Agence France-Presse
January 04, 2023
Butterflyfish off the coast of Australia's Christmas Island are getting into more unnecessary fights due to a lack of food
Fish that have lost food due to mass coral bleaching are getting into more unnecessary fights, causing them to expend precious energy and potentially threatening their survival, new research said Wednesday.
With the future of the world's coral reefs threatened by climate change, a team of researchers studied how a mass bleaching event affected 38 species of butterflyfish.
The colorfully patterned reef fish are the first to feel the effect of bleaching because they eat coral, so their "food source is hugely diminished really quickly", said Sally Keith, a marine ecologist at Britain's Lancaster University.
Keith and her colleagues had no idea a mass bleaching event was coming when they first studied the fish at 17 reefs off Japan, the Philippines, Indonesia and Christmas Island.
But when one of history's worst global bleaching events struck in 2016, it offered "the perfect opportunity" to study how it affected the fish's behavior, Keith told AFP.
The researchers returned within a year and were "shocked" to see the devastation of the once beautiful reefs, she said.
Donning their snorkels or scuba gear, the team watched the fish "swimming around looking for food that just isn't there anymore," she added.
"There was a bit of crying in our masks."
Losing battle
The bleaching particularly affected Acropora coral, the main food source for the butterflyfish.
That "changed the playing field of who's eating what," Keith said, putting different species of butterflyfish in increased competition for other types of coral.
When a butterflyfish wants to signal to a competitor that a particular bit of coral is theirs, they point their noses down and raise their spiny dorsal fins.
"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 for about 50 meters (165 feet) once, that was quite tiring, they're very fast," Keith said.
The team observed 3,700 encounters between butterflyfish.
Before the coral bleaching event, different species of butterflyfish were able to resolve disputes using signaling around 28 percent of the time.
But that number fell to just 10 percent after the bleaching, indicating many "unnecessary attacks," according to the new study in the journal Proceedings of the Royal Society B.
"Making poor decisions about who to fight, and where to invest their really valuable energy, could be that little bit that tips them over the edge towards actual starvation," said Keith, the study's lead author.
It is not clear if the fish will be able to adapt to the changes brought about by coral bleaching quickly enough, the researchers warned.
It could also have knock-on effects between species and up the food chain, she added.
Human-driven climate change has spurred mass coral bleaching as the world's oceans get warmer.
Modeling research last year found that even if the Paris climate goal of holding global warming to 1.5 degrees Celsius is reached, 99 percent of the world's coral reefs will not be able to recover. At two degrees of warming, the number rose to 100 percent.
© 2023 AFP
Reef fish must relearn the “rules of engagement” after coral bleaching
Mass coral bleaching events are making it harder for some species of reef fish to identify competitors, new research reveals
Peer-Reviewed PublicationIMAGE: CHAETODON ADIERGASTOS view more
CREDIT: DR SALLY KEITH
Mass coral bleaching events are making it harder for some species of reef fish to identify competitors, new research reveals.
Scientists studying reefs across five Indo-Pacific regions found that the ability of butterflyfish individuals to identify competitor species and respond appropriately was compromised after widespread loss of coral caused by bleaching. This change means they make poorer decisions that leave them less able to avoid unnecessary fights, using up precious limited energy.
The scientists behind the study believe these changes 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.”
The researchers took more than 3,700 observations of 38 species of butterflyfish on reefs before and after coral bleaching event, and compared their behaviours.
After coral mortality caused by the bleaching event, signalling between fish of different species was less common, with encounters escalating to chases in more than 90% of cases – up from 72% before the event. Researchers also found the distance of these chases increased following bleaching, with fish expending more energy chasing away potential competitors than they would have done previously.
The researchers believe the environmental disturbances are affecting fish recognition and responses because the bleaching events, in which many coral die, are forcing fish species to change and diversify their diets and territories. Therefore, these large-scale environmental changes are 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.”
Chaetodon_trifascialis on Acropora table
DEAD ACROPORA TABLES
Chaetodon_guttatissimus
CREDIT
Dr Sally Keith
The findings are outlined in the paper ‘Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterfly species’, which has been published by the journal Proceedings of the Royal Society B.
The paper’s authors are Dr Sally Keith, Dr Lisa Boström-Einarsson, Dr Ian Hartley of Lancaster University, Dr Jean-Paul Hobbs or the University of Queensland, and Prof 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.
JOURNAL
Proceedings of the Royal Society B Biological Sciences
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Rapid resource depletion on coral reefs disrupts competitor recognition processes among butterfly species
ARTICLE PUBLICATION DATE
4-Jan-2023
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