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A 'pandemic' among sea urchins could be on the rise, Florida researchers find

A long-spined black sea urchin on a white rock.
University of South Florida
Sea urchin at the University of South Florida St. Petersburg.

“It spread so rapidly in the Caribbean, which suggests it could spread quickly through the Pacific," said Isabella Ritchie, a Ph.D. student at USF and the lead author of a recent study.

There's evidence to suggest that a disease killing sea urchins could be turning into a pandemic.

A ciliate, a single-celled organism, killed 95% of long-spined sea urchins called Diadema antillarum in affected areas between Florida and the Caribbean back in 2022.

The parasite burrows into the urchins’ tissue causing them to lose their spines and also lose control of their tube feet, which they use to walk.

Even if the disease doesn’t fully kill them, the symptoms make them susceptible to getting eaten by other marine life. It has so far only been observed to affect sea urchins.

Scientists with the University of South Florida College of Marine Science have now found that the same parasite is attacking another species of long-spined sea urchin called Diadema setosum 7,000 miles away in the Sea of Oman.

The USF lab used infected urchin specimens and genomic tests to make the determination.

Isabella Ritchie, a Ph.D. student at USF, is the lead author of a recently published peer-reviewed study in The ISME Journal.

Blonde woman smiling holding up a black long-spined sea urchin in her cupped hands.
University of South Florida
Isabella Ritchie, Ph.D. student at USF's College of Marine Science.

She said sea urchins are important because they eat the algae that competes with corals for light and space.

"When urchins are removed, there tends to be a really big overgrowth of algae, which obviously has negative impacts on coral reefs which are already struggling," Ritchie said.

Corals are already having to battle pollution along with human-driven warming and acidifying waters.

In the 1980s, there was a very similar mass mortality event of the same Diadema antillarum sea urchin species in the Caribbean, Florida, and Bermuda, but the cause of that was never determined. The average population densities 30 years later were about 12% of those before the die-off.

If the ciliate parasite continues to spread, Ritchie said this could negatively impact ecosystems globally.

“It spread so rapidly in the Caribbean, which suggests it could spread quickly through the Pacific since D. setosum are so widespread,” she said.

"I think it's really going to be a team effort between different entities across the globe to get an idea of where it's spreading, how, and to whom.”

Such a spread could be called a pandemic, said Philip Gravinese, a researcher and assistant professor in marine science at Eckerd College who specializes in how environmental stressors impact the physiology and behavior of marine life.

He wasn’t part of this study, but read it and weighed in.

"It's something that we've been seeing periodically, throughout the Caribbean, and now in other parts of the world as well. So yeah, it's something to definitely be concerned about," Gravinese said.

He said the authors of the study did a good job at identifying, through molecular techniques, the organism behind the disease outbreaks.

But Gravinese would like to see a larger sample size. He shared some questions he has for any future studies on the subject:

“Are these ciliates moving in the water as well? And do we see higher density of them in certain locations and others? And then does that kind of create a vector for transmission? Basically, are they surfing the currents to get downstream? And is that resulting in why we see these locations getting affected?” Gravinese asked.

Isabella Ritchie and her colleagues don’t yet know where the parasite came from.

“It could either be a completely new pathogen that evolved and somehow came from a different location and it wasn't there before, or it could be something that was already in the environment and didn't cause issues and then some sort of environmental factors could have caused it to become pathogenic,” Ritchie said.

Her collaborators are looking into whether it could have been accidentally transported on international ships, dive gear, or through the aquarium trade. Determining how the ciliate spreads may help mitigate future die-offs.

Ritchie said some scientists are also looking at anti-parasite treatments as a possible solution.

My main role for WUSF is to report on climate change and the environment, while taking part in NPR’s High-Impact Climate Change Team. I’m also a participant of the Florida Climate Change Reporting Network.