University of Bremen: Young corals give an insight into the recovery after coral bleaching

The ocean warming caused by climate change and the resulting increasing frequency and severity of coral bleaching represent the greatest threat to coral reefs worldwide. How quickly coral reefs can recover from such bleaching is therefore of great interest – the number of young corals gives a good insight. Scientists from an international research project of the Department of Marine Ecology at the University of Bremen in partnership with the Seychelles Islands Foundation (SIF) have researched this in a remote atoll in the Indian Ocean and found something very promising: within four years of the coral bleaching in 2016, the number rose Young corals 2 to 3 times compared to the situation immediately after the bleaching.

“Like adult corals, young corals can be badly hit by bleaching and die off. However, coral bleaching also affects the reproductive capacity of adult corals. This means that the reproduction and therefore the number of young corals can remain suppressed even several years after bleaching, ”explains Professor Christian Wild, head of the Marine Ecology working group at the University of Bremen.

Dr. Anna Koester, who recently received her doctorate from the University of Bremen, is the first author of a study that was recently published in the journal PLOS ONE . The marine ecologist says: “The rapid increase in young corals that we have observed in the four years after the coral bleaching bodes well for the recovery of the reefs of Aldabra Atoll and complements the results of our previous work .”

The Aldabra Atoll is one of only 50 marine UNESCO World Heritage Sites and is located far out in the Indian Ocean. Man-made local factors such as the input of nutrients and overfishing play almost no role there, explains the scientist. Nevertheless, the last coral bleaching in 2016 killed up to two thirds of the corals there. So the ideal place to find out how damaged reefs are changing when they are not exposed to direct human-made stressors.

In order to get a basic understanding of the reproduction of corals at Aldabra Atoll, the scientists also took a closer look at the colonization of coral larvae in the study. “Our results suggest that coral spawning at Aldabra Atoll occurs mainly between October and December. This is important information for further studies that investigate which reefs in the region receive coral larvae from Aldabra and therefore also benefit from the protection of Aldabra, ”says Koester.

“Due to climate change, we expect an increase in the frequency of coral bleaching. This means that the periods of time for the reefs to recover between coral bleaching are getting shorter and shorter, ”emphasizes Wild. Reducing the causes of coral bleaching, especially ocean warming, is therefore essential, because otherwise even remote and strictly protected reefs such as the Aldabra Atoll will soon not be able to recover quickly enough.

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