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A fatal pathogen affecting the long-spined sea urchin decimated populations of this important herbivore in the 1980s. A similar disease emerged in 2022, and its identity has been revealed by USGS and partners—providing a key piece of information for reef managers to begin planning mitigation strategies.

Diadema antillarum, the long-spined sea urchin, is an ecologically important species in Caribbean coral reef habitats where it controls algal growth and coverage and helps keep reef surfaces clear for corals to grow and settle. This species of urchin experienced mass mortality from an unknown cause in the early 1980s, which decimated populations and led to shifts in coral reef community structure. The cause of this mass mortality was never established, but it ultimately contributed to the continued decline of coral reef ecosystems.

long-spined sea urchins on the seafloor. left urchin with spines intact. right is nearly bare surrounded by fallen spines
Here, a healthy urchin is seen on the left with spines intact. On the right, another urchin is in the process of losing its spines—which usually occurs within 1-2 days of infection. Photo by Ian Hewson, Cornell University. Used with permission. 




In early 2022, the remaining D. antillarum populations began experiencing mass mortality in the Caribbean again with disease signs reminiscent of those seen nearly 40 years ago. The mortality events are extremely rapid, occurring over 1-2 days from seemingly normal urchins to bare tests surrounded by a pile of spines. With reefs already under tremendous stress from changing environmental conditions, warming and rising seas, and coral disease, identifying and stopping the spread of this fatal urchin event is critical for protecting coral reefs into the future.




An oval-shaped microbe with small hairs, or cilia, swims around under a microscope
Using molecular and pathology approaches, the team determined that a scuticociliate most similar to Philaster apodigitiformis is the organism responsible for the urchins’ mass mortality. Video by Mya Breitbart, University of South Florida. Used with permission.




Drs. James Evans, Christina Kellogg, and Thierry Work of USGS were part of an international team that investigated the cause of this mass mortality event through combined molecular, biological, and veterinary pathologic approaches to identify the pathogenic microbe. The team compared diseased and normal urchins from 23 sites across the Caribbean Sea and determined that a scuticociliate that is most similar to Philaster apodigitiformis is the organism responsible for the mass mortality of these urchins.





a scientists holds a small black, spiny sea urchin in her hand while another scientists collects a sample
 Isabella Ritchie (University of South Florida College of Marine Science) holds a small, black, spiny sea urchin in her hand while James Evans (USGS SPCMSC) collects a sample in the aquarium room at USFCMS, where part of the investigation took place. Photo by Mya Breitbart. Used with permission.






While the team recognizes important gaps in knowledge of the pathogen’s environmental distribution, origin, transmission vectors, and the susceptibility of alternate hosts, this is a critical first step to addressing this disease and helping managers develop effective disease mitigation strategies. USGS scientists are actively testing potential treatments on the ciliate in the lab, working to develop field deployable options that reef managers can use.








A group of scientists in masks inside a room with aquaria and scientific equipment
Here, a part of the team stands together in the aquarium room at the University of South Florida College of Marine Science (USFCMS), where part of the investigation took place. From left to right: Ian Hewson (Cornell University), Isabella Ritchie (USFCMS), Mya Breitbart (USFCMS), Christina Kellogg (USGS SPCMSC), and James Evans (USGS SPCMSC). Used with permission.





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