Coral reefs have long been seen as some of the first and most severe victims of global warming. In new research published by the journal Proceedings of the Royal Society B, we found how mass coral bleaching events can change the future of ecological communities on Earth

According to new research, mass coral bleaching events are making it more difficult for certain species of reef fish to recognize their competitors.

A new study conducted by scientists across five Indo-Pacific regions has discovered that the ability of butterflyfish to identify and appropriately respond to competitor species has been impaired due to mass coral bleaching events. This has resulted in poor decision-making and an increased likelihood of unnecessary fights, which can drain the fish’s limited energy.

As explained by the team, the negative impacts of coral bleaching on the behavior of butterflyfish could have consequences for the species’ survival as global warming increases the likelihood of coral loss.

According to the study’s lead author, Dr. Sally Keith, Senior Lecturer in Marine Biology at Lancaster University, “By recognising a competitor, individual fish can make decisions about whether to escalate or retreat from, a contest – conserving valuable energy and avoiding injuries.

“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 butterflyfish. It’s not yet clear whether these fish have the capacity to update their rule book fast enough to recalibrate their decisions.”

The research team observed the behaviors of 38 species of butterflyfish on reefs both before and after coral bleaching events, collecting over 3,700 observations in total.

The study found that after a coral bleaching event caused mortality, interactions between fish of different species became less common and more likely to escalate into chases. These chases occurred in over 90% of encounters, up from 72% before the event. The distance of these chases also increased, resulting in the fish expending more energy chasing away potential competitors than they would have before the bleaching event.

According to the researchers, the environmental disturbances caused by coral bleaching events are disrupting the ability of fish to recognize and respond appropriately to other species. These bleaching events, in which significant amounts of coral die, are forcing fish to alter their diets and territories, disrupting the long-standing, co-evolved relationships that allow multiple fish species to live together.

“By looking at how behaviour responds to real-life changes in the environment, and by seeing that those changes are the same regardless of location,” Dr. Keith added, “we can start to predict how ecological communities might change into the future. These relatively small miscalculations in where to best invest energy could ultimately push them over the edge.”

Image Credit: Dr Sally Keith

Source: 10.1098/rspb.2022.2158