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Deep-sea aliens hitched ride by submarine to pristine area

Todd Haney / Field Museum

Some of the 38 deep-sea limpets found aboard the research sub ALVIN. Each is less than half an inch long.

Sure, it sounds like a sci-fi movie: Alien species deep below the ocean latch onto scientists' gear, surface and cause havoc. But it could happen, scientists reported Thursday in a study that concludes those free rides can ruin ecosystems.

"I don't worry too much about deep-sea aliens taking over," lead researcher Janet Voight told msnbc.com, "but the worse-case scenario would in fact be a fundamental change in the ecosystem" if the new species brought with it a disease or parasite.

What triggered the study was the discovery of 38 deep-sea limpets, a kind of saltwater snail, inside a suction system aboard the research submarine ALVIN. They were found just after a dive in 2004 to the deep-water hydrothermal vents along the Juan de Fuca Ridge off Washington state -- and didn't seem like limpets native to the zone.

Voight, who was the mission's chief science officer, said, "I examined the specimens, and contacted my co-authors to help me understand why these limpets were apparently collected on Juan de Fuca Ridge." 

Further research determined that the limpets were from Gorda Ridge, a deep-water site 400 miles to the south where ALVIN had been a few days before the Juan de Fuca dive.

Janet Voight / Field Museum

Clumps of limpets are seen among sea worms at the bottom of Gorda Ridge, from where 38 limpets were mistakenly taken for a ride to another ecosystem.

"We realized instead that they had been collected on Gorda Ridge and 'stowed away'," said Voight, a biologist with the Field Museum of Natural History in Chicago.

Most surprising was that the limpets had survived the pressure change that comes from rising 8,900 feet in a submersible. 

"Our small limpets and their associates accrued somewhere in the suction sampler, perhaps in the corrugated hose, where enough water pooled to keep them alive," the researchers wrote in their study.

So while ALVIN was busy collecting new samples at Juan de Fuca, the Gorda Ridge limpets were hiding out in the hose.

Ships and even air travelers, via shoes or clothes, are also known to redistribute species to new areas, potentially altering local ecosystems.

"In retrospect, we should have cleaned the sampling gear more thoroughly, but we honestly believed that no animals could survive on ALVIN at sea level pressure for more than a day it took to get to the next dive site," Voight said. "We were naive. This is why we are admitting to our mistake, which could have, but we don't think did, introduce this species to Juan de Fuca Ridge. We want to warn other scientists that it is possible."

Raymond Lee

Limpets easily attach themselves to other objects, as seen in this photo of research equipment.

The danger at Juan de Fuca, Voight said, is that the Gorda Ridge limpets could have established themselves, along with parasites or disease, and potentially wiped out the native limpets.

Voight doesn't think that happened because the Juan de Fuca dive was some 300 feet from any vents, which the limpets need to survive. Still, she adds, "it might be worthwhile to go back to that spot" to check things out.

The team's advice? "We urge our colleagues to assume that physiologically tough stowaways are present on deep-sea research tools and to guard against transport of non-native species by clearing hoses and rinsing containers with freshwater, or even a peroxide solution, and drying tools before transporting them to different sites," they wrote.

The peer-reviewed study was published in the journal Conservation Biology.

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