Effect of particle concentration on filtration efficiency of the bay scallopArgopecten irradiansand the oysterCrassostrea virginica

Abstract

Filtration efficiency of the bay scallop Argo Pecten irradians and the oyster Crassostrea virginica was examined in the laboratory using dilute algal suspensions, over a range of concentrations from 0.88 to 10.89 mg wet algal weight. 1^-1. Efficiency of retention was measured in flowing seawater for each of 8 size classes of particles (1.73 to 9.97 μm diameter) by comparing number of particles in both inhalent and exhalent water. Algal suspensions were composed of isogravimetric amounts of Dunaliella tertiolecta, lsochrysis galbana, Platymonas suecica, and Thalassiosira pseudonana. In low algal concentrations, A. irradians and C. virginica showed no change in filtration efficiency for particles larger than 7 and 3 μm in diameter, respectively. As algal concentration increased, A. irradians became more efficient in retaining small (2 to 4 μm) particles, due to increased mucus (pseudofecal) production. Conversely, as algal concentration increased, C. virginica periodically became less efficient in retaining small particles, probably due to changes in effective ostial size. A. irradians conditioned to feeding on a large (10 μm) alga showed the same filtration efficiency as scallops conditioned on a small (4 μm) alga. These results indicate that both species show adjustments of filtration efficiency in concentrations of particulate matter representative of coastal and estuarine environments, and that these changes are utilized to control the amount of food collected for ingestion.