Die Verankerung (the mooring): part 2

"Do you want to grab sample tubes and come over?" Theresa signaled with her hands to compensate for the noise. The winch was still whirring as more of the mooring came aboard, and the helicopter was trying to land on the upper deck. I nodded and started heading toward my lab. Theresa's water sampler had been deployed at the very top of the mooring, just 25 m below the surface, and it was covered in biological fauna. I was grateful she let me have a pass at the instrument before cleaning it off for re-deployment.

I filled 7 or 8 tubes with hydroids, mussels, and scallops. Theresa pointed to a limp red blob on the frame of her instrument: "I think this one is a slug." She was using the common name in German, Nacktschnecke, which literally translates to "naked snail." I nodded and pulled it off the instrument with my forceps, then grabbed several others like it.

Back in the lab, I put the "naked snail" in a dish of seawater. Immediately, elaborate limbs floated away from the main body. They were attached to the animal's back and branched at the tips. I stuck my face closer to the dish until my nose was almost touching the surface. Delicately, I rolled the animal over with my forceps, and this action revealed a row of spots along the animal's side, then another along its belly. My mind immediately kicked into warp speed, racing through the archives of invertebrate zoology stored therein. I examined the mouthparts, the appendages, the shape, the texture.

The sea cucumber

This animal was no naked snail.

It was a sea cucumber.

Here's why this is cool: sea cucumbers are benthic invertebrates. There are some rare examples of benthopelagic ones that swim right over the floor in the deep sea, but this was no swimming cucumber. It had brightly-colored appendages that would blend in with marine vegetation, and its mouth was designed for feeding on something more substantial than dirt. Both these characteristics make me believe this species lives in shallow-water habitats, possibly among algae. It had settled on an instrument at 25 m depth, so it's at least capable of living that shallow.

BUT that instrument – in fact, the whole mooring – was located far offshore, in 2500 m of water. Any cucumber larva that tried to settle on the benthos at that location would have no chance of survival at all. The seafloor is just too far down. So what in the world was it doing there?

Sometimes observations leave me with more questions than answers, and this is definitely one of those cases. I expect the species will be easy to identify once I get home and check my photographic guide to North Atlantic fauna. I'm mostly curious whether the cucumber already has an established population in Svalbard, or whether the larvae might have come from northern Norway. There's a current that runs up the Norwegian coast and past Svalbard into the central Arctic called the West Spitsbergen Current. Maybe, just maybe, that current might be bringing the species north.

I will keep you posted as I find out more. It was very exciting to find the cucumber!