Jncc coastal Directories Project Region 11 The Western Approaches

which limpets and barnacles dominate.  Sheltered shores
have a greater dominance of algae, particularly the knotted
wrack Ascophyllum nodosum, which provides shelter for the
anemone Actinia equina, winkles and small crustacea.
The Lundy marine algal flora is very rich and totals
316 species, many of which are southern in origin.  The
sublittoral fringe is characterised by the kelps Alaria
esculenta and Laminaria digitata, the rock surface being
almost entirely covered by pink encrusting calcareous algae.
Below this, a kelp forest of Laminaria hyperborea extends to
8 m depth below chart datum, with foliose algae continuing
to 22 m.  The richest animal communities occur below the
zone of algal domination, with erect and encrusting
sponges, sea anemones, soft corals and sea fans in amongst
a turf of hydroids and bryozoans.  On vertical and
overhanging rock surfaces off the sheltered east coast are
communities of great scientific interest, which include the
rare cup corals Caryophyllia inornatus, Hoplangia durotrix,
Leptopsammia pruvoti and the soft coral Parerythropodium
coralloides (see also 
section 5.4
).  Other colourful
Mediterranean-Atlantic species that thrive in similar
conditions include the anemone Parazoanthus axinellae, the
sea fan Eunicella verrucosa and the soft coral Alcyonium
glomeratum.  Monitoring studies over a number of years
have found many of these species to be very long-lived and
slow-growing and to have a poor capacity for recovery
because they replace their numbers slowly at the margins of
their distribution.  The mixed sediments of gravel, mud and
muddy-sand off the east coast of Lundy are colonised by
distinctive communities, several of which are rarely found
elsewhere in Britain.  Burrowing species of particular
interest include the angular crab Goneplax rhomboides, the
anemones Mesacmaea mitchellii and Halcampoides purpurea,
and the eel-like red band fish Cepola rubescens.  
Table 4.2.2
summarises the importance of the marine communities of
high scientific interest around Lundy.
From Morte Point eastwards, the coastline resumes a
north-facing aspect, with rocky shores interspersed with
small sandy coves backed by high cliffs.  Many species reach
the eastern limit of their distribution here, as a transition
occurs between the open coast and the Bristol Channel.  The
area from Morte Point to Combe Martin has been identified
by English Nature (1994a) as a Sensitive Marine Area
(extending 2-3 km offshore) and in 1994 was also declared a
Voluntary Marine Conservation Area.  The rocky shores are
moderately exposed to wave action and contain a variety of
habitats.  At Rockham Bay, boulder-filled gullies, abundant
rockpools and overhanging surfaces add to the overall
interest of the site.  Further east at Smallmouth, overhanging
and vertical rock surfaces support rich communities.  A
number of rare species have been recorded from the coast
between Ilfracombe and Combe Martin, including the cup
corals Balanophyllia regia and Hoplangia durotrix and the
colonial anemone Isozoanthus sulcatus (see also 
section 5.4
).
In addition, several species rarely recorded on the shore are
present, such as the Devonshire cup coral Caryophyllia
smithii and the sponges Polymastia mammilaris and Tethya
aurantium (English Nature 1994a).  Sublittoral habitats and
communities for this section of coast are best represented in
the area from Rillage Point to Sandy Bay (Hiscock 1981).  To
the east of Combe Martin, Wild Pear Beach was considered
by Powell et al. (1978) to be of marine biological importance.
The bladderless form of bladderwrack Fucus vesiculosus var.
evesiculosus was noted at more exposed locations, and two
other species of particular interest were the strawberry
anemone Actinia fragacea and the honeycomb worm
Sabellaria alveolata.  Beyond Combe Martin, the shores of
Exmoor are predominantly of boulders with occasional
rocky reefs and some stretches of sand, backed by steep
cliffs.
The Inner Bristol Channel: Foreland Point to Nash Point
Foreland Point marks the western limit of a transition zone
to the inner Bristol Channel/Severn Estuary biota, with a
strong boundary being present a little further to the east in
Porlock Bay (Hiscock 1981).  A similar boundary is found on
the northern side of the Bristol Channel in Swansea Bay.
The Severn Estuary has been proposed as a possible SAC for
its sublittoral sandbanks, intertidal mudflats and sandflats
and estuarine habitats.  The physical conditions that exist
within the estuary have a direct effect on the marine
communities present.  Besides the inflow from the River
Severn itself, the estuary receives a large volume of fresh
water from five other rivers: the Parrett and Avon on the
south shore and the Wye, Usk and Taff on the north shore.
This leads to a gradual reduction in salinity the further east
one goes.  It also introduces a considerable load of silt to the
estuary, kept in suspension by strong tidal streams resulting
from the particularly large tidal range.  The scouring action
of this silt-laden water reduces larval settlement on the few
rocky outcrops present.  Shallow areas sheltered from these
streams may consist largely of ‘liquid mud’, providing very
poor conditions for colonisation by benthic species.  
The estuary contains a variety of intertidal habitats,
which makes it one of the largest and most important
intertidal zones in Britain.  Thirteen community types have
been identified from areas of littoral sediment within the
Severn Estuary (Severn Tidal Power Group 1989).  Their
distribution appears to be determined primarily by
sediment type and the level of consolidation, with salinity
being of lesser importance.  Communities within sediments
are characterised by polychaete worms (the most dominant
species being ragworms Nereis spp. and Neanthes spp. and
the lugworm Arenicola marina) and amphipod crustacea
(Corophium spp. and Bathyporeia spp.); those on top of the
sediment are characterised by gastropod molluscs (in
particular the spire shell Hydrobia ulvae).  The rich
invertebrate biomass present within these extensive
intertidal sediment flats supports internationally important
numbers of wading birds.  Limited patches of eelgrass are
present on some sheltered mudflats and sandbanks.  All
three species of Zostera occur, with the most common,
Z. marina, extending to 4 m depth below chart datum
(English Nature 1994a).  Dives were undertaken off Porlock
Bay, Greenaleigh Point and Watchet as part of the South-
west Britain sublittoral survey (Hiscock 1981).  All of these
sites had a low species richness compared with open coast
sites further west.  Algae were recorded only above chart
datum level.  Stable hard substratum was characterised by
the reef-building polychaetes Sabellaria alveolata and
Sabellaria spinulosa, with the sea squirt Dendrodoa grossularia,
mussels Mytilus edulis and the polychaete Polydora ciliata
common at some sites.  
In the sublittoral, the Severn Tidal Power Group (1989)
identified ten species associations within the Severn Estuary
from grab samples, the associations again being determined
largely by sediment type and exposure to tidal currents.
Region 11  Chapter 4  Marine and estuarine environments
72

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