Populations of the Caribbean long-spined sea urchin (Diadema antillarum) have suffered catastrophic mortality due to a fast-acting disease identified as Diadema antillarum scuticociliatosis (DaSc). The disease, caused by a scuticociliate most closely related to Philaster apodigitiformis, swept across the Caribbean in the spring and summer of 2022, wiping out large numbers of urchins at affected sites.
Rapid Disease Outbreak Devastates Long-Spined Sea Urchins
Scientists first learned of the extensive die-offs in February 2022 in St. Thomas within the U.S. Virgin Islands. The illness progresses with extreme rapidity; affected urchins typically die within one to two days of exhibiting initial signs of sickness. Observable symptoms include excess mucus on their spines, reduced spine mobility, loss of spines, and a complete inability to attach to the reef.
Ecological Impact and the Threat of Algal Overgrowth
The long-spined sea urchin is considered one of the most critical herbivores in Caribbean reef systems. By consuming algae, these urchins act as natural cleaners that prevent algal overgrowth and give foundation corals the space they need to grow and thrive.
The recent mortality event mirrors a historical catastrophe in 1983, when a region-wide die-off killed more than 95% to 97% of Diadema across the Caribbean. Four decades later, very few Diadema populations have fully recovered from that initial event. Scientists note that the persistent absence of these urchins has triggered a phase shift across many Caribbean regions, turning areas once dominated by corals into environments fully dominated by algae.
Global Spread and Vulnerable Species
Beyond the Caribbean, affected urchins within the Diadematidae family have been reported in the eastern Mediterranean, the Red Sea, and the Arabian Gulf, alongside anecdotal reports of mass mortality in the Seychelles and Reunion Island in the Indian Ocean. The condition has been observed in multiple species, including Diadema antillarum, Diadema setosum, and Echinothrix calamaria, while leaving other co-occurring non-Diadematidae urchins unaffected.
Researchers including Mya Breitbart of the University of South Florida, Chris Kellogg of the US Geological Survey in St. Petersburg, and Omri Bronstein of Tel Aviv University are supporting investigations into the mass mortality. Institutions with molecular biology facilities can coordinate with researchers for the detection of DaSc using PCR primers and protocols.
Prevention and Best Practices for Marine Safety
Because the exact transmission mechanism of the parasite remains under study, experts recommend several biosecurity best practices to prevent further spread:
- Avoid moving affected or normal urchins from one location to another.
- Wash all SCUBA and snorkeling gear—including buoyancy-compensating device air bladders—with freshwater and dry equipment thoroughly between sites.
- Install filters on both inflow and outflow systems in aquariums to retain particles greater than 1 micrometer.
- Replenish vessel firefighting wells or ballast far out at sea rather than near shore.
Work is currently underway to explore treatments for affected urchins, which remains a primary focus for aquaculture facilities and aquariums seeking to protect vulnerable marine populations.
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