Scientists investigate how to save corals, and the answer could lie in the Devonian age
Devonian extinct coral fossils can tell scientists what awaits modern-day corals and how we can help them. Preliminary studies indicate that in the distant past, the corals most susceptible to environmental changes were those living in symbiosis with unicellular algae.
Forecasts for modern-day coral reefs are not optimistic. Reports presented at the Ocean Sciences Meeting 2020 in the US show that virtually all coral reefs could be destroyed by the warming and acidification of the oceans by 2100. In the next 20 years, this could happen to 70-90 percent reefs. More and more of them succumb to so-called bleaching, which results in the death of the symbiotic algae that live in them, stops the growth of the corals themselves and, as a consequence, the reef dies. Working with algae is crucial for corals. By taking carbon dioxide from the microenvironment around the coral for photosynthesis, algae facilitate its skeleton formation, but also feed the coral with sugars produced in photosynthesis. The coral, in turn, provides algae with shelter.
The period of the greatest development of coral reefs in the history of our planet was during the Devonian, about 419 to 358 million years ago. But by the end of that time, about 372 million years ago, along with the great extinction of species that occurred at that time, coral reef ecosystems also collapsed. It was a long process, it took several hundred thousand years, but the corals almost completely died out.
Today, the remains of those corals found in various parts of the world are being studied by palaeontologists including Dr. Mikołaj Zapalski from the Faculty of Geology at the University of Warsaw, who studied such remains in the Świętokrzyskie Mountains.
As part of the Bekker Programme, he recently conducted research in Australia together with specialists from the James Cook University and the Centre of Excellence for Coral Reef Studies in Townsville. As a result of this collaboration, he discovered a previously unknown type of Devonian reef in Queensland, similar to modern coral reefs. The study of this unusual, extremely shallow-water Devonian reef dominated by corals was published in the prestigious journal Coral Reefs.
Among the 100 species of Devonian corals, the remains of which have been discovered over the years, also in the Świętokrzyskie Mountains and the Ardennes, a team of researchers including Dr. Zapalski tried to select those elements of the skeleton that were also found in contemporary corals.
He told PAP: “We wanted to see if there was a trait or set of traits that allowed ancient corals to survive the various stages of extinction. Do any of the skeletal traits predispose the corals to survive or die out? We also wanted to see the possible scenario for modern reefs based on the Devonian scenario and show which of the groups that form reefs today have a potentially greater chance of surviving environmental changes, and which are more exposed.”
We know that some of the physiological mechanisms of Devonian corals were different, the researcher says, but there are similarities, too. For example, the skeletons they formed are similar to those of today. Both the prehistoric and the modern ones are made of calcium carbonate, only its forms are different. Devonian corals were made of calcite, modern-day ones use aragonite.
By collecting data on skeletal structures, scientists find various analogies between modern-day and Devonian corals. According to Dr. Zapalski, this may suggest that environmental changes similar to the current ones influenced how they lived, grew and formed skeletons.
Initial results show that the so-called photosymbiotic corals, ones that live in symbiosis with single-celled algae and build almost all coral reefs in the world, were most susceptible to environmental changes. Those that could remain algae-free had better survival rates and were less at risk due to environmental fluctuations. Corals with large polyps, a few, sometimes 10 mm in diameter, also coped better with the temperature increase.
Zapalski said: “Currently, virtually all reefs are built by photosymbiotic corals. Most of the reefs we know have a good chance of becoming extinct. There are also corals that are not photosymbiotic today, but they live in environments at great depths of 200 - 400 meters, where light practically does not reach, and in cold seas, for example off the coast of Norway.”
The environmental changes that corals have faced and are facing primarily include significant temperature increases. In the Devonian, temperatures were above 32 degrees C. Palaeozoic ocean waters differed somewhat in their chemical composition from today's, much more acidic oceans (which also favours the erosion of coral skeletons), but the environmental threats to corals were similar to some extent.
PAP - Science in Poland, Ewelina Krajczyńska
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