| Summary: | The purpose of this study was to investigate the population structure, influence on local native communities, and filtration capability of the Pacific oyster, Crassostrea gigas. C. gigas was first introduced into the UK for commercial purposes in 1964. The success of initial growth and survival trials of introduced individuals in the River Yealm, Devon then led to a number of hatcheries becoming established. This study, involving the examination of C. gigas at four sites within one location, looks at the subsequent establishment of the species in the Yealm Estuary which has possibly resulted from the settlement of larvae from these initial hatcheries. A study of distribution and population structure concluded that despite displaying a clear vertical distribution pattern on the lower mid-shore, there was no such definitive horizontal trend. Size structure at each of the four sites was found to be dependant on the location in the Estuary. Community structure was investigated with regards to oyster density. Species richness was not found to differ when these densities varied between high, medium, low and absent. In areas of high density oyster patches, however, a significantly greater number of mobile invertebrates were recorded in comparison to the remaining three densities. Furthermore, community assemblages were found to differ between areas of high and absent, as well as between low and absent densities of oysters. It is probable that the presence of C. gigas is helping to shape these communities by providing a refuge space. Estimates of filtration capabilities revealed higher filtration rates at sites with greater oyster .abundance. This finding was considered with respect to previous studies in the literature and it was postulated that consequences may result m increased sedimentation and reduced surface velocities. These fmdings indicate that C. gigas exerts a small, yet influential, impact on the communities with which it cohabits. Faculty of Science, The Marine Biological Association of the United Kingdom
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