A single-celled organism known as a ciliate was the cause behind the extensive mortality of long-backed sea urchins, posing a threat to coral reef ecosystems ranging from the Caribbean to the east coast of Florida.
The investigation into the 2022 event that led to the significant decline of the long-backed sea urchin population in the Caribbean and Florida’s east coast has concluded. An assembly of scholars led by Mya Breitbart, a Distinguished University Professor at the College of Marine Science at the University of South Florida, pinpointed a single-celled organism, a ciliate, as the instigator of a large-scale mortality event for a marine species crucial to the vitality of coral reefs.
The findings were disclosed on April 19 in the publication
A glimpse of ciliate culture through a microscope. Credit: Mya Breitbart USF College of Marine Science
“We are delighted to have unraveled the mystery of 2022 and somewhat astounded by the promptness of our achievement,” expressed Breitbart, the primary author of the Science Advances study and an expert in marine genomics. “By assembling an exceptional team and employing the necessary tools, we conducted an oceanic scientific equivalent of a forensic inquiry.”
Ciliates are minute organisms equipped with hair-like structures called cilia that facilitate movement and feeding. They can be found in almost any water source, and a majority of them are not causative agents of diseases. Nevertheless, a particular
of ciliate – referred to as a scuticociliate – has been linked to the mortality of several other marine species, such as sharks, in the past.
A series of images displaying the sea urchin before and after an infection by the ciliate in the USF aquarium research facility. Recognition: Makenzie Kerr USF College of Marine Science
The research group, by scrutinizing urchins collected from 23 Caribbean locations, utilized various methods to verify the cause of the die-off incident.
Having identified the ciliate in all affected urchin specimens through genomic methodologies, the group cultured ciliates in the laboratory and carried out infection trials at the USF College of Marine Science. Upon introducing the pathogen to otherwise robust urchins in an aquarium tank, the urchins perished within a few days – mirroring the events in the ocean and authenticating the ciliate as the origin of the disease.
“We’re thrilled to disseminate this data to a broad audience, ranging from reef overseers to additional researchers, enabling further exploration and attempts to halt its dissemination,” Breitbart mentioned.
The elongated spine sea urchins thrive in shallow tropical waters, consuming algae that would otherwise devastate a reef. They commenced shedding their spines shortly after contracting an unidentified disease and perished in large numbers starting in January 2022.
An analogous mass mortality event occurred in the early 1980s, eradicating 98 percent of the lengthy spine sea urchin populace. The perpetrator behind that mass die-off remains unsolved.
Hewson received notice of the ongoing die-off by the end of March 2022. He promptly gathered a team composed of Ian Hewson, primary author of the report and a marine ecologist at Cornell University; Christina Kellogg, a microbiologist from the U.S. Geological Survey in St. Petersburg, Fla. with extensive experience in coral reef diseases; and USF graduate student Isabella Ritchie.
“During that period, uncertainty plagued us regarding the cause of this die-off – whether it was pollution, stress, or another factor – it was all unknown,” stated Hewson, an authority in diseases causing extensive sea star die-offs, who traveled from New York to the Caribbean Islands to witness the situation.
Despite uncovering the source of the mystical die-off, inquiries still persist. For instance:
- Is this ciliate an unfamiliar presence in the region, or did it exist before the die-off?
- If it was already present, what environmental conditions promoted its propagation and why did it infect the urchins?
- Can it impact other urchin species?
“One hypothesis we are considering is that the ciliates thrived under the high-productivity situations witnessed in the Caribbean at the beginning of the die-off,” Kellogg speculated. “We are also intrigued by the geographic overlap in areas where this die-off occurred and where the stony coral tissue loss disease is causing coral depletion.”
Reference: “A scuticociliate causes mass mortality of Diadema antillarum in the Caribbean Sea” by Ian Hewson, Isabella T. Ritchie, James S. Evans, Ashley Altera, Donald Behringer, Erin Bowman, Marilyn Brandt, Kayla A. Budd, Ruleo A. Camacho, Tomas O. Cornwell, Peter D. Countway, Aldo Croquer, Gabriel A. Delgado, Christopher DeRito, Elizabeth Duermit-Moreau, Ruth Francis-Floyd, Samuel Gittens, Leslie Henderson, Alwin Hylkema, Christina A. Kellogg, Yasunari Kiryu, Kimani A .Kitson-Walters, Patricia Kramer, Judith C. Lang, Harilaos Lessios, Lauren Liddy, David Marancik, Stephen Nimrod, Joshua T. Patterson, Marit Pistor, Isabel C. Romero, Rita Sellares-Blasco, Moriah LB Sevier, William C. Sharp, Matthew Souza, Andreina Valdez-Trinidad, Marijn van der Laan, Brayan Vilanova-Cuevas, Maria Villalpando, Sarah D. Von Hoene, Matthew Warham, Tom Wijers, Stacey M. Williams, Thierry M. Work, Roy P. Yanong, Someira Zambrano, Alizee Zimmermann, Mya Breitbart, April 19, 2023, The progress of science.
DOI: 10.1126/sciadv.adg3200
The study received financial backing from the National Science Foundation, the Atkinson Center for Sustainable Futures Rapid Response Award, AGGRA, the National Oceanic and Atmospheric Administration, the National Fish and Wildlife Foundation, the Florida Keys Marine Sanctuary, and the Florida Fish and Wildlife Conservation Commission.
Image Source: Engineer studio / Shutterstock
