But animals placed either six feet (two meters) or 12 feet (four meters) away ended up wandering around randomly. Starfish displaced about three feet (a meter) from the reef walked back home in pretty much a straight line. Their behavioral observations involved moving individual blue sea stars off of a coral reef near Okinawa, Japan, to see if the animals could make their way back or not. "A lens can help you create a better-resolved image," said Garm, "or it can help you collect more light." Since blue sea star eyes don't have lenses, the images they form are fairly rough. One such measure gave researchers an idea of how wide the sea star field of view was: large enough to pick out a coral reef in front of them.Ī second measure looked at the ability of the eyes to resolve images. Garm and colleagues combined physical measurements of the eye itself with behavioral experiments to come to their conclusions. For instance, blue sea star eyes lack lenses, unlike arthropods' eyes. Starfish have compound eyes, like the ones on arthropods such as insects or lobsters, but the resemblance ends there, Garm says. So being able to locate a reef-likely the only big, static object in a starfish's immediate vicinity-is very important for these animals. If it wandered off to the sandy flats surrounding those reefs, it wouldn't be able to find food and would eventually starve. This species is tightly tied to coral reefs. "It only has about 200 pixels."īut it's enough to enable the blue sea star to recognize large, immovable structures, he said. "The image formed in the starfish eye is a very crude image," says study co-author Garm. Home Sweet Homeĭespite the confirmation of sea star sight, the animals won't be developing reputations for great vision any time soon. Previous research suggested sea star eyes were sensitive to light, possibly giving the animal an idea of the location of dark and light spots in their dappled underwater world. Part of the reason is that it's been hard to get any physiological information out of the eyes until recently, thanks to advances in scientific equipment, he said. Scientists have known about sea star eyes for about 200 years, but aside from studying their structure, not much research has been done on them, said Anders Garm, a neurobiologist at the University of Copenhagen in Helsingor, Denmark. "In fact, behavior and body form have been shown to be remarkably complex ," he explained. Oceans 101 Low Expectations for ComplexityĮxpectations for complexity in these animals have been low because historically, sea stars were viewed as "simple creatures without complicated behavior," said Mah, who was not involved in the study. The new study was published by different researchers on February 7 in the same journal. Scientists studied a starfish species found in the tropical Indian and Pacific Oceans, known as the blue sea star ( Linckia laevigata), and published their findings online Januin the journal Proceedings of the Royal Society B. Of the 13 species researched, two were also bioluminescent, meaning they could likely use light flashes to communicate with potential mates.
Now, a new study shows that some Arctic deep-sea starfish also rely on their vision for navigation. "This represents a significant breakthrough in our understanding of how sea stars perceive the world," wrote Christopher Mah, a researcher at the Smithsonian's National Museum of Natural History in Washington, D.C., in an email. In 2014, research suggested that the eyes of tropical sea stars-the term scientists prefer, as the invertebrates aren't actually fish-can form rough images, preventing the animals from wandering too far from home. Since their eyes are also relatively simple and because they lack a brain, it was difficult to figure out how or even if they could see.
Starfish have historically been thought of as simple animals. Starfish have eyes-one on the end of each of their arms-but what they do with them was anyone's guess.
Update, February 7, 2018: This story has been updated with information on the 2018 study on deep-sea starfish in the Arctic.
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