Sargassum a threat to turtle nesting

As large mats of sargassum continue to float to shore on all three islands, Department of Environment staff and volunteers are monitoring the impact this has on turtle nesting.

The annual arrival of the seaweed usually coincides with start of the turtle nesting season, which traditionally runs from May to November, when sea turtles come ashore to dig nests and lay their eggs.

Jane Hardwick, who heads up the DoE’s Sea Turtle Programme, in an interview with the Compass on Thursday said, “What we find is when we have these really big influxes [of sargassum], it can actually prevent the females from coming ashore to nest, because it acts as a physical barrier between the sea and the beach.”

The matted and rotting brown seaweed that lines many local beaches also leads to problems for the turtle hatchlings as they try to make their way into the sea after emerging from their sandy nests.

“Sometimes, the hatchlings get caught in the sargassum or they can’t get over it, and that can end up causing hatchling mortality,” Hardwick said, adding that there had been at least one report this season from Cayman Brac of hatchlings being found dead in the seaweed.

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To try to ensure that the baby turtles can get through, staff and volunteers from the turtle nest monitoring teams hand-clear pathways through the seaweed.

A large sea turtle makes its way through sargassum as it returns to the sea in Little Cayman last month. – Photo: Norma Connolly

Decomposing sargassum on the beach can also affect the temperature of the sand at nearby nests “and that can impact hatch success”, Hardwick said.

While clearing sargassum using handheld hoes or rakes is the preferable way of removing it from beaches, in cases where there are very large influxes, the only option is to use heavy machinery, but that also causes problems for the nesting turtles and their eggs, and can lead to beach erosion.

“Heavy machinery compacts sand and that can also damage turtle nests,” Hardwick said. “We do as much hand-clearing as we can but because the sargassum is coming in so frequently at the moment, that is a big challenge for the volunteers and for the turtle team.”

But sargassum is not always bad news for turtle populations. When it’s floating out at sea, it plays an important role in nurturing sea turtle hatchlings.

Hardwick explained, “At sea, sargassum is actually a really important habitat for turtles. When they first hatch and swim out to deep water, they use the floating sargassum as a refuge. It’s an important habitat to protect them from predators, and they use it to float on the surface and to feed.”

Beaches across the Cayman Islands are being inundated with sargassum, causing threats to the seasonal nesting turtles. – Photo: Alvaro Serey

She added, “It’s only when it washes up in these really large amounts that it starts to pose a problem for sea turtles.”

Her colleague Wendy Johnston, head of the DoE Environmental Management Unit, said it is forecast that Cayman and the Caribbean will again see large influxes of sargassum this year, though it is predicted to be slightly less in 2018, which was recorded as being a particularly bad year in terms of sargassum levels.

Turtles are not the only marine creatures that are affected by sargassum washing up on land and near shore.

Johnston said that when it sits in shallow water just off shore, it decomposes and reduces the oxygen levels of the sea around it, having a negative effect on other marine life, and fish kills in the area of rotting sargassum have been reported.

Sargassum is a region-wide challenge. In this photo, a sea turtle manoeuvres its way over the seaweed at a beach in Barbados. – Photo: Robert Bourne, courtesy of Barbados Sea Project

She added that there had also been reports of “quite extensive seagrass die-off”. This occurs when the sargassum decomposes on the surface of the water, shading the seagrass from sunlight which it needs for photosynthesis to occur.

Johnston said the collection and removal of the seaweed from local beaches is just one part of the issue, but said the “end use, what happens when it’s removed” also needs to be explored.

“What the DoE would like to see is innovative ways for sargassum to be handled once it’s removed off the beaches,” she said. “Other Caribbean countries are looking at alternative ways of using the sargassum. Investigations are being carried out on if it can be used for animal feed [for examples]. … It would be nice not to end up in the landfill and use it in sustainable ways in the future.

“However, one of the challenges in finding alternative uses for the seaweed is the high levels of heavy metals and micro-plastics often found in sargassum, she said.

The DoE is encouraging people to help keep track of where sargassum is washing up and how long it is remaining in place, by downloading the Epicollect Sargassum Watch app.

Also anyone who wants to find out more about volunteering to help monitor sea turtle nests across any of the three islands can contact the DoE on [email protected] or visiting the department’s website.

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