2012 Natural England (NE) Solent Maritime SAC - Intertidal Survey

Centre for Marine and Coastal Studies (CMACS) Ltd were contracted by Natural England to carry out feature condition monitoring on intertidal features within the Solent Maritime Special Area of Conservation (SAC) which encompassed Chichester Harbour, Langstone Harbour, Southampton Water, West Solent and the northern coast of the Isle of Wight. Surveys were based around transects with a 400m wide corridor (i.e. 200m either side of the transect) and with locations for target notes placed at 50m intervals within the survey corridor. Surveys were carried out on foot where the intertidal area was small and/or firm underfoot and from a hovercraft where soft sediments were present. Target notes and photographs of visible flora and fauna were supplemented with 0.01m2 core samples consisting of five faunal replicates and a further one for particle size analysis (PSA), as well as 1m2 quadrats dug out to 20cm to aid biotope classification. Samples were sieved at 0.5mm and all invertebrates enumerated and biomass estimated by wet weight by species. Chichester Harbour was characterised by mud habitats in the upper reaches with sand shores to the south of Thorney Island and near to the harbour mouth. Algal mats were recorded in the upper reaches of the harbour, notably Bosham Channel, where seagrass was also present but extensive beds were only discovered recorded from the southwestern corner of the harbour. Fauna in the muddy areas was dominated by oligochaetes and cirratulid polychaetes especially Tubificoides benedii and Tharyx killariensis as well as the small gastropod Hydrobia ulvae. In sandy areas, the fauna was characterised by the lugworm Arenicola marina, the orbiniid polychaete Scoloplos armiger and tanaid crustaceans. Langstone Harbour was also characterised by mud habitats almost throughout the entire area but with some areas of coarse mixed sediment on the upper shore which supported a wide variety of macroalgae but which also showed signs of bait digging. Algal mats were much more prevalent in Langstone Harbour than in Chichester Harbour but seagrass was also much more extensive. The fauna of the samples from Langstone Harbour was very similar to that of Chichester Harbour with a numerical dominance of cirratulids, oligochaetes and Hydrobia ulvae. In Southampton Water, there was a greater mix of habitats from tide-swept coarse sediment to fine silt and clay. The tide-swept gravels and pebble at the mouth of the Hamble Estuary supported a diverse assemblage of macroalgae and epifauna which included ascidians, barnacles, bivalves and sponges. Within the Hamble Estuary itself, there were very soft fine sediments which supported cockles but there were also thick algal mats which supported large numbers of Hydrobia ulvae but caused anoxia at the mud surface. Soft, fine sediments were also encountered on the western side of Southampton Water from Calshot to Hythe with a fauna dominated by Tharyx killariensis but with large numbers of cockles and Hydrobia ulvae near Calshot itself. On the seaward side of Calshot, to western side of the Beaulieu Estuary, there were coarse mixed sediments which supported ephemeral algae, small actiniarians, and a rich fauna of polychaetes, amphipods and molluscs. There was also a large seagrass bed on the lower shore at Calshot and evidence of bait digging in these areas, particularly at Lepe Beach. Within the Beaulieu and Lymington Estuaries the habitats were fine, soft sediments with a similar fauna to the mud areas of Chichester and Langstone Harbours but with a greater prevalence of ragworm and tellins. The north coast of the Isle of Wight was characterised by protrusions of clay and outcrops of bedrock which supported piddocks and a rich crustacean fauna as well as a variety of macroalgae predominantly fucoids. In addition, the habitats of Thorness Bay included mixed coarse sediment supporting barnacles and littorinids and sand supporting sand mason worms and small patches of seagrass beds. The very sheltered areas of Newtown Harbour and the Medina Estuary where typically mud habitats with cockles and thick algal mat but also with some mixed sediments mid estuary which supported cockle, sponges and littorinids.