Ciliates Identified as Culprit in Sea Urchin Die-Off in Caribbean and Florida Waters
A team of scientists has identified the cause of a devastating sea urchin die-off that occurred last year along the waters of the Caribbean Islands and Florida. It is probable that ciliates, which are tiny organisms, caused the extinction of sea urchins that consume algae. Researchers took healthy urchins to the University of South Florida, where they were infected with the ciliate. After four days, they exhibited symptoms of sickness which confirmed the parasite as the cause. The team grew ciliates in the lab and performed infection experiments at the USF College of Marine Science. The ciliate, identified as the source of the disease, was confirmed when otherwise healthy urchins introduced to an aquarium tank died within a few days, replicating the same pattern observed in the ocean.
The culprit was identified as Philaster apodigitiformis, a unicellular eukaryote that is part of a group of 8,000 species called ciliates. It is established that P. apodigitiformis is a protozoan parasite found in fish. Though scientists do not yet know how to treat P. apodigitiformis infections, discovering the parasite's identity may help them design strategies for maintaining health in Diadema sea urchins that are being raised for restocking efforts across the region.
By grazing on algae, sea urchins are crucial in preserving the health of coral reefs and other marine ecosystems. By preventing the overgrowth of algae and suffocation of corals, a balanced ecosystem is maintained. During the early 1980s, the population of long-spined sea urchins in the Caribbean suffered a nearly complete extinction, with an unidentifiable factor causing a 98% decrease from previous figures. After three decades, their numbers recovered, but only by about 12% from their pre-outbreak populations.
“Rarely are we afforded the opportunity to understand marine disease events in this detail, where we can actually work out a cause of it,” said marine ecologist Ian Hewson, professor of microbiology at Cornell University and lead author of the study, “A Scuticociliate Causes Mass Mortality of Diadema antillarum in the Caribbean Sea,” which published in Science Advances.
The National Science Foundation, Atkinson Center for Sustainable Futures Rapid Response Award, AGGRA, National Oceanic and Atmospheric Administration, National Fish and Wildlife Foundation, Florida Keys Marine Sanctuary, and Florida Fish and Wildlife Conservation Commission provided funding for the project.
Caribbean sea urchins have experienced a recent die-off event caused by ciliates, which are small water-dwelling creatures decorated with cilia, hair-like extensions. Ciliates utilize these cilia for locomotion and feeding, and are generally benign, occupying diverse aquatic environments. Previously, the deaths of other marine creatures, such as sharks, have been attributed to a particular species of scuticociliate.
The ciliate has been implicated in die-offs of other marine species such as sharks. Belonging to the phylum Echinodermata, which comprises starfish, sea cucumbers, and sand dollars, sea urchins are captivating marine animals. Science Advances reported their findings.
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