A longfin damselfish patrols its algae garden off the coast of Bonaire. Damselfish kill a section of the coral, and then wait for algae to grow in the dead spot. On this coral, only a few live sections remain. Henry DeBey

by Richard Harris Scientists say the world’s coral reefs could go extinct during our children’s lifetimes. Human activities are putting this beautiful ecosystem at risk. Some risks are obvious — such as global warming, which results in overheated seas. Others are more subtle. Consider the case of the damselfish: Looking off the coast from the Caribbean island of Bonaire, the glistening, aquamarine sea looks peaceful. But just under the waves, there’s a war going on. It’s between the fragile and colorful corals, and a creeping menace: algae. It’s a turf battle for precious real estate. And it’s a fight to the death. Both the corals and the algae have natural allies. Corals get help from parrot fish, which eat the intruding algae from the reef. And algae get help from certain species of damselfish. “Damselfish are these little fish and what they do is they make little yards on the bottom of the reef,” says marine biologist Mark Vermeij. These yards — or pastures, you could call them — are patches of algae that the fish actually farm right on the coral. “And in order to make a place for one of these yards, they basically kill the coral,” Vermeij says. “So they go to the coral, they start sucking on little polyps until they die. And then when that happens, little algae establish on that died-off patch.” … People don’t eat these little damselfish, but Vermeij says people do eat bigger fish on the reef. And that’s where the story takes a twist. “Twenty years ago, life on these reefs for little fish was basically annoying. Because there were all these big fish around that would eat you if you weren’t paying attention. And then because a lot of people took the big fish out, it’s a much safer environment for these little fish,” Vermiej says. As a result, the damselfish population has boomed. …

Tiny Damselfish May Destroy A Caribbean Reef