Starfish die-off

Massive Starfish Die-Off Baffles Scientists

The waters off British Columbia, Canada, are littered with dead starfish, and researchers have no idea what’s causing the deaths.

A decomposing P. helianthoides starfish still clinging to a rock. Photograph courtesy Jonathan Martin

National Geographic,

9 September, 2013

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. (Related pictures: “5 Animals That Regrow Body Parts.”)

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.

Searching for a Cause

Still without any answers, Martin wrote to invertebrate expert Christopher Mah, a researcher at the Smithsonian Institution in Washington, D.C., and author of the Echinoblog. In his email, he 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.”

On his blog, Mah speculated as to some causes, including a type of parasite that lives on starfish—the leading hypothesis at the moment, Martin said. (See more starfish pictures.)

A lone starfish arm. Photograph courtesy Jonathan Martin

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.

Starfish Not Alone

Yet what’s especially alarming to Martin, Mah, and other marine biologists is the fact that this die-off might not be restricted to P. helianthoides or the northern Pacific. Martin has spotted other dead invertebrates besides the sunflower starfish, including its predator, the morning sun star (Solaster dawsoni).

The morning sun star (Solaster dawsoni) is also affected by the die-off. Photograph courtesy Jonathan Martin

Earlier this summer, researchers also noticed a massive die-off of another starfish species on the U.S. East Coast. Scientists at the University of Rhode Island first noticed the large numbers of deaths of Asterias species—part of the same family as the sunflower starfish in British Columbia—in 2011, and since then, dead starfish have been documented along the eastern seaboard from Maine to New Jersey.

Fisheries and Oceans Canada is worried enough that they’ve asked Martin to go back out and collect samples for them to test in the lab. Although the agency has expressed interest in the die-off, Martin says that starfish aren’t a major research priority, and the main burden of investigation and discovery has fallen on him and other divers with an interest in marine ecology.

Meanwhile, Martin cautions people to not jump to conclusions.

“When I posted this on Facebook, some people immediately thought that this was due to global warming or other human-related activities. While that’s certainly a possibility, it’s all speculation.”