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At the opening of COP 27 in Egypt, more and more studies are showing the important role of seagrasses for the sustainability of the oceans and the fight against climate change, like sharks. Recently, cameras attached to tiger sharks allowed scientists to find the largest seagrass bed known to date. It is located in the province of the Bahamas, in the southeastern part of the country, 92,000 square kilometers. Thus holding almost 25% of the global carbon stock, it is a discovery full of hope for climate change.
Seagrass ecosystems play an increasingly recognized role in supporting ocean health. They promote biological productivity, marine biodiversity, fisheries resources and carbon sequestration, while protecting coastlines from storms. These areas permanently trap and store large amounts of carbon in sediments, contributing about 17% of the total organic carbon buried annually in ocean sediments – called blue carbon.
Unfortunately, the rapid loss of seagrasses in the past decades has reduced the sequestration capacity of these ecosystems, while releasing more carbon into the atmosphere.
Therefore, their conservation is of global importance to manage greenhouse gas emissions, while protecting many endangered species. But this requires a reliable knowledge of their distribution and extent. Yet these pastures 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 increased unexpectedly.
In fact, an international group of researchers led by Dr. Austin Gallagher, founder of the non-governmental organization Under the Waves, put cameras on the sharks to track their movements. The results exceeded expectations. Thanks to this device, scientists have discovered the largest seagrass bed known today, more than 92,000 km² – a little less than the area of Hungary. Good news in the context of the climate crisis. Their work was published in the journal Nature Communication.
Explore the ocean through the eyes of sharks
It should be noted that the shores of the Bahamas are vast areas defined by carbonate sediments, supporting a large biodiversity of mobile consumers (sharks, turtles, dolphins, manatees). The substrate, carbonate sand, warm temperature regime and abundant light reaching the sea floor are suitable conditions for seagrass beds.
To map the total area covered by these ecosystems in the Bahamas, the team used remote sensing, while combining previous satellite image assessments to create a composite environmental assessment. These records were combined with extensive ground validation, involving more than 2,400 surveys by divers across the area.
In addition, they collected data through video cameras attached to tiger sharks, which made it possible to map a large area of the ocean floor. In fact, these sharks travel about 70 km a day and reach deep places, which are difficult for divers to access.
Dr. Carlos Duarte of the King Abdullah University of Science and Technology and co-author of the study, explained in a statement: Beneath The Waves research shows that tiger sharks spend approximately 72% of their time patrolling seagrass beds, visible on the 360° cameras we’ve deployed, a first for sharks. “.
Based on this data, researchers estimate that the seagrass bed may reach 92,000 km², twice the size of Australia’s coastline, which was once believed to be the largest in the world. . The new discovery expands the known global seagrass coverage by about 41%, according to the study.
This first collaboration between a tiger shark and a scientist led to this great discovery and provided a model for working with large marine animals to explore the oceans. 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 25% of the world’s stock of blue carbon. .
In fact, during a TED conference on seaweed, Dr. Duarte claims that one hectare of seagrass sequesters as much carbon as 15 hectares of Amazon forest. This is mainly because they are the most productive ecosystems on Earth, pumping large amounts of CO2 into organic matter through photosynthesis, much of which is placed directly underground in the form of roots and rhizomes. He added: ” The loss of oxygen slows decomposition, and the absence of fires that return most of the forest’s carbon to the atmosphere promotes its long-term storage. “.
The importance of sharks against climate change
Not to mention that scientists believe that sharks, in fact exist, have a role in playing greenhouse gases in the oceans, from the atmosphere. For example, tiger sharks, in Australia, are afraid of sea turtles, which flee away from the sea grass. In doing so, the sharks prevent the turtles from grazing on the seagrass beds. As previously mentioned, the seagrass bed is an important reservoir of blue carbon. The decline in shark numbers means more sea turtles depleting sea beds that, when destroyed, release their stores of blue carbon and contribute to global warming.
You should also know that the shark’s body is another source of blue carbon. They contain 10 to 15% carbon. If they die naturally, their bodies sink – along with this carbon – to the depths of the ocean. They have been deep-sea carbon reservoirs for thousands or even millions of years.
But overfishing of sharks means that most of the carbon is taken out of the oceans and ends up in our atmosphere. Fear of sharks has also hindered many names.
Finally, Dr. Austin Gallagher concluded: “ This discovery should give us hope for the future of our oceans. It also shows how everything is connected. Because the tiger shark has been protected in the Bahamas for many years, we have been able to study and monitor the ancient processes carried out by these animals for millennia. Sharks take us to the seagrass ecosystem of the Bahamas, which we now know is probably the most important blue carbon sink on the planet “.
He added: ” If protected, these seagrasses can play an important role in mitigating the climate emergency, as the world tries to deploy different strategies to remove carbon from the atmosphere. “.