The strange “melting” of sea stars in Puget Sound and along the West Coast has attracted much media attention. Below, Seattle Aquarium staff veterinarian Lesanna Lahner shares an update on our participation in the effort to understand the disease.
Low-grade disease in sea stars is not uncommon. It’s previously been documented on a waxing/waning, potentially seasonal, occurrence in both captive and free-ranging sea star populations along the West and East coasts. In the past, these events have been mild. However, since October of 2013, a higher prevalence of disease in the wild population of several sea star species has been documented near Vancouver, B.C., and the Seattle waterfront.
A bit of background on sea stars: commonly called “starfish,” sea stars are echinoderms and one of the most familiar marine invertebrates. Roughly 1,500 species of sea stars exist between the intertidal zone and deep abyssal depths of over 20,000 feet. Sea stars are considered a top predator and a keystone species as their diet includes many animals— including sea urchins, barnacles, snails, limpets and mollusks—that have few natural predators.
As part of a multi-institutional collaborative effort to quickly respond to this unusual mortality event in sea stars, Seattle Aquarium divers Jeff Christianson and Joel Hollander were able to collect some healthy and diseased stars from the waters surrounding the Seattle Aquarium in late October. Seattle Aquarium divers have also monitored levels of disease along the waterfront over the past month, since the disease was first noted.
The animals collected in late October were sampled according to a protocol carefully developed by several institutions, and samples were sent to our collaborators in New York at Cornell University and the Wildlife Conservation Society. Investigators are looking for viral, bacterial and other potential causes of disease and are also processing samples collected by the Vancouver and Monterey Bay aquariums.
At this time, no definitive cause of disease has been identified. Samples have also been sent to local laboratories and a local veterinary pathologist, Dr. Michael Garner of NW ZooPath, to aid in the efforts to determine the cause of disease. Within the last several weeks, the U.S. Geological Survey National Wildlife Health Center has also become involved and is helping to coordinate efforts and investigate other potential causes of disease including toxins and fungal infections.
Determining the cause of disease in wild animals, such as sea stars, takes time due to the complexity involved in identifying normal flora versus disease-causing pathogens, as well as evaluating for things such as environmental changes caused by factors such as contaminants and changes in water quality. There have been suggestions that radiation from Japan may be involved in the sea star wasting syndrome; however, a recent report by the Washington Department of Health shows that no abnormal levels of radiation have been found in several species of fish and shellfish from the Pacific coast of Washington. Teams of marine biologists, wildlife veterinarians, microbiologists, pathologists, and others are working together to determine the cause of the unusual mortality event seen in sea stars along the western coast of the United States and Canada.
We’ll post more updates on this issue as information becomes available.