In 2021, Scotland celebrates the Year of Coasts and Waters, and COAST celebrates 25 years of the community of Arran’s efforts to protect our seas.

Here we bring you a little bit closer to what lies beneath our waves with a focus on the underwater meadows of Seagrass we find in Scotland’s seas.

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On land we take grass for granted. Underwater, seagrass can only thrive in very specific conditions and so is quite unusual to see. It is a very special plant which is only found at certain locations in the waters around Arran, where it generally grows in sandy seabeds. Although seagrass may not sound very exciting, it is responsible for creating a vitally important underwater habitat.

Seagrass is actually a true flowering plant, the only flowering plant able to live in seawater and pollinate and produce seeds while submerged. The two seagrass species we have in the UK – eelgrass and dwarf eelgrass – are both found in the Clyde, but it is the larger of the two, eelgrass (Zostera marina) that is found around Arran.

Like other plants, seagrasses need sunlight to survive and can only live in well-lit, shallow water just a few metres deep. They are usually found in quite sheltered conditions and can grow closely together forming dense underwater meadows or seagrass beds. One of the largest remaining seagrass beds in the Clyde is just off shore at Whiting Bay and, together with other areas of seagrass, is part of the special interest underpinning the establishment of the South Arran Marine Protected Area (MPA).

The importance of Seagrass

There’s SO many amazing and important things about seagrass, where do we even start?!

The thin, tall seagrass leaves can grow up to a metre long – depending on local conditions – and acts as shelter, feeding and nursery areas for many different species. Studies show that seagrass beds provide good nursery grounds for a number of commercially important fish including juvenile cod, whiting and pollock.

Within the seabed itself, a specialised root system anchors the plants, helping to stabilise and consolidate the seabed material. This has been shown to help to reduce sediment erosion and thus provide a form of natural coastal defence.

We’d highly recommend exploring Arran’s seagrass beds yourselves, as the accessibility of some to swimmers, snorkellers and divers provides an opportunity to enjoy this special marine habitat. On sun-lit days, seagrass beds are magical places, with dappled light and the sun’s flickering rays highlighting the constantly swaying seagrass blades.  Small fish dart amongst them and there is always the opportunity of a chance encounter with other fascinating marine life, including rather docile small-spotted catsharks.

Special Species

Picking out specific species to shout about that rely on seagrass as a habitat is extremely hard. Why?! Because studies have shown that over 30 times more animals live within seagrass compared to adjacent sandy habitats; a single acre of seagrass may support as many as 4,000 fish and 50 million small invertebrates!

One of the most common questions we get asked is “do you find sea horses in seagrass?” Well, you do, but not here off Arran. We have no records of sightings of seahorse around Arran, and there are currently no records north of SW Wales in the NBN Atlas for their genus. This said, we are lucky to have frequent sightings of their cousins – the pipefish. Most often we spot the Great pipefish (Syngnathus acus), but there is a reported sighting of a Nilsson’s pipefish (Syngnathus rostellatus) in the waters around Arran.

If you take a dive or snorkel over a seagrass bed, you have to focus your eye to marco setting to really see the wonderful life these habitats support. Many different species of nudibranchs and other sea slugs cling to the blades floating in the currents, and many also lay their eggs on them. Watch out though, you may get surprised by a spider crab or two, who perfectly blend in with the seagrass so as not to be spotted!

This footage was gathered by a University of York MSc student in 2017. Kam studied the effects of wireweed on fish species composition and population densities within seagrass beds around Arran. To do this, he used Baited Remote Underwater Videos (BRUVs) to capture footage for analysis.

In this BRUV footage, you can see numerous juvenile cod (with the checkerboard pattern) and a juvenile haddock (rather plain except for a distinct black dot on their side) which both rely on the seagrass beds as nursery grounds. You also see a small spotted catshark cruising by, and it heads for cover in the meadow.

Human Benefits

Where to start with the benefits that seagrass provides to us humans… we’ll highlight a few of the key benefits!

Carbon Capture
Seagrass beds are VERY effective at capturing and storing carbon, locking it away in the seabed sediments. Globally it is suggested that they are responsible for about 15% of the total carbon storage in the ocean. They also capture this at a rate greater (35 times more efficiently) than that of tropical rainforests!

