The “Canaries of the Reef” Are in Trouble

The evolutionary arms race underwater means many marine organisms have adapted to depend on coral reefs as part of their survival strategy against predators. Take the butterflyfish -- it traded its formerly slim, armored, hunter-like body for a squatter, more mobile one that's better for hiding in coral reef crags.

So says Jennifer Hodge, an evolutionary biologist at the University of California in Davis. Her research team collected 351 fossilized butterfly fish, representing 87 different species, and analyzed their physical attributes alongside their foraging behaviors. They found that the coral grazers' evolution has left them with smaller, less sensitive eyes, too. "Our findings constitute the strongest evidence to date that corals have influenced the evolution of fish morphology," Hodge says.

Those evolutionary changes may be limiting their future lifespans on the reefs, according to a study published in Nature Climate Change by a research team at Lancaster University in the United Kingdom. After spending 600 hours observing butterflyfish, they observed that their aggressive behavior had decreased by about two-thirds on reefs where bleaching had killed off most of the coral. Instead of feeding on a wide range of corals, their diet was more limited because they were no longer accustomed to foraging far from home.

"This matters because butterflyfishes are often seen as the 'canaries of the reef' due to their strong reliance on coral," says Nathan Sanders, an ecologist at the University of Vermont. "They are often the first to suffer after a disturbance event."

The Lancaster University team opines that monitoring butterflyfish behavior might provide scientists with an early warning system for preventing more declines of coral reefs and their inhabitants.