Association and distribution of the ciliate Orchitophrya stellarum with asteriid sea stars on the west coast of North America

Abstract

The association of the scuticociliate Orchitophrya stellarum with 3 species of asteriid sea stars from the west coast of North America was studied by flushing the gonopore region with seawater and spawning the sea stars, along a latitudinal gradient of 2549 km between Pigeon Point, California, and Kodiak, Alaska. Asterias forbesii and A. rubens from the Isles of Shoals, New Hampshire (east coast), were also sampled. The ciliate was found on the aboral surface of both sexes of reproductively ripe Evasterias troschelii, Leptasterias spp., and Pisaster ochraceus with a maximum intensity of association occurring at Cape Arago, Oregon, and Clallum Bay and Manchester Dock, Washington. A survey of gonad smears and hematoxylin and eosin-stained sections indicated that the ciliate was only present in males. Spring-spawning E. troschelii and P. ochraceus are more negatively impacted by the ciliate than are winter-spawning Leptasterias spp. as judged by a skewed sex ratio and sex size differences, which may be associated with seasonal differences in water temperature affecting the growth rate of O. stellarum. The external morphology of O. stellarum appears to be similar throughout the geographical range surveyed.

Effects of temperature, season and locality on wasting disease in the keystone predatory sea star Pisaster ochraceus

“…Therefore, sex or size-biased mortality from wasting disease can not explain the heavily skewed sex ratios in Vancouver Island populations (e.g. Stickle & Kozloff 2008). Leighton et al (1991) proposed that the emerging ciliate parasite Orchitophyra stellarum found infecting the testes of male sea stars drives male-biased mortality.…”

“…We also conducted experiments to compare the progression of wasting disease in specimens collected in early versus late summer, and from localities that varied in wave exposure. Because Pisaster populations on Vancouver Island are heavily female-biased at larger size classes (Leighton et al 1991, Stickle & Kozloff 2008, we also tested for sex or size-biased infection. …”