Seagrasses offer effective coastal protection. They slow waves, hold together sand and sediments, and prevent erosion far beyond their own borders.
Though they might not seem impressive at first glance, through their existence alone, seagrass meadows fundamentally change the “balance of power” between the land, waves and ocean, and contribute to coastal protection by slowing waves, holding together sediment particles and strengthening dunes; further, they serve as sediment traps, which ensures, to put it simply, that nearby coastlines never run out of sand. But how do they manage to do it all?
One of the secrets of their success: the high plant density to be found in many seagrass meadows. When countless thousands of delicate leaves grow upward, side by side, they create a flexible but highly effective bulwark for braking waves and local eddies. As a result, the water masses move more slowly, which produces two positive effects. First of all, the waves hit the shore with far less force, and take away less sand and sediment from the beach when they roll back out to sea. Accordingly, beaches and dunes near seagrass meadows remain intact longer and need to be restocked with sand by humans less frequently. Nevertheless, seagrass meadows don’t offer a panacea for coastal erosion, as they primarily grow in sheltered coastal areas.
Secondly, the slowed water movement over and near seagrass meadows gives the sediment and particles in the water a chance to sink to the seafloor – and ideally, to become trapped in their leaves. In this way, the underwater meadows not only filter suspended particles out of the water; they also gather such large amounts of sediment that they can even more effectively protect the nearest coastline from erosion. The steady influx of sediment from above also allows them to grow higher, helping to compensate for sea-level rise. Those meadows that rise in step with the sea level will be able to keep providing coastal protection in the future – as long as the sea level doesn’t rise faster than they can accumulate sediment.
In fact, for certain tropical regions it has been confirmed that seagrass meadows make a major contribution to ensuring that coastal areas enjoy a steady, reliable supply of new sediment, protecting them from erosion-related damage. In this regard, the secret to the meadows’ success lies in the calcareous algae and diatoms that live in them. When they die, their calcium carbonate or silica shells are left behind, helping to replenish beaches with new sediment.
Sediment particles that land in seagrass meadows have very good chances of not being washed away by the current. Just like trees on the edge of a cliff, seagrasses’ dense network of roots stabilizes the sandy ground. Simply put, it holds it all together, protecting it from the erosive and pulling effects of the ocean.
Seagrass leaves, which can be torn free by the wind or waves and subsequently wash up on shore, perform a similar function. In areas where they stack up, sometimes as high as a meter, they offer effective protection from the wind and water, especially for dunes.
The importance of seagrass meadows for coastal protection grows with every millimeter that sea level rises in response to climate change. But compared to levees or seawalls made of concrete, these underwater landscapes offer two critical advantages: they autonomously grow in step with sea-level rise, and they can repair themselves, e.g. after being damaged by a storm surge.
Consequently, preserving, protecting and reintroducing seagrass meadows in their native locations are among the most effective nature-based means of protecting the environment, human beings and our coasts from the grave impacts of climate change.
Ocean currents, wave action and eddies are some of the greatest challenges in the context of reintroducing seagrass meadows, even in the Baltic. Accordingly, the joint project SeaStore has set itself the goal of designing a growing aid that offers newly planted seagrasses firm footing until their roots are strong enough to take over the task.
The researchers plan to use extensive field and laboratory experiments to determine the tool’s size, design and material, as well as the local conditions under which it is needed to begin with. They will also gather data and conduct test runs in a wave channel and a 3D wave and current basin.
The experts also plan to develop new methods for selecting the best sites for new meadows. In this regard, they will use computer models to simulate and precisely analyze the currents and flow conditions in the southern Baltic Sea.
You can find detailed information on SeaStore research efforts.
Restoring seagrass meadows means
providing a tremendously important service not just for the ocean, but for all
Yet the success of restoration efforts depends on a complex interplay of factors, all of which are being investigated in the joint project SeaStore.