Seagrasses are submerged flowering plants that have adapted to live in the marine environment. They occur on shallow, sheltered intertidal & subtidal sediments, forming extensive ‘meadows’ or ‘beds’.

Key Characteristics

  • Site: Shallow, sheltered coastal waters
  • Main Species: Angiosperms; eelgrasses: Zostera spp. & Ruppia spp.

Habitat Description

  • Seagrass beds are unique habitats, consisting of true flowering plants (angiosperms) that photosynthesize. Therefore, they are typically occur in shallow & sheltered coastal waters, anchored in sand or mud bottoms.
  • Seagrass beds can be found in marine inlets, bays, lagoons & channels sheltered from strong wave action (WWF, 2005).
  • Five species of seagrass are found around Britain & Ireland, three of which are the eelgrasses: Zostera marina (common seagrass) occurs mainly in the sublittoral, Z. angustifolia (narrow-leaved eelgrass) is found on the mid to lower shore & Z.noltii (dwarf eelgrass) is found highest on the shore. Two tassel weed species, Ruppia maritima & R.cirrhosa, may partly replace Zostera species. In Northern Ireland the Ruppia species are not as common as Zostera species.

Current Status in UK & Northern Ireland

  • Intertidal Zostera spp. in the northern half of Strangford Lough cover an estimated 850 ha (Preston, Portig et al., 1999; 2000; NIEA, 2003).
  • Seagrass beds also occur in Lough Foyle. Z.noltii is the main species, although Z. angustifolia occurs, but less commonly. The Zostera spp. beds cover an estimated 1000 ha, mainly on the upper half of the shore (Allen & Tickner, pers comm.; NIEA, 2003).
  • Z. marina beds can be found in a wide range of habitats. There is an area of seagrass beds behind Great Skerrie, which was found in good condition. A previously unrecorded area of seagrass was found in Church Bay (Rathlin Island) & Red Bay (Sublittoral Survey of Northern Ireland, 2006).
  • Seagrass beds have been recorded in Belfast Lough, Larne Lough, Killough Harbour, Dundrum Bay & Carlingford Lough.
  • A recent study (Waycott et al., 2009) has revealed that seagrass beds are declining worldwide. In NI they are also a threatened habitat, subjected to:
    – Physical damage such as trampling, dredging, mooring, mobile bottom fishing gear, land claim & construction of sea defences.
    – Marine pollution: common eelgrass accumulates tributyl tin, other metals & organic pollutants, which may reduce nitrogen fixation & build up in the food chain.
    – ‘Wasting disease’, a fungal infection that attacks the leaves, caused loss of Z. marina across the UK in the 1930s, & symptoms have been recorded in Strangford Lough.
    – Climate change: increased summer temperatures may restrict the distribution of intertidal species due to desiccation in these areas. Increased sea levels may restrict the lower limit of Zostera spp. in the sub-tidal zone
    – Introduced species: Cordgrass Spartina anglica & Japweed Sargassum muticum are of concern. The latter species has colonised large areas of Strangford Lough (Strong et al., 2006)
    – Increased turbidity & eutrophication alters the light regime & can reduce growth of seagrass beds.

Designated Sites

  • Larne Lough
  • Lough Foyle
  • Rathlin Island
  • Roe Estuary
  • The Skerries

Further Information