Seagrasses are found up and down the coast of the United States and in many other parts of the world. Together they form meadows that are productive ecosystems, providing food and shelter to a wide range of animals. One important, often overlooked, function of seagrasses relates to their impact on the world’s climate.
One of climate changes greatest challenges is limiting the amount of carbon that is in our atmosphere. One mitigation technique is to revitalize or create carbon sinks. Carbon sinks fight climate change by capturing and absorbing carbon dioxide and preventing it from being released into the atmosphere. Seagrasses act as a surprisingly efficient carbon sink.
Seagrass meadows, per square kilometer, are able to store up to 83,000 metric tons of carbon; whereas a typical terrestrial forest, per square kilometer, is only able to store about 30,000 metric tons of carbon. That means seagrass meadows can sequester over twice the amount of carbon a terrestrial forest can given the same amount of space.
Unfortunately, seagrass meadows only occupy less than 0.2% of the world’s oceans. Despite their underwhelming presence, they are still responsible for over 10% of all carbon sequestered in the ocean per year.
Seagrass meadows’ ability to act as a carbon sink are threatened in a couple different ways.
One major threat to seagrass meadows is over-exploitation. Sharks that routinely patrol these ecosystems are being unsustainably exploited for a number of reasons. Some fishermen catch sharks solely for their fins. The fins are then sold to make shark fin soup. Other times, sharks are incidentally the product of bycatch. Whatever the reason, shark populations are drastically declining, and are becoming more threatened with each take.
Sharks are important to the seagrass meadows because they feed on the animals below them in the food chain. As apex predators, they feed on animals that would otherwise eat the seagrass. The sharks maintain a healthy ecosystem by limiting the populations of their prey, thus allowing the meadows to remain at healthy levels.
Another major threat to seagrasses are heatwaves. Seagrasses are temperature sensitive, and a strong heatwave (which are becoming more abundant with the rise of extreme weather due to climate change) can seriously decimate an entire meadow. Once the seagrass density drastically dips, it is difficult for the meadow to recover because it creates increased competition for all the fish, dugong, and other animals that eat the seagrass.
The lack of sharks compounds the rebounding issues. Without the threat of sharks patrolling the meadows, animals are able to further decimate the seagrasses because there is no threat of predation.
One potential solution would be to follow in the footsteps of Palau. In 2009, Palau became the first country to create a shark sanctuary and ban shark fishing in its exclusive economic zone. This move protected about 240,000 square miles of ocean (about the size of France). The presence of sharks maintains the health of the ecosystem and allows the seagrasses to rebound in the event of a decline due to some climatic event, like a heat wave.
This will not provide the solution to climate change. However, protecting sharks, and thus protecting seagrasses, will hopefully allow for the expansion of an efficient carbon sink, creating a positive feedback cycle and increasing its positive effects.