The cause of sea star wasting disease (SSWD), which affects more than 20 species of sea star on the west coast of North America and has killed more than five billion sunflower sea stars, has been identified. Knowing the bacterium responsible, Vibrio pectenicida, will benefit recovery efforts for sunflower sea stars and the kelp forests impacted by their loss.
Sea stars with the disease, which first struck in 2013 and is highly transmissible, rapidly deteriorate as their tissues develop lesions and then disintegrate. Identifying the pathogen was a painstaking process. By conducting controlled exposure experiments, genetic analyses, and making field observations, scientists closed in on the culprit.
After identifying the agent, “there was a huge celebration,” says Dr Melanie Prentice of the University of British Columbia (UBC) and the Hakai Institute and lead author of the study published in Nature Ecology & Evolution. "But we are just getting started,” she adds.
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Sunflower sea stars (Pycnopodia helianthoides), a species particularly susceptible to SSWD, are now critically endangered.
Growing to the size of a bicycle tyre, they are voracious predators of kelp-eating grazers such as sea urchins. The decline of this species has meant a proliferation of urchins and a widespread loss of kelp.
Efforts are already underway to raise sunflower sea stars in captivity for release back into the wild to boost kelp forest restoration.
“It’s incredibly hard to work on solutions without knowing what the pathogen is. Getting this information makes management and recovery possible,” explains Prentice. Diagnostic tests are now being developed that will help with the movement of captive sea stars and identify areas suitable for their reintroduction.
“It is possible that there are resistant sunflower sea stars out there,” adds Professor Alyssa Gehman of the Hakai Institute and UBC, senior author of the study. “If there are, then we can select for those animals that are resistant and try and breed them.”
The link between outbreaks and ocean temperatures is also under investigation. Vibrio bacteria have been coined ‘the microbial barometer of climate change’ and outbreaks of SSWD have been linked to warming water temperatures.
For Ashley Kidd, co-founder and conservation project manager of Sunflower Star Laboratory in California where sunflower sea stars are being captively reared, knowing the pathogen responsible for SSWD is a significant milestone. “It is a huge step to understanding how safe it is out there and the resilience of these sunflower sea stars,” says Kidd. “Now we can move forward.”
In pictures: sea star wasting
Top image: sunflower sea star in Knight Inlet. Credit: Grant Callegari, Hakai Institute | Additional images by Pat Webster can be found on his social media @underwaterpat
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