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According to a new long-term study conducted in Seychelles, the repeated bleaching of corals caused by rising sea temperatures has led to lasting changes in fish communities.
Large predatory fish such as snappers and very small fish such as damselflies have declined considerably in number and have been largely replaced by seaweed-loving fish such as rabbits.
Publication in the journal Biology of global change, the researchers clearly demonstrate that coral bleaching in 1998 has resulted in changes in biodiversity and permanent changes in the range of coral reef fish species that are still in place.
Some coral reefs studied rebounded and recovered after bleaching, but other reefs moved to algal fields.
Changes in fish communities were most apparent on these predominantly algal reefs, but the "herbivore" fish that feeds on algae has become a dominant part of the community on all the reefs of the sea. # 39; study.
Researchers believe that these same changes are likely to occur in similarly damaged reefs around the world and could be described as the "new normal state" for post-laundered reefs.
Lancaster University's research followed re-establishment of the Seychelles reefs for 16 years, before another major coral-bleaching event affected the reefs in 2016. Despite the the time between these two major coral bleaching events, the fish populations have not recovered. whitening condition.
Where previously there were more large predatory fish such as snappers and groupers, as well as very small fish such as damselflies and butterflies, after whitening a new community dominated by parrots feeding algae, rabbits and invertebrates such as as emperors and wrasses, took over.
These changes are due to the collapse of the structure of the fish habitat, corals. When the corals have not recovered and the algae have invaded the space, the number and composition of the fish have changed considerably.
Surprisingly, even on reefs where corals have gradually recovered between whitening episodes, the number of fish species has recovered, but has not returned to its species composition. d & # 39; origin.
Other studies have shown that the time interval between whitening periods is being reduced and that it is generally less than 10 years old. In this study, the delay between the 1998 coral bleaching and the next large episode was over 18 years old – but fish communities were still unable to recover. This leads the researchers to conclude that other reefs will undergo similar changes, especially as bleaching episodes become more and more common.
Dr. James Robinson, lead author of the Lancaster University study, said: "Although the 18-year period preceding mass bleaching has allowed corals to recover on some reefs, we have found evidence that fish populations could not return to their waters.The Seychelles case study suggests that current levels of ocean warming – where the average frequency of bleaching episodes is less than 10 years – changes permanent in the reef the fish are likely on most coral reefs in the world. "
Professor Nick Graham of Lancaster University added, "The new standard for coral reefs will be reef fish communities that have fewer species and are dominated by herbivores and fishes feeding on fish. Invertebrates will affect the functioning of coral reefs and fishing opportunities for coral reefs, coastal communities adjacent to coral reefs. "
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Material provided by Lancaster University. Note: Content can be changed for style and length.
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