Sea Star Wasting Disease in Southwest Alaska

Sea stars, a keystone species and alpha predator in the oceans circle of life, are in danger. There have been large mortality events in sea star populations in the past, and it seems it may be happening again. The sea stars' food, mussels, multiply without being eaten, changing the habitat if sea stars were to leave. This danger to the sea stars is called Sea Star Wasting Disease (SSWD), and it is an epidemic. It is very difficult, if not impossible, to filter out of water. The disease is viral, not being filtered by a 0.22 µm filter. At least 20 species of sea stars are affected by the disease, and high mortality has been experienced in the United States west coast. Several locations in southeast Alaska, Western Prince William Sound, and Kachemak Bay have experienced the disease. Stars often lose arms when infected and die within a few days of exhibiting symptoms. 

Figure 2: Sites that were surveyed in Prince William Sound (1) and National Parks that border the Northern Gulf of Alaska (1), Kachemak Bay (2), and the Western Aleutian Islands (3).

The National Park Service, U.S. Geological Survey, UAF, NOAA, and GulfWatch Alaska began looking for the disease together in 2014, in southcentral Alaska. Researchers searched for the disease both in long-term monitoring sites and outside the boundaries of the long-term monitoring, in the Western Aleutian Islands.

Figure 3: GulfWatch Alaska long-term monitoring sites. Kenai Fjords NP surveyed in 2014, Prince William Sound surveyed in 2015

Nine of 1,588 sea stars across 30 sites were found to be infected with SSWD in 2014. All nine were found in Kenai Fjords National Park. In 2015, 69 of 2,016 observed sea stars had the disease. Almost all were found in Kachemak Bay. In Prince William Sound, 2 of 884 had the disease, also in 2015. Only 2 sea stars were found exhibiting the disease in the Western Aleutian Islands. Even with the small prevalence increase in 2015, diseased star occurrence is still low compared to the lower 48 and southeast Alaska. More information is needed to determine why Kachemak Bay harbored the most sea stars exhibiting the disease.

https://www.nps.gov/articles/sea-star-wasting-disease.htm

And for another blog post on this disease, you can visit this page. 

Sea Star Wasting Syndrome

There is a new threat to sea stars called ‘sea star wasting syndrome’, which is responsible for mass killings of these important keystone species.  In November 2013, the disease killed up to 95 percent of the sea star populations from Alaska to Orange County.  Little is known about the origins of the syndrome, or even what causes it.  Scientists are trying to determine the cause of this lethal disease before time runs out.

Picture by Jonathan Martin

Typically, a sea star infected with the syndrome will have lesions that appear in the ectoderm followed by decay of tissue surrounding the lesions, which leads to eventual fragmentation of the body and death (see picture above).   A deflated appearance can precede other morphological signs of the disease.  “True” wasting disease will be present in individuals that are found in suitable habitat, often in the midst of other individuals that are affected.  The progression of wasting disease can be rapid, leading to death within a few days, and its effects can be devastating on sea star populations. 

“They essentially melt in front of you,” said Pete Raimondi, chairman of the Department of Ecology and Evolutionary Biology at UC Santa Cruz's Long Marine Lab.  The University of California Santa Cruz is currently mapping all events along the West Coast, and people are encouraged to report these sea star wasting events to them.  They classify the syndrome into four categories, with 1 being mild, and 4 being severe.  Pictures and descriptions for the severity of the syndrome can be found here.   

At first, the disease only infected one species, Pycnopodia helianthoides, also known as the sunflower star.  Then the disease began to affect a more common sea star species, Pisaster ochraceus (Robert Paine’s keystone species).  Now, there are about 12-15 species that are dying along the West Coast from sea star wasting syndrome.  And wild sea stars are not the only ones in danger-- in September 2013, sea stars in an aquarium at the Gulf of the Farallones National Marine Sanctuary visitor center at the San Francisco Presidio contracted the syndrome in water pumped from the ocean.  Eels, sculpin and anemones that were in the same aquarium were unaffected.

The probable cause of the disease on the west coast of the US is caused by a pathological agent, such as bacterium (vibrio), although a recent wasting event on the east coast of the US has been attributed to a virus.  Sea star wasting events have also occurred from British Columbia down to the Gulf of California, the Mediterranean and the North Atlantic coast of North America, but not in the Southern Hemisphere.  Some researchers have suggested that Fukushima could be a cause, but the sea stars are being affected on the east coast, so this is not likely.  The ultimate cause is not clear although such events are often associated with warmer than typical water temperatures as was the case for the major die off in southern California in 1983-84 and again in 1997-98.  Sea stars are susceptible to bacterial infection, and warmer water boosts bacteria growth, Raimondi said.  

If the cause for sea star wasting syndrome is not uncovered, ecosystem balance can be disrupted with the disappearance of sea stars.  As we have learned in class, removing Pisaster ochraceus from tide pools causes unchecked population growth of mussels and other organisms.  Also, with global climate change, temperatures will rise in the ocean, which could have significant or even profound effects on populations.  Hopefully the cause of sea star wasting syndrome can be solved before it is too late.

Sea Stars Develop a New Strategy

New research has been conducted on sea stars that has proven that they have a back up strategy that helps them stay cool when the tides recede leaving them on the rocky shorelines absorbing massive amounts of sunlight. This strategy is one that scientists were unfamiliar with, but many scientists knew that sea stars had a way of protecting themselves from the heat. Sylvain Pincebourde, the author of this study, and his team conducted an experiment to test their hypothesis that the sea star strategy has something to do with fluid-filled cavities that are found on a sea stars arms. The experiment required the sea stars to be placed in aquariums in varied water levels to have different tidal patterns. Some sea stars experienced hotter temperatures than others with the use of a heat lamp. The results showed that sea stars that experienced hotter temperatures a lower tides had a higher body mass after the high tide occurred. Pincebourde and his team concluded that hot low tides seem to be a cue for sea stars to soak up more water during the next high tide so when the next low tide occurs they will have enough water consumed in their bodies to keep themselves cool. The amount of water sea stars can hold is a remarkable amount, but the only issue Pincebourde and his team are concerned about is the fact that climate change may negatively influence this cooling strategy because sea water has to remain cooler than air for the strategy to be successful.

The source I used for this post is below and reading the full article will give more information on this new strategy.
Photo is from NOAA/National Marine Sanctuary Web Site- Ochre sea star

• http://www.sciencedaily.com/releases/2009/11/091117161127.htm