Are there any sea stars left in the San Juans?
by Morgan Eisenlord and Drew Harvell
We have not yet solved the vexing mystery of why the San Juan Islands were skipped by the sea star wasting disease epidemic last December (see Tidebite #5), while Alki Beach, Mukilteo, Vancouver, and all of California were being hammered. However, we can reject some of our initial hypotheses and begin to consider new ones. The fact that our populations were devastated this summer allows us to rule out the once appealing idea that they were immune. Similarly, the combination of unseasonably cool water last fall and record-breaking hot water this summer allows us to implicate temperature in some patterns of mortality. We're pleased that we can report exactly what happened in the San Juans this summer, thanks mostly to hard work from Team Seastar (see end of the next paragraph) and the unique funding sources listed at the bottom of this Tide Bite.
The Ochre star in the intertidal zone and Sunflower star in the subtidal zones overwintered in good condition and looked healthy when we started our surveys in March 2014. With coordination from Pema Kitaeff (Dive Safety Officer at FHL), student divers counted over 40 sunflower stars under the FHL dock and off Cantilever Point. Soon after stars from under the dock sickened, Morgan Eisenlord activated a larger survey effort, complete with deploying temperature loggers to survey key sites around the Islands throughout the spring warming. Team Seastar included high school students from Spring Street International School, undergrads and graduate students at FHL, and local volunteers. Volunteers got into the water and out into the rocky intertidal around the Islands to conduct sea star health surveys (Figure 1). Team Seastar for the San Juan surveys included: Morgan Eisenlord, Mo Turner, Natalie Rivlin, Pema Kitaeff, Bella Bledsoe, Robyn Roberts, Zula Mucyo, Phil Green, and Katie Dobkowski.
At first, the results were encouraging; lots of healthy stars were found both subtidally and in the intertidal. Previous research suggested temperature was a key contributing factor to sea star wasting disease. The San Juans had yet to reach the hottest months of the summer and the lowest tides, when exposure to warm air would be greatest. As this summer progressed, the incidence of the wasting disease increased at all our survey sites, slowly at first and then dramatically as the summer water temperature hit record highs. Through May and June, the seastar numbers remained around 5-10% sick. Following this, the percentage of sick stars increased rapidly by mid-July. Once home to several thousand Pisaster, Eastsound was the worst-hit and experienced 96% wasting disease prevalence (Figure 2). In mid-July, we made the sad discovery that thousands of baby star recruits were also getting sick and dying. By mid-August 2014, disease levels at all sites exceeded 50%, with many of the sites littered with dead seastars. Due to our repeated sampling every few weeks, we were able to track the rate of disease intensification over a variety of habitats and temperature conditions around San Juan County (Figure 3). These data, coupled with satellite remote sensing and underwater temperature loggers, will help us understand what environmental factors drive the differences in disease prevalence at different locations. For more explanation, click here to view a video by Morgan Eisenlord. There are some healthy sea stars left in a few isolated pockets and places, but they are the rare survivors of an extremely lethal epidemic. We are hopeful now that as water temperatures drop the few survivors will recover. We are also hopeful because we know that stars in northern B.C. and Alaska fared better than in the San Juans.
In such warm sea conditions (this August was a world and local warm temperature record-breaker), other ocean inhabitants were also sick. Sandy Wyllie-Echeverria noted an intensification of sea grass disease in Fisherman’s Bay on Lopez Island. We followed up on both projects in our Ecology of Infectious Marine Disease course, a 5-week FHL course funded by NSF and taught by Drew Harvell, Carolyn Friedman, and Steven Roberts with T.A. Lisa Crosson. Carolyn, Steven, and Lisa all work in UW's School of Aquatic and Fisheries Sciences. We had a dream team this summer of superb Ph.D. students, including Morgan, the co-author on this article. The students focused on two main projects: the immune response of sea stars to the wasting disease, and fighting back the Labyrinthula (Laby) protistan infections of sea grasses.
To understand how sea stars respond to the wasting infection, students mined the data we had in order to compare the genetic response of seastars exposed to wasting disease and uninfected seastars (the control group). While the results are still being completed, the students noted significant differences across important gene families. This may give us a way to study the immune systems of surviving super-stars. The students plan to submit the work for publication. For more explanation, click here to watch Allison Tracy’s video of the steps the students followed in this project.
In the seagrass infection project, the students explored two potential ways to mitigate the disease: culling (physical removal of sick individuals), and using shellfish as bio-filters to remove the Laby pathogen from the seawater. They found that culling decreased disease prevalence in sites where disease levels were high before the treatment, and the oyster treatments showed signs of removing Laby from seawater in a lab experiment. The students on this project are also planning to publish their results. Highlights of the course included the weekly videos the students made. Click here for Sarah Gignoux-Wolfson’s week 1 video, where you can get a snapshot of the non-stop action.
The sea stars and ocean health in general seem to have friends in high places. Congressman Denny Heck’s office contacted Drew for help in crafting an Emergency Marine Disease Bill, which they introduced to Congress on September 19, 2014 (click here to read more). We are very grateful to see action regarding this horrific hit to our Pacific Ocean biodiversity, and hope this bill will actually survive the challenges of the Senate and go on to help promote ocean health.
Funding sources for this important research have included: FHL Advancement Board Chair Kevin Schofield, Vicky Bailey’s 6th graders, and The Nature Conservancy.
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