Where the pink sponge grows

It is 9:45 pm, and I have been at the microscope for 10 hours today. I knew the analysis would have to happen fast, before the animals on the settlement plates rotted and wasted away. I saved half of the plates in ethanol to buy myself some time and kept the rest in cold water, sitting in nature’s refrigerator on the deck of the ship. After two days of work, I just finished the refrigerated plates, but I already have some very cool results.

A Cladorhiza gelida recruit on one of the plates

For starters, I’ve found about 15 species on the plates. That’s not very many in the grand scheme of things, but it’s actually more than I expected. Every time I find a new species, I photograph it, pick it off the plate with my forceps, and save a sample to identify later. Some of the species I can recognize and identify right way because their adults occur on rocks in the area, but others have me clueless. It’s going to be a fun adventure to figure out what they are!

One of the most common species on the plates is a sponge, Cladorhiza gelida. It’s a spiky species, and the small pink recruits look like a corn dog wrapped in velcro, or like a piece of cactus on a stick. The desert imagery doesn’t stop there, because in photos from the deep seafloor, Cladorhiza adults resemble tumbleweed. They’re a mess of white branches, and the colonies roll across the seafloor, blown by the current. We actually had a clump of Cladorhiza roll past the ROV during a dive earlier this trip. Sometimes, a clump of Cladorhiza will get caught next to a stone and stop rolling. Held stationary by a rock, the sponge often dies, but its skeleton remains and becomes colonized by sponges and soft corals. It’s pretty common to see dead Cladorhiza skeletons with their epibionts next to dropstones in the Fram Strait.

Cladorhiza is a very cool, ecologically important species, and it also has a unique way of feeding itself. Most sponges filter the water for their food, catching and consuming the microscopic particles within it, but Clardorhiza isn’t content just to eat crumbs. It wants steaks. Cladorhiza gelida is carnivore.

A new C. gelida recruit with a copepod stuck to it.
Photographed with a dissecting microscope

At first it may seem impossible for a sponge to be carnivorous (trust me, I didn’t get it at first either), but I assure you there are many such sponges in the world. All of them use the same basic principle. They have microscopic hooks all over their body, which they use to skewer copepods. (In case you don’t know, copepods are tiny swimming crustaceans.) I have a photo I’ll have to upload later, but one of my Cladorhiza recruits actually had a copepod attached to it, helplessly velcroed to its predator. Imagine sticking a lobster to a cactus – that’s what it looked like. Crazy thing is, the copepod was just about as big as the sponge!

Cladorhiza is one of the most common recruits on my plates, and I can learn a lot about its growth and population dynamics by examining the juveniles. I’m looking forward to learning more about an important Arctic sponge!