September 12, 2013 – CANADA – The waters off British Columbia, Canada, are littered with dead starfish, and researchers have no idea what’s causing the deaths. At the end of August, marine biologist and scuba enthusiast Jonathan Martin was out on his usual Saturday dive with some friends when he noticed something unusual. “We just started noticing dead starfish that looked like they had their arms chopped off,” Martin said. They were sunflower starfish (Pycnopodia helianthoides), a major marine predator in the area that feeds mostly on sea urchins and snails. Like most starfish, the sunflower starfish can regenerate lost limbs—it can have up to 20—and can grow to be up to three feet (a meter) across. Since Martin was diving in an area frequented by crabbers, at first he thought the sunflower starfish had gotten caught in some of the crab traps and had lost limbs escaping. But Martin kept seeing large numbers of dead starfish as he and his friends swam to a marine park where such crab fishing is illegal. Martin knew then it wasn’t the traps that were causing the starfish deaths. After returning from the dive, he visited friends at a local dive shop who were active in marine conservation. Without any definitive answer, he shared photos on Flickr and videos on YouTube—taken at Lion’s Bay and Whytecliff Park in Vancouver—to try to get ideas from others about what was going on.
“It really struck a chord in other divers who were seeing it on Facebook and social media, both locally and as far away as California, who had been seeing similar things,” Martin said. “[The starfish] seem to waste away, ‘deflate’ a little, and then just … disintegrate. The arms just detach, and the central disc falls apart. It seems to happen rapidly, and not just dead animals undergoing decomposition, as I observed single arms clinging to the rock faces, tube feet still moving, with the skin split, gills flapping in the current. I’ve seen single animals in the past looking like this, and the first dive this morning I thought it might be crabbers chopping them up and tossing them off the rocks. Then we did our second dive in an area closed to fishing, and in absolutely amazing numbers. The bottom from about 20 to 50 feet [6 to 15 meters] was absolutely littered with arms, oral discs, tube feet, gonads and gills … it was kind of creepy.” Both Mah and Martin also wonder if a population explosion of the species, which began about three years ago, has something to do with the deaths. “It was an unprecedented increase, so maybe what we’re seeing is just sort of a bursting of the bubble. The animals just reached a density that was unsustainable,” Martin suggested. –National Geographic
contribution Jenny M.