Seagrass can reduce cliff erosion by up to 70% thanks to the way its rootmats bind sand, according to researchers from the University of Gothenburg in Sweden.

“We have seen that seagrass meadows in the coast are valuable assets in mitigating erosion," says Eduardo Infantes, a marine biologist at the University of Gothenburg. "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.”

Common eelgrass is kind of seagrass that grows along Sweden’s coasts, and in some areas, there are large seagrass meadows growing in sediments on the seabed. In other places, the seagrass has disappeared altogether, which not only represents an ecological loss, it can also mean that the coast becomes more vulnerable to erosion.

The sea devours large tracts of land when storms washout sand from the coast. Coastal erosion is a global problem that is often combated by replenishing the coast and beaches with new sand in locations where storms wreak the greatest havoc. In places like the Netherlands, dikes and defences are build of stone and mud.

As the climate changes, there is a risk that storms become more powerful, which can lead to an increase in coastal erosion. Approximately 8% of the world’s population live in areas at an elevation of less than 10 metres above sea level, so rising sea levels may see many more people affected by coastal erosion.

“This is why it is even more important to preserve those seagrass meadows that still exist today and to replant seagrass in those places where it has disappeared," says Infantes. "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."

In this study, the researchers took samples of sandy sediment, with and without common eelgrass, from a number of sites, and placed them in a large tank capable of simulating waves. The experiments demonstrated that the sand is eroded far less by waves when seagrass is growing in it.

The researchers also took samples from muddy seabeds, but found that the effect of the seagrass there was less. However, this matters less since muddy seabeds are most commonly found in fjords and other areas that are less exposed to waves.

The next step will be to move out of the laboratory environment and take measurements of sand erosion on an exposed shoreline along the coast. Other factors such as currents, traffic on the water, inflows from rivers etc. can then affect the erosion.

“It’s more complicated in the field, but we have created realistic storm waves in our experiments and the seagrass has clearly shown a protective effect against erosion. I think we will be able to demonstrate the similar effects in field tests,” says Infantes.