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.
