Bermuda’s seagrass meadows are disappearing at an alarming rate. One of the main reasons behind the decline: Green turtle grazing has put unprecedented pressure on the habitat, ultimately leading to its local collapse.
Bermuda is known for its dreamy pink-sand beaches and turquoise waters. But did you know that the territory is surrounded by vast stretches of seagrass? When swimming through these swerving underwater grasslands, you can encounter parrot fish, turtles, seahorses, queen conches, snappers, rays and many more species.
While seagrass acts as a refuge for numerous marine animals, including some endangered and endemic species only found here, it is also a crucial link in the food chain. It removes carbon dioxide and turns it into oxygen, holds sediments in place through its large root systems and thereby reduces erosion of coastlines, protects and enhances biological diversity and provides food for marine animals such as snails, small fish and turtles. In short, it is one of the ocean’s real superheroes.
But like so many marine environments around the world, Bermuda’s seagrass beds have become critically endangered. Over the years, shoreline development, dredging, ocean dumping and land creation, concrete installations, boat propellers and anchoring have all affected the inshore seagrass meadows around Bermuda. The decline started as early as 1996, and experts found that of 900 visible hectares of offshore seagrass meadows in 1997, around 475 hectares were absent or in obvious decline in 2004 – a loss of around half of offshore seagrass spots since 1997.
In recent years, another culprit responsible for the seagrass decline has entered the stage: the green turtle. Due to its overgrazing of the seagrass beds, the species has become an issue in the region. And while more turtles might sound like a good thing, it ultimately shows an ecosystem out of balance, caused by human activity. In a healthy marine ecosystem, turtles and seagrass co-exist and thrive alongside each other. But due to heavy overfishing of sharks, the natural predator of green turtles, in the north Atlantic, even the weakest turtles survive. Sharks not only control the size of the green turtle population, they also restrict the amount of time green turtles spend eating seagrass.
Most green turtles around Bermuda tend to hatch on nesting beaches around the Caribbean Sea or Florida and arrive on the Bermuda Platform via ocean currents as small juveniles as Bermuda has no turtle nesting beaches of its own. Successful conservation efforts on those Caribbean and Floridian beaches have resulted in increasing numbers of turtle hatchlings which, without the predation of sharks, led to an increasing number of green turtles arriving in Bermuda. Add this factor to the human pressures on Bermuda’s seagrass meadows and we can begin to understand the need for restoration efforts of both seagrass and sharks.
“This decline impacts already reduced fish stocks, lobster stocks and the overall health of the ecosystem,” says Stephen Castree, a founder and director of Climate Wise, a global organisation that is part of a public-private initiative focused on restoring seagrass through the Bermuda Seagrass Project. “With improved seagrass comes an improved marine environment; adding a safe place for turtles to graze will allow locals and tourists alike to spend time with our sea turtle neighbours, all whilst creating seagrass pastures which can act as incredible carbon sinks and help contribute to the improvement of our damaged climate,” he continues.
That’s why the Bermuda Seagrass Project is currently trying to restore seagrass habitats around Bermuda with a simple, yet effective solution: caging and fencing seagrass patches so that they are protected from further grazing by green turtles. Stephen explains: “A metal mesh cage was designed which, when installed, allows seagrass to grow, and to be protected from the various items which caused its reduction, including turtles. As the turtles can access parts of the seagrass to graze, it permits them to eat a portion of what is grown, while the cages allow the seagrass beds to restore.”
This system will also allow the caged Bermuda seagrass to flower and produce seeds that, in turn, can be distributed among refuges. If and when Bermuda’s marine ecosystem is fully restored, which includes the return of healthy turtle and shark populations, the seagrass in the caged refuges can grow out from under the cages and independently colonise other seabed areas.
“By protecting areas of seagrass in this project, the intent is to allow the seagrass to re-grow and re-create the vibrant and balanced system that is currently out of balance. This process of re-generating the seagrass meadows has multiple benefits to the species that live in and around the seagrass,” says Stephen.
He adds: “One of the key benefits of the Bermuda Seagrass Restoration Project is that seagrass is an incredibly high source of carbon sequestration. As seagrass grows, it absorbs carbon dioxide. This carbon sink acts like trees on land. But seagrass, just like mangroves, are far better at removing carbon from circulation than many land-based solutions. While the seagrass is restored, a natural carbon sink is created which will then contribute to the incredibly important task of reducing the world’s carbon footprint. And ultimately, the Bermuda Seagrass Restoration project is providing live scientific analysis on the impact of the restoration and measuring the carbon impact of that which can then be shared with other locations who may be able to benefit from this research to accelerate their own projects.”
Ultimately, it is a project that can benefit the environment, all while supporting the community, local businesses, tourism, and ensuring the protection of the marine environment around Bermuda – if shark populations can be restored throughout the north Atlantic.
With a total goal of covering 2,384 square metres of remnant seagrass habitat with restoration cages by the end of 2021, the goals are set high. But the stakes of losing such an important aid in fighting climate change are even higher.
If you want to read more about seagrass in the UK, click here.
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