Page 68 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
The greatest diversity of sponges was at Braye Rock (Site 11a) with 18 species recorded.
Many of these were typical of clean water rocky environments in SW Britain with such
conspicuous species as the hedgehog sponge, Polymastia boletiformis, elephant-hide sponge,
Pachymatisa johnstonia and yellow staghorn sponge, Axinella dissimiis. A similar variety of
sponges was present at the other two deeper circalittoral sites, Les Étacs (Sites 13a and 14a)
and The Grois Rocks (Site 7a).
The three most commonly recorded molluscs all had a widespread distribution and are
common around much of the British Isles. The grey topshell, Gibbula cineraria is commonly
found on seaweeds in shallow water, the painted topshell, Calliostoma zizyphinum is rarely
found on the shore but commonly seen on shallow sublittoral rocks, and the netted dog whelk,
Hinia reticulata is a scavenger and seen both on rocks and soft sediments. The most
significant mollusc recorded was the ormer, Haliotis tuberculata, the signature mollusc species
of the Channel Islands. This species was recorded at three of the shallow water sites (Sites
4a, 10a and 12a) however it is likely to be much more widespread. The ormer is not found on
the northern side of the English Channel and thus the Alderney records are likely to be the
most northerly (Wood, 2007).
A wide range of seaweeds were recorded within the shallow coastal sites. The greatest
diversity of species was found at Cats Bay/Les Hommeaux Florains (Site 4a), The Lugg at
Burhou (Site 15a) and in Longis Bay (Site 1a). The deeper sites had few seaweeds and the
diversity was also low in Hannaine Bay (Site 12a) probably due to the exposure and nature of
the seabed (Wood, 2007).
The brown seaweeds include most of the large species, including the kelps. In most parts of
the British Isles the primary kelp forest species is cuvie, Laminaria hyperborea. Whilst this
species is commonly recorded on Alderney, particularly deeper down, two other kelps are
equally common. Furbelows, Saccorhiza polyscides, distinguished by its flat belt-like stalk,
typically colonises disturbed areas. Its prevalence on Alderney may well reflect the level of
disturbance occurring naturally through winter storms and the strong tidal streams. The
densest forests of this species were in shallow water at Bibette Head (Site 8a) and in Hannaine
Bay (Site 12a). The third forest kelp is the golden kelp, Laminaria ochroleuca . This is a south
westerly species only common in England in the Isles of Scilly. In Alderney it is most common
at tide-wept sites such as outside Les Hommeaux Florains (Site 4a) and in St Esquere Bay
(Site 3a). The peacock’s tail, Padina pavonica, a leafy brown seaweed, was also recorded in
Longis Bay (Site 1a). It has very restricted distribution in the British Isles with relatively few
records on the south coast of England (Wood, 2007).
Seasearch 2008 Survey
A further three sites were surveyed by Seasearch in 2008 to include habitats and biotopes
which were under-recorded in the 2007 survey. They were all wave and tide exposed sites
with rocky surfaces in the lower infralittoral and circalittoral zones (Figure 11). A total of 62
animal species were observed at the three sites, of which six had not been recorded in 2007.
Seaweeds were not recorded, except for the large brown kelp characterising species. These
were represented by the biotopes IR.HIR.KFaR - Kelp forest on high energy infralittoral rock -
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