If a human diver tried to map underwater seagrass, it would be slow going. Limited to fairly shallow waters, the person would need to come up for air and take breaks from swimming. So, to better understand where these marine flowering plants grow, a team of scientists turned to some unusual allies: sharks.
In a new study published Tuesday in Nature Communications, researchers mapped out what might be the world’s largest seagrass ecosystem using cameras and trackers attached to tiger sharks (Galeocerdo cuvier).
They estimate the patch, located in the Bahamas, could be as large as 35,521 square miles—double the size of a seagrass ecosystem off the coast of Australia that was previously thought to be the world’s largest. The new find expands the known seagrass coverage globally by about 41 percent, per the study.
The massive meadow of seagrass, which is known to store carbon, is good news for the climate.
“This discovery should give us hope for the future of our oceans. It demonstrates how everything is connected,” lead author Austin Gallagher, the chief executive officer of the nonprofit Beneath the Waves, tells Nick Kilvert of the Australian Broadcasting Corporation (ABC). “The sharks led us to the seagrass ecosystem in the Bahamas, which we now know is likely the most significant blue carbon sink on the planet.”
Blue carbon is carbon captured and stored in marine and oceanic ecosystems. Per the World Wildlife Fund, seagrass captures carbon up to 35 times faster than tropical rainforests do. This means that on top of providing important habitat and food for marine creatures, including imperiled manatees and endangered green sea turtles, seagrass meadows could also help combat climate change.
“Our results indicate that seagrass in the Bahamas may contain 19.2 to 26.3 percent of all the carbon sequestered in seagrass meadows on Earth,” Wells Howe, a program manager on Beneath the Waves’ Blue Carbon project, tells Popular Science’s Laura Baisas.
To make their discovery, researchers attached cameras to the sharks with biodegradable cables and swivel connectors that were designed to corrode in seawater after 24 hours. Between 2016 and 2020, they affixed six sharks with front-facing cameras. A seventh shark toted the “first-ever deployment of a 360-degree camera borne by a marine animal,” write the authors. They also attached satellite tags to eight other sharks to record data on water temperature and swimming depth.
The animals were capable of “covering areas that were not logistically possible for human access,” traveling both deeper and farther than humans can, the authors write.
This isn’t the first time that researchers have used animals to find seagrass meadows, Professor Michael Rasheed, head of the Seagrass Ecology Lab at James Cook University, tells the ABC.
“There are some really neat stories of [satellite] tagged green turtles turning up in places where people think, ‘Why would they be out there?’” Rasheed tells the publication. “And when people have gone and had a look, they've found these magnificent seagrass meadows in the middle of the Indian Ocean.”
Rasheed, who did not participate in the research, questions whether this find is truly the largest seagrass meadow in the world. Some seagrass systems join together, so it's not always easy to pinpoint where one meadow ends and another begins. Nevertheless, the new discovery is “certainly a large seagrass system,” he tells the ABC.
In the future, Beneath the Waves plans to embark on a multiyear journey to explore and document seagrass meadows with the environmental nonprofit SeaLegacy, writes Forbes’ Melissa Cristina Márquez.
“What this discovery shows us is that ocean exploration and research are essential for a healthy future,” Gallagher tells the publication. “The untapped potential of the ocean is limitless.”