As a result of coral bleaching, reef fish needs to relearn the rules of interaction

Photo by Francesco Ungaro on

New research shows that mass coral bleaching events are making it tougher for some reef fish species to distinguish between rivals.

After widespread loss of coral due to bleaching, scientists studying reefs in five parts of the Indo-Pacific discovered that butterflyfish individuals’ capacity to detect competing species and respond appropriately was compromised. As a result of this change, the butterflyfishes are less likely to make good choices and more likely to get into fights that aren’t necessary.

Researchers think these changes may affect species’ chances of survival as the effects of climate change continue to worsen.

Proceedings of the Royal Society B released the study’s findings in an article titled “Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterfly species.”

According to the study’s senior author, Dr. Sally Keith of Lancaster University’s Department of Marine Biology, by detecting a competitor, individual fish can make judgments about whether to advance, or retreat from a conflict thereby saving energy and avoiding harm.

These ground rules of engagement developed on a certain field, but that field is shifting. Butterflyfish rely on corals for food, yet repeated disturbances like bleaching occurrences change both the quantity and variety of corals. When it comes to making adjustments to their behavior, it’s unclear if these fishes have the capacity to keep up with their rule book.

More than 3,700 observations of 38 different species of butterflyfish were made on reefs before and after coral bleaching events and compared their behaviors.

Less signaling occurred between fish of different species after the bleaching event, and more than 90% of fish interactions escalated into chases (up from 72% before the event). After bleaching, fish chased off potential rivals for longer distances, using more energy than they would have otherwise.

Researchers believe environmental disruptions are impacting fish recognition and responses because bleaching events, which kill many corals, are causing fish species to alter and diversify their diets and territories. Therefore, these widespread alterations to the environment are upsetting the delicate balance that has allowed many different kinds of fish to coexist.

The researchers can start to anticipate how ecological communities can evolve in the future by examining at how behavior responds to real-world changes in the environment and seeing that those changes are the same regardless of location.  These seemingly minor mistake in deciding how to use energy could prove fatal.


Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterflyfish species, Proceedings of the Royal Society B: Biological Sciences (2023). DOI: 10.1098/rspb.2022.2158