Who's who in a coral condo? - soft coral colonies attract many animals that dart about among them - Illustration

Ranger Rick, July, 1997 by Ellen Lambeth

Is this some kind of weird underwater cauliflower plant? No, it's a tree coral colony--a large group of tiny ocean animals growing together. Except for a few bristly neighbors, the colony looks a little lonely right now. But there's a whole lot more here than first meets the eye.

This coral isn't like the kind that builds rock-hard reefs. It's a soft coral that sways in the water's currents. But like hard coral, it's made up of many individual coral animals called polyps (POL-ips). Each polyp has eight feathery tentacles .

And each tentacle is filled with stingers. The polyp uses its tentacles to zap tiny creatures that float by. That's how the coral gets its food.HOME, SWEET HOME There are many different kinds of soft coral colonies. The kind in this story is called a tree coral because it looks like a tree trunk complete with branches. And like a tree in a forest, this underwater "tree" attracts many other kinds of creatures.

A few feed on the coral. Some dart in for a quick hideout or to eat something else living there, and then they move on. Others move in for good and live nowhere else. So come on--swim in for a closer look!

The pale coral crab at right is holding tight to a branch of the tree coral. But its claws are open and ready to nip. See how well the color of the crab's body matches the color of the coral stem? That helps the crab hide from its prey when the crab's on lunch patrol. Blending in also makes it harder for predators to find the crab and turn it into lunch!

Speaking of blending in, check out the sea snails at left. They are the same colors as the coral. They even seem to have waving tentacles that look like those of the coral polyps. Can you make out the snail eggs on the coral? Since the eggs are see-through, predators may have a hard time finding them. The coral's stinging tentacles may help protect the eggs too. The snails seem to "have it made" living here. They even feed on the coral!

Look hard if you want to find the pipefish at left. This seahorse relative really seems out of sight, doesn't it? It's the long, spiky thing in the mid- dle of the photo--head down and tail sticking up above the coral. It's just visiting the colony, in search of other little creatures to eat. Another great disappearing act is the tiny transparent shrimp shown below. This kind of shrimp makes the coral its permanent home.

Now look again at the pipefish, even more closely. Can you see what's left of one of these shrimp sticking out of the fish's mouth? The fish may have fooled the shrimp with its disguise. But the shrimp sure didn't fool the fish!Some creatures can't seem to blend in enough! The crab shown below already matches its coral home with its color and thorny shell. But it sometimes goes one step further: It nips off some polyps and sticks them on its back. The polyps make a great disguise.

By the way, see how the polyps on the coral have their tentacles tucked in? They do that when something attacks or bumps them or when they're not feed- ing.You can find several kinds of small fishes besides the pipefish in a tree coral. Some spend almost all their time there. Others, such as this hawkfish, zip in once in a while to huddle among the coral's branches.

Like a hawk perched in a tree, the hawkfish might be waiting patiently for something tasty to turn up. Or it might be hiding from a larger predator.Now you can see that the tree coral wasn't really lonely at all. In fact, after a year of having so much company, it's looking a little worn out. Maybe too many coral-nibbling snails and fish have been in the neighborhood.

See the colorful feather stars on top of the coral? Like the coral, they depend on brisk ocean currents to bring food their way. They aren't really hurting the coral. But they may be stealing space from some of the polyps. Being on top lets the stars be the first to snatch the biggest batch of "fast food" floating by. For these starfish relatives, the coral is one "tree" that's terrific for climbing!