Oct. 22 (UPI) -- Coral bleaching events breed apathy among reef fish, according to a new study.

Previous studies have revealed a link between temperature and aggression. Hotter temperatures tend to trigger more aggressive behaviors among animals, including fish. But new research suggests, under certain circumstances, hotter temperatures can also lead to apathy -- and a decrease in aggressive behavior.


Scientists spent 600 hours over two years observing butterflyfish living among reefs off the coasts of Japan, the Philippines and Indonesia. During the observational period, an extreme bleaching event spread across the region, offering scientists a unique opportunity to study the impact of coral bleaching on fish behavior.

In the wake of the bleaching event, scientists characterized the dynamics of several thousand encounters between individual fish. Researchers observed interactions among 38 different butterflyfish species.

"We observed that aggressive behavior had decreased in butterflyfish by an average of two thirds, with the biggest drops observed on reefs where bleaching had killed off the most coral," Sally Keith, an ecology researcher at Lancaster University, said in a news release. "We think this is because the most nutritious coral was also the most susceptible to bleaching, so the fish moved from a well-rounded diet to the equivalent of eating only lettuce leaves -- it was only enough to survive rather than to thrive."

In other words, the fish were too malnourished to be their normal selves. Researchers shared their observations and analysis this week in the journal Nature Climate Change.

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

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The study's findings suggest ecologists could anticipate environmental changes by closely monitoring fish behavior. Researchers think follow up studies are needed to better understand how changes in aggression level impact ecosystem dynamics.

"Our work highlights that animals can adjust to catastrophic events in the short term through flexible behavior, but these changes may not be sustainable in the longer-term," said Andres Baird, a researcher at James Cook University.