Almost a cartoon

I've been working on photos of a delicate pink algae, but it's infested with bouncy skeleton shrimp. This couple made me laugh.

Six-legged bully

I try not to anthropomorphize my critters, to remember that they have their own lives that don't necessarily mesh with ours. But sometimes the temptation is strong. I know the face on that poor victim is just a fluke of camera angles; she* doesn't really have a down-turned mouth and a pug nose. She's not really going to be forced to hand over her lunch money. It just looks that way.

But some things are almost universal, among humans, animals, and even plants: the struggle for place, for food, for sex or its equivalent. And these skeleton shrimp are fighters; they cross paths often, and when they do, they hit and bite at each other. Usually it ends quickly, as the smaller one backs away.

A few seconds later; fight ended, all is forgiven and forgotten.

These tiny beasties are usually standing upright on swaying seaweeds. Nothing seems to dislodge them, even when I pick up a handful of algae and swish it around in the water to shake out any muck or unsuspected hitchhikers. When I drop the algae back in the tank, there are all the skeleton shrimp, standing tall, as if nothing had happened.

When they move from one branch of seaweed to another, or travel down a blade of eelgrass, they bend over, grasp the path ahead with their big, hooked "hands" (gnathopods), then bring up the back legs, the way an inchworm moves. But as soon as they've reached their destination, they stand up again.

Those six prehensile legs explain how they maintain their footing.

*She's carrying young; see her swollen brood pouch? The larger one is probably a male.

Bullies!

"All bark and no bite," I said, about the black-clawed crabs in my tank, because they'll threaten me with amputation, but then sit meekly in my hand, all threats forgotten.

I was wrong. They're bullies, only attacking smaller and weaker neighbours. Not only snails, proper crab food, but other crabs, hermits, and, I think, bubble shells and polychaetes.

Ready for action.

The aquarium has been a good place for them; in five months, the big male has  grown from under 1/4 inch across the carapace to somewhat over an inch, with extended pincers twice that again. I've provided them with clean, cold water, gourmet crab dinners, a handy rock pile to live under; there was no need to beat up on the other residents.

But. Their neighbours included two shore crabs, male and female, grown up in the tank. The female, a large adult, disappeared. I didn't even find her remains. A few weeks later, the smaller male was gone, too.

I kept finding maimed and dying hermits. And the bubble shells that had lived all winter in the tank couldn't be found. The nudibranch got eaten. Even a big polychaete worm, one of the ones that can grow up to a foot long, even in a small tank, just wasn't there any more. And now there were only two black-clawed crabs; the female had seemingly evaporated.

But everything seemed right; I checked temperatures, salinity, acidity, current, filtering; all normal. So a couple of weeks ago, I brought home another three shore crabs to liven up the tank with their antics.

Two days ago, the largest (still smaller than the large black-clawed crab) turned up with three legs and a pincer gone on one side. Who would do this to him? Only another crab, and suspicion centered on that big black-clawed male, sitting so peacefully under his stone. While I pondered this, a second shore crab lost two legs.

So tonight, I've hunted down and arrested both black-clawed crabs. They're in solitary confinement, for now; the first trip to the beach, they'll go with me. And won't come home.

Small black-clawed crab, 1/2 inch across the carapace.

Now that I've got them out where I can watch them, I see that the small crab is terrified of the large one, and keeps a good distance away. He probably has good reasons.

The two traumatized shore crabs got extra goodies, in a bowl away from competition, and seem to be recovering.