Mass coral bleaching events are making it harder for some species of reef fish to identify competitors, new research reveals.

Scientists studying reefs across five Indo-Pacific regions found that the ability of butterfly fish individuals to identify competitor species and respond appropriately was compromised after widespread loss of coral caused by bleaching.

This change means they make poorer decisions that leave them less able to avoid unnecessary fights, using up precious limited energy. The scientists behind the study believe these changes could have implications for species survival as further global warming increases the likelihood of coral loss.“

By recognizing a competitor, individual fish can make decisions about whether to escalate, or retreat from, a contest—conserving valuable energy and avoiding injuries,” said Sally Keith, a senior lecturer in marine biology at Lancaster University and lead author of the study.

“These rules of engagement evolved for a particular playing field, but that field is changing. Repeated disturbances, such as bleaching events, alter the abundance and identity of corals—the food source of butterfly fish. It’s not yet clear whether these fish have the capacity to update their rule book fast enough to recalibrate their decisions.”

“The impacts of global change on biodiversity are increasingly obvious,” said Nate Sanders, a professor in the University of Michigan Department of Ecology and Evolutionary Biology and a co-author of the study. “This work highlights the importance of studying the behavioral responses of individuals in light of global change.”