For sea turtles and sargassum, the relationship is complicated

A sea turtle struggles back to sea after laying its eggs on a sargassum-strewn beach in Antigua: - Photo: Sargassum Monitoring

Inundations of sargassum on Caribbean beaches may be impacting turtle nesting.

At sea, sargassum provides vital shelter for a variety of species. Young turtle hatchlings even hitch rides on these floating mats, as they venture into the open ocean.

But when the algae comes ashore in significant quantities, this beneficial relationship is betrayed.

Seaweed-clogged beaches are no longer accessible by female turtles for nesting. Later, hatchlings may find themselves trapped in the mounds and die.

“A moderate amount of sargassum on beaches does not interfere with turtle nesting,” says Janice Blumenthal of the Department of Environment.

“However, massive sargassum influxes can prevent female turtles from nesting, deprive turtle nests of oxygen, interfere with the emergence of baby turtles from the sand, and make it more difficult for baby turtles to reach the open ocean.”

Beyond creating a physical barrier, sargassum can alter turtle habitat in other ways, such as temperature, explains researcher Brigitta van Tussenbroek with the Caribbean Seagrass Lab of the National Autonomous University of Mexico.

A turtle hatchling in Cayman Brac navigates the seaweed. – Photo: Department of Environment

The sex of sea turtles is determined by egg temperature during incubation.

Van Tussenbroek says researchers in Mexico are keeping an eye on how changes in beach temperatures, created by mounds of sargassum, could alter the sex ratio of hatchlings.

Another threat to turtle nests, van Tussenbroek says, is that the mass of organic material on the beach can cause the eggs to rot.

Why not just remove the sargassum?

Preventing sargassum-related turtle deaths isn’t as easy as simply clearing away the seaweed, unfortunately.

Using heavy machinery to move beached sargassum, for example, can compact the sand and crush turtle nests.

This is one reason the Department of Environment requires consultation before cleaning sargassum from beaches.

“The DoE’s Environmental Management Unit issues same-day letters of approval for sargassum clearance on turtle-nesting beaches so that turtle nests in the area can be protected,” Blumenthal says.

Property owners who wish to use machinery will need to contact the Environmental Management Unit at [email protected]

The department will then advise if there are any known turtle nests on the beach.

Blumenthal and van Tussenbroek differ on their assessment over whether sargassum influxes should be harvested on land or at sea.

In Mexico, van Tussenbroek says researchers in Quintana Roo are advising government to tackle the problem at sea to minimise environmental damage.

“When it’s at the beach, the damage is already done. That’s the problem. Even if you collect it quickly, which most of the time you can’t … the huge masses cause beach erosion,” van Tussenbroek says.

“The huge masses cause what we have started to call ‘sargassum brown tide’ and they cause anoxia, lower pH and light inhibition. They kill basically all the benthos [marine organisms] that are there. The benthos also fixes the sand, so [that’s] more beach erosion.”

She adds the nutrients in sargassum can also flood the reef system.

In Cayman, however, environmental authorities discourage collection at sea.

“Collection of sargassum in the open ocean is not recommended due to its significant ecological value for hundreds of marine species,” Blumenthal says.

“However, the collection of sargassum close to shore is something that is currently being trialled by at least one private sector company on Cayman with the DoE’s oversight.”

The near-shore approach would result in little sand removal, she explains.

Another method being explored in Cayman is capturing sargassum in booms or containment nets at sea and rerouting the seaweed to the open ocean.

“However, since the presence of moderate amounts of sargassum is known to assist with the recovery of eroded beaches (and this has also been observed in Cayman) the DoE is keen to ensure that we strike the right balance with respect to sargassum removal generally,” Blumenthal says.

Across the Caribbean, coastal communities are grappling with the same dilemma over sargassum best practices.

Much remains to be researched across the region, including the long-term effect of sargassum influxes on sea turtle populations.

“At this stage, the impact on turtles is still being quantified, but we believe the biggest impact is due to indiscriminate use of heavy equipment on beaches to clear sargassum,” Blumenthal says.