INFESTATION OF THE TESTES OF THE JAPANESE SEA STAR ASTERIAS-AMURENSISBY THE CILIATE ORCHITOPHYRA-STELLARUM - A CAUTION AGAINST THE USE OF THIS CILIATE FOR BIOLOGICAL-CONTROL

Male infertility is a new phenomenon affecting populations of the Japa nese sea star Asterias amurensis. The agent causing partial or total c astration of the testes was identified to be Orchitophyra stellarum, a parasitic ciliate endemic to the north Atlantic. A. amurensis is a ne w host for O. stellarum, apparently due to the recent introduction of the ciliate to the Pacific Ocean. This ciliate disrupts the germinal l ayer and phagocytoses sperm. Male infertility of A. amurensis is large ly effected by the phagocytic response of host's cells with each cell engulfing numerous sperm. O. stellarum is highly contagious in A. amur ensis with 100% of the males in some populations infested. The absence of male sea stars in some populations is also linked to ciliate disea se. This report of O. stellarum from the western Pacific Ocean complet es the circumboreal distribution of this parasite. The contagious spre ad of O. stellarum in Japan and its ability to parasitize several aste roid genera cautions against its use for biological control of A. amur ensis in Japan and of recently established pest populations of this as teroid in Australia.