Mystery solved: Scientists ID Caribbean sea urchin killer

Sea urchins in the Caribbean began to become sick last year, losing their spines, dying off, and upsetting the balance of reef ecosystems. In this maritime murder mystery, experts now believe they have the culprit in their sights.

According to research published on Wednesday in the journal Science Advances, a small single-celled parasite is to responsible for the severe die-off.

Mya Breitbart, a marine microbiologist at the University of South Florida and the study's author, declared that "the case is over."

These Diadema antillarum long-spined sea urchins are spiky, black, and may be found on Caribbean reefs. According to Breitbart, they are essential "lawnmowers" of the reef because they consume algae that develops on corals.

But, beginning in January 2022, these creatures began exhibiting odd symptoms (such as their sharp spines drooping and dropping off and their suction-cup feet losing their grip) before passing away in great numbers all across the Virgin Islands, Puerto Rico, and Florida.

It was déjà vu for marine experts because a similar die-off that hit the area in the 1980s reduced sea urchin numbers by almost 98%.

It was an unsolved case. But this time, a global team of scientists sprung into action, collecting samples from ill and healthy sea urchins around the Caribbean to seek for genetic hints.

According to study author Ian Hewson, who studies marine illnesses at Cornell University, they found no evidence of viruses or bacteria. But, scientists did find evidence of ciliates, small single-celled creatures that only appeared in ill urchins.

Although the majority of ciliates are harmless, this particular species has been connected to past aquatic outbreaks, making it a prime suspect, according to Hewson.

Scientists put the parasites in aquariums with healthy urchins raised in captivity to observe how they would behave, hoping to catch the killer. 60% of the 10 urchins that were tested against the small invertebrates perished after exhibiting the identical symptoms as those seen in the wild by the researchers.

According to Breitbart, it's probable that the die-off in the 1980s was also brought on by this parasite.

Also, they haven't developed a cure for the sick urchins. Nonetheless, scientists are optimistic that figuring out the cause of the die-offs may benefit in reef conservation, particularly if they discover more about how the parasites propagate, according to Breitbart.

Don Levitan, a marine biologist at Florida State University who was not involved in the study but observes coral reefs, emphasized that the urchin fatalities and other stressors had already altered the reefs.

Levitan remembered witnessing reefs in the U.S. Virgin Islands covered in the prickly animals before the first sea urchin die-off. These reefs now appear very different, engulfed in algae, afflicted by coral disease, and overworked by the rising temperatures.

The Caribbean's coral reefs are in danger, according to Levitan. "Our current situation differs from where it was 30, 40 years ago."

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