Well, at least some of them. Matthew, our resident author, just called my attention to this video showing a sea anemone swimming to avoid predation. Although sea anemones are in the phylum Cnidaria along with jellyfish and box jellies, I’ve always thought of them as completely sessile. Well, some of them are, but not all. This one takes off and starts swimming about 55 seconds in:
The YouTube notes give a bit more information:
This PAL footage and other can be purchased via website http://www.rendezvousdiving.com/footage/htm
Surprising ability to swim from an animal that is usually fixed to its spot. Filmed during a scuba dive in Barkley Sound , Vancouver Island Canada
Apparently a few species are permanently pelagic: not affixed to a substrate but floating freely in the water.
The star doesn’t seem to be attacking very aggressively. One wonders if it was placed there by the diver to provoke the anemone into action.
And where’s the second half of the story? How does the anemone choose a place to set down and re-attach itself? Apparently the diver had no interest in that part of it.
Sea stars move really really slow. You’d need hours of footage to see it being «aggressive.»
Well, even if the sea star was placed there by the diver, the behaviour by the anemone is genuine and quite startling (to me, anyway). It would be equally startling if the anemone had swum in response to the diver prodding it with a stick.
Fine, but now that we know that anemones have such behavior, it seems reasonable to ask the next question about what triggers it. Was it the star, or the diver, or some combination of the two? Given that the star is basically motionless throughout the video, why did the anemone choose that particular moment, while the camera was running, to detach itself?
(First, an admission – I thought your first post was a little dismissive and missed the point of the truly remarkable behaviour by the anemone – I now think I was too hasty and I apologise.)
As to what triggered it, I’m sure it was the star. It wasn’t the diver, how would the anemone know he was there?; and when it swims it comes towards the diver. Those stars have thousands of little sucker feet on stalks and, though the definition in the video is too poor to see them, most likely they were feeling up the anemone’s foot. And the anemone leans over three times and feels the star with its tentacles, I think that tells it it’s time to get out.
In this video:
http://www.youtube.com/watch?v=orFXn_pJONU
an anemone is allowed to ‘feel’ a star’s ‘arm’ for a couple of seconds and it immediately starts swimming, even though the star has been withdrawn. I’d say it’s an automatic response, maybe triggered by recognising some characteristic (chemical? – it’s ‘smell’?) of the star.
*its* smell. Pedant. 🙁
Stars are basically motionless. Sometimes I amuse myself measuring starfish speeds. Speeds are typically one third to half a millimeter per second in uneven rocky ground (chasing sea snails). In clean flat sand I’ve seen them sprint at about 2-3 millimeters per second.
Two chicks hatched at Cornell hawk cam.
Not more than a minute after learning a new word (sessile), I was able to use it in a sentence when my wife walked by and asked me if I was getting off the couch today.
well-played!
Too bad there isn’t an amusing pop song from the 80s to explain its meaning like there is with Jessie’s Girl & the word, “moot”.
Amazing that the swimming style of the anemone actually works, I wonder how long it can keep it up for.
What impresses me about this video is that it shows predation and predation avoidance by two animals without brains.
Seems to me that this says brains aren’t necessary for behavior, but only to speed behavior up.
But brains don’t speed up behavior. They slow it down by interposing more processing between stimulus and response. Reflexes are faster than conscious action.
What brains speed up is learning. With a brain, you don’t need generations of selective pressure to learn new behaviors, or new situations in which to apply old behaviors. You can learn them and profit from them within a single lifetime.
I don’t think an animal with a brain would have taken so long to decide that it was time to scoot. Besides, have you ever seen a starfish hunt? Better use timelapse.
Have you seen a Venus flytrap hunt? Better use a high-speed camera.
I have, and they don’t hunt. They trap. And it’s not really that fast. Downright slow compared to quick strike animal predators.
It’s fast enough to catch the fly — which has a brain.
Another much larger anemone species, Urticina picivora, also detaches in response to the same sea star species (called the leather star, Dermasterias imbricata). But instead of swimming away it rolls over on top of the sea star and will eat the sea star if possible (and if the sea star is not too big). Hazards of trying to eat a predator like a big anemone.
page could not be found for swimming sea anemones
It almost appears that the anemone is reacting initially trying to strike at the sea star. Does anyone know if that’s the case? Would its venom affect a sea star at all?
Anenomes go where they want. If they live in your reef aquarium, that usually means you’ll find them sitting on top of your favorite coral.