Lily of the sea

Friends, I would like to tell you about another common species on the settlement plates. Its scientific name is Bathycrinus carpenterii, but you can call it a sea lily. Sea lilies are echinoderms, related to sea stars, brittle stars, sea urchins, and sea cucumbers. Like all echinoderms, they have radial symmetry (they look the same no matter which way you turn them) and arms in multiples of 5. The main difference between sea lilies and other echinoderms is that sea lilies live on stalks and filter the water for their food. They look very flower-like, with a long, tall stem and narrow, finger-like petals.

Up until the mid-1800s, sea lilies were only known from the fossil record. The discovery of living, extant sea lilies in the deep sea lead to a hypothesis that the deep sea was a sort of refuge for “living fossils,” ancient organisms that had died out everywhere else. The hypothesis has now been disproven, but sea lilies mark an important step in the history of deep-sea biology.

A large Bathycrinus carpenterii recruit on one of my plates

Bathycrinus is pretty common in the Fram Strait. We see it in photos of the seafloor, standing tall above the muddy sediment like widely-spaced flowers in a field of dirt. I had always been told that Bathycrinus settled on tiny pebbles and only appeared to be living on the sediment because the pebbles got buried. I had a hard time picturing it but now fully understand that Bathycrinus is a hard-bottom species because it was all over the settlement plates. It loves hard surfaces!

Species that filter the water for their food generally like to be as high off the seafloor as possible because the current is faster the higher up you go. More current means more food, which means animals have an easier time making a living. I haven’t run the numbers yet, but it seemed there were more Bathycrinus on the settlement plates that were higher up off the seafloor. It also settled on the ropes that held the plates to the frame and on the frame itself – anything to get up high into the water column.

One cool thing about sea lilies is that they’ll always show you which direction the current is flowing. Much like moss growing only on one side of a tree, sea lilies tend to face into the current to feed. Their stalks are flexible enough that they can bend and sway as the current changes. In a lot of the seafloor photos, you’ll see Bathycrinus individuals all facing the same direction.

The appearance of Bathycrinus on my settlement plates promises to tell me a lot about the species’ life cycle, growth, and reproduction. I’m glad for the chance to learn more about a common Arctic species!