University of Glasgow

Understanding coral bleaching on the Great Barrier Reef

By Dr Nick Kamenos, Reader in Global Change at the University of Glasgow.

Coral reefs provide an important ecosystem for life underwater, they protect coastlines by reducing the power of waves hitting the coast and provide a crucial source of income for millions of people.

When corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn white. This phenomenon is known as coral bleaching. Corals can survive a bleaching event, but they are under stress and if the algae aren’t replaced, they will die.

Coral bleaching is of great global concern and mass coral bleaching events over the last 20 years have raised concern about the future of these key ecosystems and the implications that their loss could have for biodiversity, the economy, and the services they provide to humans.

Despite these mass bleachings, little is known about bleaching frequency prior to 1979, which is when regular modern systematic scientific observations on the Great Barrier Reef began.

Using cores taken from long-lived corals, we have shown that bleaching events have steadily affected more and more corals, and are happening more frequently than in the past. It’s clear in the core data we examined that bleaching has been occurring on the Great Barrier Reef for at least four centuries, but the frequency of bleaching events has increased markedly since the early 1800s and those events have affected 10% more corals since the late 1700s.

What we found was fascinating and provides vital additional context for the observations carried out over the last half-century

We can see that corals have been able to acclimate and recover from past bleaching events. However, the increase in bleaching frequency and the numbers of corals affected since temperatures started consistently increasing in the modern era raises serious concerns about whether corals are approaching a critical threshold beyond which their long-term survival is uncertain.

Many thanks to Dr Sebastian Hennige from the University of Edinburgh’s School of Geosciences and our funders the Natural Environment Research Council (NERC), the Royal Society of Edinburgh, and the Scottish Government. Read here the research paper in Frontiers in Marine Science.

With thanks to Dr Nick Kamenos.

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