Researchers have discovered that bay-sized starfish from the West Coast have disappeared

Massive sunflower starfish, once plentiful on the west coast of North America, have disappeared from the waters of the region at astonishing speed due to their disease and their growth , researchers report in a new study.

Since 2013, the disappearance of starfish has killed thousands of echinoderms from Mexico to Alaska. The disease causes lesions on the skin of starfish, the arms dissolve and often end in death.

Sunflower starfish – huge animals the size of a manhole – are particularly affected. Scientists now assume that the population in California and Washington has declined by 80 to 100 percent in some areas.

"Abundant in coastal waters, sunflower starfish are currently off the coast of California and rare in Alaska," said Drew Harvell, a Cornell professor of ecology and evolutionary biology, in a statement. Harvell was the co-author of the study, which was published Wednesday in the journal Science Advances with researchers from UC Davis.

In parts of their southern habitat, starfish are considered endangered by scientists, Harvell said.

Climate Change, the researchers That is, the temperature in oceanic waters is increased, the effects of wasted starfish disease are exacerbated.

"It's a deadly disease, and if you add a higher temperature, it kills faster and causes a bigger impact," Harvell said.

The disappearance of the Sunflower Sea Star – a predator that is known to soar above the ocean floor with the enthusiasm of a street sweeper – is likely to have far-reaching repercussions on the fragile ecosystem of the oceans. Sunflower starfish eat sea urchins, and without the predator keeping their numbers in check, sea urchins have exploded in some places, greatly reducing the seaweed.

This threatens "seaweed forests and biodiversity," said Joseph Gaydos, a leading author of the paper and director of the program of the UC Davis SeaDoc Society in the press release. "This cascading effect has a really big impact."

Read the latest stories from Michelle Robertson and send her news tips to mrobertson@sfchronicle.com .

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