Sea Star Populations Threatened by New Marine Infectious Disease

Photograph: National Oceanic and Atmospheric Association.

Sunflower sea star populations from Alaska to Mexico have been decimated by a deadly disease which is likely exacerbated by warming ocean temperatures, leaving marine ecosystems vulnerable to collapse, a study finds.

This sea star species is predominantly found in shallow Pacific water along the West Coast of North America. The sunflower sea stars are critically endangered, and the number of individuals is rapidly declining.

“At one time plentiful in the nearshore waters, the sunflower sea stars right now cannot be found off the California coast and are rare into Alaska,” said Drew Harvell, lead researcher of the Science Advances study.

Harvell and a team of researchers studied the sea stars' decline from 2013 to 2015. The researchers conducted thousands of trawl and diving surveys to determine the population size and the factors behind the rapid drop in population.

Divers completed 10,000 surveys off the coast of Washington, Oregon and California between 2006 and 2017. The study found that sea star populations declined by 60%. Across North America, sunflower sea star populations in the studied 3,000 km range decreased by 80% to 100%.

This study is beginning for the sunflower sea star. Northern sea star habitats have not been fully researched and the size of the population is unknown.

“Numbers of the sea stars have stayed so low in the past three years, we consider them endangered in the southern part of their range, and we don’t have data for northern Alaska,” Harvell said.

The fatal disease causes the infected animals to suffer dermal lesions and limbs that detach from the central disc. Once deceased, the sea stars appear as a pile of arms and skeletal fragments.

The persistence of sea star wasting disease coincides with warmer water temperatures. Many marine infectious diseases, like sea star wasting disease, thrive in warm habitats.

Researchers found that the disease kills faster in warmer water. Scientists expect that the eradication of the sunflower sea star is related to warmer temperature exposure.

“The heat wave in oceans—a product of increasing atmospheric temperatures—is exacerbating the sea star wasting disease,” said Harvell. “It’s a lethal disease, and when you add a higher temperature to that, it kills faster, causing a bigger impact,”

If the sea stars' population continues to decline, the entire ecosystem is at risk. The sea stars eat sea urchins and other organisms that would otherwise ravage the kelp forests.

In some regions, the sunflower sea star is the only predator of urchins. These same locations are likely to see a short-lived population explosion of urchins who face starvation if kelp beds are devoured.

The combination of ecosystem imbalance and the warm water which aggravates the disease is described by researchers as the ‘perfect storm’ for the sea stars. The ecosystem, environmental and disease influences are pushing the species closer to extinction.

Marine illnesses can dismantle functioning ecosystems by just harming one species. The sunflower sea star is one of at least 20 species suffering from aquatic infections. Another sea star species in California, commonly known as the gulf sea star, was driven near extinction by a marine illness in 1978.

The International Union for the Conservation of Nature estimates that more than 42,000 species are threatened with extinction, including the sunflower sea star. Infectious diseases are one of many factors pushing endangered species closer to the extinction vortex.