Growth, reproduction, and unicellular endosymbiotic alga in the giant scallop, Placopecten magellanicus (Gmelin), in Port au Port Bay, Newfoundland.

Naidu, K. S. (1969) Growth, reproduction, and unicellular endosymbiotic alga in the giant scallop, Placopecten magellanicus (Gmelin), in Port au Port Bay, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Aspects of the growth of the giant scallop, Placopecten magellanicus (Gmelin), in Port au Port Bay are presented. Von Bertalanffy growth equations have been fitted to selected shell dimensions of the mollusc. It was shown that there is no difference in the growth rate of male and female scallops. When growth rates of the bivalve from different beds within the bay are compared it was found that the largest and most prolific bed had the slowest growth rate. Growth differences are attributed to density-dependent and local sediment composition factors since other environmental influences within the bay are relatively uniform. Fine clay-silt was found to be a less favourable environmental substrate than larger sediments. -- Age and height composition data suggest that the scallop stocks have recovered sufficiently from the overfishing during the early 1950's. -- Gametogenesis and spawning are described. Histological changes accompanying the breeding cycle are also presented. Spawning is protracted, some scallops first spawning in June. This is followed by a major spawning in the fall. The spring spawning is minor and only a few individuals seem to take part. -- Some aspect~ of a heterospecific relationship between the scallop and a unicellular endosymbiotic alga tentatively reported as a zoochlorella are presented. The association is not universal. The presence of adequate light seems to be an essential factor limiting its incidence to shallow-water populations of the species. The effect of the alga upon the molluscan host is discussed. Present evidence indicates that the endosymbiont is a facultative parasite.

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