Abstract

This study was conducted to investigate the impacts of shell-boring polychaete worms and biofouling organisms on the overwintering oysters (Magallana gigas) cultivated in the southern coast of Korea during May 2023. The mean biomass of biofoulers in Jaran Bay was 25.7 g wet/oyster which is 34.5% of mean oyster biomass. The proportion of biofoulers per oyster increased to 40.2 g wet corresponding to 47.8% of oyster biomass in Jinhae Bay. The main biofouler was different between two oyster farms; colonial ascidians were major biofouler in Jaran Bay while ghost sea squirts were dominated in Jinhae Bay. The individual number of shell-boring worms per oyster was in the range of 0 to 7. There were no significant correlations between the fresh weight or condition index and the shell-boring worms or biomass of biofoulers in this study during this period. We discussed the possibility of increasing impacts from biofouling and shell-boring before oysters are completely harvested until September of this year.