Walking Corals

Most corals are homebodies. They settle in one spot, link with hundreds or thousands of their friends, and never move. They build the structures we recognize as corals: rock-like spires, branches, domes, and others.

But a few corals “walk” along the sea floor. They don’t go very far. And they certainly don’t get there in a hurry. But their mobility helps them find more stable waters, avoid being buried in the sediments, and have a safe space to reproduce.

A recent study showed how one species gets around. Biologists in Australia placed mushroom corals—which are only an inch or two long—in aquariums. They put white lights on one side of the tanks—like the light in shallower waters. And they put blue lights—like deeper waters—on the other side. And they recorded the “action” on video.

When they turned on one set of lights or the other, 87 percent of the corals went toward the blue light. And when they turned on both sets, all of the corals moved toward the blue light—showing a preference for greater depths.

The corals didn’t sprint toward the deep end, though—they averaged less than two inches per day, with a maximum of about nine inches.

The video showed that the corals moved in a way similar to jellyfish. The corals inflated tissues at the edges of their bodies, then squeezed and twisted muscles on their sides, causing them to “hop” forward.

Each tiny hop took an hour or two—a slow but steady pace for a walking coral.