Priority Habitats | Coastal | Seagrass Beds
Description of Seagrass Beds
Seagrass beds occur mostly near sea loughs on shallow, sheltered sediments. Seagrass itself needs nutrients and sunlight to grow. Their leaves are thin and long (like grass) and the beds can cover the whole sea floor.
Seagrass beds support a wide variety of different species of animals (one hectare may host up to 125 million small vertebrates and almost 10,000 fish).
Strangford Lough, Lough Foyle, Belfast Lough, Larne Lough, Killough Harbour, Carlingford Lough and Dundrum Bay support seagrass beds in Northern Ireland. These beds help prevent coastal erosion, produce oxygen and allow sediments to build up.
Five different species of seagrass grow in Northern Ireland’s seagrass beds:
- Zostera marina
- This seagrass is a perennial plant, living for more than two years. They reproduce by seed and by clonal growth, meaning, that the plant can grow by itself without pollination by other plants of the same species.
- Zostera augustifolia
- Z. augustifolia is an annual plant, which dies at the end of autumn/early winter.
- Zostera noltii
- Not much is known about this seagrass. Like Z. marina this plant is perennial and grows from seed or clonal growth.
- Ruppia maritime and Ruppia cirrhosa
- Both these seagrasses are not as common as Zostera spp. Only a few individual plants have been observed. The main habitat for these plants is saline lagoons.
Historical info about Seagrass Beds
Seagrass is not a seaweed (algae). It has evolved from land plants and has roots, leaves, flowers and seeds. They are able to photosynthesise (using carbon dioxide and water to grow).
Seagrass, through its roots, is able to use nutrients from the soil (sand or sediment). Seaweeds can’t do this. It has only small “roots” to anchor it to surfaces so it isn’t washed away by waves and tides. Seaweeds also produce spores instead of seeds.
The flowers of seagrass - in winter and spring - are very small and the pollen reaches the female plant with help of the sea. The fruits (containing the seeds) are carried away from the mother plant by water also.
Seagrass were used by the French for mattresses and were collected as fertilizer for sandy soil. It is used for furniture and as a woven material, called “rattan”.
Species living in and around Seagrass Beds
Seagrass beds represent a special habitat for various species. Fish use the plants as shelter when young, wildfowl overwintering in Northern Ireland use the beds as a valuable food resource. Mute swans, whooper swans, light-bellied brent geese and wigeon are well known for this. Molluscs and seaweeds use this habitat for parts their life cycle.
Threats to Seagrass Beds
A “wasting disease” caused a past decrease of Z. marina. It is not known if there are currently any problems with wasting disease in seagrass around Northern Ireland.
Stable ground (sediment) conditions are necessary for seagrass. Disturbance caused by changes in flow and sedimentation (caused by human intervention), moorings, dredging, storms and powerboats/jetskis damages the beds, causes erosion and leads to a loss of habitat.
Seagrass can recover in a few weeks if only the leaves are damaged. Destruction of roots and rhizomes leads to the death of plants.
Eutrophication (too many nutrients) and overfishing increase the decline of such areas.
References
http://www.sms.si.edu/IRLspec/Seagrass_Habitat.htm
Environment&Heritage Service (2003): Northern Ireland Habitat Action Plan, Seagrass Beds. Belfast. http://www.ni-environment.gov.uk/seagrass_beds_web_version_april_03.pdf [last access: 26 August 2008]
http://www.archipelago.gr/en/Actions/SeagrassBedsindanger/tabid/91/Default.aspx