– A recent article in The Guardian highlights the initiative of a Spanish chef, who is trailing seagrass as an alternative to rice. Early tests hint that seagrass seeds could contain 50% more protein than rice, and be a source of omega-6 and -9 fatty acids, as well as being gluten-free.
– Approximately 20% of the world’s fisheries are supplied by seagrass meadows.
– Up to 3billion people gain vital nutrition from seagrass meadows and around 400 million people in the third world get 50% of their animal protein from species supported by seagrass.

Threats to Seagrass

We have lost large areas of seagrass from around the whole of the UK coastline due to a variety of reasons. A drastic decline of seagrass beds in the 1930’s is attributed to an outbreak of a wasting disease and seagrass has been struggling to recover from this ever since as it has been hampered by other ongoing impacts such as pollution, disturbance from dredging, moorings and anchoring, and coastal development. Globally, estimates suggest we lose an area of seagrass around the same size as two football pitches every hour!

In parts of Arran, the invasive non-native seaweed known as wireweed (Sargassum muticum), a large brown seaweed from the north-west Pacific, is another potential threat to seagrass. At Kildonan, the natural breakwaters of the rock dykes provide sufficient shelter for seagrass to grow in this otherwise exposed location. The seabed here is more stony, an unusual situation to find seagrass in. The stones allow wireweed to get a foothold and, where it does, its large, spreading growth can create a canopy that blocks out the sunlight and shades the seagrass affecting its growth.

The presence of commercial fish and shellfish make sand and gravel habitats a target for fisheries, some of which can have a significant and lasting impact on the marine life communities that live in them. Some of our burrowing bivalve (two shelled) animals are extremely vulnerable to bottom trawling which results in direct mortality of the animal when disturbed. Damaging fishing methods also destroy habitats to the extent they are no longer suitable as nursery grounds for juvenile fish.

Can we protect Seagrass?

A report released in March 2021 confirmed a catastrophic decline of seagrass meadows had been observed in the UK, with more than 90% of the Nation’s seagrass meadows lost in the last century or two. This said, moves are underway to look at how seagrass beds can be actively restored in Scotland’s coastal waters and elsewhere around the UK, recognising the importance and value of this essential marine habitat. Project Seagrass aims to restore 30km2 of seagrass across the UK by 2030, and in 2020 they planted the final seeds in the two hectares of seagrass that represents the UK’s largest restoration project to date.

Education is a key tool in the protection of seagrass meadows, and there is ongoing work looking at mooring systems that reduce the physical impact that boating activities have to these habitats. Seagrass is recognised as a Priority Marine Feature by Marine Scotland, as beds are “functionally important, biodiverse, sensitive, slow to recover and if lost completely may not recover.” This recognition, coupled with seagrass being listed as a threatened and declining habitat by OSPAR, means that seagrass has fortunately been afforded fisheries protection in many Marine Protected Areas.

By protecting seagrass areas, such as those within the Lamlash Bay No Take Zone and Arran’s MPA, we can hopefully begin to ensure a better future for these special underwater meadows, whilst also presenting an opportunity to mitigate climate change.

Get involved to make a difference!

How can you personally help protect our marvellous seagrass habitats we hear you ask?!

Report seagrass sightings! SeagrassSpotter is part of Project Seagrass and is a global education and conservation tool for people to help locate seagrass. Using this application, ocean enthusiasts around the world can become citizen scientists who contribute to marine conservation with just a few taps of their phone. Spot it. Map it. Protect it.

If you are a boat user think about best mooring practices; use mooring buoys or pontoons over free-laying anchors, and do some research into areas before anchoring if it is unavoidable. There are projects underway for “Advanced Mooring Systems” which are more eco-friendly and less damaging to the seabed as the chains no longer drag through the seabed.

Support a seagrass project in your area – from the Ocean Conservation Trust and Project Seagrass to the Wildlife Trusts and the Marine Conservation Society, there are many conservation organisations working to help protect these Blue Carbon habitats and biodiversity hotspots.

Featured image: Seagrass in the Sun by Howard Wood.