Spawning and Setting of the American Oyster, O. Virginica, in Relation to Lunar Phases

Abstract

A revival of interest in the relation between the lunar phases and periodicity in the breeding of marine animals has been recently stimulated by Korringa's (1947) article. Although his article is chiefly devoted to a review of the literature on this subject and its analysis, the author, nevertheless, incorporates in his own observations on the periodicity of swarming of the larvae of the European oyster, Ostrea edutlis, in the Oosterschelde, Holland, during the period from 1935 until 1946. Korringa's extensive data led him to the conclusion that in his district there is a well-defined periodicity in the spawning of 0. edulis and swarming of its larvae, and that this periodicity is directly correlated with the phases of the moon. Korringa found that the important maxima of extrusion of the eggs (heavy spawnings) into the mantle cavity of female oysters take place at the spring tides, occurring 2 days after full and new moon. About 8 days after spawning the larvae are released from the mother's mantle chamber and appear in the water in large numbers. This phenomenon, known as swarming, happens about 10 days after full or new moon. Of course, the dates of spawning are of primary importance because swarmings follow them almost automatically. Korringa thinks that periodicity in the spawning of 0. edulis is caused by the rhythmical differences in the water pressure occurring between the neap and spring tides. According to Korringa (1947) it is the rhythm of the tides which does the trick. Since an extensive review of literature on the relation between the phases of the moon and the periodicity of spawning of marine animals has already been offered by Korringa, is not necessary to discuss at length in our paper. We shall confine ourselves to those references that concern oysters. Orton (1926), working in Fal-Estuary, England, on 0. edulis came to the conclusion that there was a periodicity in its spawning, the maxima occurring near full moon. He thought, however, that periodical spawning was noticed only in normal oysters, while dumpy or irregularly-shaped oysters showed no such rhythm. Orton suggested that the rapid rate of change in hydrostatic pressure at the spring tides accompanied by an increase in temperature acted as a stimulus to induce spawning. Later on, however, Orton (1937) wrote that his further observations showed no relation between the maxima of spawning and the full moon tides, and that he never again observed lunar periodicity in the spawning of oysters. Spdrck (1929) working on the same species in Limfjord found no lunar periodicity in its spawning. However, since the tidal changes and the changes in hydrostatic pressure in Limfjord are small, the lack of periodicity there could be ascribed to that reason. In this country the nearest relative of 0. edulis is Ostrea lurida, a larviparous species, intensively cultivated in some sections of Puget Sound. A description of the spawning, larval development and setting of this oyster has been given by Hopkins (1937). Hopkins found no lunar periodicity in the spawning and swarming of 0. lurida, but established that spawning is a continuous process extending for a period of at least 5 months, although is most active for approximately 6 weeks. Once spawning begins, usually slowly increases to a maximum and then gradually diminishes. Schaefer (1937) studied spawning and setting of Japanese oysters, Ostrea gigas,