Page 71 - Alderney Regional Environmental Assessment of Renewable Energy: Environmental Report

Alderney Regional Environmental Assessment of Renewable Energy:
Environmental Report
human activities and are a Biodiversity Action Plan habitat in the UK. This particular eelgrass
bed is notated on the Admiralty Chart as an anchorage (Wood, 2007).
Seastar 2010 Survey
Seastar Survey Ltd. undertook an acoustic and environmental baseline survey of an area to the
south of Alderney encompassing a sandbank area known as the Alderney South Banks
(Figure 11) (Axelsson et al., 2011). A summary of the habitats and species recorded in the
Alderney South Banks survey area are provided in Appendix B, Table B1.
The seabed environment in all the Alderney South Banks survey area was dominated by
coarse sand and shell sand material, particularly in the southern and central sections of the
survey area. Coarse sand was typically found in gullies and channels as well as in the
surrounding seabed environments but also often as a thin layer across the rocky outcrops.
Rocky habitats were found in the area to the northeast which is dominated by a mixed rocky
seabed environment consisting of predominantly cobbles and boulders with sections of
bedrock. There is also a rocky outcrop section centrally along the southern boundary of the
survey area.
A total of 16 biotopes / biotope complexes were identified in the Alderney South Banks survey
area (see Table B1, Appendix B). The SS.SCS.CCS biotope complex was the most frequently
identified habitat in this study, characterised by coarse sand, sand waves and very little visible
fauna or flora (Axelsson et al., 2011).
The CR.HCR.FaT.CTub biotope, known as tide-swept communities or tidal rapid communities,
is of national importance, listed under the UK Biodiversity Action Plan (UKBAP, 2008). During
the Alderney South Banks survey this biotope was identified at the edges of the survey area in
areas surrounding the main sandbank. The marine life associated with these habitats is
abundant in animals fixed on or in the seabed, and typically include soft corals, hydroids (sea
firs), bryozoans (sea mats), large sponges, anemones, mussels and brittlestars in dense beds
(UKBAP, 2008).
The CR.HCR.XFa.ByErSp biotope is found on wave-exposed circalittoral rock in moderate to
strong tidal streams. It is characterised by bryozoan turf and erect sponges but there is some
variability within this biotope and a large number of species might be present. In the current
survey area this biotope was primarily found along the north-eastern boundary but a few
locations were also found centrally along the southern boundary (Axelsson et al., 2011).
From a total of 11 grab samples taken within the Alderney South Banks survey area a total of
898 individuals from 17 taxa were identified. Overall, the macrofauna were dominated by
Annelida, which represented 98.6% of the total individuals found. Crustaceans and
Echinoderms contributed with 1% and 0.4% respectively. In general, the faunal diversity was
low at all of the sites. The sites sampled in the south of survey area had highest total number
of individuals and different taxa but low diversity and low equitability. These sites were
characterised by extremely high numbers of one taxa (Polygordius sp.). The sites to the north
of the survey area had fewer total individuals and species, but the numbers were more evenly
spread across the taxa present, resulting in higher diversity values (Axelsson et al., 2011).
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