Researchers at Florida Atlantic University have found that increasing amounts of sargassum seaweed on Florida’s beaches are slowing down sea turtle hatchlings as they attempt to reach the ocean, potentially raising risks to their survival.
The study, conducted by FAU’s Charles E. Schmidt College of Science, focused on leatherback, loggerhead, and green turtle hatchlings from Juno Beach, Jupiter, and Boca Raton. Researchers set up controlled sand crawlways with mats of sargassum up to 19 centimeters high at the end of a 15-meter path. A dim light was used to simulate natural cues that guide hatchlings toward the water. The experiment aimed to measure how much more difficult it is for hatchlings to cross these obstacles.
After crawling through the setups, researchers measured blood glucose levels in the turtles and tested their ability to right themselves when placed upside down in water—a basic test of physical condition. Sand temperatures were also recorded throughout each trial.
Findings published in the Journal of Coastal Research show all three species took significantly longer to complete their journey when sargassum was present. Many hatchlings struggled or failed to climb over even moderate heights of seaweed within the time allowed.
Median values indicated that leatherbacks took 54% longer in light sargassum and 158% longer in heavy coverage; loggerheads slowed by 91% and 175%, respectively; green turtles experienced delays of 75% and 159%. Loggerheads had the most pronounced decrease in crawl speed among the species studied.
“The longer a hatchling stays on the beach, the more at risk it becomes – not just from predators like birds and crabs, but also from overheating and dehydration, especially after sunrise,” said Sarah Milton, Ph.D., senior author and chair and professor at FAU’s Department of Biological Sciences. “When sargassum piles are higher – some can be over a meter high on South Florida beaches in the summer and extend for hundreds of meters down the beach – we can expect more failed attempts, particularly when hatchlings have to cross multiple bands of seaweed just to reach the ocean.”
The research team observed frequent “inversions,” where hatchlings flipped onto their backs while trying to scale sargassum mats—one individual flipped over twenty times during a single trial. These events further increased time spent exposed on land.
Despite these challenges, there were no significant differences in blood glucose levels between turtles that crawled through sargassum and those that did not across all three species. Glucose remained within expected ranges, suggesting short-term energy reserves were not depleted by encountering seaweed barriers. Only leatherbacks who did not crawl showed noticeably higher glucose levels.
“For sea turtle hatchlings, reaching the ocean is already a race against time – and survival. Now, increasingly large mats of sargassum are adding new challenges to this critical journey,” Milton said. “As these seaweed accumulations grow taller and more widespread, they risk blocking hatchlings entirely, draining their limited energy or leaving them stranded. Beyond impeding movement, sargassum may also reduce nesting space and alter incubation conditions.”
The study suggests that growing amounts of sargassum could quietly threaten long-term conservation efforts unless addressed by improved beach management strategies.
Abbey M. Appelt co-authored the study; she is an FAU Department of Biological Sciences graduate and currently works as a sea turtle nesting specialist at Ecological Associates Inc., an environmental consulting firm based in South Florida.
