Some corals may yet weather climate change. For now

Most coral reefs around the oceans will likely be gone by mid-century unless we cut back on our CO2 emissions. Climate change presents corals worldwide with significant challenges. As water temperatures rise, corals often cast off the symbiotic algae that inhabit their tissue, which causes them to starve and turn white in a process known as “bleaching.” Once “bleached,” fragile corals become far more prone to diseases and less able to withstand environmental stresses.

To make matters worse, the vast amounts of carbon dioxide that human societies keep belching unceasingly out into the atmosphere is turning oceans more acidic, which prevents corals from calcifying properly. Worse still: it isn’t just climate change that is posing a threat to the planet’s fragile reefs. So is plastic waste. Reefs in the Asia-Pacific region have been swamped with billions of pieces of plastic waste, large and small, which has increased the threat of disease to fragile corals, say researchers who have published a study in the journal Science about the threat of plastic debris to corals.

After examining more than 124,000 reef-building corals, the scientists found that 89% of them that had been covered with bits and pieces of plastic were visibly sick. By comparison, only a mere 4% of corals without plastic waste on them showed signs of disease. According to the researchers, contact with plastic waste made corals 20 times more susceptible to become diseased.

The double whammy of climate change and plastic pollution are a clear and present danger to corals everywhere. And if the reefs go, so will many of the species that rely symbiotically on them for their survival. That, needless to say, will be an ecological disaster as coral reefs are among the most biodiverse areas of the planet’s oceans.

However, not all is gloom and doom, it turns out. Not just yet, at any rate. That’s because not all corals will likely succumb to rising water temperatures and a simultaneous increase in water acidity. Researchers at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, for instance, have found that mountainous star corals boast an evolutionary adaptation that allows them to endure higher water surface temperatures and increased acidity.

“Stressful periods of high temperature and increasingly acidic conditions are becoming more frequent and longer lasting in Florida waters,” said Chris Langdon, a professor of marine biology and ecology professor who was the lead author of a new study. “However, we found that not all coral species are equally sensitive to climate change and there’s hope that some species that seemed doomed may yet develop adaptations that will allow them to survive as well.”

During heat-sensitivity tests the researchers found that staghorn corals, so named for their stony cylindrical branches, were more sensitive to heat stress. A rise of 1.5 degrees Celsius in water temperatures caused them all to die after 25 days. Yet mountainous star corals managed to survive for 62 days under the same conditions.

This study’s findings are in line with similar pieces of research that indicate that some corals may be able to weather more extreme weather conditions caused by climate change, at least for a while. An international team of scientists recently found that local corals in the Gulf of Aqaba in the Red Sea are resistant to warming and acidifying waters.

Local corals “are living under suboptimal temperatures right now and might be better prepared for future ocean warming,” report the scientists, who published their findings in the journal Royal Society Open Science. They believe that Red Sea corals, which grow nowhere else, have evolved a high degree of thermal-resistance due to the stressful climatic conditions that prevail in the area.

In fact, the corals responded well to artificially induced stressful conditions under which the scientists have placed them. “Most of the variables that we measured, such as energy metabolism or building a skeleton, were actually improved [in such conditions],” one of the researchers said.

Nor are these corals the only ones that seem capable of withstanding extreme conditions. Recently, Australian researchers discovered another type of hardy coral, in the waters of New Caledonia, in the South Pacific. These corals, too, thrive in unhospitable settings: within the salty, warm and murky waters of mangrove forests. Like their counterparts in the Red Sea, they have apparently turned resistant to extreme environmental stresses over time.

“All these kind of discoveries are really exciting,” said David Suggett, an associate professor working for the Future Reefs Program at the University of Technology in Sydney. “What we’re starting to learn is that corals are surviving in waters that are really hot, really acidic, have very little oxygen and these are the conditions we’ve predicted under climate change.”