Bembridge Marine Life
Bembridge and St Helens are situated at the eastern tip of the Isle of Wight on the south coast of England. The area has long been a popular venue for the study of marine life and continues to be important both regionally and nationally for its marine biodiversity. The area is included within the South-Wight Maritime Special Area of Conservation (SAC).
The interest in the region partly stems from the diverse range of marine and maritime habitats in the vicinity including: Rocky Shores, Sandy Shores, Bembridge Harbour, Brackish Lagoons, Sub-littoral Reefs.
The Key Reference, from which most of this information has been taken is:
Collins, K.J., Herbert, R.J.H. & Mallinson, J.J (1990).
The Marine Fauna and Flora of Bembridge and St. Helens, Isle of Wight. Proceedings of the Isle of Wight Natural History & Archaeological Society. 9:41-85. (Journal ISSN 0140-3729)
To the south of Bembridge, the chalk of Culver Cliff extends a short distance below the low water mark. The rapidly receding cliffs, composed of Eocene clays and sands, form a backdrop behind sandy beaches. Bembridge Limestone (Oligocene) forms hard intertidal ledges which extend north to St Helens and below the low-water mark. Soft, easily weathered mudstones between the bands of limestone have caused the formation of eulittoral lagoons which separate the reefs.
The shores along this coast are relatively sheltered from strong prevailing south-westerly winds although a moderate to fresh easterly wind can result in high waves over the ledges. From an ecological
perspective, the shores may be regarded as ‘moderately sheltered’; between 4-5 on the 8 point Ballantine scale (Ballantine, 1961). The spring tide range varies between 3.1-3.9m, and in common with the whole Solent region, experiences a prolonged stand at High Water Spring Tides attributed to the double tide phenomenon local to the Solent region.
The extensive intertidal limestone ledges have been a focus for most of the studies on seaweeds and marine animals. The relatively flat topography helps to retain shallow standing water at low tide creating large pools. This enables some species that normally found lower on the shore, to survive at higher tidal levels e.g. the sponge Halichondria panicea and red alga Chondrus crispus.
The pattern of species distribution on shores immediately south of Bembridge Lifeboat Station is shown in the kite diagram in Fig.1.
Figure 1: Zonation at Bembridge rocky shore
There is a narrow upper ledge of Bembridge Limestone which is colonised by the green alga Enteromorpha, brown spiral wrack Fucus spiralis, rough periwinkles Littorina saxatilis grp. and beadlet sea anemone Actinia equina. A narrow sandy beach, often colonised by lugworm Arenicola marina, separates the upper and middle ledges. The middle ledge is broad and extensive and dominated by serrated wrack Fucus serratus. There are large shallow pools on this ledge that contain many other algal species including the green algae Codium fragile & Cladophora rupestris, invasive brown japanese seaweed Sargassum muticum and red algae Chondrus crispus and Ceramium rubrum. There is also a large population of flat periwinkles Littorina mariae. Shore fish in these pools are common and include the shanny (Blennius pholis), 5-bearded rockling (Ciliata mustela) and Rock goby (Gobius paganellus).
Actinia equina Cladophora rupestris
On the outer edge of this ledge is a narrow zone of limpets (Patella vulgata) and barnacles (Semibalanus balanoides & Elminius modestus). Also found in this area is the dog-whelk Nucella lapillus, purple topshell Gibbula umbilicalis and the red alga Osmundea pinnatifida (=Laurencia pinnatifida). Immediately below the lower ledge are broken limestone boulders where the broad-clawed porcelain crab Porcellana platycheles is common.
Semibalanus balanoides Nucella lapillus
In the Eulittoral lagoons that separate the middle ledge from the outer reefs, the eel grass Zostera marina may be found with associated flora that includes Japanese seaweed Sargassum muticum and pod weed Halydris siliquosa. The stalked jellyfish Halyclystus auricula and snakelocks anemone Anemonia viridis are often found attached to these weeds. Edible crabs (Cancer pagurus) and lobster (Hommarus gammarus) are also found in these shallow waters. The Corkwing Wrasse (Crenilabrus melops) is commonly seen (and caught) in these shallow lagoons.
Halyclystus auricula Cancer pagurus
Hommarus gammarus Crenilabrus melops
The lower and outer reefs are dominated by brown serrated wrack Fucus serratus, the oarweed (kelp) Laminaria digitata and red weeds Chondrus crispus, Lomentaria articulata, Ceramium rubrum, Palmaria palmata and Osmundea (=Laurencia) species. There is also a sizable population of edible periwinkles (Littorina littorea) and grey topshells (Gibbula cineraria). In empty mollusc shells, hermit crabs Pagurus bernhardus are common.
