Jncc coastal Directories Project Region 11 The Western Approaches

during winter).  Many marine species recorded within the
islands are unrecorded on the mainland, and some species
considered common on the mainland are rare in the islands.
The exceptionally clear water allows algae to grow at
greater depths than in mainland coastal waters; the kelp
Laminaria ochroleuca for instance has been recorded at depths
of up to 30 m.
Areas of intertidal sediment consist of a coarse-grained
granite sand with rich communities characterised by
polychaetes, bivalves and the burrowing heart urchins
Echinocardium cordatum and E. pennatifidum.  Well-developed
sheltered beds of eelgrass Zostera marina, amongst the best
in Britain, are present between several of the islands, with
an associated diverse community including rare red algae,
anemones, stalked jellyfish, polychaetes, molluscs and
echinoderms (English Nature 1994a).  The communities on
rocky shores vary with the degree of exposure, from the
very exposed shores of the Western Rocks, where only the
hardiest of species survive, to the relative shelter of enclosed
shores, where boulders have rich under-boulder
communities.  Algal communities in particular are
important because of their high species diversity and the
presence of many rarities.  
In the subtidal below the algae-dominated zone, vertical
rock surfaces are dominated by colourful anemones, soft
corals and encrusting sponges.  Deeper still, on the sheltered
east-facing coast of St. Mary’s, several south-western species
are found, including the zoanthid anemone Parazoanthus
axinellae, the rare hard corals Leptopsammia pruvoti and
Hoplangia durotrix and the sea fan Eunicella verrucosa.  A
survey in 1983 identified eighteen sublittoral rock habitats
and six sublittoral sediment habitats within the archipelago,
together with a number of other ‘restricted’ habitats such as
caves, overhangs, crevices and under-boulders (Hiscock
1984).  Most communities identified had a strong southern
element.  Tide-swept cobble habitats had rich algal
communities, considered to be of national importance.
The Marine Park is bounded by the 50 m depth contour,
encompassing all of the islands and rocks.  A number of
Special Areas have been identified within the Park as being
particularly vulnerable to damage, including the intertidal
sandflats between Samson, Tresco and St. Martin’s; areas of
deep sheltered bedrock off the east coast of St. Mary’s; the
boulder shores and rockpools of St. Agnes; sublittoral
pebbles and cobbles in Smith Sound and St. Mary’s Road;
and the exposed Western Rocks.  Monitoring work within
the Marine Park over the past ten years has revealed
marked changes in the populations of the Devonshire cup
coral Caryophyllia smithii (Fowler & Pilley 1992) and the re-
appearance in 1991 of the Zostera ‘wasting disease’ (caused
by a slime mould of the genus Labyrinthula), which
decimated the eelgrass beds in the 1930s and 1940s (Raines
et al. 1993).
Land’s End to Hartland Point
This section of coast has some of the most dramatic coastal
scenery in England, with its rugged cliffs and extensive
sandy bays.  At the southern end of Sennen Cove just north
of Land’s End there are large granite boulders sitting on
bedrock with dense growths of thongweed Himanthalia
elongata on the low shore amongst a luxuriant covering of
red algae.  From Cape Cornwall to St. Ives, the exposed
rocky shores have a typical covering of barnacles, limpets
and fucoid algae.  Within rockpools on the lower shore, the
south-western brown alga Bifurcaria bifurcata and the limpet
Patella aspersa are unusually abundant (Powell et al. 1978).
Extensive bedrock platforms occur in the sublittoral, with
the kelp forest, dominated by the southern species Laminaria
ochroleuca, extending to over 20 m below chart datum
(Hiscock 1981).  Below this, a bryozoan/hydroid turf covers
rock surfaces, with encrusting sponges, barnacles, the soft
coral Alcyonium digitatum, jewel anemones Corynactis viridis
and the white anemone Actinothoë sphyrodeta.
St. Ives Bay and the Hayle Estuary have been declared a
Sensitive Marine Area by English Nature (1994a), largely on
account of their overwintering bird populations.  The
marine life is not particularly outstanding, being typical of
that associated with mud and sand, though of note are the
large numbers of the sponges Leucosolenia spp. and Sycon
ciliatum, and the anemones Anemonia sulcata and Corynactis
viridis, attached to hard substrata.  Published marine
biological information is sparse for the stretch of coast north
from Godrevy Point to Trevose Head.  The most extensive
rocky shores on the north Cornwall coast are found close to
Padstow, at Trevone and Trebetherick.  These were
considered by Powell et al. (1978) to be of primary marine
biological importance because of their rich intertidal flora
and fauna.  Besides the midshore mussel/limpet/barnacle-
dominated zone, unusual features include a low-shore zone
of the brown peacock weed Cystoseira tamariscifolia at
Trevone and the rare Celtic sea-slug Onchidella celtica at
Trebetherick Point.  Sublittoral communities found at The
Bull near Trevose Head were distinctly different from those
further north, being dominated by mussels Mytilus edulis
and the small red sea squirt Dendrodoa grossularia (Hiscock
1981).  Within the Camel Estuary, sandy sediments have rich
populations of the lugworm Arenicola marina and dense
beds of the cockle Cerastoderma edule.  At Rock, the common
mussel Mytilus edulis and the Mediterranean mussel Mytilus
galloprovincinalis have populations alongside each other - an
unusual occurrence.  At the mouth of the estuary, rock
habitats are subject to strong tidal streams and support
dense growths of sponges, sea squirts, hydroids and
anemones.  The small sea squirt Pycnoclavella aurilucens
nears the northern limit of its distribution here.
Below low water on the open coast, much of the sea bed
consists of a flat or gently-sloping sand plain with rock
outcrops and broken reefs.  Sand is clearly an important
influence on the structure of communities in the area, except
around headlands (Hiscock 1981).  The restricted depth
limits of algal species (for instance kelp only extends to 3 m
below chart datum) are attributed to the presence of
suspended sediment in the water column, limiting light
penetration.  Characterising species on bedrock deeper than
15 m include the bryozoan Pentapora foliacea, the sea squirt
Stolonica socialis and the sea fan Eunicella verrucosa.  The
south-west Britain sublittoral survey (Hiscock 1981) found
species richness for benthic communities to be generally
low, with the richest and most representative site for the
area being at Kellan Head.  The whole of the area from
Trevose Head to Boscastle, including the Camel Estuary,
falls within English Nature’s North Cornwall SMA (English
Nature 1994a), and is notable for the variety of habitats and
exposure conditions present.  At Boscastle, rock extends a
considerable distance offshore and is dominated to depths
in excess of 20 m by algae, there being little sand along this
section of coast.
Region 11  Chapter 4  Marine and estuarine environments
70

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