Seagrass: A Swimmer’s Guide

Do you usually bodyswerve swimming over sea vegetation to avoid feeling the tickle on your toes and the fear of whatever might lurk beneath? It’s time to take a deep breath and fall in love with seagrass

Martin Stevens @sensoryecology

The humble seagrass has been receiving increasing attention in recent years. This is in no small part due to the seemingly perpetual ripple effect of the BBC’s Blue Planet series, which since it premiered in 2001 has continued to raise awareness of marine environment and its issues to unprecedented levels. One of the first beneficiaries of this was of course the marine plastics campaigns, which have gone from strength to strength.

Yet, quietly at first, seagrass has risen up the conservation agenda. Seagrass meadows around the UK were severely depleted over the last century, but efforts are now underway to restore them. As well as providing important shelter for wildlife, seagrass is also increasingly being recognised as a strong candidate for a nature-based solution to climate change. Fancy swimming over it now? We thought so. The OSS’ Beth Pearson spoke to the conservation officer at Project Seagrass, Bethan Thomas, to find out all about it. 

Seagrass likes similar conditions to many outdoor swimmers

Seagrasses are flowering plants – the only flowering plant able to live in saltwater and pollinate underwater. They have bright green strap-like leaves and can form vast meadows when unimpeded. Due to their great need for sunlight to photosynthesise, they are found in water up to around four metres deep. “Seagrasses thrive in sheltered, shallow bays and estuaries, without extremes of conditions like storms – they get ripped up by storms,” says Bethan. “You can often find it the same places you find boats in harbour.” 

Seagrass is an indicator species for clean water

“In areas where seagrass is being lost, you realise there is something wrong with the water chemistry,” says Bethan. “Seagrass needs a lot of light to photosynthesise, so it engineers its own environment. Seagrass beds slow down wave energy – when you view it underwater, you can see it moving with the current; it attenuates wave energy as the water hits the seagrass meadow. Because of this, the wave drops the sediment it is carrying. When you’re snorkelling near seagrass, you can see the change in water from clear to murky as you move away from the seagrass meadow. The roots of the seagrass also stabilise the sediment, which helps prevent coastal erosion.”

Martin Stevens @sensoryecology

Where there is seagrass, there is interesting wildlife

“Some resorts are directly removing seagrass beds in places such as the Maldives as some tourists believe it spoils the clear view of the sea,” says Bethan. “We need to change the perception – if you want to see turtles on holiday, you need seagrass. Many resorts have pledged to protect their seagrass.” Seagrass meadows provide an ideal habitat for many species, especially juvenile fish and sea creatures. The seagrass species in the UK include eelgrass, which stands at 2m tall. “Juvenile seahorses wrap their prehensile tails around seagrass to avoid drifting away,” says Bethan. “You can also spot juvenile cod, plaice and herring, as well as pipefish, cuttlefish, and dog fish (pictured above). Seagrass is amazing for biodiversity.” 

Catastrophic loss – and restoration

An important research paper has estimated 39% of seagrass meadows in the UK have been lost since the 1980s, which is a higher rate than the global average. Historically, the loss could be up to 92%. Much of the depletion of seagrass meadows around the world is a result of human activity, in the form of agricultural and industrial pollution as well as physical disturbance of the habitat through clearing and recreation. A key restoration project has taken place at Chesapeake Bay, in Virginia, USA, which began in 1978 to not only restore lost seagrass meadows but research the best methods for doing so. In the UK, large-scale projects have included those at Plymouth Sound, England, and Dale, in West Wales.

A nature-based solution to climate change

Increased attention is being given to ecosystems that absorb and store carbon, in an urgent effort to address climate change. It is estimated that while seagrasses occupy only 0.1 per cent of the seafloor, 11 per cent of carbon absorption in the ocean (so-called “blue carbon”) can be attributed to it – figures such as this put it in the top four ecosystems for carbon sequestration alongside tundra, mangrove forests and salt marshes. Carbon is sequestered in the oxygen-free sediment layer of the seabed, where it decomposes far slower than on land. The more seagrass meadows are restored, the greater the amount of carbon stored. To hear more about this, including contributions from Project Seagrass, listen to the ‘Sublime Seagrass‘ episode of BBC Radio 4’s 39 Ways to Save the Planet series.

Ben Jones, Project Seagrass

“It’s nice to just cruise through a seagrass meadow, and not expend too much energy on swimming”

Advice for swimming in a seagrass meadow

Bethan recommends borrowing or investing in a good snorkel set, as well as flippers because “it’s nice to just cruise through a seagrass meadow, and not expend too much energy on swimming”. We recommend borrowing kit, looking for second hand options, or if you have to buy then choose quality to ensure it lasts as long as possible. Due to the shallow waters in which seagrass is found, it’s important to be very wary of boats and stay safe. “It’s always a good idea to wear a surface marker buoy, particularly if snorkelling as you may not always be aware of what’s happening above the water,” adds Bethan.

Swimmers will also be interested to know that seagrasses reduce our exposure to bacterial pathogens, which can cause some people to become ill. One study found that where seagrasses are present, there is a 50% reduction in bacterial pathogens capable of causing disease to humans and marine organisms. “If we want to swim in clean waters, protecting our seagrass meadows is a great place to start,” says Bethan.

Citizen swimmers: how you can get involved

There are loads of ways to get involved with seagrass conservation and restoration. Project Seagrass runs a SeagrassSpotter platform, which enables the public to contribute sightings of seagrass around the UK. There are also several projects which enable volunteers to get involved in planting seagrass meadows (because seagrasses are flowering plants, meadows can be sown with seeds as they would on land). Alternatively, fundraise for organisations restoring seagrass meadows to enable them to do even more.  

  • The Outdoor Swimming Society is donating 10% of all Longest Swim tickets to Project Seagrass
  • For more information on Project Seagrass visit the website