INTRO: You might not think of crabs as creatures that live on mountains. But in fact, a number of deep-sea crab species have made a niche for themselves on the sides of undersea volcanoes known as seamounts. Recently, with the help of a deep-diving submersible, Alaska scientists had a rare opportunity to study these crabs. Doug Schneider has more in this week's Arctic Science Journeys Radio.
STORY:Three years ago, crab researchers used the manned deep-diving submersible Alvin to take their first look at the Patton Seamount, a long-dormant undersea volcano in the Gulf of Alaska, about 300 miles south of Kodiak Island, Alaska. There, at depths ranging from a few hundred feet to more than a mile below the waves, they found ten species of crabs crawling about on the volcano's rocky slopes. They saw golden and scarlet king crabs, a small king crab relative known as paralomis, and a type of long-legged spider crab never before described in Alaska waters.
But what stood out, besides the variety of species, was that each kind of crab was very particular about where on the volcano it made its home. Brad Stevens is a biologist with the National Marine Fisheries Service in Kodiak, Alaska.
STEVENS: "Each of the crabs out here has a particular depth distribution. The golden king crabs live in what we call the shallowest water, from about 200 meters down to 600. They overlap a little bit with the scarlet king crabs from 500 down to about 900. Then you get into the paralomis that go on down to about 2,000 meters. The big spider crabs start at about 1,000 meters and go down to as deep as we've ever dove."
This summer the Ocean Exploration program of the National Oceanic and Atmospheric Administration arranged for the research ship Atlantis, along with Alvin, to return to Alaska. It was a chance for researchers to find answers.
For one, if each kind of crab is limited to a certain depth, well, how did they get there in the first place? Tom Shirley is a professor of biology at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. He's trying to understand how crabs managed to colonize these undersea mountains.
SHIRLEY: "Well, if you're talking about marine crabs, they could just walk from one seamount to the other. Well, that's not really true. Some of these seamounts are 15,000 feet high. The only way the crabs can get from one seamount to the other, if they live within a narrow zone, is through their larvae."
In other words, the researchers think that tiny newborn crab, or larvae, ride along on ocean currents until they finally settle onto the seafloor. Shirley says that over time, the seamounts have become an undersea oasis, a place where fish, crabs, even brightly colored sponges and corals, flourish.
SHIRLEY: "These seamounts provide structural complexity. They intercept currents so they generate a lot of current activity around the seamounts. It makes for great feeding areas for suspension feeders. And that forms a base for a food web, and so lots of fish and crabs and other things can live there. We're also seeing the importance of things like soft corals. All the fish and the crabs are in fact either on or around these soft corals that are like bushes you'd find around an oasis. They provide habitat complexity, a place to hide, a place to get out of the current, and a place for food. And that's the sort of thing that, if you were sampling remotely, you wouldn't see the relationship of the organisms to each other."
On this cruise, researchers brought some of the crabs back to the surface alive—particularly egg-bearing females. At this point, Shirley says, researchers don't even know the basics about deep-sea crab reproduction, such as whether the golden king crabs have a distinct mating season, or how long it takes for their eggs to hatch into larvae.
Stevens and Shirley plan to collect eggs from adult females and then hatch them and raise the larvae in a lab. They painstakingly collected five live crabs in one dive using a manipulator arm on Alvin specially modified for that purpose. Shirley says catching the crabs wasn't easy.
SHIRLEY: "As soon as they know you're there, they hightail it out of there."
Weeks later, Brad Stevens reports that two golden king crabs successfully mated while in captivity. Researchers hope their clutch of eggs will produce both baby crabs and some big answers.
OUTRO: Thanks this week go to science writer Sonya Senkowsky and the NOAA Ocean Exploration Program. This is Arctic Science Journeys Radio, a production of the Alaska Sea Grant Program at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences. I'm Doug Schneider.
Audio version and related websites
Thanks to the following individuals for help preparing this script:
Dr. Tom Shirley
Dr. Brad Stevens
Arctic Science Journeys is a radio service highlighting science, culture, and the environment of the circumpolar north. Produced by the Alaska Sea Grant College Program and the University of Alaska Fairbanks. The shortcut to our ASJ news home page is www.asjnews.org.
The URL for
this page is
Listen to story on Real Audio
Related Web sites