A partnership between sharks and humans leads to one of the biggest marine discoveries of the last decade.

⇧ [VIDÉO] You may also like this partner content (after ad)

As COP 27 opens in Egypt, more and more studies show the crucial role of seagrasses for the survival of the oceans and the fight against climate change, just like that of sharks. Recently, cameras mounted on tiger sharks allowed scientists to find the largest seagrass bed known to date. Located in the Bahamas, it covers 92,000 square kilometers. So, with nearly 25% of the world’s carbon stocks, it’s a hopeful discovery for climate change.

Seagrass ecosystems play an increasingly recognized role in supporting ocean health. They promote biological productivity, ocean biodiversity, fishery resources, and carbon sequestration, while protecting coastlines from storms. These areas permanently trap and store massive amounts of carbon in sediments, contributing about 17% of the total organic carbon buried each year in marine sediments, called blue carbon.

Unfortunately, the rapid losses of seagrasses in previous decades have reduced the sequestration capacity of these ecosystems, while releasing large amounts of carbon into the atmosphere.

Therefore, their conservation is of crucial global importance to manage greenhouse gas emissions, while safeguarding the many endangered species. But it requires reliable knowledge of its distribution and extent. However, these meadows remain poorly mapped in many areas.

Not to mention the importance of sharks in maintaining these ecosystems, by regulating the population of sea turtles or other herbivores that feed there. But the role of these predators has unexpectedly expanded.

In fact, an international team of researchers led by Dr. Austin Gallagher, founder of the non-governmental organization under the waves, equipped the sharks with cameras to track their movement. The results exceeded expectations. Thanks to this device, scientists have discovered the largest seagrass bed known to date, more than 92,000 km², slightly less than the surface of Hungary. Good news in the context of the climate crisis. His work is published in the magazine NatureCommunications.

Explore the ocean through the eyes of sharks

It should be noted that the Bahama Banks are vast areas defined by carbonate sediments, supporting a large biodiversity of mobile consumers (sharks, turtles, dolphins, manatees). The substrate, the carbonated sand, the warm temperature regime and the abundant light that reaches the seabed are suitable conditions for seagrass beds.

To map the total area covered by these ecosystems in the Bahamas, the team used remote sensing, while integrating previous estimates from satellite imagery to generate a composite estimate of the environment. These records were combined with extensive validation on land, involving more than 2,400 surveys by divers throughout the area.

In addition, they collected data via video cameras attached to the tiger sharks, allowing a substantial area of ​​the seafloor to be mapped. Indeed, these sharks travel about 70 km in a day and reach deep areas, difficult for divers to access.

Dr. Carlos Duarte of King Abdullah University of Science and Technology and co-author of the study explains in a statement: Research by Beneath The Waves has shown that tiger sharks spend approximately 72% of their time patrolling seagrass beds, which can be seen with the 360° cameras we have deployed, a first for sharks. “.

Based on this data, the researchers estimate that the seagrass bed could span 92,000 km², twice the size of the one found off the coast of Australia, previously thought to be the largest in the world. . The new discovery expands the known global seagrass cover by around 41%, according to the study.

Maps showing (top) aggregated estimates of seagrass cover from existing data sources (bottom) and from 2022. © Gallagher et al., 2022.

This first partnership between tiger sharks and scientists led to this important discovery and provides a model for working with large marine animals to explore the ocean. The research team also collected sediment cores from the vast seagrass ecosystem to assess the amount of carbon stored in the sediments, ultimately revealing that the Bahamas likely holds up to 25% of the world’s blue carbon stocks.

A and B: Thalassia testudinum dense meadow photographed in the southern Great Bahamas Bank and data collected in an erosion zone. C: Adult tiger shark swimming over Little Bahamas Bank. D: Point of view of a tiger shark, through a camera, north of the Great Bahamas Bank. © (in order) Cristina Mittermeier/Austin Gallagher/Gallagher et al. 2022.

In fact, during a TED talk on seagrasses, Dr. Duarte revealed that one hectare of seagrasses sequesters as much carbon as 15 hectares of Amazonian forest. This is mainly because they are the most productive ecosystems on Earth, pumping huge amounts of CO2 into organic matter through photosynthesis, much of which is placed directly underground in the form of roots and rhizomes. He adds : ” The absence of oxygen slows decomposition, and the absence of fires, which return much of the forest carbon to the atmosphere, promotes its long-term storage. “.

The importance of sharks against climate change

Not to mention, scientists believe that sharks, by the very fact that they exist, have a role to play in keeping greenhouse gases in the oceans out of the atmosphere. Tiger sharks, in Australia for example, scare sea turtles away from seagrass beds. In doing so, the sharks prevent the turtles from overgrazing the seagrass beds. As mentioned above, seagrass beds are an important reservoir of blue carbon. Declining shark numbers mean more sea turtles deplete seagrass beds which, when destroyed, release their blue carbon stores and contribute to global warming.

You should also know that the body of a shark is another source of blue carbon. They are made up of 10 to 15% carbon. When they die naturally, their bodies sink, along with this carbon, to the depths of the ocean. They become deep-sea carbon reservoirs for thousands or even millions of years.

But shark overfishing means much of that carbon is pulled from the ocean and ends up in our atmosphere. Fear of sharks also hampers many rank designations.

Finally, Dr. Austin Gallagher concludes: “ This discovery should give us hope for the future of our oceans. It also shows how everything is connected. Because tiger sharks have been protected in the Bahamas for many years, we have been able to study and monitor the ancient processes these animals have been involved in for millennia. The sharks took us to the Bahamas seagrass ecosystem, which we now know is probably the most important blue carbon sink on the planet. “.

He adds : ” If protected, these seagrasses can play a crucial role in slowing the climate emergency as the world strives to implement a wide range of strategies to capture carbon from the atmosphere. “.

Source: Nature Communications

Leave a Reply

Your email address will not be published. Required fields are marked *