‘Gruesome’ undersea ‘massacre’ which baffled scientists finally answered after decade of research

The worst-hit species, the sunflower sea star, lost approximately 90 per cent of its population in the first five years of the outbreak.

Alyssa Gehman, a marine disease ecologist at the Hakai Institute in British Columbia, Canada, helped to pinpoint the cause of the epidemic.

Healthy starfish have “puffy arms sticking straight out”, however the wasting disease causes them to grow lesions and “then their arms actually fall off”, Gehman said.

“It’s really quite gruesome,” she added.

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The worst-hit species, the sunflower sea star, lost approximately 90 per cent of its population in the first five years of the outbreak

According to a study published on Monday, bacteria are to blame for the epidemic.

Rebecca Vega Thurber, a marine microbiologist at the University of California, Santa Barbara was not involved in the study – but she said the “findings solve a long-standing question about a very serious disease in the ocean”.

Early research pointed towards a virus as the cause.

But the study’s co-author, Melanie Prentice from the Hakai Institute, said it became clear the densovirus which scientists initially focused on was actually a normal resident inside healthy starfish, and was not associated with the disease.

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Starfish usually keep sea urchin numbers in check

Further probes in the decade-long research project missed the culprit because scientists studied tissue samples of dead starfish which no longer contained the bodily fluid which surrounds the organs.

It was inside this fluid that the bacteria responsible for the disease was eventually found.

Blake Ushijima, a microbiologist at the University of North Carolina, said: “It’s incredibly difficult to trace the source of so many environmental diseases, especially underwater.”

Although not involved in the research, he commended the work done by the team, saying it was “really smart and significant”.

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Kelp forests are crucial within the ecosystem, providing vital food and habitat for a wide variety of animals including fish, sea otters, and seals

Now that the cause has been found, scientists are hoping to be able nurse the starfish population back to good health – which is vital for the entire Pacific ecosystem.

Gehman said that while sunflower sea stars “look sort of innocent when you see them, they eat almost everything that lives on the bottom of the ocean”.

She explained they are “voracious eaters” which gobble up excess sea urchins.

Due to the largely decreased numbers of starfish, sea urchin populations have exploded – which have in turn eaten 95 per cent of the kelp forests in northern California within the decade.

These kelp forests are crucial within the ecosystem, providing vital food and habitat for a wide variety of animals including fish, sea otters, and seals.