Some corals becoming resilient to rising temperatures

New research offers a “glimmer of hope” that at least some species of coral are acclimatising to rising ocean temperatures.

Successive and sometimes annual bleaching events on Australia’s Great Barrier Reef, and other reef formations around the world, have raised fear that reefs, and the ecosystems they underpin, may be doomed.

A major 2018 study looking at 100 reefs around the world found that the average interval between bleaching events had decreased by half since 1980.

“Such narrow recovery windows do not allow for full recovery,” the researchers wrote. 

“Furthermore, warming events such as El Niño are warmer than previously, as are general ocean conditions. Such changes are likely to make it more and more difficult for reefs to recover between stressful events.”{%recommended 8507%}

That prognosis remains substantially unaltered, but now a new paper written by a team led by Thomas DeCarlo of the Australian Research Council Centre of Excellence for Coral Reef Studies suggests that some coral species might be developing resilience to warming waters.

To make their finding the researchers looked closely at the skeletal cores of a particularly long-lived coral genus, Porites, investigating specimens that had been living since at least 1815. Samples were taken from the northern Great Barrier Reef, the Coral Sea and New Caledonia.

Corals, in the same manner as trees, show annual growth rings, and the contents of each forms essentially a record of prevailing conditions, and the coral’s response thereto.

A bleaching event will leave a high-density stress band. DeCarlo and colleagues were able to verify this because the first one found in the Porites specimens correlated with a known strong pre-industrial El Niño event in 1877.

As expected, stress bands became more frequent as anthropogenic climate change-induced bleaching events increased in frequency in the second half of the twentieth century and then kicked into even higher gear in the early years of the twenty-first.

However, the researchers found that the proportion of specimens showing stress bands for the past several years actually decreased “despite increasing exposure to heat stress”.

The results, the researchers conclude, “demonstrate an increase in the thermal tolerance of reef-building corals and offer a glimmer of hope that at least some coral species can acclimatise fast enough to keep pace with global warming”.

The research is published in the journal Proceedings of the Royal Society B.