The aim of this study was to investigate an area identified as potentially containing bedrock, stony or biogenic reef, protected habitats listed under Annex I of the EU 'Habitats Directive' (92/42/EEC).
To the north and northwest of Anglesey four such areas had been identified by the British Geological Survey, covering an area of approx 140 km squared. These mapped areas, which were identified as potential bedrock or stony reef, defined the four Survey Areas for this project.