LOCAL AND SITE-SPECIFIC FACTORS AFFECTING BIVALVE POPULATION ESTABLISHMENT: A CASE STUDY OF GROWTH AND REPRODUCTION OF CRASSOSTREA GIGAS (THUNBERG, 1793) IN POOLE HARBOUR

participantThe Pacific oyster Crassostrea gigas (Thunberg, 1793) is a commercial bivalve species that has been extensively introduced for aquaculture. At present, this commercial species has naturalized in areas such as the Northeast Atlantic and West European coasts. Poole Harbour in the United Kingdom is an important site for cultivated molluscs where the Pacific oyster was cultured starting in the 1980s. Interestingly, naturalized population has not been observed in Poole, unlike the aforementioned sites in higher latitudes. It is hypothesized that local, site-specific factors influence reproduction and post-settlement survival of oyster larvae to juvenile spats, thus affecting recruitment in an area. This study investigates the growth, reproduction and recruitment of C. gigas in Poole Harbour in relation to environmental parameters such as food availability (e.g. chlorophyll) and temperature. Growth monitoring in an on-growing farm in the site and collection of mature oysters to determine annual reproductive cycle using standard histological methods are being done. Preliminary results that cover the months of November 2009 to April 2010 are analyzed and additional samples will be collected, covering the rest of the seasons. Plankton tows to look into presence of larvae in the water column and deployment of spat collectors to determine benthic recruitment will be conducted. Feeding and respiration under different temperature regimes in tank experiments will also be done. Further sampling is necessary to determine patterns and effects of local factors on performance, survival and establishment or failure to do so, of natural Pacific oyster population in the area

Enhancing the recovery of depleted Tripneustes gratilla stocks through grow-out culture and restocking

Grow-out culture in sea cages and restocking were undertaken to help rebuild the spawning population of Tripneustes gratilla in Bolinao, Philippines. Higher population densities and incidence of recruits in 2004–2006, as well as steady increase in the catch per unit effort of gatherers, indicate that the sea urchin population is recovering. Growth of reseeded, hatchery-produced sea urchins in two sites was high and comparable to those in grow-out cages. However, natural mortalities were very high (91–99%). Good growth, high survivorship, and potential reproductive output of sea urchins in grow-out cages, aside from immediate socio-economic benefits, demonstrate that grow-out culture is a cost effective option for reestablishing effective spawning populations. Higher recruitment success in Lucero, compared to other sites, may be attributed to local favorable biophysical conditions and to maintenance of an effective spawning population due to enforcement of marine sanctuary rules, size regulation, and the presence of broodstock cages. Results suggest that the establishment of a network of marine protected areas in tandem with grow-out culture may be strategic in enhancing the recovery of depleted populations by maintaining larval exchange to sustain the production of sea urchin fishery stocks along NW Luzon