Sunflower sea stars are vanishing after mass mortality event

Sunflower sea stars may never recover from a marine epidemic that emerged in 2013, according to a population study led by Oregon State University. As a result of this research, the sunflower sea star has been listed as critically endangered by the International Union for Conservation of Nature.

“These sea stars used to be easy to find and were a hit with students and divers because they are unforgettable – they can be as big as a trash bin lid with 20 slimy arms covered in suction cups,” said OSU’s Sarah Gravem, a research associate in the College of Science and the lead author on the study. “Unfortunately, your chances of finding one now are next to nothing in most of the contiguous United States – this listing is one step above extinction – and I don’t think they’re coming back without help like captive rearing and reintroduction and reducing direct harvest and accidental harvest.”

Beginning in 2013, a disease known as sea star wasting syndrome caused catastrophic declines across populations of the sunflower sea star. The mysterious disease was characterized by twisted arms, lesions, deflation, and ultimately the loss of arms and death. The mass mortality event affected at least 40 different species of sea stars.

In collaboration with The Nature Conservancy and more than 60 institutions, the Oregon State team analyzed more than 61,000 population surveys from 31 datasets. The study revealed that sunflower sea star populations declined by an average of 90.6 percent. The team estimated that as many as 5.75 billion animals died from sea star wasting syndrome.

Furthermore, the researchers found no signs of recovery in any region in the five to seven years since the outbreak.

The sunflower sea star, Pycnopodia helianthoides, plays an important role in maintaining kelp forests and sustaining marine life along the West Coast from Alaska to Baja, California. 

The sea stars are vanishing from Mexico, as well as from the contiguous United States, according to the researchers. No stars have been spotted in Mexico since 2016 or in California since 2018.  

In the absence of sunflower sea stars, the purple sea urchins they prey on have exploded in numbers. The urchins are devouring kelp forests, which are already under severe threat from marine heat waves. 

“Because most people aren’t out in the ocean every day, we don’t realize how much it’s being changed and impacted by humans,” said study co-author Sara Hamilton.

“We need to think creatively about how to keep our ocean healthy. While drawing down carbon emissions is the most pressing need, rebuilding key predator populations, like the sunflower sea star, can be an important piece of the puzzle too.”

The study is published in the journal The Nature Conservancy.

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By Chrissy Sexton, Earth.com Staff Writer