How tiger sharks wearing cameras revealed the world’s largest seagrass ecosystem

By Nell Lewis and John Lewis, CNN

(CNN) — The largest apex predator in the tropical seas, tiger sharks are notoriously fierce. They can grow to more than six meters (20 feet), have sharp serrated teeth and are second only to great whites in number of reported attacks on people. But in The Bahamas, tiger sharks have taken on a rather less ferocious role, as assistants to marine scientists.

Between 2016 and 2020, a team of researchers fixed tags equipped with cameras onto tiger sharks so that they could view the ocean floor from a new perspective. The data they collected revealed what is the world’s largest known seagrass ecosystem, an area of up to 92,000 square kilometers (35,000 square miles) in the Bahamas. According to their study, published in 2022, this extends the total known global seagrass coverage by more than 40%.

This is significant as seagrasses trap and store massive amounts of carbon in the sediment and are therefore a vital tool in mitigating climate change.

Dr. Austin Gallagher, one of the report’s co-authors and founder and CEO of ocean research organization Beneath the Waves, believes that tiger sharks and other marine life can help scientists to map ocean ecosystems and lead to other significant discoveries. As guest editor for Call to Earth, he spoke to CNN about what it’s like collaborating with tiger sharks and the importance of protecting the ocean’s carbon sinks.

The following interview has been edited for length and clarity. 

CNN: When did the idea to put a camera on a tiger shark come about?

We’ve been putting cameras on animals for decades in the scientific community and we’ve been doing that in the field of sharks for many years now. So, it wasn’t completely novel, but we wanted to advance our work on tiger sharks to get a better understanding of what a day in the life of a tiger shark looked like. To do that, we needed to be able to see what the animals were seeing because we can infer all sorts of types of patterns based on their movement: where they go and how much time they spend in certain areas and habitats. When we did that, it opened a whole Pandora’s box of new questions and it eventually put us down a path of radical discovery here in The Bahamas.

CNN: What did you discover from the tiger shark data?

We knew that tiger sharks spend a lot of time over the shallow water carbonate banks here in The Bahamas and we knew that there is an expansive seagrass ecosystem here, but it wasn’t until we got the data back from those camera-equipped tiger sharks that we really saw how important and expansive the seagrass might be. It turned the light bulb on for the first time: that we need to map out how much seagrass is here.

We knew that we had to map it out from space, because while tiger sharks gave us a dozen or so good traces with those camera tags, we had to take Earth-orbiting satellites and a remote-sensing approach to map out how much was there. It would never be possible as humans, or as tiger sharks, to do the entire exclusive economic zone of The Bahamas. So we did that and we were able to map it out. We put divers in the water to validate all the predictions from space, we took pictures ourselves of the sea floor, and we then used more data from tiger sharks, including 360-degree camera tags that gave us a full comprehensive look at what the animals were seeing.

It ended up validating a prediction of up to 93,000 square kilometers (35,000 square miles) of seagrass ecosystem here in The Bahamas, which makes it by far the largest on Earth. It was hiding in plain sight.

CNN: What more is there to discover?

We’re just at the beginning of understanding how valuable and how important this seagrass asset is, and what role tiger sharks, sea turtles and other threatened biodiversity plays in that relationship. And let’s also not forget about humans and the role that we play in the future of preserving these ecosystems.

Mapping and discovering them is just one part of it. Then it’s creating new protections around them and working with governments and environmental decision makers to really put all these data into the right packages and submit them to the right bodies that will eventually issue things like carbon credits that can be used to leverage protections, but also create financial benefits and ultimately long-term financial returns for places like The Bahamas.

CNN: What is blue carbon and why is it so valuable?

Blue carbon is a term for all the carbon that ends up in the ocean. It happens naturally and it is stored and sequestered in the ocean in its various sediments, largely through plants – things like seagrasses, mangroves, salt marshes. These are what we call blue carbon ecosystems, and through natural processes like photosynthesis, these plants sequester and store massive amounts of carbon – significantly more than their terrestrial counterparts.

If we want to try and create new protections for the ocean, if we want to try and build resiliency, particularly in low-lying countries and small island developing states, we have a real objective to build resilience in the place of climate change. One of the ways that we can do that is by working in partnership with nature: seagrasses, mangroves, they are what we call a nature-based solution to climate change. If we want to try and enhance coastal protection and create benefits for communities and biodiversity, going out and quantifying how much carbon and what the extent of that looks like is incredibly important for ocean research.

CNN: What is the end goal of your scientific research and work?

The ultimate goal of the work that I’m doing is to create empathy for the ocean and to also preserve what we have for future generations. To live harmoniously with these ecosystems, to find ways to live harmoniously with sharks, to protect these ecosystems like seagrass. It’s creating marine protected areas, it’s enhancing existing conservation measures for threatened species like sharks, but it’s about making sure that the legacy of these incredible ecosystems remains as intact as possible for as long as possible.

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