Scientists make major marine discovery thanks to tiger sharks

1 Nov 2022

A tiger shark swimming in over a patch of seagrass. Image: Beneath The Waves

Researchers from Trinity College Dublin were part of the team that helped discover the world’s largest seagrass ecosystem.

Humans and sharks have worked together to discover what is now thought to be the largest seagrass ecosystem in the world.

The ecosystem is located in an area in The Bahamas and is estimated to be up to 92,000 sq km.

Researchers had known that such an ecosystem existed in The Bahamas. However, they did not know its true extent because they were not able to adequately survey the area.

“We thought that The Bahamas likely had an extensive seagrass ecosystem, but the true spatial estimate had never been properly quantified, because surveying this vast area remains challenging,” said one of the study authors, Dr Carlos Duarte from the King Abdullah University of Science and Technology in Saudi Arabia.

“Seagrass meadows cannot be readily mapped from space, as they yield signals similar to those of seaweed and are often covered by carbonate deposition, which returned a glare – backscatter – similar to that of bare sand.”

But Duarte and his colleagues were able to overcome this problem by enlisting the help of tiger sharks. The team worked with US marine science research non-profit Beneath The Waves to deploy cameras on the sharks as they swam throughout the area.

Previous research led by Beneath The Waves found that tiger sharks spend up to 72pc of their time patrolling seagrass beds, making them ideal candidates for the task of surveying the area.

The sharks were obviously less constrained than human divers would have been in similar conditions. Not only that, but they were also able to cover a lot of ground – up to 70km in one day.

Working with the tiger sharks meant that researchers were able to raise their initial estimates of the size of the seagrass ecosystem in The Bahamas from a minimum of 66,000 sq km up to 92,000 sq km.

The research team included scientists from the School of Natural Sciences at Trinity College Dublin, who helped deploy the video cameras on the tiger sharks.

Nicholas Payne, assistant professor at Trinity, said the study has led to an “exciting and important discovery” for a number of reasons.

“Here in Ireland, we have a huge coastal area that likely supports significant seagrass ecosystems. However, as was The Bahamas, we don’t have a great understanding of their distribution and extent,” he explained.

“It’s important that we now put more research effort into mapping these crucial habitats, especially so we can design the best ways to conserve them.”

An aerial view of the seagrass ecosystem in The Bahamas.

An aerial view of the seagrass ecosystem in The Bahamas. Image: Beneath The Waves

The research team also collected sediment cores from the seagrass ecosystem to evaluate how much carbon is stored in the sediment. They found that The Bahamas likely holds up to 25pc of the global stock of seagrass-based blue carbon.

Seagrass ecosystems play an increasingly recognised role in supporting ocean health. Seagrasses promote biological productivity, ocean biodiversity, fishery resources and carbon sequestration, while also protecting shorelines from storms.

The discovery by the sharks and scientists provides “hope for the future of our oceans,” said Dr Austin Gallagher from Beneath The Waves.

Seagrasses trap and permanently store large amounts of organic carbon in their sediment. This means seagrass can be an effective nature-based solution to mitigating the effects of the climate crisis.

“If protected, these seagrasses can play a crucial role in slowing the climate emergency, as the world moves to deploy a diverse range of strategies to capture carbon from the atmosphere,” Gallagher added.

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Blathnaid O’Dea was a Careers reporter at Silicon Republic until 2024.