Caribbean coral reefs are dying

Coral cover in the Caribbean has declined by 48% since 1980, while macroalgae cover has risen by 85% in the same time, according to a major new report by the Global Coral Reef Monitoring Network (GCMRN). The GCMRN, an operational network of the International Coral Reef Initiative (ICRI), found that these changes are largely driven by climate change-induced heat stress, overfishing, and diseases.

• Hard coral cover declined by 48% from 1980 to 2024, meaning that hard corals now occupy half of the benthic cover they occupied in 1980.
• Hard coral cover declined sharply in 1998 (-9.0%), 2005 (-17.1%), and 2023 (-16.9%) due to bleaching events induced by thermal stress.
• Hard coral assemblage shifted from branching species to more massive species, thereby decreasing the structural complexity of Caribbean coral reefs.
• Macroalgae cover increased by 85% from 1980 to 2024 due to the decline in herbivorous species (e.g., parrotfish, sea urchins) and the increase in nutrients.
• Mean sea surface temperature over coral reef areas across the Caribbean increased by +1.07°C between 1985 and 2024, driven by climate change, representing a warming rate of +0.27°C per decade.
• The number of people in the Caribbean living within 20 km of coral reefs increased by 27.6% from 2000 to 2020 at the regional scale, representing an increase of 13 million people.
• Coral reefs of the GCRMN Caribbean region cover 24,230 km², which represents 9.7% of the world’s coral reef extent.

As reefs degrade, their ability to provide food, sustain fisheries and buffer coasts from storms and hurricanes is compromised. The number of people living within 20km of coral reefs has increased by 27.6% since 2000 (an additional 13 million people), which has not only increased pressures, but also increased reliance on these systems—raising the number of people at risk from diminishing coral reef services.

The climate crisis is currently considered the greatest threat to the world’s reefs, and 14 percent of them were lost because of it between 2009 and 2018 alone. According to the Intergovernmental Panel on Climate Change, even limiting global warming to 1.5 degrees Celsius beyond pre-industrial levels would still see 70 to 90 percent of tropical reefs wiped out.

An extreme ocean warming event in 2010 placed Caribbean coral reefs under severe stress resulting in widespread coral bleaching and threatening the livelihoods that rely on them. 

Mass coral bleaching is one of the major threats to coral reef ecosystems exacerbating coral reef decline in the Caribbean region . Often mass coral bleaching events are as a result of the prolonged exposure of corals to unusually warm ocean temperatures, resulting in the expulsion of symbiotic algae from host corals. However, not all coral taxa are equally susceptible to bleaching. Some taxa may bleach, whereas others exposed to the same heat stress may not bleach or show intermediate signs of bleaching.

The warmest year since temperature records began in 1880, 2005 witnessed massive coral losses through severe bleaching, up to 95 percent in several islands including the Cayman Islands, Jamaica, Cuba, and the French West Indies. There were also 26 named storms, including 13 hurricanes, that year.

The greatest overall changes in coral and macroalgal cover occurred between 1984 and 1998, after which there was little overall change at the great majority of locations except for places most strongly affected by the extreme warming events of 2005 and 2010. 

However, increases in stress‐tolerant and weedy corals have slowed or reversed since the 1980s and 1990s in tandem with intensified coral bleaching and disease. These patterns reveal the long history of increasingly stressful environmental conditions on Caribbean reefs that began with widespread local human disturbances and have recently culminated in the combined effects of local and global change.

This phase shift followed disease outbreaks that killed en masse the Acropora corals and the sea urchin Diadema antillarum in the early 1980s as well as coral bleaching outbreaks that became widespread in the late 1980s. The appearance and intensification of coral disease and bleaching epidemics in the Caribbean and elsewhere have been linked to elevated sea surface temperatures from global climate change, algal overgrowth from overexploitation of herbivorous reef fishes and increases in land-based runoff.

Since systematic reef monitoring began in the 1970s, researchers have documented a dramatic ‘phase shift’ on Caribbean reefs whereby habitats previously dominated by reef-building corals (in many locations, primarily branching corals from the Acropora genus) are now dominated by macroalgae and low-relief corals tolerant of lower water quality (higher turbidity and nutrient) conditions.

The iconic elkhorn and staghorn corals that once dominated Caribbean reefs first began declining in the 1950s and 1960s, earlier than previously thought. This timing is decades before climate change impacts, indicating that local human impacts like fishing and land-clearing set the stage for the widespread coral declines that are now accelerating in response to warming oceans.