Physiological ecology of the Pacific oyster Crassostrea gigas and sea squirt Halocynthia roretzi cultured in suspension in a temperate bay on the southern coast of Korea

Abstract

Physiological ecology of marine molluscs was examined during the entire culturing period in Geoje-Hansan Bay of Korea by growth dynamics and relevant gross biochemical compositions and physiological processes. Primary productivity of phytoplankton peaked during the summer monsoon period when diatoms dominated the phytoplankton community, accounting for a high growth rate of oysters during that period. Growth dynamics of the longline cultured oysters was related well with culturing depths and sites. Growth curves of somatic tissue showed higher growth in the surface than in the bottom layers in the inner bay and also advanced summer growth in the inner bay compared with winter growth in the outer bay. Such growth patterns of oysters were better explained by hydrodynamic effects with temperature and food availabilities. I also calculated energy budget of oyster individuals during the entire culturing period. Adjusted physiological activities to relatively low concentrations of food materials lead to positive energy balance under high culturing density during the entire culturing period. Biodeposition and ammonia excretion of oyster were relatively low, suggesting low feedback effects of the culturing oysters on benthic and pelagic environments. On the other hand, warmer winter temperatures made fishermen adopt to new nursery grounds for spat cultivation of sea squirts. When spat reared in different localities before and after warming winter were used, no difference in growth performance of sea squirts was observed. Gross biochemical composition and physiological measurements supported the successful adaptation strategy by fisherman under the winter-spring warming conditions. Finally, a combined ecological model of physical, biogeochemical, and ecophysiological models was applied to growth dynamics of oysters to provide information for the management of culturing ground regarding stocking density and feedback effects.