Coral bleaching: how rising sea temperature causes permanent changes in fish biodiversity

An image to illustrate coral bleaching
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A new study showed that coral bleaching caused by rising sea temperature has caused lasting changes to fish biodiversity in the Seychelles.

The study from Lancaster University is published in Global Change Biology and shows that coral bleaching in 1998 has led to changes in fish biodiversity in coral reefs which still remain in place today. Some reefs shifted to fields of seaweeds. However, even the reefs where corals recovered between the bleaching events and the number of fish species recovered, the coral reefs did not return to their original composition of species.

Permanent changes to fish biodiversity

Some examples include the dramatic reduction of large predator fish such as snappers and very small fish such as damselfish. These were largely replaced by fish which consume seaweed, such as rabbitfish.

The lead author of the study, Dr James Robinson, 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. ”

“The Seychelles case study suggests under current levels of ocean warming – where the average frequency of bleaching events is less than 10 years – permanent changes to reef fishes are likely on most coral reefs globally.”

How coral bleaching will alter how coral reefs function

Bleaching events are becoming more frequent, so the researchers believe that other coral reefs will suffer similar long-term shifts in fish biodiversity.

Professor Nick Graham of Lancaster University, added: “The new normal for coral reefs will be reef fish communities which have fewer species and are dominated by herbivores and invertebrate feeding fish. This will alter the way coral reefs function, and the fishery opportunities for coastal communities adjacent to coral reefs.”

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