Filtration of particles from suspension by the American oyster Crassostrea virginica

The oyster Crassostrea virginica is a suspension feeder which retains suspended particulate material on its gills. These are lamellar and composed of rows of fila ments in groups that constitute folds (plicae) in the lamellar surface (Nelson, 1960) . Water is pumped through small interfilamentary openings (ostia) by the action of cilia on the filaments. The actual manner in which particles are retained on the gills is not completely understood (Jorgensen, 1966). Suggested mechanisms include entrapment in mucus, straining action of large latero-frontal cilia, and limitation of passage through the gills by the size of the interfilamentarv ostia. Two methods have been commonly used to study particle filtration by bivalves. One involves channeling water into and from shell cavities with devices which collect all water flowing through the gills (Galtsoff, 1928; Loosanoff and Engle, 1947; Tammes and Dral, 1955). These studies have been criticized because oysters may not behave normally when subjected to the stress of the collecting device. The second involves measurements of rates at which undisturbed lamelli branchs clear particles in standing water. This latter method has been used extensively by many workers in recent years (Jorgensen, 1949, 1960: Ballantine and Morton, 1956; Chipman and Hopkins. 1954: Jorgensen and Goldberg, 1953; Willemsen, 1952). Objections to studies in standing water are that previously filtered material may be resuspended and refiltered (recycled) and also that particle concentrations will change with time. With only several exceptions, as exemplified by the work of Loosanoff and Engle (1947), particle density was niea sured indirectly by techniques such as isotope labeling, per cent light transmission, etc. Results of these studies differ widely in respect to the efficiency at which various size particles are filtered from suspension. No one has correlated the results of these investigations with the structures and mechanisms which deternine them (Jorgensen, 1966). The purpose of this investigation was to establish more precisely the size of the smaller particles removed from suspension by the American oyster Crassostrea virginica and the efficiency of removal and to relate our results to the most probable mechanism involved