Tuesday, March 4, 2014

Brawlers and Pistol Packers: Creature-Watching With My Nephew

There is no one standing over evolution with a blue pencil to say, "Now that one, there, is absolutely ridiculous, and I won't have it."  
- Annie Dillard, Pilgrim at Tinker Creek
My nephew Ben and I share a fascination with small ridiculous creatures. He's 11, so while I may have trouble connecting with him over comic books or Garfield cartoons, if one of us finds some weird little creeping thing, we've got things to talk about.

A few days ago I met up with Ben's family in Florida. We went out to a gorgeous white-sand beach at Fort Desoto Park, near Tampa, and set about looking at what had washed ashore. There were a few nice little shells, but the most interesting thing I found was a piece of dead sponge. Bending down to look at it, I noticed that its crevices were still inhabited by several dime-sized crabs. So I carried it down the beach to show the rest of the gang. When Ben heard about the crabs, he decided to tear the sponge apart to see what else was in there. We found a red brittle star the size of a quarter, several more crablets, and a variety of tiny worms. Then Ben found a prize: a little orange shrimp about 3/4 inch long, with one oversized and oddly-shaped claw. We admired our menagerie for a while, and then took the pieces of sponge to a lagoon to give the residents a chance in some calmer water.

We didn't know it at the time, but that shrimpy little orange critter had a secret--it was packing heat, in a very literal sense. When I got home I happened to see an article on pistol shrimp, and realized that's what we had found.

Pistol shrimp have one of the strangest weapons in nature. When prey or rivals come into their crosshairs, they aim that big claw, cock it open, and then...Blam! The claw snaps shut so fast it causes a tiny area of water to boil, forming a bubble called a cavitation bubble. This implodes with enough force to create temperatures approaching those at the surface of the sun, along with a brief flash of light and a loud pop. The recoil knocks the little shrimp backward and stuns its target. It's a wonder it doesn't tear its prey apart--cavitation bubbles created by high-speed propellers can actually dig pits in the metal. The phenomenon is amazingly violent, and quite loud. Colonies of pistol shrimp sound like bubble-wrap sizzling in bacon grease. The noise is loud enough to play havoc with sonar systems, and makes pistol shrimp competitive with singing whales for the title of Loudest Creature in the Sea.

As odd as its weaponry is, the pistol shrimp doesn't look all that strange. When it comes to full-on alien freakiness, it can't compete with some other small crustaceans Ben and I found a couple of summers ago. We were on a rocky shore in Maine, and I was laying on my belly on a floating dock, peering into the water to watch lobsters prowl around the rocks below. Then I noticed some red seaweed right in front of my eyes, attached to the dock. It looked like little clumps of red moss waving back and forth with the current. But something was funny about the motion. When I looked closer, I saw that some of the seaweed wasn't seaweed at all, but spindly little red arthopods with branched antennae on their heads, making them look like those Kokopelli petroglyphs from the southwest. They would have blended into the seaweed perfectly, but they couldn't stand still. In fact, they seemed to be brawling, clambering around in a weird inchworm motion and lashing out at their neighbors with their claws, like skinny little dreadlocked boxers.

I called Ben over to show him this spectacle. We watched them fight for a while, and then headed up to the cabin to find out what they were. We learned they're called skeleton shrimp or ghost shrimp, thought they aren't actually shrimp at all, but a different kind of crustacean called an amphipod. Skeleton shrimp attach themselves to seaweeds or sedentary sea creatures, and wait for food to float by, which they grab with claws resembling those of the preying mantis. The males are much bigger than the females, and--as is often true in such species--they fight with each other enthusiastically. The female only mates after she's just shed her skin. But that doesn't mean she's defenseless. In fact, in some species she kills her mate with a venomous claw after she's done with him. Then she starts growing about 40 eggs in a special brood pouch. In just a few days, the eggs hatch inside the pouch and she gives birth to a bunch of babies, which look like small versions of adults--ready to start the whole bizarre life cycle once again.

I don't mean to brag, but when it comes to finding aquatic oddities, Ben and I have stumbled upon some of the oddest ones out there. But there are a lot of beaches in the world, with inhabitants neither one of us has dreamed of. I can't wait for our next seaside expedition. It's hard to imagine it will turn up anything stranger than what we've already found, but then, nature is full of surprises.   

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