FILTRATION OF PARTICLES FROM SUSPENSION BY THE AMERICAN OYSTER CRASSOSTREA VIRGINICA

Abstract

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.

Decline of the Chesapeake Bay oyster population: a century of habitat destruction and overfishing

“…2 to 4 1 d-l g-' oyster tlssue) (Lam & Wang 1990), which provide conditions favorable for increased growth and survivorship (Peterson 81 Black 1987, Frechete et al 1989. Relatively intense flow evidently mitigates the negative effects of siltation and biodeposition, and increases consumption rates (Lund 1957, Haven & Morales-Alamo 1970, Keck et al 1973, Bahr 1976, Peterson & Black 1987, Seliger & Boggs 1988a, Frechete et al 1989, Lam & Wang 1990). noxious to oysters comes from several origins: (1) from point sources external to the bars, (2) from oyster faeces, and (3) pseudofaeces (Loosanoff & Tommers 1948, Lund 1957, Bahr 1976, Winter 1978, Heral et al 1983.…”

Effect of oysters Crassostrea virginica and bottom shear velocity on benthic-pelagic coupling and estuarine water quality

“…C. virginica filters large volumes of water and efficiently filters particles larger than 3 µm from the water column (Haven & Morales-Alamo 1970). At high particle loads, oysters do not stop filtering but produce more pseudofeces (Haven & Morales-Alamo 1966).…”

Latitudinal compensation in oyster ciliary activity

“…Oysters feed by filtering planktonic food from the water using a ciliated gill (Galtsoff 1964;Haven & Morales-Alamo 1970;Winter 1978;Ward et al 1994). The gill is also used as a respiratory organ, and the cilia control the movement of water over the gill (Jorgensen 1990).…”