Blue Carbon Collaboration

Scientists fixed bio-logger tags equipped with cameras on tiger sharks in the Bahamas to map the ocean’s seagrass meadows. Photograph: Diego Camejo/Beneath the Waves

We thank Laura Paddison for this underwater news, published in the Guardian, that has implication for climate change mitigation:

Scientists discover ‘world’s largest’ seagrass forest – by strapping cameras to sharks

New study, carried out using tiger sharks in the Bahamas, extends total known global seagrass coverage by more than 40%

Tiger sharks are notoriously fierce. The huge animals, which can grow to more than 16ft, are ruthless predators and scared of absolutely nothing – recent research found that while other shark species fled coastal waters during strong storms, tiger sharks “didn’t even flinch”.

But recently they have a new role that could help burnish their reputations: marine scientists.

In an attempt to measure the extent of seagrass meadows in the Bahamas, researchers attached cameras and trackers to the dorsal fins oftiger sharks to give them access to hours of ocean floor footage.

The data they collected revealed what the researchers say is the world’s largest known seagrass ecosystem, stretching across up to 92,000 sq km (35,000 sq miles) of Caribbean seabed. This discovery extends the total known global seagrass coverage by more than 40%, according to the study published in Nature Communicationson 1 November.

“This finding shows how far are we from having explored the oceans, not just in the depths, but even in shallow areas,” said the report’s co-author, Prof Carlos Duarte, of Saudi Arabia’s King Abdullah University of Science and Technology.

Seagrass meadows have long been under-researched – estimates of their total global area range wildly from 160,000 sq km to 1.6m sq km. Mapping is hugely challenging: meadows in deep or cloudy water cannot always be spotted by planes or satellites, while smaller ones can be sparse or interwoven with other marine plants making them tricky to identify.

This means seagrass meadows have to be “ground truthed” ie confirmed by someone – or something – at the site. But sending human divers to photograph vast tracts of ocean floor is expensive, logistically challenging and very slow.

Tiger sharks are a different story. The highly mobile animals are able to reach significant depths, have a large range and spend a lot of time in seagrass meadows. They are also unburdened by mundane human constraints such as needing a boat, having to surface frequently and reliance on calm ocean conditions.

Between 2016 and 2020, researchers fixed camera packages, equipped with satellite and radio tags, to the dorsal fins of seven sharks. They caught the animals using circle hook drumlines, which hook into the animals’ jaws. It is the “safest way to catch sharks” and causes no long term damage, said Oliver Shipley, a senior research scientist at Beneath the Waves, a marine science non-profit, and co-author of the report.

Read the entire article here.

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