Plymouth Sound and Estuaries

General site character

• Marine areas, Sea inlets (50%)
  
• Tidal rivers, Estuaries, Mud flats, Sand flats, Lagoons (including saltwork basins) (40%)
  
• Salt marshes, Salt pastures, Salt steppes (5%)
  
• Coastal sand dunes, Sand beaches, Machair (2%)
  
• Shingle, Sea cliffs, Islets (3%)
  

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

• 1110 Sandbanks which are slightly covered by sea water all the time

  Plymouth Sound and Estuaries, on the south-west coast of England, has been selected for its extensive areas of sublittoral sandbanks, which consist of a range of sandy sediments within the inlet and on the open coast. These sediments include tide-swept sandy banks in estuarine habitats, sandy muds north of the Breakwater, muddy sands in Jennycliff Bay, fine sands with eelgrass Zostera marina and a rich associated flora and fauna in the Yealm entrance, as well as tide-swept sandy sediments with associated hard substrates colonised by distinctive communities of algae and invertebrates.

• 1130 Estuaries

  Plymouth Sound and Estuaries is representative of ria estuaries in south-west England. The Rivers Tamar and Lynher are linked at their mouths. The upper parts of the Tamar and Lynher include a very well-developed estuarine salinity gradient. As a consequence, they exhibit one of the finest examples in the UK of changing estuarine communities with changing salinity regime. Rocky reefs in low salinity estuarine conditions far inland on the Tamar are very unusual and support species such as the hydroid Cordylophora caspia. The Tamar is one of few estuaries where zonation of rocky habitats (intertidal and subtidal) can be observed along an estuarine gradient.

• 1160 Large shallow inlets and bays

  Plymouth Sound and Estuaries on the south-west coast of England includes the rias of the rivers Tavy, Tamar, Lynher and Yealm. The first three of these join at the wide, rocky inlet of Plymouth Sound and the Yealm enters the adjacent Wembury Bay. The Yealm has good examples of habitats and communities characteristic of sheltered marine inlets with little freshwater input, including a range of sponge- and worm-dominated communities on lower shore mixed sediments. The Plymouth Sound complex has a high diversity of habitats and communities characteristic of different salinities, in contrast to the Fal and Helford. Some of these support extremely rich marine flora and fauna, which include abundant southern Mediterranean-Atlantic species rarely found in Britain, such as the carpet coral Hoplangia durotrix. Particularly notable habitats include (i) littoral and sublittoral limestone reefs extensively bored by bivalves and harbouring a rich fauna; (ii) offshore sublittoral tide-swept reefs; (iii) tide-swept limestone channels with animal communities rarely encountered in other marine inlets; and (iv) subtidal sediments with rich and often diverse invertebrate communities.

• 1170 Reefs

  Plymouth Sound in south-west England has a wide variety of intertidal and subtidal reef biotopes. Of particular importance are the limestone reefs running along the northern shore from West Hoe to Batten Bay, which are one of only two coastal areas in south-west Britain with Devonian limestone. This relatively soft rock is extensively bored by the bivalve Hiatella arctica and the spionid worms Polydora spp., and harbours a rich fauna. In the sublittoral this steep-sided, wave-sheltered reef is dominated by a dense hydroid and bryozoan turf with anemones and ascidians. A number of rarely-recorded low shore biotopes also occur along the shores from Devil’s Point to Batten Bay, at Wembury, Penlee, Hoo Lake Point, and in the mouth of the River Yealm. The sublittoral is of particular importance for its kelp- and animal-dominated habitats. The area off Batten Bay contains the south-western kelp Laminaria ochroleuca, together with other uncommon species including the rare sea slug Okenia elegans and trumpet anemone Aiptasia mutabilis. Most circalittoral rocky reefs occur in areas of the Outer Sound, such as off Wembury, the Mewstone, Penlee Point and south of the breakwater. In the approaches to Plymouth Sound, abundant populations of the slow-growing, long-lived, nationally important pink sea-fan Eunicella verrucosa occur.

• 1330 Atlantic salt meadows (Glauco-Puccinellietalia maritimae)

  This site is representative of a ria system in south-west England. The well-developed salinity gradient supports Atlantic salt meadow together with natural transitions to brackish and freshwater communities, including reedbeds supporting the only UK population of triangular club-rush Schoenoplectus triqueter. Some stands of saltmeadow are structurally and botanically diverse and include sea club-rush Scirpus maritimus and saltmarsh rush Juncus gerardii, with red fescue Festuca rubra, sea rush J. maritimus and thrift Armeria maritima at higher levels. The locally common parsley water-dropwort Oenanthe lachenalii is also found in some parts of the site, and there are stands of sea-purslane Halimione portulacoides, which is unusual in Cornwall. The Atlantic salt meadows make a vital contribution to the structure and function of the estuary and the other habitats within it.

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

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

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

• 1441 Shore dock Rumex rupestris

  One of the chief rocky-shore strongholds for shore dock Rumex rupestris on the UK mainland, in 1999 comprising 15 colonies and 42 plants. The site also holds a sizeable area of additional suitable habitat.

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

• 1102 Allis shad Alosa alosa