Quantities of suspended matter removed by oysters (Crmsostrea &rginica) and deposited as feces or pseudofeces varied seasonally, reaching maxima in September.Below 2X, measurable quantities wcrc not produced.At certain seasons, levels of suspended solids influenced quantities of biodeposits. Laboratory studies indicated that the oysters on 0.405 hectare of an estuarine bottom may produce up to 981 kg of feces and pseudofcces weekly. Of the particles, 95% were under 3 fi in diameter.

1. Particle filtration by the oyster Crassostrea virginica was studied in the 1.0 to 12.0 µ size range in relation to naturally occurring particles and to kaolinite suspensions in filtered river water. 2. Oysters were held in troughs of flowing water under conditions similar to their natural environment. Particle number and volumes entering and leaving the troughs were enumerated using a Coulter electronic particle counter. Particle diameter was expressed as that of a sphere having a volume equal to the particle. 3. Results of the study were expressed as per cent of total particles removed in various size increments or in volumes removed over the same size range. 4. Oysters filtered naturally occurring particles in the 1.0 to 3.0 µ range with about one-third the efficiency as larger particles. Above 3.0 µ there was no change in efficiency with increasing particle size. For kaolinite particles, oysters removed particles in the 1.0 to 2.0 µ range with about half the efficiency as larger particles. Above this size there was no change. 5. When results are expressed in terms of per cent removal, the importance of the small sized particles is minimized. In terms of volume, particles in the 1.0 to 3.0 µ range constitute the largest single size fraction over the 1.0 to 12.0 µ range. 6. The consistent presence of an inflection point at a particle size around 2.0- 3.0 µ in the curve for per cent removed vs. particle size is an indication that the distance between adjacent latero-frontal cilia is the factor that determines the smallest particle size that can be completely retained by the oyster gill. 7. Presence of the inflection point is also interpreted as negating the existence of a mucous sheet over the gills, as suggested by MacGinitie (1941). 8. Particles in the 1.0 to 3.0 µ range may play an important role in the nutrition of oysters and other lamellibranchs. Their removal by these organisms may also be an important factor in sedimentary processes.

Filter feeders, such as mollusks, tunicates, and barnacles, ingest particles as small as 1 micron during their feeding process and void them in fecal pellets which range from 500 to 3,000 microns in length; these pellets settle at a much faster rate than their component particles. Feces and pseudofeces that settle to the bottom are termed biodeposits. Oyster biodeposits contain 77 to 91 percent inorganic matter, 4 to 12 percent organic carbon, and about 1.0 gram per kilogram of phosphorus. Fecal pellets are alternately deposited and resuspended by tidal currents. They settle and accumulate in areas of estuaries where the fine particles themselves would not. A portion of the biodeposits settling on sediment surfaces is mixed into subsurface deposits and may alter the textural and chemical properties of the original sediments.

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