Researchers at Lancaster University have discovered that bleached coral reefs experience lasting change to their fish communities.
Specifically, there would be less large predator fish (like snappers and groupers) and very small fish (like damselfish and butterflyfish). In their place would be more seaweed-loving fish (like rabbitfish and parrotfish) and invertebrate-feeding fish (like emperors and wrasses).
This was because the bleaching had caused the collapse of the fish’s habitat structure and this allowed seaweed to take over the space. Thus, the number and composition of fish was substantially changed.
Writing on their findings in the Global Change Biology journal, the researchers related their study on the coral reefs in the Seychelles. There, they tracked reef recovery (after a bleaching event in 1998) before another major bleaching event struck the reefs in 2016.
It was found that despite the recovery period between the two coral bleaching events, the original fish populations did not recover to pre-bleaching numbers.
Lead author Dr James Robinson, of Lancaster University, said, "Although the 18-year period between major mass bleaching events allowed corals to recover on some reefs, we found evidence that fish populations were not able to return to their pre-bleaching levels, and they were substantially altered on the reefs that become dominated by seaweeds."
According to other studies, the time period between bleaching events is now reducing, and it is typically less than 10 years.
Given that the respite between the two bleaching events in the University of Lancaster’s study was 18 years and that was still insufficient for fish populations to fully recover, the researchers anticipate that other reefs will experience similar shifts, with bleaching events becoming a more frequent occurrence.