 _ 50 μm • Develop a spreadsheet model that estimates non-oyster "filtration capacity," in terms of both total volume of water cleared of particles and mass of particles transferred to the sediments.