Dear Editor,
The March 27, 2014 article entitled “A constellation of a keystone species” referenced a decline in abundance of the purple sea star (Pisaster ochraceus) in recent decades and mentioned that the purple sea star had not suffered as much as other species of sea stars in the recent die off. The sunflower star was reported to have a 99% die-off and other sea star species to have a 25-75% die off. Sea star wasting disease is thought to be an important causative agent for mortalities of the species of sea stars. Marine enthusiast Adam Taylor mentioned that the purple sea star has been infected by a ciliate parasite which attacks male gonads and kills males.
We have published seven papers on the relationship between the ciliate (Orchitophyra stellarum) and three species of sea stars in the Salish Sea ecosystem: the mottled sea star, species of the six armed sea star, and the purple sea star. All three species are associated with this ciliate. It lives outside of sea stars until the testes ripen. It then enters the testes and eats sperm, likely reducing the number of sperm available for reproduction. In our opinion, the ciliate is not a potent pathogen of these species of sea stars. So, while the ciliate may impact the fertility of the sea stars, it does not seem to otherwise harm them.
Males of the winter spawning six armed sea star are less severely impacted by the ciliate than the spring spawning mottled and purple sea stars, probably because of warmer seawater and air temperatures.
Thank you,
Bill Stickle
Professor of Biological Science at Louisiana State University.
