As the global sea level rises due to rising temperatures, the action of waves at higher altitudes increases the chances for extensive coastal erosion. The extent and severity of the problem are increasing at an alarming pace — but researchers may have found a way to reduce at least some of the problem.
Seagrasses are flowering plants that evolved on the land (and then moved back to the sea) about 100 million years ago. They flower once per year during their reproductive season and rely on marine creatures such as crabs and shrimp for pollination, playing a key role in many marine ecosystems.
As with other kinds of grasses on land, seagrasses are connected by underground structures called rhizomes. These are similar to roots that grow below the sediment. Most seagrass grows as shoots (or bundles of leaves) that emerge from a rhizome. A single plant can sprout many shoots over a long period of time.
We don’t know as much as we should about seagrass, especially given how important it seems to be. For instance, the estimates for seagrass cover range between 0.15 and 4.6 million square kilometers, a huge interval. While previous studies have shown seagrass has an important role in raising the sediment surface and preventing erosion, its effect on cliff erosion remains largely unknown – even though cliffs are common in this type of ecosystem.
“We have seen that seagrass meadows on the coast are valuable assets in mitigating erosion. We already know that their long canopies serve as breakwaters, but now we can show that their root mats also bind together the underwater sand dunes, effectively reinforcing them,” Eduardo Infantes, lead author, said in a statement.
The potential of seagrass
Infantes and the team from the University of Gothenburg focused on the common eelgrass, a seagrass species that grows on the bottom sediments along Sweden’s coasts. While some parts of the coast are filled with eelgrass, in others it has disappeared altogether. This is an ecological loss and also makes the coast vulnerable to erosion.
Infantes and colleagues took samples of sandy sediments with and without common eelgrass from a number of sites and put them in a large tank capable of simulating waves. The experiments showed that the sand is eroded less by waves when seagrass is growing in it. Cliff erosion rates were lowered up to 70% in the sediment with high seagrass.
“In our research, we have made successful attempts to restore common eelgrass meadows on the Swedish west coast, but if such replanting efforts are to succeed, there is a need for detailed studies of the current status seabed environment,” Infanets said. “We need to preserve the seagrass meadows that still exist today.”
Up next, the team will move out of the laboratory environment and take measurements of sand erosion on an exposed shoreline along the coast. There are other factors that can affect erosion, such as currents, water traffic and inflows from rivers, they said. However, they are confident of finding similar effects in the upcoming field tests.