Bleached Coral Stops Fish From Smelling Predators

Damselfish living on damaged reefs could be missing chemical indicators that help them survive.
(Photo: Csaba Tökölyi/Getty Images)
May 14, 2016· 1 MIN READ
Taylor Hill is an associate editor at TakePart covering environment and wildlife.

More than 90 percent of the 1,400-mile-long Great Barrier Reef is suffering from coral bleaching due to climate change. As oceans warm, reefs slough off algae that protect corals.

While corals only cover about 1 percent of the ocean’s floor, they serve as critically important habitat for about a quarter of the world’s marine species. Now scientists are starting to discover how coral bleaching is affecting creatures that depend on reefs for their survival.

Researchers at James Cook University in Queensland, Australia, have been studying how fish react to large coral bleaching events, finding that the smell left by dead coral hampers the ability of fish to detect predators. Their study was published in the journal Proceedings of the Royal Society B.

“Baby fish use chemical alarm signals released from the skin of attacked individuals to learn the identity of new predators,” Mark McCormick, a marine ecology professor at James Cook University, said in a statement.

In a first-of-its-kind experiment, McCormick and his fellow researchers tested how coral-dwelling juvenile damselfish reacted to a bleached coral environment.

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The team placed drops of chemicals mimicking the scent of a predator in one aquarium tank with live, healthy coral and in another one with bleached coral.

A predatory dottyback lines up to eat a juvenile ambon damselfish. (Photo: Christopher Mirbach)

Damselfish are covered with taste bud cells that can pick up the scent of a predator or that of a wounded damselfish, signaling that they should retreat into the protective nooks and crannies of the coral.

But the researchers found the damselfish living on bleached coral did not react to such chemical cues.

Oona Lönnstedt, a marine biologist at Uppsala University in Sweden who worked on the study, said the dead corals could be emitting an odor that masks the fish’s ability to identify danger.

“If the process of cataloguing and avoiding predators is hindered in some species by coral degradation and loss, then much of the diversity of reef fish could be lost too,” Lönnstedt said in an email.

Now the scientists want to see if other small fish species are responding similarly to dead coral environments.

“The Great Barrier Reef is currently experiencing the worst mass coral bleaching event in its history, and coral cover on the majority of reefs is declining sharply,” McCormick said. “If dead coral masks key chemical signals used to learn new predators, the replenishment of reefs could be seriously threatened.”