The Rate of Attachment of the Larvae of the Japanese Oyster, Ostrea Gigas, as Related to the Tidal Periodicity

Abstract

The behavior of the larvae of the oyster is affected by a large variety of factors during the critical and precarious period of their existence when they settle and attach themselves to fixed objects. Recent observations indicate that cyclic changes in the sea water corresponding to the tidal periodicity are correlated with variations of a similar period in the behavior of oyster larvae during the settling process. Prytherch ('34) has demonstrated that the setting of the larvae of Ostrea virginica at Milford Harbor is directly correlated with the daily tidal cycle, as a result of the tidal effects on the content of copper in the sea water. Recent work by Hopkins ('37) and Bonnot ('37) has shown that the behavior may also be correlated with the longer tidal periods. These workers have demonstrated that the larvae of 0. lurida set most abundantly on the series of spring tides. Hopkins' data indicate, in addition, a still longer period. The data presented in this paper were accumulated as part of an investigation, in 1936, of the reproduction of the Japanese common oyster, Ostrea gigas, introduced to the United States from Japan. Because of unfavorable hydrographical conditions in most of the localities where this species was introduced, reproduction occurs only at a few limited places on the Pacific Coast. The present observations were made at Quilcene Bay in Puget Sound. Japanese oysters introduced here as spat in 1931 commenced propagation in 1934, and have continued to reproduce successfully each year since. This bay is particularly suitable for a study of the setting process because of the clear, silt-free water, which greatly reduces the fouling of the spat collectors.