COUNTRYSIDE COUNCIL FOR
WALES
SITE OF SPECIAL
SCIENTIFIC INTEREST:
CITATION
YNYS MÔN GLANNAU PORTHAETHWY
Local Planning
Authority: CYNGOR SIR YNYS MÔN
Date of
Notification: 1957, 1971, 2003
National Grid
Reference: SH 581740 to SH 5417122?11
OS Maps: 1:50,000
Sheet number: 115
1:10,000
Sheet number: SH57SE & SH57SW
Site Area:
67.5 6 ha (approx)
Description:
The site extends along 4
km of the shore of Menai Bridge/Porthaethwy in the Menai Strait from Britannia
Bridge to Craig y Don, and has been selected for its marine biological
features. This south-east facing shore
is sheltered from wave-action and consists of a mixture of mud, bedrock,
pebbles, cobbles and boulders. The
shores of the islands of Ynys Gorad Goch, Ynys Welltog, Ynys Benlas, Ynys
Tysilio, Half Tide Rock, Ynys Faelog, Ynys Tobig, Ynys Gaint, Ynys Castell and
Ynys y Big are also included in the site.
The shore is
of special interest as it is the most extensive sheltered rock shore in the
area between Bardsey Island and Great Orme’s Head and because it supports the
greatest diversity of marine plant and animal communities on this type of shore
within this area. The shore is also
important for the presence of five marine communities
of restricted national distribution, five diverse rockpool and overhang
communities, and for exhibiting the most comprehensive community zonation patterns characteristic
of sheltered rocky shores.
In areas such as Ynys
Welltog and beneath the Menai Bridge, rocky shore communities form visible
‘zones’ down the shore. Such patterns
of zonation are the result of different species’ tolerance’s to desiccation,
temperature extremes and sunlight and their differing abilities to compete with
other species for space. Above mean
high water, rock surfaces subject to sea-spray support a zone of yellow and
grey lichens. Beneath this zone the
black-tar lichen Verrucaria maura grows on bedrock, cobbles and pebbles,
forming a wide band. A band of channel
wrack Pelvetia canaliculata and spiral wrack Fucus spiralis
occurs just below this level, followed by successive zones lower down the shore
of knotted wrack Ascophyllum nodosum, bladder wrack Fucus vesiculosus,
and serrated wrack Fucus serratus.
Mixed kelps such as oarweed Laminaria digitata, sugar kelp Laminaria
saccharina and cuvie Laminaria hyperborea dominate the lower reaches
of the shore in a narrow band, with a diverse range of associated seaweeds
including sea-oak Halidrys siliquosa, bootlace weed Chorda filum,
and the red seaweeds Cystoclonium purpureum, Cryptopleura ramosa,
Phycodrys rubens and species of Ceramium.
The area of the Menai
Strait known as the Swellies experiences strong tidal currents of up to 8 knots
during spring tides and, as a result, supports a wide range of filter-feeding
animals, including four tide-swept communities of restricted national
distribution. After the Menai Strait,
the second largest concentration of these communities in Wales is within
Milford Haven, with a few small patches of certain of these communities on the
Gower Peninsula, Ramsey Island and St. Tudwal’s East. These tide-swept communities are individually characterised by
knotted wrack, serrated wrack on bedrock, serrated wrack on mixed substrata, or
by oarweed, as well as a diverse array of filter-feeding animals. Such species, occurring on seaweeds and rock
surfaces, include the sponges Hymeniacidon perleve and Esperiopsis
fucorum, the bryozoans Dynamena pumila, Flustrellidra hispida,
Membranipora membranacea and Bugula plumosa, the ascidian Botryllus
leachi and star ascidian Botryllus schlosseri, and hydroids. Near Church Island an abundant population of
the daisy anemone Cereus pedunculatus is associated with the tide-swept
oarweed community. Another unusual
community – species of small marine worms and molluscs in sheltered muddy
gravel – is found at three locations along this shore. In Wales, this community is restricted to
the Menai Strait and Milford Haven.
Distinct
communities of plants and animals inhabiting rockpools and the surfaces under
rock overhangs are particularly diverse on this shore. Sediment-floored rockpools with fucoids and
kelps and hydroid-dominated pools on mixed substrata are present throughout the
site. Deeper rockpools dominated by
serrated wrack and oarweed are found on the shore between the two bridges, and
on Ynys Gorad Goch. Overhanging
surfaces on the Menai Suspension Bridge support a diverse community that
includes purse sponge Grantia compressa, breadcrumb sponge Halichondria
panicea, the sponge Ophilitaspongia seriata and the red seaweeds Lomentaria
articulata, Membranoptera alata, and dulse Palmaria palmata. Other lower shore rock overhangs on the site
support a diverse community of filter-feeding animals, such as sponges,
ascidians and bryozoans. Species
commonly found here include the sponges Hymeniacidon perleve, Haliclona
rosea and breadcrumb sponge, the bryozoan Dynamena pumila, dahlia
anemone Urticina felina, plumose anemone Metridium senile and the
star ascidian.
Owing
to its close proximity to Traeth Lafan, an internationally important site for
wading birds and wildfowl, relatively undisturbed parts of this shore provide
important high tide roost areas for waders that feed at Traeth Lafan and
elsewhere in the Menai Strait. For
example Ynys y Bîg provides an important roost site for oystercatchers. Additionally, otters have been recorded in
and around the Afon Cadnant.
Remarks:
Certain areas of the site below mean high water form part of Y Fenai a Bae Conwy/Menai Strait and Conwy Bay candidate Special Area of Conservation (cSAC), under the EC Habitats Directive (Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora 1992). The site contains areas of Intertidal Mudflats and Sandflats and Reefs; habitats listed on Annex I of the Directive which are important features of the cSAC.
Between 1957 and January 2001, the site was notified as
Menai Strait Shore SSSI under the National Parks and Access to the Countryside
Act, 1949.
This
site is part of the Ynys Môn AHNE/ Isle of Anglesey Environmentally Sensitive Area
andArea of Outstanding Natural Beauty. both I
think.