St. John’s, Antigua – A mysterious disease is once again decimating populations of long-spined sea urchins across the Caribbean, sparking fears for the health of fragile coral reef systems.

Marine ecologist Ruleo Camacho of the Antigua and Barbuda National Parks Authority (NPA) confirmed that die-offs have been recorded around the island, echoing a catastrophic event from the 1980s when more than 90 percent of the region’s sea urchins perished in just two years.

The long-spined sea urchin (Diadema antillarum) is a critical herbivore that helps control algae on reefs. Without them, algae smother corals, preventing new growth and weakening the marine ecosystem. “If you take a regular walking step and make a one-meter square box, there would have been about 10 urchins in that box 50 years ago,” Camacho explained. “Now, you’d have to do that 10 times to find just one.”

In mid-February, reports of mass urchin deaths surfaced in St. Thomas and quickly spread to Belize, Jamaica, Grenada, Dominica, St. Vincent, and Antigua. Camacho said the pattern closely resembles the 1983 die-off, though this outbreak appears to be spreading even faster. Scientists suspect human activity, including yacht and boat traffic, may be contributing to the disease’s spread.

“The disease, the progression between a healthy urchin and an unhealthy slash dying urchin, seems to take between two to five days,” Camacho explained. “The first thing that happens is that they lose their tube feet… the spines essentially just fall off… then they just get washed around.”

In Antigua, the first signs appeared in Falmouth Harbour before spreading to English Harbour and other coastal areas. The disease progresses rapidly: within days, affected urchins lose their grip on rocks, their spines fall off, and they wash ashore as lifeless shells. Residents have been encouraged to report sightings, and many have already sent photos and messages through social media to aid monitoring efforts.

To better understand the outbreak, local and regional teams have joined the Diadema Response Network, collaborating with scientists across the Caribbean.

Tissue samples from both healthy and diseased urchins are being collected in Antigua and sent to Cornell University for genetic analysis. Researchers hope to finally identify the cause of the pathogen—something that eluded them in the 1980s.

“This time we’re on the cutting edge of science,” Camacho said. “We want to know not just how fast it’s spreading, but why some populations remain healthy while others collapse. Any data we get is extremely valuable.”

The implications extend far beyond sea urchins. Coral reefs are the backbone of Caribbean marine life, providing shoreline protection, supporting fisheries, and giving the region its famous turquoise waters. Without healthy urchins to keep algae in check, reefs could decline further, threatening biodiversity and livelihoods tied to tourism and fishing.

“It means that we don’t have as much time to try and figure out what’s going on and see if we can come up with a mitigation factor. Right now, we’re not sure… but any kind of data is extremely important.”