Half of the Planet's Coral Reefs Have Been Lost Since 1950

Although forests still cover 31% of global land area, they’re disappearing at a rapid clip, according to the Food and Agriculture Organization of the United Nations (FAO), which says the world has lost approximately 420 million hectares of forest since 1990 and continues to lose an additional 10 million hectares of forest every year.

As bad as it is on land, however, deforestation—or rather, the marine equivalent of it: coral bleaching—might be even worse at sea, suggests a new study by researchers at the University of British Columbia (UBC). Published in the journal One Earth, it says half of the world’s coral reefs have been lost since the 1950s. Along with overfishing and habitat destruction, it pinpoints pollution and climate change as major reasons why.

It’s not just the size of coral reefs that have declined, however. It’s also their productivity, according to the study, which says biodiversity and fishing in coral reefs have both diminished since the 1950s. Biodiversity is down 63%, for example. Catches of reef-associated fish, meanwhile, peaked in 2002 and have been falling ever since despite increased fishing effort. The catch per unit effort—a common measurement of species abundance—is 60% lower today than it was in 1950.

“It’s a call to action,” said the study’s lead author Tyler Eddy, who conducted the research while he was a research associate at the UBC Institute for the Oceans and Fisheries (IOF), and is now a research scientist at the Fisheries & Marine Institute at the Memorial University of Newfoundland. “We know coral reefs are biodiversity hotspots. And preserving biodiversity not only protects nature, but supports the humans that use these species for cultural, subsistence and livelihood means.”

The reason coral reefs are perishing so rapidly is that they’re ultra-sensitive to changes in water temperature and acidity, reports Smithsonian magazine daily correspondent Corryn Wetzel.

“[Coral] are animals with symbiotic partners,” explains Wetzel, who says coral polyps are highly dependent on zooxanthellae, colorful algae that live in coral tissue and produce food on which coral subsist. “When the polyps are stressed by changes in light, water temperature, or acidity, they break that symbiotic relationship and expel the algae in a process called bleaching. Corals have a short window to regain their symbiotic algae, but if corals are stressed for too long, their death is irreversible.”

The role of climate change in coral bleaching is well established. The International Union for Conservation of Nature (IUCN), for example, points out that greenhouse gas emissions from fossil fuel consumption have led to increased retention of heat in Earth’s atmosphere. In turn, that heat has caused the average global sea surface temperature to rise by approximately 0.13 degrees Celsius per decade every decade for the last century, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

“The ocean absorbs most of the excess heat from greenhouse gas emissions, leading to rising ocean temperatures,” IUCN explains on its website. “Rising temperatures cause coral bleaching and the loss of breeding grounds for marine fishes and mammals.”

The impacts of climate change on coral reefs are especially devastating to indigenous communities on coasts, which typically consume large amounts of seafood—15 times more seafood than non-indigenous communities, in fact.

“It’s heart-wrenching for us to see photos and video of wildfires or floods, and that level of destruction is happening right now all over the world’s coral reefs and threatening people’s culture, their daily food, and their history,” says study co-author Andrés Cisneros-Montemayor, an IOF research associate at the time of the study, now an assistant professor at Simon Fraser University. “This isn’t just an environmental issue; it’s also about human rights.”

Although there is a solution—curbing greenhouse gas emissions would halt the warming of the oceans and help preserve surviving coral reefs—the world is far from realizing it, according to IOF Director and Professor William Cheung, yet another co-author of the study.

"Finding targets for recovery and climate adaptation would require a global effort, while also addressing needs at a local level,” Cheung says. “Climate mitigation actions, such as those highlighted in the Paris Agreement, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services, and the Intergovernmental Panel on Climate Change, all call for integrated action to address biodiversity, climate, and social challenges. We are not there yet.”