Pagurus bernhardus Carcinus maenas (in berry)
Necora puber Helcion pellucidum
Other decapod crustaceans include the shore crab Carcinus maenas, velvet swimming crab Necora puber, spider crabs Macropodia rostrata, Pisa tetraodon, Maja squinado, squat lobster Galathea squamifera. Attached to the kelp, Blue-rayed limpets Helcion pellucidum occur.
Bembridge Harbour is a busy inlet and harbour to many small craft and fishing boats. At low tide the harbour drains almost entirely and the boats are left to sit on the mud. The north-east side of the Harbour is protected by St. Helens Duver, a sand and shingle spit partly owned and managed by the National Trust. The harbour is fed by the Eastern Yar river, although salinities are not greatly reduced. The harbour and sandy shores at Bembridge Point are important for over-wintering wading birds including Dunlin, Redshank and Sanderling. The invertebrate fauna within the harbour is dominated by annelid worms that include the ragworm Nereis diversicolor, burrowing amphipod Corophium volutator and bivalve mollusc Macoma balthica. All these species are important prey items for birds. Flounder (Platichthys flesus) and Bass (Dicentrarchuslabrax) have been caught in the harbour. At the east end of the harbour a small area of saltmarsh, dominated by Spartina anglica, has colonised the old St Helens Mill Pond. The brown channelled wrack Pelvetia canaliculata may also be found here attached to small cobbles on the upper shore; one of two stations for this species on the Isle of Wight.
Two brackish lagoons have been found behind the harbour embankment wall on the other side of the coast road. These lagoons receive saltwater from the harbour and contain highly specialised species tolerant of hypo and hypersaline conditions. Of particular importance is the rare starlet anemone Nematostella vectensis for which site is the species Type Locality; the first ever description of this species was from material collected here by Stephenson (1935). The lagoon also supports the rare foxtail stonewort Lamprothamnion papulosum.
The typical offshore substrate is a mixture of gravel, sand and flint cobbles although the limestone and chalk reefs do extend a short way below the low water mark. Massive slabs of limestone are also a feature of the underwater environment and the scenery and diversity of marine life is most spectacular here. The sublittoral ecology is influenced much by water depth and substrate type. Below a depth of about 10m, seaweeds are virtually absent, due to low light intensity, and the rocks are covered by hydroids and bryozoans.
Immediately below extreme low water mark there are kelp forests dominated by Laminaria digitata and L. hyperborea. Closer to St.Helens this can be replaced by bootlace weed Chorda filum. Sargassum muticum may also be quite common although does require both shallow and sheltered conditions.
The Sunstar Crossaster papposus has been found at depths of 10m. Red algae are able to grow at the greatest depths and include Plocamium cartilaginum and Callepharis cilliata. The sides of boulders are often covered in sea-squirts including Clavelina lepadiformis, Morchelium argus and sponges Haliclona oculata and Dysidea fragilis. In deeper water the soft coral Alcyonium digitatum (dead-mans fingers) may be found.
Crossaster papposus Clavelina lepadiformis
In the muddy areas, the slipper limpet Crepidula fornicata is common, as it is in much of the Solent. The shells of this species provide a hard substrate for the attachment of epibenthic animals including hydroids Kirchenpaueria pinnata and Hydrallmania falcata. In areas of clean sand the sand mason worm Lanice conchelega and lugworms Arenicola marina may be found together with the burrowing anemone Cereus pedunculatus.
Much of the region is designated for its biological and geological interest as a Site of Special Scientific Interest (SSSI) by English Nature. The presence of rocky reefs are a habitat that is protected within the Special Area of Conservation (SAC). The brackish lagoons are included with the Isle of Wight Lagoons SAC.
Apart from the diverse nature and vulnerability of these communities there are species that are particularly notable and/or rare. Some of these are southern species that are at the edge of their geographic range in the English Channel; limits being set by a variety of factors including intolerance to the cooler winters further east up Channel.
Gibbula umbilicalis (Purple topshell)
Patella ulyssiponensis ( China limpet)
Patella depressa (Black Foot Limpet)
Melarhaphe neritoides (Small Periwinkle)
Aeolidiella alderi (a sea slug)
Anemonia viridis (Snakelocks Anemone)
Cereus pedunculatus (Daisy Anemone)
Other particularly rare and or unusual species recorded include:
Grateloupia filicina var. luxurians