Study Reveals Corals Use Ancient Method To Cope With Warming

cushion coral copy

Cushion corals - Cladocora caespitosa - in the Mediterranean

Scientists have discovered a survival strategy for global warming being used in living coral reefs previously only known in the fossil remains of long-extinct corals.

In a rare bit of good news for hard-pressed corals, the study, published in the journal Science Advances, shows that some species of colony-building corals in the Mediterranean are using a process known as ‘rejuvenescence’ to recover from the devastating impacts of warming events.

Diego Kersting and Cristina Linares, who are from the Freie Universität Berlin and Spain's University of Barcelona, respectively, have been monitoring how cushion corals - Cladocora caespitosa - deal with repeated exposure to bouts of high sea temperatures.

Their study shows that isolated polyps from threatened coral colonies exhibit an ability to recover from sea warming and thereby led to an unexpected and rapid recovery from such events.

Kersting said: ‘Today climate change is probably causing the most coral cover declines. Warming stresses corals up to a point that may cause death. Some corals bleach before dying. Other corals do not bleach but die directly, such as Cladocora caespitosa, the coral in this study.’

He added: ‘Our findings are important because this survival strategy was only known from fossil corals that existed hundreds of millions of years ago. It is the first time that it is found in a living coral. This strategy is allowing this coral to slow down its decline caused by warming-related mortalities.’

For their research, Kersting and Linares monitored 243 colonies of the endangered reef-building coral in Spain's Columbretes Islands Marine Reserve over 16 years, starting in 2002.

A summer heatwave in 2003 led to a 25 per cent reduction in coral cover in the islands, according to the researchers. But they were stunned to discover a far more rapid than expected bounce back.

‘What happens is that some polyps in a coral colony—sometimes just one—reduces drastically its dimensions and partially retreats from its skeleton,’ Kersting said. ‘Once the stressful event is over, the shrunken or rejuvenated polyp recovers its size and builds up a new skeleton. Eventually, it begins to reproduce itself through budding and begins to cover the dead colony surfaces.’

He continued, "The results were very surprising because I started to observe colonies that were dead years ago, that were showing living parts many years after their death.’

The only known fossils that displayed this ability lived hundreds of millions of years ago, according to the researchers. This survival strategy may have been overlooked until now because colony recovery takes a long time, so only long-term monitoring studies can reveal the process. Over a decade, 13 per cent of the colonies affected by warming in the study experienced a full recovery.

The scientists warned that this is only a glimmer of hope for some corals and any substantial recovery of reefs will need us to halt global warming.



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