Ecological Observations on Spawning and Early Larval Development in the Olympia Oyster (Ostrea Lurida)

Abstract

The native oyster of the Pacific coast is biologically different, in some respects, from the common Atlantic coast species (0. virginica). Like the European oyster (0. edulis) it is hermaphroditic as well as viviparous, as described by Stafford ('13, '14). More recently Coe ('31a, '31b) investigated the species and found it to be clearly protandric. He described spermatogenesis in detail and demonstrated that throughout the life of each individual there is an alternation of male and female phases, although in either phase the germ cells of the opposite sex may be found. The process of spawning was well described by Stafford ('14). He stated that eggs are discharged into the bronchial chamber in which they are held as in a brood sac. Spermatozoa, on the other hand, are discharged directly into the surrounding water. At this time they are in clusters, or sperm balls, from which the individual sperms escape when brought into contact with seawater, according to Coe ('31b), who estimated that each ball is made up of from 250 to 2,000 or more sperms. According to both Stafford and Coe the sperms are brought into the mantle chamber of functionally female specimens with the water pumped by the gills, resulting in fertilization. It is probable that the sperms stimulate spawning in this species, as was found by Galtsoff ('30a, '32) in other species of oysters, though this has not been demonstrated. It is remarkable that although the oviducts of oysters open into the cloacal chamber the eggs are finally discharged from the mantle chamber, suggesting that they must pass through the ostia of the gills in a direction opposite to that of the normal flow of water. Stafford ('15), referring to 0. lurida, described this activity as follows: Eggs and sperms are liberated from the gonaducts into the suprabranchial chamber, and make their way through the water-tubes and gill-slits to the bronchial chamber, which also serves as a brood chamber. In doing this they are assisted by the pressure of their mass. . . . Sections of oysters at the spawning season show eggs in the cavities of the gills. They do not pass readily through the gill-slits on account of the narrowness of the latter, but with increasing mass and pressure the gills become stretched and the slits enlarged, and besides the gills appear in places to suffer disintegration. Galtsoff (unpublished manuscript) made a recent study of the matter in 0.