Every year, sea turtles hatch on Florida's beaches and make their way from the sand to the ocean – a critical journey that determines their chances of survival. As these hatchlings navigate obstacles such as artificial lights, beach debris and predators like birds and crabs, a new hazard looms. Sargassum seaweed washing up on Florida's shores in record amounts is more than just a nuisance for beachgoers – it's becoming a serious threat to vulnerable sea turtle hatchlings.
While it's long been known that obstacles on the beach can slow down hatchlings and put them at risk, little research has focused specifically on the impact of sargassum. A new study is beginning to fill that gap.
Researchers from Florida Atlantic University 's Charles E. Schmidt College of Science set out to explore whether sargassum buildup makes it more physically demanding for hatchlings to crawl to the ocean – and whether that added effort could affect their survival.
The study focused on three common species in Florida: leatherbacks (Dermochelys coriacea), loggerheads (Caretta caretta) and green turtles (Chelonia mydas) from three beaches – Juno Beach, Jupiter and Boca Raton.
Researchers created controlled crawlways on the sand to simulate a hatchling's natural path to the water, adding loose mats of sargassum up to 19 centimeters high (about 7.5 inches) at the end of a 15-meter path. A dim light was placed several meters ahead to guide the hatchlings forward, simulating the natural light over the ocean that they instinctively follow. This method allowed them to directly measure the physical toll of crawling through sargassum and observe the hatchlings from a distance to avoid interfering with their natural behavior.
After completing the crawl, hatchlings had their blood glucose levels measured to assess energy use. Researchers also tested how quickly each turtle could flip itself upright when placed upside down in water – a simple test of physical condition. To account for environmental factors, researchers also recorded sand temperature at the beginning, middle and end of each crawl.
Results of the study, published in the Journal of Coastal Research , reveal that all three species of hatchlings took significantly longer to complete their crawl when sargassum was present, and the time it took to climb up and over the seaweed piles was the primary reason. Even with the lower heights (7-9 centimeters) tested in the study, some hatchlings – across all three species – were unable to complete the climb within the time limit.
Based on median values, leatherbacks took 54% longer to crawl through light sargassum and 158% longer through heavy sargassum. Loggerheads were slowed by 91% in the light sargassum treatment and 175% in the heavy treatment. Green turtles also saw delays of 75% in light sargassum and 159% in heavy. The crawl speed decreased sharply for all species in sargassum sections, with loggerheads showing the most significant slowdown.
"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, FAU 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 study also found that hatchlings often flipped upside down – referred to as "inversions," while trying to climb the sargassum, especially in the heavy coverage trials. One hatchling flipped more than 20 times in a single trial. These inversions not only extended the time hatchlings spent on the beach but also increased their risk of predation and heat exposure.
Interestingly, despite these delays and the physical challenges of navigating the seaweed, the study found no significant differences in blood glucose levels between the hatchlings that crawled through sargassum and those that didn't, across all three species. Glucose concentrations remained within expected ranges, suggesting that while the added obstacle increased the effort and risk, it didn't immediately deplete their measurable energy stores. Only leatherbacks in the no-crawl control group had noticeably higher glucose levels, indicating that the act of crawling in general, rather than the sargassum itself, has the stronger physiological impact – at least in the short term.
"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," said Milton. "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."
This growing issue calls for smarter, more responsive beach management strategies. Without action, these dense mats could quietly undermine hatchling success and, ultimately, long-term conservation goals.
Study co-author is Abbey M. Appelt, a graduate of the FAU Department of Biological Sciences and a sea turtle nesting specialist at Ecological Associates, Inc., a South Florida environmental consulting firm.
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