Seagrass could help conserve crumbling UK coasts

Seagrass can capture carbon up to 35 times faster than tropical rainforests

Seagrass' root mats can reduce coastal erosion up to 70%. Researchers at the University of Gothenburg used a wave tank to show how the roots bind the sand dunes (Pekka Tuuri)

Around the UK’s coastline, up to 92 per cent of seagrass meadows have been lost in just the last century, and globally these critical carbon storing facilities are continuing to decline at a rate of 7 per cent per year.

A new study done in Sweden reveals the loss of these meadows doesn’t just hit biodiversity and the planet’s ability to draw down carbon dioxide from the atmosphere, but has shown that seagrass can reduce cliff erosion by up to 70 per cent.

This is because the plant’s strong roots form a huge mat across the seabed, binding the sand, holding it in place, while the plant itself acts as a breakwater during storms, minimising the impact of the waves.

Across Europe, the sea devours large tracts of lands when swells wash sand from the coast further out to sea.

As sea levels rise faster and faster due to the climate crisis, the researchers argue that preserving and reintroducing sea grass could help protect people and properties, while also boosting biodiversity and sequestering climate-altering greenhouse gas.

In total, around 8 per cent of the world’s population live in areas at an elevation of fewer than 10 metres above sea level, so measures to protect coastlines are becoming increasingly important.

According to a 2016 survey conducted by the Geological Survey of Sweden, 12 per cent of southern Sweden’s Skåne region’s coastline is vulnerable to increasing rates of coastal erosion. It is an even bigger issue in the Netherlands, where the coastline is protected through the construction of dikes made from stone and mud.

In the UK, areas including Suffolk and Norfolk have seen rapidly accelerating rates of erosion due to sea level rise and increasing storm frequency.

According to the UK’s Project Seagrass, which is aiming to reverse the trend of losing seagrass from our coasts, as well as boosting biodiversity, seagrass meadows’ ability to weaken storm surges is among the numerous other services they can provide to coastal communities.

“We have seen that seagrass meadows on the coast are valuable assets in mitigating erosion," said Eduardo Infantes, a Marine Biologist at the University of Gothenburg and the lead author of the erosion study.

"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,” he said.

To conduct the study, the research team took samples of sandy sediments 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.

“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, Dr Infantes added.

"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."

According to the WWF seagrass is the world’s only flowering plant capable of living in seawater, and it can be "an incredible ally" in the race to tackle the climate crisis.

The plant can capture carbon up to 35 times faster than tropical rainforests and, even though it covers less than 1 per cent of the seafloor, it globally accounts for 10-18 per cent of total ocean carbon storage.

"In the UK, seagrass meadows also support biodiversity providing important nursery habitat for important commercial fish species, as well as habitat for two endangered seahorse species, an array of invertebrates, greater and lesser spotted dogfish, grey seals, octopus, and sand eels," the organisation said.

The team said 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, and inflows from rivers can all affect 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,” said Dr Infantes.

The research is published in the journal Marine Ecology Progress Series.