Effects of the dinoflagellate Karenia mikimotoi on larval settlement of Pacific oyster Crassostrea gigas

To evaluate the effects of harmful red tide dinoflagellate Karenia mikimotoi on the settlement and survival of pedi-veliger larvae of the Pacific oyster Crassostrea gigas, exposure tests with cultured K. mikimotoi (0, 500, 5000 cells/mL) were performed using artificially bred pedi-veliger larvae. Most of the larvae used in the test settled on spat collectors and the inner of the beaker in 0 cells/mL and 500 cells/mL of K mikimotoi. However, the larvae settlement number was considerably lower in 5000 cells/mL. Moreover, the ratio of larvae settled on spat collectors was lower, and that for settling on the beaker was higher. These results indicate that, since it is difficult for some larvae to reach the position of the spat collectors in the beaker, they settle on the inner surface of the beaker, and especially on the bottom. According to our results, K mikimotoi red tide has a possible risk of spat collection failure in the field, which indicates an adverse effect on oyster farming.