Effect of Suspended Silt and Other Substances on Rate of Feeding of Oysters

Abstract

The rate at which oysters pumped water through the gills under normal conditions and when the water was made turbid was recorded on the kymograph. Changes in shell movements were also recorded. On adding silt to make water turbid, even when as little as 0.1 gm./l. was added, the shell movement changed and the rate of pumping decreased considerably. A decreased rate of pumping always occurred when cones, of 0.25, 0.5, 1, 2, and 4 gm./l. of sea water were made. In concs. of 1 gm. of silt/1., pumping decreased over 80%, reaching a decrease of 94% in concs. of 3 and 4 gm./l. Addition of as small amts. as 0.1 gm./l. of kaolin or chalk markedly decreased the rate of pumping. This became more evident as the concs. increased. Fuller''s earth, 0.5 gm./l., reduced the rate of pumping by 60%. Although feeding was greatly depressed, oysters could ingest small amts. of particles even in very turbid water. The increase in turbidity, however, usually caused a decrease in the rate of pumping and, therefore, feeding. In highly turbid water the shell movements were of greater amplitude and of a different type than normal. When turbid water was replaced with regular sea water, shell movement and pumping rate returned to normal. The immersion in turbid water rarely exceeded 6 hrs.