The numbers of parrotfish, which graze on algae that otherwise would smother coral reefs, are plummeting and putting the fate of Caribbean reefs at risk, researchers say.
Overfishing has decimated parrotfish in the region, and a follow-on effect is reefs are slowly deteriorating from colorful habitats full of marine life to dead husks covered in algae.
Protection of parrotfish should be the No. 1 priority in efforts to protect the well-being of coral reefs, a Caribbean-wide analysis has shown.
That's because the colorful herbivores with a voracious appetite for algae spend as much as 90 percent of their days grazing on the reefs, keeping algae under control.
With overfishing, researchers with the Global Coral Reef Monitoring Network of the international Union for Conservation of Nature say, there are insufficient numbers of the marine "landscape artists" and the reefs are becoming increasingly furred with algae.
The problem has been exacerbated with an accompanying drop in sea urchins, the other key herbivore that helps keep reefs free from excess algae.
Most of the region's sea urchins were killed off by an unidentified disease in the early 1980s.
"We saw that reefs with no grazers ended up getting smothered by algae," says Carl Gustaf Lundin, director of IUCN's Global Marine and Polar Program. "And after a period of time they see a significant or even complete collapse of the reef area."
The researchers analyzed date collected in 35,000 surveys of reef health at 90 locations in the Caribbean going back to 1970 in their Status and Trends of Caribbean Coral Reefs: 1970-2012 (PDF).
During that time, they say, there's been a 50 percent decline in Caribbean corals, and just one-sixth of the amount of original coral in the regions still exists.
"The rate at which Caribbean corals have been declining is truly alarming," Lundin says.
The 38 Caribbean countries surrounded by the reefs must combat overfishing, he says, put better zoning laws in place to stop construction of tourist hotels too near shorelines, and be better at managing their waste water.
Some areas that have already banned or restricted fishing for parrotfish, such as the U.S. Flower Garden Banks National Marine Sanctuary in the northern Gulf of Mexico, and Bonaire and Bermuda, still have large populations of the fish and some of the region's healthiest reefs, the IUCN report said.
But areas where protections for parrotfish are lacking, including the U.S. Virgin Islands, the Florida Reef Tract and Jamaica, have suffered "tragic declines" in their reef ecosystems, it said.
But the devastation can be reversed, Lundin says.
"The fate of Caribbean corals is not beyond our control and there are some very concrete steps that we can take to help them recover," he says.