Seagrass: The unlikely ecosystem fighting climate change
When discussing ocean ecosystems, the example that’s often used are coral reefs. Healthy reefs are rich with biodiversity, and their decline is having an unprecedented impact on our planet. However, another ocean ecosystem is under threat, and is far less talked about than corals—and that’s seagrass.
Seagrass only covers roughly 0.1% of the ocean floor, but these meadows provide shelter and feeding grounds for countless fish, turtles, seahorses, and other marine species. Seagrasses are also responsible for capturing and storing huge amounts of excess carbon from the atmosphere—35x more than the Amazon rainforest! Yet despite being one of the most important coastal habitats on Earth, it is one of the most threatened. Over the last 300 years, seagrasses have declined 29%.
What is seagrass?
Seagrasses are marine flowering plants found in shallow, coastal waters all over the world. Often covering vast areas, seagrass meadows are complex and biologically rich habitats. Seagrasses belong to a group of plants called monocotyledons, which is the same family as their relatives on dry land. Around 100 million years ago, terrestrial grasses took a U-turn and began to adapt to salt water, expanding into coastal shallows. This evolution means that seagrass has a lot more in common with grasslands than they do with seaweed. Seagrass also behaves like grass, with roots and leaves, photosynthesizing sunlight. They spread by releasing pollen and seeds into the water which drift along the currents.
Even more fascinating, some species of seagrass have the ability to clone itself over and over. Poseidon's ribbon weed (Posidonia australis) in Australia’s Shark Bay is one such plant. The entire 180 square kilometer meadow is a single organism, and as a result has been named the world’s largest plant. This is just one example of how diverse seagrasses around the world are, with around 72 different species on every continent except Antarctica.
Why is seagrass important?
Seagrass beds are vital shelter for mollusks, fish, squid, and other small crustaceans, and often serve as foraging grounds for sea turtles. Seagrasses have a number of important functions in ocean ecosystems.
Removes carbon from the atmosphere
Seagrasses biggest superpower is its ability to store enormous amounts of carbon dioxide, making them critical in the fight against climate change. In fact, seagrass meadows are 35x faster than tropical rainforests when it comes to absorbing carbon, despite covering just 0.2% of the ocean floor. Seagrass meadows can then store that carbon in underwater sediment for hundreds of years. In total, seagrasses are responsible for roughly 10% of the ocean’s global carbon storage, which is roughly 27.4 million tons of CO2 annually.
Nature’s water filter
Seagrass is often referred to as ‘nature’s water filter,’ because it traps sediment and absorbs pathogens from the water. Seagrass-dominated ecosystems also oxygenate water through photosynthesis which improves water quality. In fact, they produce around 100,000 liters per hectare, per day!
A single acre of seagrass can support as many as 40,000 fish
Seagrass meadows are important habitats for many species of marine life, including fish, crustaceans, and sea turtles. They provide vital shelter, breeding grounds, and nursery habitats for young marine species. Seagrass meadows support high levels of biodiversity and are crucial for the survival of endangered species like dugongs and manatees—a single acre alone can support a million unique species!
Erosion prevention
The vast root systems of seagrasses help to stabilize the seafloor. This prevents erosion and protects coastlines from storm surges and the impact of waves. They are ecosystem engineers that bring stability to coastal waters. They also help reduce flooding from storm surges and hurricanes by dissipating wave energy.
Indicator of ocean health
Seagrass is an indicator species, which means it acts like a health check for marine ecosystems. When seagrass beds are abundant and thriving, it’s usually a sign that the water is clean and the ecosystem is in good balance. When the seabeds start to die or shrink, it’s usually a sign that something is wrong.
How does seagrass benefit the planet?
A 2012 journal found that coastal seagrass beds store an enormous 83,000 metric tons of carbon per square kilometer, which is the same amount as forests on dry land. This finding highlights just how important seagrasses are to the future of our planet, as it plays such a key role in mitigating the impact of climate change. What’s more, a single acre of seagrass can support as many as 40,000 fish and 50 million small invertebrates like crabs and oysters. Losing such an important habitat would have unforeseen consequences on the wider ecosystem.
Why are seagrass meadows threatened?
There are many threats facing the planet’s seagrass meadows, including rising sea levels, tourism, and illegal fishing methods.
Rising sea levels
Seagrasses thrive in shallow coastal waters, where they can access lots of sunlight and important nutrients that drift in from the deeper ocean. As we are acutely aware, sea levels are rising which puts seagrasses at risk of losing their access to life-giving sunlight and shallow water they need to thrive.
Tourism
Seagrasses are easily damaged by boat anchors, propeller scarring, and dredging for coastal developments like marinas or resorts. Increased tourism often leads to water pollution which reduces water clarity and impacts seagrass growth.
Illegal fishing methods
Sustainable fishing is one of the best ways to protect our seagrass meadows, but unfortunately commercial fishing has other ideas. Trawling, which is a practice that involves pulling a large fishing net through the water, catches anything and everything in its path. Bottom trawling is a similar practice, but this time the net is sunk to the ocean floor and dragged across seagrasses to capture fish, crustaceans, and even sharks. This practice in particular not only destroys seagrass beds, but it devastates the ocean floor and any oceanic habitat in its path. What’s more, illegal bottom trawling releases millions of tons of carbon back into the atmosphere.
How can we protect seagrass?
Around the world, nations are starting to understand the importance of seagrass to the planet. In May 2022, the United Nations declared March 1 as World Seagrass Day, in an effort to highlight the urgent need for the conservation of seagrasses, and to raise awareness of its importance.
When the world’s largest seagrass meadow was discovered in the Bahamas, the government of the Bahamas took steps to protect this important habitat. With an area approximately the size of Portugal, the Bahamas Bank increased the documented global seagrass by 40.7%! In response, new legislation was implemented to map and safeguard the future of the seagrass in the Bahamas.
In some parts of the world, like the Mediterranean waters off the Italian Coast, fishermen are taking matters into their own hands. Paolo Fanciulli, a fisherman and environmental advocate from Tuscany, is fighting back against the illegal trawlers destroying the seagrass meadows along the Italian coastline. His solution is to stop the practice by adding large concrete blocks into the water that damage nets that try to fish this way. To draw attention to the project, Paolo has created an underwater sculpture garden for snorkelers and divers to enjoy—as well as protecting the coastal waters of the Mediterranean. Watch our latest mission video to see how:
Despite seagrasses covering such a small area, they are hugely important to our planet. Not only are they home to billions of individual species, but they absorb huge amounts of CO2 from the atmosphere. Protecting seagrass meadows needs to be a top priority for law makers and environmental advocates, alongside the rest of the endangered ocean habitats.
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