Fish deprived of food by mass coral bleaching are fighting more unnecessarily, causing them to waste precious energy and potentially threatening their survival, new research said yesterday.
With the future of the world’s coral reefs threatened by climate change, a team of researchers studied how mass bleaching events are affecting 38 butterfly species.
The colorful coral reef fish are the first to feel the bleaching effects of eating coral, so “the food source is rapidly diminishing”, says Sally Keith, a marine ecologist at Lancaster University in the UK.
Mass bleaching
Keith and his colleagues were unaware of the mass bleaching event when they first studied fish on 17 reefs in Japan, the Philippines, Indonesia and Natal Island.
But when one of the worst global bleaching events in history occurred in 2016, it presented a “perfect opportunity” to study how it affects the fish’s behavior, Keith told AFP.
Researchers returned in a year and were “surprised” to see the destruction of the once beautiful coral, he said.
Using snorkels or scuba gear, the team watched the fish “swim around looking for food that was no longer available,” he added.
“There are some tears in our masks.” Losing the Bleaching battle mainly affected Acropora corals, the main food source for butterflies.
That “changes the playing field of who eats what”, Keith said, putting different species of butterflies in increased competition for other types of coral.
Signal
When a butterflyfish wants to signal to a competitor that a certain reef is its, it points its nose down and raises its spiny dorsal fin.
“It’s almost like raising your hackles,” Keith said. If that fails, one fish will chase the other, usually until the other gives up.
“I followed one [fish] for about 50m once; which is quite tiring, they are very fast,” said Keith. The team observed 3 700 encounters between butterflyfish.
Prior to the coral bleaching event, different butterfly species were able to resolve disputes using signals about 28% of the time.
But only 10% after the bleaching event, bringing many “unnecessary attacks”, according to a new study in the journal Proceedings of the Royal Society B.
“Making poor decisions about who to fight and where to invest your precious energy might be tips [the fish] over the edge into real hunger,” said Keith, lead author of the study.
It is unclear if fish will be able to adapt to the changes brought about by rapid coral bleaching, the researchers cautioned.
Bleaching can also have effects across species and up the food chain, he added. Human-driven climate change has caused mass coral bleaching as the world’s oceans warm.
Model research last year found that even if the Paris climate target of holding global warming to 1.5ºC is reached, 99% of the world’s coral reefs will not recover. At two degrees of warming, the figure will rise to 100%.