Caribbean coral reefs could ‘disappear’ within a few decades

Caribbean coral reefs, some of the most distinctive and unique natural underwater structures in the world, will “virtually disappear” within a few decades if steps are not taken to protect their habitat, a new report said Wednesday.

Only one-sixth of the original coral cover is left, with an average of 50 percent loss observed across the wider region's 38 countries since the 1970s. Researchers believe overfishing and the introduction of invasive species, including diseases, are the main reasons behind coral reef decline in the Caribbean — though ocean warming could pose a future threat.

“The rate at which the Caribbean corals have been declining is truly alarming,” Carl Gustaf Lundin, director of the Global Marine and Polar Program for the International Union for Conservation of Nature (IUCN), the oldest and largest global environmental organization, said in a press release. “But this study brings some very encouraging news: the fate of the Caribbean corals is not beyond our control and there are some very concrete steps that we can take to help them recover.”

The IUCN report is the most detailed and comprehensive study on the subject, taking in analysis from more than 35,000 surveys taken at 90 sites across the Caribbean since 1970.

The Caribbean is home to 9 percent of the world’s coral reefs, and is unique because the tropical ocean is the most geographically and oceanographically isolated on the planet.

The highly distinctive coral reefs declined rapidly in 1983 when an unidentified disease caused a mass die-off of sea urchins — an important predator necessary to keep the coral habitat in balance. And overfishing throughout the 20th century pushed the parrotfish to the brink of extinction.

Both of these were herbivores that fed on macroalgae, a form of large seaweed that grows on coral reefs. Without these natural consumers, macroalgae smothered the reefs, the report said.

Macroalgae can lead to virulent diseases in reefs and can release toxins that cause coral bleaching or death. Coral bleaching occurs when a reef becomes stressed and its symbiotic relationship with photosynthetic algae that lives in its tissue breaks down — leaving the white calcium carbonate skeleton visible.

Invasive species, including foreign diseases, are another major factor identified by the report that has led to coral reef die-off. An unidentified pathogen during the 1960s and 1970s led to the mass mortality of sea urchins. The disease was likely introduced via foreign boats, as it came as the same time as an increase in shipping and began just miles from the entrance of the Panama Canal, according to the report.

The study said tourism could have a negative effect on the reefs when there are not proper environmental protections in place, adding that locations with more visitors and no regulations have less coral cover.

Though ocean warming and climate change have played a role in coral reef die-off in other areas of the world, in the Caribbean, researchers found only a weak correlation. But they cautioned that ocean acidification caused by climate change will likely compromise corals in the future.

“Even if we could somehow make climate change disappear tomorrow, these reefs would continue their decline,” Jeremy Jackson, lead author of the report and IUCN’s senior adviser on coral reefs, said in a press release. “We must immediately address the grazing problem for the reefs to stand any chance of surviving future climate shifts.”

In other oceans, climate change is believed to have had a more severe impact on coral reefs. Researchers warned in 2009 that ocean warming, acidification and associated coral bleaching could doom the reefs and species that depend on them.

Scientists have warned that damage to certain environmental systems, including coral reef die-off, could lead to abrupt and irreversible changes that could have a devastating impact on the world in just a matter of years.