Seagrass beds

Seagrass Beds © Paul Kay

Seagrasses (also known, for their long thin leaves, as eel grass) are grass-like flowering plants with dark green, long, narrow, ribbon-shaped leaves. They are one of the very few groups of flowering plants that live in the sea. Three species of eel grass are found in England and are considered to be scarce.  They grow in sheltered waters such as inlets, bays, estuaries and saltwater lagoons.

Common eel grass is the only species that occurs below low water mark, and it can form dense underwater lawns.  It grows mainly on sand, but also fine gravel, typically down to a depth of 4m.

The dwarf eel grass grows on sheltered seashores, between the tides. Ruppia maritima, otherwise known as beaked tasselweed is also found growing in sheltered coastal waters on soft sediments

Seagrass beds provide important food for wildfowl, such as brent geese, and nutrients to support animal communities on the seabed. Their roots catch and trap sediments, reducing coastal erosion.  Submerged seagrass beds are also used as a nursery area, protecting young fish and shellfish, and provide a sheltered home for many other animals, such as pipefish and seahorses.

Seagrass beds are threatened by pollution, and by increased amounts of sediment in the water, which block sunlight and prevent seagrass growth.  Seagrass beds are also affected by physical disturbance such as trampling, dredging, anchoring, and the use of mobile bottom-fishing gear.  Plants introduced by people also compete with seagrass for space on the shore, and seagrass can be devastated by disease. Areas affected by disturbance are slow to recover.

For the official habitat definition please see the documents listed below.


European distribution

Between the tides, seagrass beds can be found in sheltered bays in south-west England, Wales, Scotland and western Ireland and in similar locations on European coasts.  Vast underwater meadows of seagrass skirt the coasts of southern Europe.  In Europe, there was mass dieback of shallow water seagrass during the 1920s and ‘30s due to disease. More recently, declines have also been reported in the Wadden Sea and the UK for both shallow water and shore species.


Conservation status/need

Seagrass Beds Fact

  • This is a UK BAP Priority Habitat (BAP habitats are now Habitats of Principal Importance/Priority Habitats).
  • OSPAR List of Threatened and/or Declining Species and Habitats (declining in Region II – North Sea and Region III – Celtic Sea, and threatened in Region V – Wider Atlantic)
  • An important feature in estuary Sites of Special Scientific Interest, under the UK Wildlife and Countryside Act 1981


Official definition

UK Biodiversity Action Plan; Priority Habitat Descriptions. BRIG (ed. Ant Maddock) 2008 (updated December 2011) 

Descriptions of habitats on the OSPAR list of threatened and/or declining species and habitats (OSPAR agreement 2008/07).


Further information

OSPAR Commission – Background Document for Zostera (seagrass) beds

JNCC - UK BAP Priority Species and Habitats

Biodiversity Action Reporting System

JNCC Marine Habitat Classification

Marine Life Information Network - Zostera marina/angustifolia beds

Marine Life Information Network - Zostera noltii beds

JNCC EUNIS habitat correlations table