Surveying seagrass_Copyright NRW marine monitoring team

Seagrass-Zostera marina - Copyright-NRW.

Seagrass Zostera marina_Copyright NRW - Paul Brazier


Seagrasses are the only flowering plants (angiosperms) capable of living in seawater. Like terrestrial plants, seagrasses have roots, stems and leaves and reproduce by producing flowers and seeds. They have stems (rhizomes) that creep horizontally below the sediment surface and then shoot up above the surface forming, often dense, underwater ‘meadows’. These biogenic habitats are found in sheltered, sediment areas and can cover large areas and play an important role in supporting a variety of other flora and fauna.

There are two species of true seagrass in Wales. Zostera marina (eelgrass), found typically on sandy bottoms in the subtidal from approximately 4 m depth to the lower intertidal and Zostera noltei (dwarf eelgrass), an intertidal species. Zostera angustifolia is now considered an ecotype of Z. marina.Ruppia spp (tassel weed / Widgeon grass) is a genus of aquatic freshwater plants found in Wales, with similar niche and salinity tolerance to Zostera species and are treated as seagrasses.

Zostera beds around Wales are restricted in distribution and the majority are found in sheltered bays, inlets and estuaries and limited to less than ten known major locations. These can occur as isolated intertidal or subtidal beds or as one continuous bed where the intertidal and sublittoral stands merge (e.g. at Porthdinllaen on the north Llŷn coast). There are extensive intertidal seagrass beds in Milford Haven and scattered populations in north Wales and subtidal beds in Tremadog Bay and North Haven, Skomer. The largest bed is in the Severn Estuary, which is unusual as it is within boulder and mixed substrata and has a mixture of Z. noltii and Z. marina. Records for Ruppia spp. are far sparser but are mostly represented by isolated swards in brackish pools located within areas of saltmarsh.

Seagrasses have previously suffered significantly from a wasting disease and in the 1930s, a significant proportion of the seagrass died in the UK. The effects of this disease, along with the result of human impacts, means the extent of seagrass is much reduced today.

Role of seagrass in ecosystem function

Seagrass sequester and store carbon dissolved in our seas – this is known as ‘blue carbon’. Seagrasses are highly productive, rapidly turning over large amounts of organic carbon as leaf material. This organic carbon is often exported to other ecosystems, subsequently becoming trapped in sediments below the bed or stimulating other food webs, which can result in the build-up of long-term carbon deposits.

Seagrass beds also provide important nursery habitat for juvenile fish species. There is now increasing evidence that this role is pronounced in UK seagrass beds, with a range of studies confirming that they play such a role for numerous species of commercial importance (e.g. plaice, bass, cod). Seagrass beds constitute permanent habitats for species of principal importance for conservation in Wales such as stalked jellyfish and seahorses. They also play an important part in stabilising sediments, particularly when dense beds are present.

Seagrass beds also have a role in wave attenuation, reducing the energy of the waves reaching the shore therefore playing a role in coastal protection.

Seagrass meadows play a significant cultural role on a local scale, where communities and individuals gain well-being from their use of seagrass beds for recreation.

Protection of seagrass in Wales

In recognition of their ecological and economic importance, seagrass beds are protected through a variety of conservation legislation and polices.

Z. marina (and Z. noltei) are encompassed in the Annex I habitats of the Habitats Directive Sandbanks, Estuaries, Mudflats and Sandflats and Large Shallow Inlets and Bays. In Wales, seagrass beds are part of Annex I features in 5 Special Areas of Conservation.

Seagrass beds are included under ‘intertidal sediments, on the lists of Section 7 habitats protected under the Environment (Wales) Act 2016. Intertidal Zostera noltei and Zostera marina beds are a designated feature of a number of SSSIs in Wales in intertidal areas.

Action for seagrass

In recent years there have been a number of seagrass recovery projects in Wales.

A large amount of work has been done at Porthdinllaen, Llŷn Peninsula, where a project is ongoing to develop and implement management measures to improve the condition of the seagrass while allowing the existing use of the bay to continue.

Seagrass Ocean Rescue (a collaboration between partners including Sky Ocean Rescue, WWF, Project seagrass, Cardiff University, Swansea University and Pembrokeshire Coastal Forum) are working to trial the restoration of seagrass in experimental areas in west Wales, with the aim of expanding this to other areas of the UK.

In addition, there is a major restoration project in north Wales funded by the National Heritage Lottery Fund to restore 10 hectares of seagrass around the Llŷn Peninsula and Anglesey. It is being delivered by Seagrass Ocean Rescue in collaboration with WWF, Project Seagrass amongst others.

Marine Conservation Society (MCS) are also working to deliver the Welsh Marine Treasures project (part of Natur am Byth!). This is a Heritage Lottery and Welsh Government funded project being led by NRW. It unites nine environmental NGOs with NRW to deliver the country’s largest natural heritage and outreach programme to save species from extinction and to reconnect people to nature. This project will build on the work using Advanced Mooring Systems (AMS) to allow further seagrass meadows to recover from the damage of mooring. It will also include a review of existing seagrass health monitoring across Wales and how delivery of this monitoring can be improved.

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