Cornucopia

As I've been analyzing my samples from the moorings, I've been finding a lot of specimens of one species, Bouillonia cornucopiae. This species is an athecate hydroid, which might mean nothing to you but means a lot to me. Hydroids (there's not really a common name for them, sorry) live 

A large Bouillonia cornucopiae individual on my frames

attached to hard surfaces and filter the water to feed, and they're very commonly the first colonists on substrata in cold-water environments. Some of you may remember that hydroids completely took over the fouling panels I deployed under the WHOI pier for an experiment two years ago. Hydroids have also been ubiquitous on every recruitment experiment I've done in the Arctic, from 7 meters in a fjord right down to 2500 m at the central HAUSGARTEN station.

What's strange about B. cornucopiae is that for as many of them settle on artificial substrata, I have never seen any on natural hard objects like dropstones. I have collected B. cornucopiae specimens that settled on fouling panels, mooring lines, a robotic vehicle, and a radar reflector, but I have never seen them on a single rock – and trust me, I've seen enough photos of the seafloor from this area that I would have noticed them. So what in the world is their "natural" habitat?

The head of a Bouillonia cornucopiae, showing its gonads

One answer might be revealed by examining B. cornucopiae's lifestyle. I was already thinking it might be an opportunistic species, just based on the fact that it settles high up in the water column on everything from plastic to metal to rope, and this cruise, I've collected enough B. cornucopiae specimens that I can add other pieces to the puzzle. First of all, this species grows fast. My largest specimen was 43 mm long, not counting the head, and it had to be less than a year old because the panel it settled on had only been deployed a year ago. That's freaky fast growth. Second, I think B. cornucopiae adults might reproduce continuously, because I had specimens ranging in size from 0.2 mm (that's basically a head with no stalk) to the 43-mm monster and every size in between, suggesting they had recruited throughout the year. Add to that the fact that every single adult I collected had eggs, and it seems this species spends all its time either growing or making babies.

We usually don't think of fast-growing opportunistic species living in the Arctic deep sea, but Bouillonia cornucopiae is just that kind of a species. It takes advantage of every possible substratum. I'm still desperately confused as to where the hydroid made its home before humans started putting moorings and robots and experiments in the ocean, but maybe that answer will come in time. For now, I'm glad to analyze a beautiful and exciting species!