Coral bleaching has changed the type of fish found on the Great Barrier Reef, according to a James Cook University study.
The research has found that a decrease in coral causes a reshuffling of fish populations, however total fish growth remains stable.
The study measured fish biomass production (the weight of new fish flesh accumulated each day) on the Great Barrier Reef over 26 years.
JCU PhD student Helen Yan led the study and says it’s important to know what is happening on reefs, while the environment changes.
“Under current trajectories, it’s unlikely the coral reefs of the future will resemble those of the past,” she says.
“As multiple stressors, such as climate change and coastal development, continue to impact coral reefs, understanding the changes is important.
“Species richness (the number of different types of fish) declined following the 1998 bleaching event, but later rebounded and have remained relatively stable.
“Remarkably, the key function of fish biomass production was maintained by this altered system, despite major ongoing stressors.
“It appears the loss of corals and coral-associated fishes creates new niches that can be quickly colonised by fishes that prefer degraded reefs and are less dependent on corals.”
She says brightly coloured fish, which are associated with high coral cover, declined drastically immediately after the 1998 bleaching event and that fish shifted towards communities that are characteristic of degraded reef habitats.
“The work is important because millions of people globally are reliant on the productivity of coral reef fishes for food and financial security, and while these highly dynamic and increasingly degraded systems can still support some critical functions, it’s unclear whether these patterns will remain stable over future decades.”
Co-author Professor David Bellwood has been counting the number and types of fishes on Orpheus Island on the Great Barrier Reef, annually, for most years between 1993 and 2021.
“Following the first mass coral bleaching event in 1998, fish communities remained remarkably constant through time, despite the occurrence of multiple stressors, including extreme sedimentation, cyclones and mass coral bleaching events,” he says.
