More than 80% of the world’s reefs hit by bleaching
World’s Reefs Hit by Worst Global Bleaching Event on Record
Hawaii’s reef system is again in the crosshairs of global heating
The world’s coral reefs have been pushed into “uncharted territory” by the worst global bleaching event on record that has now hit more than 80% of the planet’s reefs, scientists have warned.
Reefs in at least 82 countries and territories have been exposed to enough heat to turn corals white since the global event started in January 2023, the latest data from the US government’s Coral Reef Watch shows.
Coral reefs are known as the rainforests of the sea because of their high concentration of biodiversity that supports about a third of all marine species and a billion people.
But record high ocean temperatures have spread like an underwater wildfire over corals across the Pacific, Atlantic and Indian oceans, damaging and killing countless corals.
The 84% of reefs exposed to bleaching-level heat in this ongoing fourth event compares with 68% during the third event, which lasted from 2014 to 2017, 37% in 2010 and 21% in the first event in 1998.
Even reefs considered by scientists to be refuges from the ocean’s rising levels of heat have been bleached, Dr Derek Manzello, the director of Coral Reef Watch, said.
“The fact that so many reef areas have been impacted, including purported thermal refugia like Raja Ampat and the Gulf of Eilat, suggests that ocean warming has reached a level where there is no longer any safe harbour from coral bleaching and its ramifications,” he said.
Many areas have seen bleaching in back-to-back years, including the world’s biggest reef system, Australia’s Great Barrier Reef, where last week authorities declared a sixth widespread bleaching event in just nine years.
Australia’s other World Heritage-listed reef along the Ningaloo coast in Western Australia has seen its highest levels of heat stress on record in recent months.
Scientists on the other side of the Indian Ocean have reported bleaching in recent weeks affecting reefs off Madagascar and the east African coast, including South Africa’s World Heritage iSimangaliso wetland park.
Dr Britta Schaffelke, of the Australian Institute of Marine Science and coordinator of the Global Coral Reef Monitoring Network (GCRMN), said the event was unprecedented. “Reefs have not encountered this before.”
“With the ongoing bleaching it’s almost overwhelming the capacity of people to do the monitoring they need to do,” she said. “The fact that this most recent, global-scale coral bleaching event is still ongoing takes the world’s reefs into uncharted waters.
Scientists in north and central America, including Florida, the Caribbean and Mexico, were among the first to raise the alarm after record ocean temperatures saw extreme bleaching in the northern hemisphere’s summer of 2023.
Corals can recover from bleaching if temperatures are not too extreme, but surveys done in the months after the event have begun to paint a picture of widespread coral death.
After the extreme heat of 2023, Coral Reef Watch was forced to add three new threat levels to its global bleaching alert system to represent the unprecedented heat stress corals had faced.
Melanie McField, the founder of the Healthy Reefs for Healthy People initiative in the Caribbean, said reefs had fallen quiet across the world.
“Bleaching is always eerie – as if a silent snowfall has descended on the reef … there is usually an absence of fluttering fish and an absence of the vibrant colours on the reef,” she said. “It’s an ashen pallor and stillness in what should be a rowdy vibrant reefscape.”
Dr Valeria Pizarro, a senior coral scientist at the Perry Institute for Marine Science that works on reefs in the Bahamas and Caribbean, witnessed extreme bleaching in the Bahamas in July 2023. She said “in a blink of my eyes” shallow reefs became white landscapes, with widespread death among staghorn corals used in restoration projects. Spectacular sea fans and soft corals died quickly. “It was like they were melting with the heat, world leaders need to really commit to quitting fossil fuels, and to switch their country’s investments into clean energy and make it a reality”, she said.
Soo..what’s happening right here on Kona reefs????
(kind of expected a local update.)
Local state reporting on the health and condition of our multi-island coral reef systems is lacking or incomplete. Most reporting is limited 50K foot view of reef health. Local University projects are designed to restore and transplant individual corals impacted by development and global heating die-offs.
Hawaii’s reefs have experienced repeated and increasingly severe coral bleaching events, particularly during marine heatwaves in 2014, 2015, and 2019. During the 2015-16 bleaching event, surveys found that 38–92% of reefs in West Hawaii were partially or fully bleached, with large coral colonies dying or dead. More up-to-date survey information is lacking.
The new administration’s emphasis on rolling back the clock on science by 100 years and gutting meaningful Federal programs, e.g. marine environmental scientific studies and limited marine management measures, even before Trump’s return to the White House did not fully address the need for more specific and present day reef health assessments of our state’s islands. I can add, from my own personal near shore reef observations, most areas and coral types within the West Hawaii Island coral system are dying, but not dead. And most never recovered from the severe 2015-16 bleaching event.
Even a 1–2°C increase above average temperatures can trigger bleaching in Hawaiian corals. Ocean acidification, driven by increased atmospheric CO₂, makes it even harder for corals to build their skeletons, further weakening reefs. These stressors have led to declines in key native Hawaiian coral genera (Porites, Montipora, and Pocillopora) and have affected local biodiversity, including species that rely on Hawaii’s reefs for food and shelter.