Infestation of the testes of the Japanese sea star Asterias amurensis by the ciliate Orchitophyra stellarum: a caution against the use of this ciliate for biological control

摘要

Male infertility is a new phenomenon affecting populations of the Japanese sea star Asterias amurensis. The agent causing partial or total castration of the testes was identified to be Orchitophyra stellarum, a parasitic ciliate endemic to the north Atlantic. A. amurensis is a new host for O. stellarum, apparently due to the recent introduction of the ciliate to the Pacific Ocean. This ciliate disrupts the germinal layer and phagocytoses sperm. Male infertility of A. amurensis is largely effected by the phagocytic response of host's cells with each cell engulfing numerous sperm. O. stellarum is highly contagious in A. amurensis with 100% of the males in some populations infested. The absence of male sea stars in some populations is also linked to ciliate disease. This report of O. stellarum from the western Pacific Ocean completes the circumboreal distribution of this parasite. The contagious spread of O. stellarum in Japan and its ability to parasitize several asteroid genera cautions against its use for biological control of A. amurensis in Japan and of recently established pest populations of this asteroid in Australia.