The Missing 24-Limbed Animals That Could Help Rescue the Ocean’s Forest

The west coast’s kelp forests are dying, and with their decline, an entire ecosystem of marine plants and animals is at risk. A large starfish with an appetite for sea urchins might come to the rescue.

One of the reasons for the disappearance of seaweeds is the enormous expansion of the sea urchin population that feeds on them, including an estimated 10,000 percent increase in numbers in recent years on a reef surveyed off the Oregon coast. And it may be that sea urchins have multiplied because one of their main predators, the sunflower sea star, has been nearly wiped out by disease. (Scientists prefer “starfish” to “starfish” because the animals are not fish.)

A team of scientists suggests that the sea urchin population explosion could not have happened if sunflower starfish had been there to prey on them, and that restoring the population of these colorful creatures could help bring back the kelp forest. and the ecosystem that surrounds it. supports the study appeared last month In Proceedings of the Royal Society B.

Scientists estimate that there were once as many as five billion sunflower starfish along the coast from Alaska to Baja California. They come in different shades of purple, brown, orange, and yellow, and can grow up to a meter wide, with up to two dozen arms. They move quickly, at least for a starfish, up to 200 feet in an hour. But starfish wasting disease, possibly caused by a virus, has killed most of them.

To test whether introducing captive-bred sunflower starfish could help, the researchers collected 24 sunflower starfish and 300 purple sea urchins near the San Juan Islands in Washington and observed them under experimental conditions, recording activity. hunting and food preferences. They were healthy, surviving starfish that were unaffected by the debilitating disease, possibly because they were resistant to the disease. The researchers hope that their offspring will share their characteristics.

The scientists discovered that starfish were passionate eaters of both juvenile and adult sea urchins. When starfish attack, urchins fight back, often tearing pieces of the starfish’s arms and driving the attacker back. If the starfish can persist, it circles the urchin and swallows it through its mouth at the bottom. After about 18 to 24 hours, it spits out the empty shell, having digested the soft parts, including the roe, which is also a delicacy among sea otters and human sushi eaters.

Is it practical to re-establish the sunflower starfish population with captive-bred animals? Aaron WE Galloway, an associate professor of marine biology at the University of Oregon and an author on the paper, thinks it could be.

“Just a few individuals of sunflower starfish can produce millions of larvae,” he said. If they succeed, she says, even a small restoration effort “could easily lead millions of starfish back into the wild.”

Dr. Galloway acknowledged that there are many other factors besides declining starfish populations that affect the health of the kelp forest, such as climate change and the increase in periodic heat waves. And he’s not saying that a healthy starfish population is the ultimate solution.

“There are many things you could try to do,” he said. “But starfish restoration is one of the most efficient levers we can pull. If we can help starfish to recover naturally, it could have ecosystem-scale effects, and it works without human intervention once it starts.”