Starfish Are Not the Wallflowers You Think They Are
This is the time of year for wandering the beaches and studying what washes up, and starfish often figure prominently in what we find, and in our memories of summer. It’s partly because they are so strangely symmetrical—often with their hundreds of small, tube-like legs still wriggling underneath. And it’s also because they seem so vulnerable caught out in the sun, even though in their own world, beneath the waves, they are in fact great predators.
But you will probably not be seeing any starfish this summer on the U.S. East Coast. Some unknown killer has devastated populations from New Jersey to Maine. Caitlin del Sesto, a graduate student at the University of Rhode Island, was one of the first to notice it, when starfish she had collected for a study began to develop white lesions and then melt away in her aquarium. Some of the sick ones actually shed all their limbs in response to the stress.
Other researchers have since reported the same disturbing phenomenon. Divers from the Marine Biological Laboratory on Cape Cod are also finding that concentrations of starfish—or sea stars, as scientists prefer to call them—have been missing from their usual locations. Del Sesto is asking scuba divers and other members of the public to email her (email@example.com) information on any large congregations of starfish seen in Rhode Island waters, including their exact location, depth, numbers, and whether the animals appear healthy or diseased.
So far the cause of the die-off remains a mystery. “We don’t know if it’s something in the water, or something inside the starfish,” says del Sesto. She and her professor, Marta Gomez-Chiarra, are beginning experiments to isolate a possible bacterial or viral pathogen. They’ll also look at whether a rise in seawater temperature, or other environmental changes, may be a factor.
“There was a big increase in sea star numbers about three or four years ago,” says Gomez-Chiarri, “and often when you have a population explosion of any species you end up with a disease outbreak. When there’s not enough food for them all, it causes stress, and the density of animals leads to increased disease transmission.”
She worries that the disease may persist, preventing recovery of the population. “Diseases don’t just completely disappear after a massive die-off,” says Gomez-Chiarri. That matters because starfish are the original keystone species, and their absence can be devastating for the diversity of other coastal species.
The importance of starfish first became evident in the 1960s in a classic experiment by the University of Washington researcher Robert T. Paine. He was studying the rocky world between high and low tides on the Pacific Coast near Seattle, where the food chain typically consists of barnacles, limpets, chitins, anemones, and particularly mussels. The mussels normally wind up concentrated closer to the high tide line, where it’s hard for starfish, the dominant predator, to get at them.
But when Paine removed the starfish from his study area to see what would happen, the mussels soon crept down toward deeper water, crowding out the barnacles and other species. Within a few years, only eight of the 15 original species still lived in that neighborhood. Paine’s study revealed the surprising importance of top predators in keeping an ecological community healthy. He called the starfish he was studying a “keystone species,” because, like the structure of an arch in a building, everything fell apart when that one piece was removed.
What happens to starfish also matters because other research this summer has revealed they are far more interesting creatures than previously thought. Look at the Wikipedia entry for starfish, for instance, and (at least for the moment) you will see that the starfish “does not have the capacity to plan its actions.” But new research from the University of Copenhagen in Denmark suggests that starfish use the eyes at the ends of their arms in essence to hunt. When researcher Anders Garm removed starfish from their feeding grounds on the coral reef and placed them a meter away on the sand, the ones who’d lost their eyes moved randomly. But the ones with their eyes intact headed straight back to the coral reef for dinner.
And in a second study, in the Journal of Experimental Biology, British researchers reveal that starfish are in fact well equipped to hunt and kill. Scientists already knew that starfish use chemosensors on their legs to detect prey. When they find a victim, their legs wriggle eagerly all around like a crowd of fingers. Then their arms fold in around the victim, typically a mussel or clam. Now the British co-authors have identified the neuropeptide that causes the starfish to make its stomach come blooming out of its mouth to engulf its prey, turning the fleshy parts into a kind of chowder that it sucks in for sustenance.
Years ago, the essayist Loren Eiseley described the starfish he found on the beach as “the things beaten in the strangling surf…the lost ones, the failures of the world.” But clearly, starfish are the monstrous little winners of the intertidal zone—assuming they can survive this summer’s mysterious killer on the U.S. East Coast.
When starfish attack: