GAINESVILLE, Fla. – A new University of Florida study focusing on manatees’ immune systems reveals how glyphosate, the world’s most commonly used herbicide, may threaten manatee health in an environment increasingly impacted by human activities.
“Our research raises important questions about how chemical exposure might influence immune function,” said lead author Maite De Maria, Ph.D., a postdoctoral researcher who supports the U.S. Geological Survey in collaboration with the Center for Environmental and Human Toxicology at the UF College of Veterinary Medicine.
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The researchers collected blood samples from manatees in the wild. They then tested the animals’ blood cells in the lab to determine how the herbicide might influence their immune system responses. The study, published in Environment International, examined lymphocyte, or white blood cell, responses to glyphosate at a range of concentrations found in aquatic environments.
White blood cells act protectively within the body, patrolling the bloodstream for harmful invaders such as bacteria, viruses, or other pathogens, and acting defensively to fight infection.
The researchers found that glyphosate can reduce immune cell activity by more than 27.3%, potentially compromising the threatened species’ ability to fend off disease.
After being listed as an endangered species since 1973, the West Indian manatee, of which the Florida manatee is a subspecies, was reclassified from endangered to threatened by the U.S. Fish and Wildlife Service in 2017.
The Marine Mammal Commission lists the current population estimate at 9,790 manatees. However, over 2,000 manatees died in 2021 and 2022 alone, according to the Save the Manatee organization.
While some of those deaths were attributed to traditional causes, such as cold stress and vessel collisions, most were attributed to starvation due to the loss of seagrass, a primary food source of manatees, in Indian River Lagoon and other warm-water estuaries.
Poor water quality is believed to be a leading factor in the drastic reduction of seagrass beds.
The U.S. Fish and Wildlife Service is currently wrapping up an investigation into a petition filed by several environmental groups in 2022 to upgrade the manatee’s status to endangered.
The agency is also considering a proposed rule to revise critical habitat for the Florida manatee and to designate critical habitat for the Antillean manatee, another subspecies of the West Indian manatee.
De Maria emphasized the importance of understanding potential cellular-level interactions between environmental chemicals and wildlife immune systems.
“These results highlight how environmental chemicals can compromise wildlife health,” De Maria said.
Glyphosate is widely used in residential and commercial landscaping, agriculture, urban maintenance, and forestry, and to control aquatic weeds.
Nancy Denslow, Ph.D., a professor of environmental toxicology at UF and a study co-author, noted the significance of basic research in understanding wildlife health.
“This study provides a foundation for understanding potential cellular-level interactions between environmental chemicals and marine mammal immune systems,” Denslow said.
Supported by the U.S. Geological Survey, the research is a culmination of De Maria’s doctoral and postdoctoral work at the college.
Other UF authors who contributed to the study include Mike Walsh, D.V.M., a clinical associate professor in the college’s aquatic animal health program, and Nicole Stacy, Ph. D., a clinical associate professor of aquatic pathology.