Australia’s Great Barrier Reef is suffering its worst coral bleaching in recorded history with 93 per cent of the World Heritage site affected.
Now researchers have found that coral bleaching and death can have dramatic repercussions for how small reef fish learn about and avoid predators.
The finding is not only bad news for the fish but the reef itself, because it could prevent the living colonies replenishing.
This occurs when warm ocean temperatures cause thermal stress, leading corals to expel tiny algae, known as zooxanthellae, which live inside their tissues and provide corals with most of their food and colour.
Without the algae, the coral’s bright white skeleton is revealed.
Habitat changes influence how animals that live there interact.
The current study, published in Proceedings of the Royal Society B, found coral death and degradation affects how a common damselfish responds to the tell-tale chemicals that indicate the presence of hungry predators.
‘Baby fish use chemical alarm signals released from the skin of attacked individuals to learn the identity of new predators,’ Professor Mark McCormick who studies coral reef fish at James Cook University explained.
‘By pairing the alarm cue from their wounded buddy with the smell or sight of the responsible predator, fish are able to learn which individuals are dangerous and should be avoided in the future.’
However, when corals die and become covered in algae, the olfactory landscape of the reef seems to change, which affects this crucial learning mechanism used by fish.
The Australian-Swedish research team found that the smell of an injured mate paired with a predator taught the ambon damselfish to learn to avoid new predators when on live coral, while their counterparts on dead coral didn’t respond to or learn any predator cues.
Interestingly, another species, which is only found living on dead coral, was able to learn the identity of a new predator using chemical alarm cues regardless of if the coral was dead or live.
Oona Lönnstedt, a researcher in marine biology at Uppsala University said: ‘If the process of cataloguing and avoiding predators is hindered in some species by coral degradation and loss, then much of the diversity of reef fish could be lost too.’
‘Many reef fish need specific habitats that only healthy coral reefs can provide,’ she added.
The Great Barrier Reef is currently experiencing the worst mass coral bleaching event in its history and coral cover on the majority of reefs is declining sharply the researchers said.
Dr Lönnstedt warned: ‘If dead coral masks key chemical signals used to learn new predators, the replenishment of reefs could be seriously threatened.’
Associated Newspapers Ltd