The Long-spined sea urchin Diadema antillarum occurs on reefs across the Caribbean and plays a key role grazing on the algae that grows on corals. But in January 2022, these animals started showing strange symptoms, their sharp spines drooping and falling off, their suction-cup feet losing grip and finally massive mortalities from the Virgin Islands to Puerto Rico to Florida.
For marine scientists though, it was a case of déjà vu as another die-off swept through the region in the 1980s and slashed sea urchin populations by around 98%. This time they were ready, and an international team of researchers jumped into action, taking samples from sick urchins and healthy ones across the Caribbean to look for genetic clues.
They didn’t see signs of viruses or bacteria, said study author Ian Hewson, who researches marine diseases at Cornell University, but they did spot traces of tiny single-celled organisms called ciliates, which only showed up in the sick urchins. To confirm they’d caught the killer, scientists placed the parasites in tanks with healthy urchins grown in captivity to see how they’d react. Out of 10 urchins who were pitted against the tiny creatures, 60% of them died—after showing the same symptoms researchers were seeing in the wild.
“The case is closed,” said study author Mya Breitbart, a marine microbiologist at the University of South Florida, and while they aren’t sure, it’s possible that this same parasite also caused the die-off in the 1980s. While they haven’t figured out a way to treat the diseased urchins yet, scientists are hopeful that knowing the source of the die-offs will help conserve the reefs, especially once they learn more about how the parasites spread.
Image: In this photo provided by researchers, University of South Florida researchers Mya Breitbart and Isabella Ritchie work with a sea urchin during a ciliate exposure experiment in the University of South Florida aquarium research facility in St. Petersburg, Fla., on July 7, 2022. A tiny single-celled organism is to blame for a massive die-off of sea urchins in the Caribbean in 2022, researchers reported Wednesday, April 19, 2023, in the journalScience Advances. Credit: Makenzie Kerr/University of South Florida College of Marine Science via AP
