Hard Substrate

There are extensive rocky shores along much of the Estuary, covering an area of approximately 1,500 ha. These intertidal areas are typically comprised of rocks, boulders, mussel/cobble scars, rocky pools and shingle. The largest areas of hard substrate are located towards the outer Estuary at Brean Down, Anchor Head and Sand Point.

The largest eel grass beds (Zostera spp.) in Wales occur on the more sheltered mixed hard substrate areas around the Welsh side of the Second Severn crossing. The Zostera beds in the Severn Estuary are unusual in that they occur in areas of mixed cobbles, sand and mud with large boulders; in other parts of Wales they are associated with mudflats.

Intertidal Sabelleria is also part of the hard substrate community of the Severn Estuary, fringing many of the low water marks where conditions are suitable.

Hard substrate habitats provide a wide range of services for estuarine species. The rocky shores of the Severn support a large number of plants and animals, including brown and green algae, barnacles, limpets and winkles. They provide an essential food source and resting place for a wide range of wintering and migratory waterfowl, such as Dunlin and Redshank. Rocky habitats also provide important roost sites at high tide for species such as Knot, Oystercatcher and Curlew.

Rocky intertidal areas are a key ‘supporting habitat’ for the conservation of many important species, including wintering and passage bird features of the SPA and Ramsar site and also the fish assemblage feature of the SAC and Ramsar site.

For more information, please see the Severn Estuary EMS Regulation 33 Conservation Advice Package.