Day and Night Characteristics of Spatfall and of Behaviour of Oyster Larvae

Abstract

Collectors were exposed at various depths in water 2.3 m. deep in tideless Gillis Cove (Bras d'Or Lake, N.S.) and renewed morning and evening. Rates of settlement of oyster spat (Ostrea virginica) as high as 0.4 spat per sq. cm. per hour were observed. The catch varied directly with depth, was heavier by day than by night, and the level of most intense spatfall was closer to the surface by day than by night. The catch on lower surfaces was heavier than on upper but the difference was less by day than by night. These and other observations suggest that ready-to-settle oyster larvae have three behaviour characteristics: they are benthic; light stimulates them to settle; and they settle most readily on lower surfaces.