Some coral reefs are weathering extreme temperatures

When it comes to the world’s coral reefs, the news these days is rarely good. Increasing water temperatures, growing acidification, mass tourism and plastic pollution are all posing threats to the planet’s beleaguered reefs. Yet now and again comes some good news.

A case in point is a scientific report that coral reefs in the Eastern Tropical Pacific region have been weathering climate change better than expected. The scientists say the area’s reefs have adapted well to heat stress, which is sparking hope that reefs elsewhere could also survive a changing climate in coming decades.

An international team of researchers has examined coral cover data in an area that stretches from Baja California to the Galapagos Islands from a period of more than four decades, between 1970 and 2014. During that time several El Niño events, which brought unusually high temperatures, battered local reefs, leading to the death of the symbiotic algae that cohabit with the corals. The results were mass bleaching episodes that decimated corals.

Yet within 10 to 15 years many of the local corals bounced back. How they did that is still a bit of a mystery as many corals elsewhere never recover from mass bleaching.

The scientists postulate that one of the reasons could be that most local corals are pocilloporids, which reproduce at high rates so after a mass bleaching episode the surviving corals can soon repopulate the area fairly fast. Local corals also support species of symbiotic algae that are especially tolerant to high water temperatures. In addition, some local areas of the ocean have heavier cloud cover or upwelling of cooler waters, which aids corals in surviving and regenerating even in the face of higher temperatures.

“The key to survival for future reefs may not be an immunity to stress, but rather an ability to recover and regrow after stress,” said James W. Porter, professor emeritus at the University of Georgia’s Odum School of Ecology. “[T]o discover a large area of the tropics where coral reefs are holding their own is very gratifying.”

Elsewhere around the tropics many coral reefs have been weathering changes in their environment less well, but even there not all hope is all lost yet. Some corals in other areas too are naturally better able to recover from bleaching episodes. Scientists posit that seeding stressed reefs with hardier species of corals could also help.