The world is about to have mass coral bleaching – 03/05/2024 – Environment

The world is about to have the fourth mass coral bleaching event, Noaa (American atmospheric and oceanic agency) reported this Tuesday (5). The phenomenon, caused by excessive warming of the sea, could result in the death of large areas of tropical reefs, including parts of Australia’s Great Barrier Reef.

Marine biologists are on high alert after months of record ocean heat driven by climate change and the El Niño weather pattern.

“It looks like the entire Southern Hemisphere is likely to experience bleaching this year,” said ecologist Derek Manzello, coordinator of NOAA’s Coral Reef Watch, which serves as the global authority monitoring coral bleaching risk.

“We are literally on the brink of the worst bleaching event in the history of the planet,” he said.

Triggered by heat stress, coral bleaching occurs when corals expel the colorful algae living in their tissues. Without them, corals become pale and vulnerable to disease and hunger, as much of their energy comes from photosynthesis carried out by these algae.

As corals are huge nurseries for fish and other species, the phenomenon can be devastating for the ocean ecosystem — as well as for economies based on fishing and tourism, which depend on healthy and colorful reefs to attract divers.

Worrying signs

The last global mass bleaching event occurred from 2014 to 2017, when the Great Barrier Reef lost nearly a third of its coral. Preliminary results suggest that about 15% of the world’s reefs experienced high mortality rates in this event.

This year, the scenario that has been emerging so far in researchers’ observations indicates that the situation is likely to be even worse.

Following last year’s Northern Hemisphere summer, the Caribbean experienced its worst coral bleaching on record. Now, the situation is repeating itself and escalating in the other half of the planet.

“The Southern Hemisphere is basically bleaching everywhere,” Manzello said. “The entire Great Barrier Reef is experiencing bleaching. We’ve just received reports that American Samoa is experiencing bleaching.”

Previous global bleaching events occurred in 2010 and 1998, a phenomenon that is often linked to El Niño, which is characterized by warming of the Pacific Ocean near the equator.

According to the World Meteorological Organization, the El Niño that began in 2023 and reached maximum intensity in December is among the five strongest ever recorded and is expected to cause above-normal heat until May.

But bleaching is also one of the consequences of the climate crisis. The world has just recorded its first 12-month period with an average temperature more than 1.5ºC above pre-industrial levels.

If recorded over a longer period, a 1.5°C rise is considered the tipping point for major coral die-offs, with estimates that 90% of the world’s coral could be lost.

Field inspections

For an event to be considered global, widespread bleaching must occur in three ocean basins: Atlantic, Pacific and Indian. Scientists evaluate sea surface temperature data and satellite imagery to determine whether reef pixels are exceeding key bleaching thresholds.

For an event to be classified as global and massive, a certain percentage of reef pixels must reveal a level of thermal stress in each ocean basin. Based on this definition alone, according to Manzello, this year “technically we’re already there.”

However, he said NOAA was still awaiting final confirmation from Indian Ocean scientists or photographs of reefs in the region to officially flag the fourth mass bleaching event.

On Australia’s Great Barrier Reef — which has recorded six localized bleaching events since 1998 — scientists are conducting flyovers of the reef to determine the extent of the damage.

“Aerial surveys are ongoing as coral bleaching has been reported across all areas of the marine park, varying in severity,” said Joanne Manning, spokeswoman for the Australian Institute of Marine Science. She added that this phase of the research should be completed in the coming weeks, following which underwater surveys should be carried out.