Monday, February 11, 2019

Monitoring for Sea Star Wasting Disease

Starting in 2013, sea star wasting disease (SSWD) has now adversely impacted over 20 species of sea stars along the west coast of North America, ranging all the way from Alaska to Mexico. In some areas, this disease has wiped out over 90 percent of certain sea star populations, and continues to affect them to this day.

Although researchers have been studying this phenomenon for many years now, there is still much to learn. We still don’t entirely understand how the disease is directly contracted in the first place, or how the disease may be transmitted to other individuals. However, the symptoms of sea star wasting disease tend to be obvious.

A sea star that has contracted SSWD may start to form white lesions across its body. As the disease progresses, the sea star may adopt a deflated appearance and begin to lose its limbs. This process is often described as the sea star “melting” or “wasting away,” which aptly gives the disease its name.

In addition to not fully understanding the disease, another issue that makes SSWD so problematic is the fact that it progresses rapidly. After contracting the disease, a sea star may only live for a matter of days.

Severely diseased Mottled star
A wasting mottled star. Photo credit: Michael Kyte
 In order to gain a better understanding of SSWD, the Multi-Agency Rocky Intertidal Network (MARINe) has been with working with citizen science groups along the west coast to document the distribution and severity of this disease. Beginning in February 2014, Port Townsend Marine Science Center has been contributing to this effort through quarterly monitoring of sea stars on Indian Island.

Every three months, citizen science volunteers from PTMSC meet at Indian Island County Park to count, measure and check for signs of SSWD for all ochre (Pisaster ochraceus) and mottled stars (Evasterias troschelii) within a set of fixed plots. When it comes time to survey, we select a day and time that has a low tide of -1.3 feet or lower, as that exposes enough of the plots to be able to count all of the sea stars within them.

When we encounter an ochre or mottled star, we measure the distance from the center of its body to its longest arm, and this gives us an idea as to how old the sea star might be. This is important because it might be able to tell us how the population is doing.

For example, if we encounter a large number of smaller sea stars, then it indicates that there was a successful spawning event and that there could potentially be many new recruits to the population.

Additionally, for every sea star that we encounter, we assign it to one of three disease categories: healthy, mild, or severe. This is determined by the immediate physical symptoms displayed by the sea star.

For example, if it has only a few lesions, we would label it as “mild.” However, if it appeared deflated and had multiple limbs missing, then it would qualify as “severe.”

A wasting ochre star. Photo credit: Melissa Miner
I first became involved with this project when I helped organize and participate in our last survey in December. Because it occurred so late in the year, the best low tides were late in the evening, around 10 p.m. to be more specific. This was an especially nice survey to participate in, as we observed a significant number of small mottled stars, which is a fantastic sign that their population could begin to bounce back.

Our next survey will occur this month, on February 19. I’m eager to see if we can observe even more that last time!

A section of the plot on Indian Island, late at night. Photo credit: Michael Siddel
By working with such a large consortium of citizen science groups along the west coast, MARINe is able to gain a more comprehensive understanding of SSWD in terms of its distribution, severity and how various populations of sea stars have responded. As we continue to gather information and learn more about this disease, we will become better equipped to deal with the issue and ensure that our sea stars populations have a chance at recovery.

Written by Michael Siddel, Citizen Science Educator AmeriCorps Member

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