Visiting the Stars
Last week, I was lucky enough to head over to the Peterson Bay Field Station with Americorp coastal ecology educator Leah Thon for a mid-winter overnight trip. Our primary purpose was to check out the much-beloved sea stars that inhabit the rocky intertidal at Otter Rock, China Poot Bay, and even the tidal lagoon right in front of the Field Station.
Two summers ago, a phenomenon called Sea Star Wasting Syndrome (or Disease) emerged on the west coast. Similar unusual mortality events among sea stars had happened before, but this one is bigger and more widespread. Alarmed by the severity of the outbreak in the Pacific Northwest, accounts of some suspicious lesions on sea stars at the Anchorage Museum, and a few distressed sea stars observed by naturalists on the Kachemak Bay beaches earlier in the summer, the Center for Alaskan Coastal Studies contacted the MARINe program (Multi-Agency Rocky Intertidal Network) through the University of California, Santa Cruz to learn more about their sea star monitoring efforts. Working closely with them, we determined that the threat of sea star wasting syndrome could exist in Kachemak Bay and that it would be valuable to establish a set of permanent plots for monitoring, and did so in the summer of 2014.
Unfortunately, we saw some symptoms of sea star wasting syndrome in these populations during our monitoring in the summer and fall. It seemed to be at a low level, but we became increasingly concerned about the fate of Kachemak Bay sea stars after hearing that true star (Evasterias troschelii) and sunflower star (Pycnopodia helianthoides) populations around Sitka, Alaska had plummeted in November and December after sustaining low levels of sea star wasting through the summer and early fall. At this point, researchers have identified a densovirus that may be linked to sea star wasting, but no one is sure yet if that is the cause or whether there are additional agents or environmental factors at play. And more frustrating, there seems to be no way to stem the spread of the disease, aside from vigilance to not carry it from location to location on our boots, hands, or equipment. We are just waiting and watching to see what happens here in Kachemak Bay. So as we hopped off the water taxi, last week, nightmarish images of Sitka's disintegrating sea stars flitted in the back of my brain. The tide was high, though, and I would have to wait until after dark to see what was actually going on with the stars.
We conducted all of our surveys by headlamp as the low tides took place in the late evening and early morning, devoid of any winter daylight. We found lots of apparently healthy true stars, sunflower stars, and leather stars (Dermasterias imbricata) at both China Poot and Otter Rock with just a few individuals showing symptoms of wasting. This is similar to what we found during July and October surveys. We also spotted a number of juveniles, something that has been observed in other areas hit harder by sea star wasting and suggests a mechanism for the recovery of sea star populations. And we saw a few less common species, all healthy, including a sun star (Solaster stimpsoni) and blood star (Henricia spp). The ghastly images vanished, at least for the time being, as we delighted in these stars and other tidpool finds, including Leah's first octopus!
At our third plot, on the beach between the PBFS stairs and dock location, we only found one juvenile true star and a little 6-rayed star (Leptasterias spp), both under a rock. I’m not sure if this low density is due to sea star wasting, or – I think more likely – some sort of seasonal or weather-related shift in sea star distribution. We’ll survey again this spring, paying special attention to whether or not we see a return of sea stars to the PBFS plot. And we'll keep sanitizing our boots and marveling in the amazing diversity and tenacity of Kachemak Bay's intertidal invertebrates! We hope to see you out in the tidepools sometime soon!