Observations of Aquatic Behavior

By Peter Mieras of Rendezvous Dive Adventures

For many divers anemone are one of the signature species of the Pacific Northwest. Especially the giant plumose anemone, which reminds you of a cauliflower, can be seen on almost every dive. It often covers a large area on dive site, creating a white forest.

Other species commonly found are the white spotted anemone, the painted anemone and the fisheating anemone. One thing they have in common is that they fix themselves on a spot and stay there. New anemones are created by little pieces breaking off the larger anemone and they themselves settle down. There is however one exception to this stationary life style.

Stomphia didemon (the swimming anemone) has a surprising ability to move around. Mind you they do this only if they have to. The leather starfish (Demasterias imbricata) is one of the more ferocious starfish and it appreciates the swimming anemone as a nice snack. For understandable reasons the anemone in question doesn’t share that enthusiasm.

If you are lucky you can see the scene in which the leather starfish sneaks up to the anemone. When getting too close for comfort the anemone displays an interesting behaviour. First it seems to elongate itself by reducing its waistline (diameter) and it stands taller. It then comes down on the starfish with its stinging tentacles like a punishment with a whip.

It does this repeatedly in the hope that the starfish aborts its approach. Unfortunately the starfish has a thick slimy mucus layer on its skin which acts like a barrier to the stinging cells. And the starfish doesn’t desist. The anemone now goes for its last resort of defense and begins to wiggle side to side, eventually taking its foot off the spot is was residing on. In a gracious yet strong fashion the anemone undulates and swims away from its siege.

After a short distance it straightens out and lets itself slowly sink to the bottom and rights itself again. It then attaches it foot and settles in on its new location. It takes luck and patience to find such a scene but when you do it pays off to stick around for a few minutes.

A video of this behaviour can be watched at www.divenewsnetwork.com or www.rendezvousdiving.com
Acknowledgements: Jackie Hildering for suggestions and corrections.