Are Warmer Waters Causing Starfish to Disintegrate?

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"Are Warmer Waters Causing Starfish to Disintegrate?"

A sickly morning sun star off the coast of Vancouver.

A sickly morning sun star off the coast of Vancouver.

CREDIT: Jonathan Martin

All along the West Coast it looks like starfish are melting. Marine researchers and beach-goers have observed the same thing — the stretched and grotesquely distorted bodies of starfish, missing limbs and barely recognizable.

“I just got back from a dive out in West Vancouver and there seems to be a huge mortality event of some kind,” wrote Jonathan Martin, a research associate at Simon Fraer University and one of the first people to document the die-off on a colleague’s blog in August.” They [the starfish] seem to waste away, ‘deflate’ a little, and then just … disintegrate. The arms just detach, and the central disc falls apart…. I observed single arms clinging to the rock faces, tube feet still moving, with the skin split, gills flapping in the current … It was kind of creepy.”

The disease has been dubbed starfish wasting syndrome. First documented off the coast of British Columbia this summer, in a large population of sunflower seastars, there have since been similar reports of die-offs all the way from Alaska down to California. And the disease isn’t limited to just one species of starfish — at least eight others have been affected. Starfish on the East Coast haven’t been safe either, with reports of outbreaks of the syndrome dating back to 2011.

Dr. Chris Mah, an echinoderm expert at the Smithsonian’s National Museum of Natural History explained that while the exact agent causing the disease — virus, bacteria, fungus — has yet to be determined, warmer waters are likely making the starfish more vulnerable to whatever the pathogen is. Many pathogens also grow more quickly in warmer water.

“We can’t say that warmer waters are causing the disease, but I know of many starfish pathogens, deadly ones, which are more likely to occur in warmer waters,” explained Dr. Mah. “And when an outbreak begins, warmer waters can also make the disease more severe.”

For example, there is a well documented link between a nasty parasite, a protozoan called Orchitophrya stellarum, and warming waters. These single-celled organisms attack the gonads of male starfish, eating their sperm and effectively leaving them castrated. In controlled lab experiments, parasite numbers boomed with a small temperature increase and infected a greater amount of the starfish gonads.

Starfish certainly aren’t the only marine species made more vulnerable by warming waters. Lobsters of the East Coast are known to suffer from shell disease when water temperatures rise above a certain threshold and coral reefs are much more likely to succumb to disease with just a slight increase in temperature.

“Starfish may seem pretty hardy, but their bodies are literally open to the ocean,” said Dr. Mah. “They have nothing protecting them from changes in their environment. They truly are the canary in the coal mine for marine ecosystems.”

The loss of so many starfish matters both to the longterm health of each of the species affected, some of which are only found in these areas, and to the overall health of the marine ecosystems. Many starfish play the crucial role of keystone predator in their environment. Keystone predators help to keep all the other species below them in the food chain in check. Just like the extirpation of wolves from the West, caused deer populations to sky-rocket, with devastating consequences for forests, the loss of starfish can lead to explosions in sea urchin populations, which mow down everything edible in their path. Scientists refer to the wasteland left behind by unchecked urchin populations as “urchin barrens.”

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