(Apologies to The Clash.)
I first heard about the Crab Spa from Stefan about a year ago, during my job interview at WHOI. I’ve studied crabs for the past decade, so the prospect of an entire undersea resort full of crabs “taking the waters” was a singularly delightful prospect. The Crab Spa certainly lived up to its name, with dozens of blind white crabs prowling the Riftia beds near warm-water outflows. Like most crabs they are predators and scavengers, on the hunt for anything, dead or alive, which will stand still long enough for them to eat it. This greed and un-pickiness are characteristics I’ve exploited before in trapping for coastal crabs.
My prior experience with deep-sea crabs, however, consisted solely of watching reruns of Deadliest Catch. Since I am insufficiently grizzled and bearded to go that route, I opted for a different approach: commercial crayfish traps from Amazon. An added complication not faced by the gentlemen of the Bering Sea is that my traps have to fit in an insulated biobox. These are thick plexiglass, sealed watertight with silicone, and keep the deep water cold during the ascent. The one we used most on the cruise is long and relatively thin, and is doing double-duty for my crab traps and Horst and Tjorven’s tubeworms. (Because of its shape and purpose, it is more colloquially referred to as the “worm coffin” by the Alvin team.)
Crab trap and tubeworms in the ‘worm coffin’.
It felt a bit surreal to fish for crabs by submarine, leaving a lone trap under 1.5 miles of ocean. One distinct bonus is that traps in the deep sea are always right where you left them, something that can’t be counted on in coastal waters. It took a few dives to find the right trap (long and skinny), and the right bait (dead tubeworms), but once I did, it worked like a charm. From the sub, we watched the crabs cruise over soon as the traps were down, climbing the mesh in an effort to get to their newfound bounty. Occasionally one claimed my trap as his own, glaring blindly at other approachers from his perch directly on top of the bait bucket.
A crab tries to fight off Alvin’s claw as it reaches for tube worms.
On the cruise, I collected these animals because they’re evolutionarily fascinating. They shuttle between vent outflows and the deep-sea floor, two starkly different environments. The first is full of food and energy, but also hot and toxic and devoid of oxygen. In contrast, the seafloor is cold and largely lifeless, though the water is healthy and oxygenated. Switching between the two is like walking outside on a beastly hot day from an office where the AC is constantly set too low: a shock to the system.
Holding a vent crab up to the light to highlight its translucence.
Back at WHOI, the harder work will begin soon. My next step will be to rifle through the crabs’ DNA and compare it to that of their shallow-water relations, looking for genes which show signs of adaptation to life at deep sea vents. These genetic breadcrumbs will help me walk backwards through the crabs’ history, piecing together their long evolutionary path towards a dark life. With a little luck, it will be the beginning of a new research direction, and more deep-sea crabbing.
