A growing number of scientists are predicting a major El Nino weather event this year, which could wreak havoc across South America and Asia as droughts, floods and other extreme weather events hit industry and farming. However, the impacts on the world’s coral reefs could be even more disastrous.
The last big El Nino, from 1997 to 1998, caused the worst coral bleaching in recorded history. In total, 16 percent of the world’s coral was lost, and some countries, like the Maldives, lost up to 90 percent of their reef coverage. The Australian Bureau of Meteorology suggests there is a 70 percent chance of an El Nino occurring this year — and all the signs are that it will rival the 1998 event.
El Nino arises out of a confluence of factors that are still not fully understood, but its outcome is clear — parts of the ocean get hotter. A band of warm water develops in the western Pacific, while the Indo-Pacific Warm Pool — a blob of heat that spans much of Indonesia — starts oscillating wildly. This could spell disaster for the Coral Triangle, a southeast Asian bioregion that is the underwater equivalent of the Amazon rain forest, home to more marine species than anywhere else on Earth.
“In 1998, the Coral Triangle started to bleach in May and continued till September,” said Ove Hoeg Guldberg, a marine biologist and head of the Global Change Institute at the University of Queensland. “The Coral Triangle sees prolonged periods of temperature anomaly during an El Nino because the equator passes through the middle of it, so it experiences both northern and southern hemisphere summers.”
Guldberg, who led the Oceans chapter of the UN’s Intergovernmental Panel on Climate Change (IPCC) report on climate change, is less than sanguine about the prospects for the region’s coral reefs.
“It only takes about half a degree on top of background sea temperatures to cause bleaching,” he said. “Atmospheric scientists are telling us we’re headed for temperatures that will trump those of 1998.”
Corals are animals that behave like plants. They are able to do this by maintaining a symbiotic relationship with dinoflagellates, a type of microbe that lives inside the coral’s tissue where it photosynthesizes, passing sugar to its host. However, when temperatures rise, the dinoflagellates stop making sugar and produce harmful free radicals instead. The corals then spit them out, stop producing their carbonate shell and steadily fade to white.
Coral bleaching is actually quite a common occurrence and bleached reefs can make comebacks — many of the reefs affected by the 1998 El Nino have made at least partial recoveries.
“The thing is, under mild conditions, corals can recover their symbiotes,” Guldberg said. “But because background temperatures are warmer, the corals can’t recover as before.”
Even when reefs do recover, old-growth corals that might have taken centuries to mature are often replaced with faster growing species that quickly colonize large areas, homogenizing the ecosystem.
Of course, the elephant in the room is global warming, and this is where things get scary.
Guldberg said current rates of ocean warming and acidification are unmatched in most if not all of the past 65 million years.
“This sends chills down the back of any biologist worth their salt, because life will have to struggle in circumstances that it’s just not evolved for,” Guldberg said.