In this image provided by researchers, Cornell University graduate student Brian Villanova Cuevas collects a swab sample from the surface of a coral reef in St. Thomas, US Virgin Islands in September 2022. Sea urchins in the Caribbean in 2022, researchers reported Wednesday, April 19, 2023, in the journal Science Advances. Credit: Ian Hewson/Cornell University via AP
Last year, sea urchins in the Caribbean began to fall ill, shed their spines, die, and throw coral reef ecosystems into chaos. Now, scientists think they have caught the killer in this marine murder mystery.
Researchers reported Wednesday in the journal A tiny, single-celled parasite responsible for the massive death Science advances.
“Case closed,” said study author Mia Breitbart, a marine microbiologist at the University of South Florida.
Long-spined sea urchins, or Diadema antillarum, are spiky black creatures that hide in coral reefs in the Caribbean. They act like “lawn mowers” for coral reefs, gobbling up algae growing on the reef, Breitbart said.
But in January 2022, these animals began showing strange symptoms—their sharp spines droop and fall off, their sticky feet losing their grip—before dying in droves, from the Virgin Islands to Puerto Rico to Florida.
For marine scientists, it was deja vu: Another wave swept the region in the 1980s and reduced sea urchin populations by about 98%.
This issue has not been resolved. But this time, an international team of researchers sprang into action, sampling sick and healthy urchins from across the Caribbean to search for genetic evidence.
They saw no signs of viruses or bacteria, said study author Ian Hewson, who researches marine diseases at Cornell University. But they did find traces of tiny single-celled organisms called ciliates, which only appeared in sick hedgehogs.
Hewson said that while most ciliates do not cause disease, this species has been linked to other aquatic disease outbreaks, making it a prime suspect.
This image provided by the researchers shows a sea urchin affected by a ciliated parasite, center, and a normal-looking urchin, left, in St. John, US Virgin Islands, in April 2022. A tiny, single-celled organism is responsible for a massive organism, researchers reported Wednesday, April 19, 2023, in the journal Science Advances, of sea urchins dying in the Caribbean in 2022. Credit: Ian Hewson/Cornell University via AP
To confirm the capture of the killer, the scientists placed the parasites in tanks with intact, captive-grown hedgehogs to see how they would react. Of the 10 hedgehogs pitted against the young critters, 60% died—after showing the same symptoms the researchers saw in the wild.
It’s possible that this same parasite also caused death in the 1980s, Breitbart said, but scientists can’t be sure.
And they haven’t figured out a way to treat sick hedgehogs. But they hope knowing the source of the deaths will help preserve coral reefs, especially once more is learned about how the parasites spread, Breitbart said.
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In this photo provided by researchers, University of South Florida researchers Mia Breitbart and Isabella Ricci work with sea urchins during a ciliary exposure experiment at the University of South Florida Aquarium Research Facility in St. Petersburg, Florida, on July 7, 2022. Researchers reported Wednesday, 19 April 2023, in the journal Science Advances that a tiny single-celled organism is responsible for a massive die-off of sea urchins in the Caribbean in 2022. Credit: Makenzie Kerr/University of South Florida College of Marine Science via AP
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This image provided by the researchers shows a ciliated microorganism Philaster apodigitiformis seen under a microscope at the University of South Florida College of Marine Sciences in St. Petersburg, Florida. A scale of 1000 micrometers equals 1 millimeter. The tiny, single-celled organism is responsible for the massive mortality of sea urchins in the Caribbean in 2022, researchers reported Wednesday, April 19, 2023, in the journal Science Advances. Credit: Mia Breitbart/USF College of Marine Science via AP
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This set of images provided by the researchers shows the same sea urchin before and after infection with ciliated microorganisms at the University of South Florida Aquarium Research Facility in St. Petersburg, Florida. Sea urchins in the Caribbean in 2022, researchers report Wednesday, April 19, 2023, in the journal Science Advances. Credit: Makenzie Kerr/University of South Florida College of Marine Sciences via AP
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This image provided by researchers shows spines falling from a sea urchin affected by ciliary parasites in Aruba in August 2022. Researchers reported Wednesday that a small single-celled organism is responsible for a massive sea urchin die-off in the Caribbean in 2022. April 19, 2023, in the journal Science advances. Credit: Ian Hewson/Cornell University via AP
These urchin deaths and other stresses have already changed coral reefs, added Don Levitan, a Florida State University marine scientist who was not involved in the study.
Back before the first sea urchin eruption, Levitan recalled seeing coral reefs in the US Virgin Islands covered in spiny creatures. Now, those reefs look a lot different—suffocated by algae, battered by coral diseases and stressed by rising temperatures.
“The coral reefs in the Caribbean are in trouble,” Levitan said. “We are in a different place than we were 30 or 40 years ago.”
more information:
Ian Hewson et al, scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea, Science advances (2023). DOI: 10.1126/sciadv.adg3200
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