Devastation from coral bleaching proves a buffet for one type of fish
“When the whole reef goes to that sort of environment very rapidly that is the perfect nutritional situation for parrotfish. It’s kind of like the buffet has been rolled out for them.”
Dr Taylor said that meant following bleaching events from 2015 to 2017 there had been an explosion of parrotfish numbers, and the individual fish were growing larger than they normally would.
“We looked at tiny ear bones in the fishes’ heads, and they’re actually just like tree rings; if you cut them in half you can see the levels of annual growth,” he said.
“We wanted to see if there was an increase in growth that corresponded to the times when we had bleaching, and that’s exactly what we found.”
Dr Taylor led a team of researchers from AIMS as well as James Cook University, the University of Auckland and the University of Lancaster in the UK.
They looked at parrotfish at two sites; around Lizard Island in the Great Barrier Reef and at the Chagos Archipelago in the Indian Ocean.
The team found parrotfish populations increased by between two and eight times at sites of mass coral bleaching and individual fish there were 20 per cent larger than similar fish living on non-bleached reefs.
Dr Taylor said because this happened at multiple locations – the sites are 8000 kilometres apart – it was shown to be a general phenomeno, not just an isolated incident.
But just as it is above the water, there’s no such thing as a free lunch under the sea.
While the current conditions were ideal for parrotfish, Dr Taylor said the algae would eventually be replaced with different types of plants the parrotfish don’t eat, and then there would be a population crash.
“I think what we’ve uncovered here is a very natural small-scale feedback loop,” he said.
“Parrotfishes love bleaching but they’re not going to love it if [the situation] continues the way it has.
“I think the scale is completely out of whack with what we would consider natural cycles.”
The research was published in the journal Global Change Biology.
Stuart Layt covers health, science and technology for the Brisbane Times. He was formerly the Queensland political reporter for AAP.