The world’s most famous research submersible may have inadvertently been carrying invasive species between the deep-water sites it has spent decades studying.

Since its creation in 1964, the venerable Alvin sub has performed thousands of dives, and its successes include surveying the Titanic and probing the first discovered hydrothermal vents.

In 2004 a team of scientists using Alvin found 38 tiny limpets of a type normally seen on hydrothermal vents in samples they had grabbed from an area with no vents. In fact, they were hundreds of kilometres north of the known range of the species they found. Their conclusion: the animals had hitched a ride on Alvin after a previous dive.

“I was so upset when I came to that realization,” says Janet Voight, a deep-sea biologist at the Field Museum of Natural History in Chicago, Illinois, and the lead scientist on that mission.

In a paper out today in Conservation Biology, Voight and her colleagues report finding the limpets after taking samples on the Juan de Fuca Ridge in the Pacific Ocean. They identified the species as Lepetodrilus gordensis (pictured, left), but this animal has only previously been found 635 kilometres to the south, in an area known as the Gorda Ridge.

Using gene sequences, isotope data and other information, they confirmed that the animals they found after the Juan de Fuca dive were identical to those found on the Gorda Ridge, where Alvin was diving just before the Juan de Fuca mission.

Voight admits that an error was made and that the team should have been more careful in its cleaning of Alvin’s sampling systems. But the survival of the limpets from one dive to the next has broader implications.

Research submersibles are cleaned after every mission, but it was widely assumed that the radical changes in pressure and temperature as they surfaced from the depths would kill any animals that were missed, says Voight. If that is not the case, researchers may have been inadvertently contaminating sites as they move a limited number of research vessels around multiple deep-sea sites.

There are dozens of submersibles used in research and other sectors, plus a host of different monitoring and sampling devices that researchers deposit into the murky depths of our oceans. All of these now have to be considered capable of unwittingly transferring species from one location to another.

“It’s agreed that we should not transplant populations among different sites,” says Voight. “But the threat of having the same instrument as a vector has been neglected.”

In addition to making sure sampling systems are carefully cleaned, researchers could consider washing subs with fresh water as one way of killing any stowaways, she suggests.

Image top: Alvin courtesy of OAR/National Undersea Research Program (NURP); Woods Hole Oceanographic Inst.
Image lower: Lepetodrilus gordensis courtesy of Ray Lee.