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

Scientists say that reintroducing the fast-moving predators to the West Coast could help control the spread of sea urchins that are devouring kelp.

The kelp forests off the West Coast 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 could come to the rescue.

One reason for the disappearing kelp is the tremendous expansion of the sea urchin population that feeds on it — including an estimated 10,000 percent increase in their numbers over the past few years in a reef surveyed off the coast of Oregon. And it may be that sea urchins have multiplied because one of their chief predators, the sunflower sea star, has been nearly wiped out by disease. (Scientists prefer “sea star” to “starfish” because the animals are not fish.)

A team of scientists suggests that the population explosion in sea urchins could not have happened if sunflower sea stars had been there to prey on them, and that restoring the population of the colorful creatures may help in the recovery of the kelp forest and the ecosystem it supports. The study appeared last month in Proceedings of the Royal Society B.

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