Strangford Lough

General site character

• Marine areas, Sea inlets (65%)
  
• Tidal rivers, Estuaries, Mud flats, Sand flats, Lagoons (including saltwork basins) (33%)
  
• Salt marshes, Salt pastures, Salt steppes (0.5%)
  
• Heath, Scrub, Maquis and Garrigue, Phygrana (0.5%)
  
• Humid grassland, Mesophile grassland (1%)
  

Annex I habitats that are a primary reason for selection of this site

• 1140 Mudflats and sandflats not covered by seawater at low tide

  The intertidal mudflats and sandflats in the north of Strangford Lough represent the largest single continuous area of such habitat in Northern Ireland. There are very extensive areas of muddy sand from Newtownards to Ardmillan Bay in the west and to Greyabbey in the east. The habitat also occurs in the south-west reaches of the Lough along the northern shore of Lecale. The northern flats support luxuriant beds of the eelgrasses Zostera noltei and Z. angustifolia. Common eelgrass Z. marina and tasselled pondweed Ruppia maritima are also present, the latter being widespread but quite local in its distribution. Such extensive beds are rare in the British Isles. The green algae Enteromorpha spp. and Ulva lactuca tend to occur where there is seepage of nutrient-enriched freshwater. Many of the invertebrate species present in muds also occur in muddy sand. However, lugworm Arenicola marina and nereid worms are generally dominant, along with bivalve molluscs such as Angulus tenuis, Mya arenaria and Cerastoderma edule.

• 1150 Coastal lagoons  * Priority feature

  The ‘Dorn’ is a silled lagoon on the eastern side of Strangford Lough in Northern Ireland. The Dorn, from the Gaelic word for ‘narrow channel’, refers specifically to the channel which connects several exceptionally sheltered bays to the main area of the lough. Near the mouth, rock barriers or sills hold back water as the tide falls, creating saltwater rapids, unique in Ireland. In the area of the Dorn rapids, abundant growths of sea anemones, sponges and ascidians clothe the rock and boulders. Several of the animals found in the area of the rapids normally occur in relatively deep water. These include the featherstar Antedon bifida, purple sun-star Solaster endeca, sting winkle Ocenebra erinacea, king scallop Pecten maximus and light-bulb sea-squirt Clavelina lepadiformis. The main trough of the Dorn supports a dense forest of sugar kelp Laminaria saccharina and sea-oak Halidrys siliquosa. The gravelly-sand bottom has unusually dense colonies of peacock worm Sabella pavonina and sand gaper Mya arenaria, with occasional native oysters Ostrea edulis and P. maximus. The channel immediately above the sill has fast tidal streams without turbulence, enabling sponges to grow to exceptional proportions. The sheltered marine ‘ponds’ feeding the Dorn feature beds of common eelgrass Zostera marina and the green alga Codium fragile ssp. tomentosoides.

• 1160 Large shallow inlets and bays

  Strangford Lough on the east coast of Northern Ireland is an outstanding example of a large, enclosed fjardic sea lough. Sea water enters the Lough through a narrow entrance, expanding into a broad, mostly shallow basin that has a central deep channel (30-60 m deep), which carries rapid currents and causes great turbulence in some parts, particularly the Narrows. With a wide range of tidal stream strengths and depths, there is a remarkable marine fauna within Strangford Lough and it is one of the most diverse sea loughs in the UK. The communities present range from the very rich high-energy communities near the mouth, which depend on rapid tidal streams, to communities in extreme shelter where fine muds support burrowing brittlestars, Dublin Bay prawn Nephrops norvegicus, and a rich community associated with horse mussels Modiolus modiolus.

• 1170 Reefs

  Reefs in Strangford Lough vary from tide-swept bedrock and large boulders in the main channel of the Narrows, through sand-scoured bedrock and boulders at either end of the channel, to more sheltered bedrock and boulders in the main central portion of the Lough and in parts of the intertidal. Beds of horse mussels Modiolus modiolus form extensive biogenic reefs within the central portion of the Lough. Tide-swept bedrock is restricted to the Strangford Narrows, where rock surfaces are entirely clothed in suspension-feeding species, notably the soft coral dead-men’s fingers Alcyonium digitatum, sponges, especially Pachymatisma johnstonia and the rock-boring Cliona celata (which reaches massive proportions), ascidians, particularly Dendrodoa grossularia and Corella parallelogramma, and sea-anemones including Metridium senile. Very large boulders strew much of the bed of the Narrows, and are subject to strong tidal streams. These boulders are clothed with encrusting sponges, such as Myxilla incrustans and Myxilla fimbriata, with abundant hydroids, especially Tubularia indivisa, and sea anemones, including Sagartia elegans, Corynactis viridis and Actinothoe sphyrodeta. Coarse sand scours rock surfaces at the sides and either end of the Narrows. Here the characteristic species is the bryozoan Flustra foliacea. Though most of the intertidal zone is clothed in sediments, glaciated or sea-worn bedrock outcrops are found at many locations. Massive boulders (glacial erratics or the cores of eroded drumlins) occur on the shore and form rocky islands known as ‘pladdies’. Whilst Silurian rocks predominate, there is sandstone at Mountstewart and limestone at Limestone Rock. The fauna and flora associated with these outcrops are dependent on the rock type, the angle of bedding-plane and degree of weathering, the position on the shore, and the degree of exposure to currents and waves. Full development of the climax biotope associated with the M. modiolus beds depends on the very sheltered, plankton-rich waters of extremely low turbidity found in the central to northern area. M. modiolus rarely occurs in such still waters. The mussels and dead mussel shells provide a hard surface in an otherwise soft-sediment environment on which numerous other species (up to 100) depend. Many mobile suspension-feeders also occur, particularly the scallop Chlamys varia which is co-dominant with M. modiolus. A similar biotope, also dominated by M. modiolus, but with brittlestars Ophiothrix fragilis and Ophiocomina nigra replacing C. varia as co-dominant, occurs in the central to south-western area where water movement is slightly greater.

Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site

• 1210 Annual vegetation of drift lines
• 1220 Perennial vegetation of stony banks
• 1310 Salicornia and other annuals colonizing mud and sand
• 1330 Atlantic salt meadows (Glauco-Puccinellietalia maritimae)

Annex II species that are a primary reason for selection of this site

• Not Applicable

Annex II species present as a qualifying feature, but not a primary reason for site selection

• 1365 Harbour seal Phoca vitulina