The Severn Estuary lies on the south west coast of Britain at the mouth of four major rivers (the Severn, Wye, Usk and Avon) and many lesser rivers. The immense tidal range (the second highest in the world) and classic funnel shape make the Severn Estuary unique in Britain and very rare worldwide. The intertidal zone of mudflats, sand banks, rocky platforms and saltmarsh is one of the largest and most important in Britain. The estuarine fauna includes: internationally important populations of waterfowl; invertebrate populations of considerable interest; and large populations of migratory fish, including the nationally rare and endangered Allis Shad Alosa alosa. The SSSI forms the major part of a larger area of estuarine habitat, which includes the Upper Severn Estuary, the Taf/Ely Estuary and Bridgwater Bay.
The estuary has a diverse geological setting and a wide range of geomorphological features, especially sediment deposits. It is important for the interpretation of coastline dynamics and land-forms, and also past changes, in sea level, sediment supply, climate and river flow. The estuary’s overall interest depends on its large size, and on the processes and interrelationships between the intertidal and marine habitats and its fauna.
Beds of eel-grass Zostera spp. occur on the more sheltered mud and sand banks. The estuary fringes have large areas of saltmarsh. These are generally grazed by sheep and/or cattle, a significant factor determining the plant communities. A range of saltmarsh types is present, with both gradual and stepped transitions between bare mudflat and upper marsh. Glassworts Salicornia spp. and Annual Sea-blite Suaeda maritima colonise bare mud on the lower saltmarshes, and disturbed areas at higher levels. Common Cord-grass Spartina anglica is abundant on the seaward fringes of marshes, where it occurs as dense monocultures, or with other species, such as Sea Aster Aster tripolium, Greater Seaspurrey Spergularia media and Common Saltmarsh-grass Puccinellia maritima. The middle marsh is mainly dominated by Common Saltmarsh-grass, and frequent associates include Sea-milkwort Glaux maritima, English Scurvygrass Cochlearia anglica and Sea Arrowgrass Triglochin maritima, together with two nationally scarce plants Bulbous Foxtail Alopecurus bulbosus and Slender Hare’s-ear Bupleurum tenuissimum. There are a few localities for an uncommon middle marsh community, which is characterised by Sealavender Limonium vulgare and Thrift Armeria maritima. Prominent species on the upper marsh are Red Fescue Festuca rubra and Saltmarsh Rush Juncus gerardi. Nationally scarce species occurring on the upper marshes include Sea Clover Trifolium squamosum and Sea Barley Hordeum marinum. Highly saline drying pans on the upper marsh support a community with abundant Reflexed Saltmarsh-grass Puccinellia distans and Lesser Seaspurrey Spergularia marina. The highest saltmarsh around the driftline is usually dominated by Sea Couch Elymus pycnanthus, with Spear-leaved Orache Atriplex prostrata. Some brackish pools and depressions on the upper marshes have small stands of Common Reed Phragmites australis or Sea Club-rush Scirpus maritimus. Corn Parsley Petroselinum segetum, a European rarity, occurs within the site.
This site is currently under consideration for inclusion in the new UK MPA network. Having marine components does not automatically qualify a site to be part of the new MPA network. As such, the marine components of this site, as well as the management efforts, are being evaluated. Check out our MPApedia page on the UK for more information!
For general information on Severn Estuary Area of Special Scientific Interest (regardless of MPA status), click here.*
*Note: this site is jointly managed by Natural England and Countryside Council for Wales (CCW); the above link will take you to the CCW page on Severn Estuary (Wales); for information from Natural England, click here.
Contacts & Resources
Original data record from World Database on Protected Areas (WDPA) via ProtectedPlanet.net [view record on site].