For the first time, scientists found that corals that were thought to have been killed by heat stress have recovered ̵
The journal Science Advances on Wednesday  reported on the accidental discovery made by Diego K. Kersting of the Free University of Berlin and the University of Barcelona during diving expeditions in the Spanish Mediterranean, [C] and co-author Cristina Linares has been conducting long-term monitoring of 243 colonies of the critically endangered reef-building coral Cladocora caespitosa since 2002, describing recurrent heat-related mass mortals in earlier work.
"At some point we saw polyps living in these colonies that we thought were dead," Kersting told AFP, adding that it was a "big surprise."
Corals are made up of hundreds to thousands of tiny creatures called polyps and secrete a hard outer skeleton of calcium carbonate (limestone) and attach themselves to the seafloor.
Heat waves kill these animals – either by essentially roasting them alive or by emitting the symbiotic agent – algae that live in them and provide them with nutrients, leading to coral bleaching.
A quarter of the coral cover of the Spanish Columbretes Islands was lost in 2003 due to a particularly extreme heatwave.
The time is running out
However, the researchers found that the polyps had developed a survival strategy in 38 percent of the affected colonies: they reduced their dimensions, partially abandoned their original skeleton and gradually left it behind Regrow period of several years and build a new skeleton.
Subsequently, they were able to colonize dead areas by buds gradually.
To make sure that the polyps were actually the same animals and not a comeback of new coral from sexual reproduction. The team used 3D computer imaging to confirm that the old, abandoned skeleton was connected to the new structure.
This process of "rejuvenation" was known in the fossil record, but has never been observed in existing coral colonies.
Kersting said the discovery opens up the fascinating possibility that other modern corals around the world – such as those found in the dying Great Barrier Reef of Australia – could find similar survival strategies, although more research is needed.
This also meant that there was a tight window of opportunity to prevent coral reefs, key ecosystem engineers protecting hundreds of fish and plant species, from dwindling as a result of climate change.
"Sure it is good news, but what we now see in the Mediterranean and in other parts of the world is that these marine heatwaves occur again and again – every summer or every other summer," said Kersting.
These corals also grow very slowly – at a rate of about 3 millimeters per year – "So if you have a heat wave every other summer and kill 10 to 15 percent of the cover, I think the numbers are clear," he added added.
] "They really need help from us, we have to stop climate change because it will not be enough."
Faster death and decay of coral, not just bleaching when the heat waves in the sea increase
D. K. Kersting of the Free University of Berlin in Berlin, among others "The living proof of a fossil survival strategy awakens the hope for heat-influenced coral" (19459014). Science Advances (19459015) (2019). DOI: 10.1126 / sciadv.aax2950, https://advances.sciencemag.org/content/5/10/eaax2950
© 2019 AFP
Back from the dead: Some corals are growing more deadly & # 39; Warming after (2019, 9th October)
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