Chemical warfare on the reef

A goby eyes up some algae that's intruding on its coral home.

Danielle Dixson

There are lots of organisms that don't have a brain, but can still communicate. Bacteria coordinate their growth, plants signal distress and lure insects in with scents and coloring. Now, researchers have listened in on some of the communication going on in a coral reef, and found that the organisms are saying the equivalent of things like "help me!" and "die!" Finding Nemo, this isn't.

At the root of these communications is a competition between corals and an algae called Chlorodesmis fastigiata. In the wild, the algae can start growing on reefs, where it is able to send a simple message to nearby coral: die. Various studies have indicated that the algae can carry coral disease and create an oxygen-depleted environment that's harmful to corals. Within three days of researchers placing the algae on a coral, the coral's photosynthetic activity dropped by about 80 percent. With the corals gone, the algae can then occupy the reef.

But, as researchers found, corals can fight back. Simply placing an extract of the seaweed near the coral caused it to emit its own message: come help me! The recipients of this message? Fish called gobies. Pairs of these fish generally occupy a nest at the base of a coral growth. But, in the authors experiments, simply exposing a bit of coral to an extract of the toxic seaweed was enough to attract most of the gobies in the area in as little as 15 minutes.

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