A team of researchers has found that microscopic ciliates were responsible for the large-scale mortality of long-spined sea urchins in Caribbean and Florida waters in 2022.
The die-off had severe consequences for the region's coral reefs and overall ecosystem as sea urchins play a critical role in regulating algae populations.
Collaborative research efforts allowed for the rapid discovery of the ciliate responsible for the die-off, and isolating the ciliates from the sick urchins may lead to potential treatments and proactive safeguards.
Although many questions remain unanswered, the outbreaks appear to have ceased since the previous fall and winter, and some regions in the Caribbean avoided exposure entirely.
The research findings highlight the importance of understanding the complex relationships within marine ecosystems and the need for continued monitoring and conservation efforts.
Microscopic Ciliate Organisms Found to be the Cause
A team of researchers has determined that the large-scale mortality of long-spined sea urchins (Diadema antillarum) in the Caribbean and Florida waters last year resulted from microscopic creatures called ciliates.
Understanding this connection is crucial, as the depletion of sea urchin populations has severe long-lasting consequences for the region’s coral reefs and overall ecosystem.
The Extent and Background of the Die-Off
The rapid decline of long-spined sea urchin populations started in January 2022, with the initial outbreaks reported around the U.S. Virgin Islands.
The die-off eventually reached as far west as Mexico and as far north as Southern Florida’s coast. In certain areas, an estimated 98% of the sea urchin population died.
Long-spined sea urchins play a critical role in their shallow tropical habitats by regulating algae populations that could otherwise endanger coral reefs’ survival.
The Caribbean experienced comparable large-scale die-offs in the 1980s, which eliminated up to 98% of the region’s sea urchins.
Over the past four decades, these urchins had been gradually recovering, with their numbers climbing back to around 12% of their original count.
However, the 2022 die-off wiped out most of that progress and the corresponding environmental advantages provided by the urchins.
The Caribbean experienced comparable large-scale die-offs in the 1980s, which eliminated up to 98% of the region’s sea urchins.
Collaborative Research Leads to Breakthrough
Marine scientists first observed the sea urchin deaths in February 2022. By the following month, a cooperative effort was set up by the Atlantic and Gulf Rapid Reef Assessment (AGRRA) and other organizations to collect data and trace the die-off’s origin.
This joint initiative, known as the Diadema Response Network, enabled researchers to swiftly identify the ciliate responsible for the die-off, as documented in the study published in Science Advances.
Mya Breitbart, a study author and biologist at the University of South Florida, credited the rapid discovery of the ciliate to the interdisciplinary collaboration involving multiple universities, government agencies, and non-profit organizations.
Pinpointing the Ciliate
The research team examined urchin samples from more than 20 sites. Through microscopic and genetic analysis, they detected the presence of ciliates in the affected sea urchins.
Ciliates are a diverse group of free-living protists, characterized by the cilia (hair-like projections) they use for movement.
The scientists managed to isolate the ciliates from the sick urchins and grow them in a laboratory setting.
This allowed them to conduct experiments demonstrating that the lab-based sea urchins exhibited similar sickness and death patterns as those affected by the outbreak when exposed to the ciliates.
A new generation of ciliates subsequently developed quickly within the lab urchins and were isolated once more.
Steps Toward Protection and Recovery
Although many questions remain unanswered, identifying the ciliate behind the die-off marks a vital step in comprehending the outbreak’s contributing factors and examining potential treatments.
This knowledge could empower scientists to proactively safeguard the remaining long-spined sea urchins, providing coral reefs with a better chance of survival.
On a positive note, the outbreaks seem to have ceased since the previous fall and winter, and there is no indication that other urchin or marine species have been directly impacted by the ciliates.
Some sea urchins survived the local outbreaks, and a few regions in the Caribbean appear to have avoided exposure entirely.
