Record amounts of sargassum seaweed washing up on Florida’s shores is becoming a serious threat to vulnerable sea turtle hatchlings, slowing them down and putting them at risk as they run the gauntlet from the sandy beaches and into the ocean.

Already plighted by artificial lights, beach debris, and predators like birds and crabs, sargassum is yet another hazard that hatchlings have to contend with. But while it’s long been recognised, little research has focused specifically on just how big an issue sargassum has become.

A new study conducted by researchers from Florida’s Atlantic University’s Charles E Schmidt College of Science aims to fill the knowledge gap to quantify whether sargassum buildup makes it more physically demanding for hatchlings to crawl to the ocean – and whether that added effort could affect their survival.

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. The study has focused on three common species in Florida: leatherbacks, loggerheads, and green turtles from three beaches – Juno Beach, Jupiter, and Boca Raton.

Results of the study – published in the Journal of Coastal Research – found 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 centimetres) tested in the study, some hatchlings – across all three species – were unable to complete the climb within the time limit.

The results indicate that leatherbacks took 54 times longer to crawl through light sargassum, and 158 times longer through heavy sargassum. Loggerheads, meanwhile, were slowed by 91% in the light sargassum and 175% in the heavy treatment. Finally, green turtles were 75% slower in light sargassum and 159% in heavy sargassum. 

“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, Florida Atlantic University Department of Biological Sciences. 

“When sargassum piles are higher – some can be over a metre high on South Florida beaches in the summer and extend for hundreds of metres down the beach – we can expect more failed attempts, particularly when hatchlings have to cross multiple bands of seaweed just to reach the ocean.”

Researchers observed 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.

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 the sargassum and the control population that didn’t. In fact, 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.

“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.”

The researchers behind the study suggest the growing issue of sargassum seaweed calls for a “smarter, more responsive beach management strategy”. Without action, these dense mats could quietly undermine hatchling success and, ultimately, long-term conservation goals.

The research – entitled Physiological Effects of Sargassum Beach Coverage on Three Species of Sea Turtle Hatchlings – has been published in the Journal of Coastal Research.

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