Relation of Spawning of the Oyster to Temperature

Abstract

References to the relation between temperature and spawning of marine animals are numerous, but in no instance has there been prolonged investigation of the breeding periods of one species with continuous recording of the temperature. The voluminous collection of data in the notes of Lo Bianco ('o0), and in the Plymouth Marine Invertebrate Fauna ('04), while in a general way fixing spawning periods as associated with particular temperatures, do not yield exact information as to the minimum temperature at which spawning of a given species will occur, nor do they show how long a latent period must elapse after the critical temperature is reached before spawning actually is begun (Nelson '28). Orton ('20), states that spawning occurs in the European oyster, Ostrea edulis, when the temperature reaches I 5-I6? C.; and he points out that whereas the oyster breeds in Norway for only a short time in August, if at all, this same species in the Gulf of Toranto is actively breeding from April to October. The American oyster of the Atlantic Coast, 0. virginica Gmelin, may spawn in the Gulf of Mexico from March or April till late summer (Moore, '07); whereas in Nova Scotia spawning occurs during two or three weeks in late July or early August in favorable years, or not at all in cool years when the temperature fails to attain 200 C. (Nelson, J., 'I7). The Australian oyster 0. cucullata has been shown by Roughley ('26) to spawn only during warm years over the northern portion of its range. Apparently there has been no adaptive adjustment to lower temperature at the northern end of the ranges of the species of this genus, or to the higher ones at the southern extremities of distribution. The American oyster of the Atlantic Coast falls in the 200 C. group of lamellibranch molluscs with respect to its spawning temperatures (Nelson, '28). How long after this temperature is reached, and how much heat must be received, before spawning actually is begun? The investigations here recorded cover a period of ten years, with an attempt at a mathematical analysis of the data for the last four years. They include temperatures taken bv standard immersion thermometers and by a calibrated, frequently checked,