Coral bleaching could have serious implications for fish species survival

Researchers have found that some species of reef fish are having difficulty identifying competitors due to mass coral bleaching events.

Researchers have revealed that mass coral bleaching events are making it harder for some species of reef fish to identify competitors. A group of scientists studying reefs across five Indo-Pacific regions have discovered that the ability of butterflyfish individuals to identify competitor species and respond appropriately was affected due to the widespread loss of coral caused by bleaching. This causes them to make poorer decisions, causing unnecessary fights that use precious limited energy.

The study, ‘Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterfly species,’ is published in the journal Proceedings of the Royal Society B Biological Sciences.

Coral bleaching affecting species survival

The team believe that this difficulty in identifying competitors could have implications for species survival as further global warming increases the likelihood of coral loss.

Dr Sally Keith, Senior Lecturer in Marine Biology at Lancaster University and lead author of the study, said: “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.”

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More than 3,700 observations of 38 species of butterflyfish on reefs before and after a coral bleaching event occurred were taken by the researchers. The team then used their observations to compare the behaviours of the fish.

It was found that coral mortality caused by bleaching resulted in signalling between fish of different species being less common, with encounters escalating to chases in more than 90% of cases – up from 72% before the event. The distance of these chases also increased following coral bleaching, with fish using more energy chasing potential competitors than they would have done previously.

Disruptions of long-established relationships between fish

The environmental disturbances are affecting fish recognition and response because when coral bleaching occurs, which causes many corals to die, fish species are forced to change and diversify their diets and territories. Large-scale environmental changes are therefore disrupting long-established and co-evolved relationships that allow multiple fish species to coexist.

Dr Keith said: “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, 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.”

The paper’s authors are Dr Sally Keith, Dr Lisa Boström-Einarsson, Dr Ian Hartley of Lancaster University, Dr Jean-Paul Hobbs of the University of Queensland, and Professor Nathan Sanders of the University of Michigan.

The study was funded by the Natural Environment Research Council (NERC), the Australian Research Council, and the Villum Foundation.

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