Studies On Plankton Assemblage, Diet Selectivity And Larval Rearing Of Mangrove Oyster Crassostrea Tulipa Towards Its Sustainable Production In Ghana

Abstract

Studies on plankton assemblage, diet selectivity and larval rearing of Crassostrea tulipa were carried out. Physicochemical parameters, plankton and oyster specimen were sampled from Narkwa and Benya lagoons, both located in the Central Region of Ghana, for one hydrological cycle. Three local microalgae isolates were tested as feed for oyster larvae in laboratory-rearing experiment. Physicochemical factors of both lagoons were generally within the acceptable range, except phosphate and nitrate which were above optimum limits. Annual mean DO, pH and turbidity were significantly higher in Narkwa, while salinity, nutrients and chlorophyll-a were notably higher in Benya. Higher number of plankton genera were recorded in Narkwa, but Benya recorded a higher annual mean density than Narkwa. Diatoms constituted ≈ 61 % of the plankton recorded in Benya, while dinoflagellates (majority of which were potentially toxic) were ≈70 % in Narkwa, with observed temporal variabilities in plankton compositions. Nutrients and pH were the significant predictors of diatoms and dinoflagellates, and these two plankton groups predominated oyster diet compositions, but diet selectivity analysis indicated a preferential selection for the less abundant groups. Prorocentrum spp were the dominant potentially toxic phytoplankton, with all year-round occurrence in the water and diet of oysters. Comparatively, Narkwa oysters were in better ecophysiological conditions. The individual local microalgal isolates supported growth and survival of oyster larvae at different scales, but a combination of all three promoted superior growth and survival of C. tulipa larvae. This scientific information is essential for the sustainable management of wild exploitation and aquaculture development of C. tulipa in Ghana.