Intertidal Monitoring of Sabellaria alveolata Reefs in Pen Llyn a'r Sarnau Special Areas of Conservation (SACs) 2010 dataset https://portal.medin.org.uk/portal/start.php?tpc=007_NRW_DS114458 The Habitats Directive establishes that the management of Special Areas of Conservation (SACs) should aim to achieve the favourable conservation status of habitat and species features listed within its Annex I and Annex II. For SACs in Wales, the Countryside Council for Wales (CCW) is therefore required to report on a regular basis on whether features are in favourable conservation status. Honeycomb reef worm Sabellaria alveolata is a sedentary, tube-dwelling polychaete most commonly found on rocky substrata in the lower shore and shallow subtidal zones of marine and estuarine areas. The honeycomb reef worm is a UK BAP Priority Habitat (BAP habitats are now Habitats of Principal Importance/Priority Habitats). Honeycomb worms build tubes from sand and shell fragments. They are found on the lower part of rocky seashores but they also need a sand supply for tube-building. They are found on the lower part of rocky seashores but they also need a sand supply for tube-building. Pen Llyn a'r Sarnau SAC is designated for five Annex 1 habitats and four subsidiary ones. Of these, Estuaries and their constituent mudflats, sandflats and reefs, large shallow inlets and bays with intertidal Zostera beds, populations of the shingle-dwelling amphipod Pectenogammarus, piddocks in clay and lower shore boulder communities and Reefs, particularly biogenic reefs of Sabellaria alveolata are the main habitats of interest within the intertidal areas of the SAC. The purpose of this data capture was to monitoring the extent of Sabellaria alveolata reefs. Field work was carried out during five days of spring tides, 6th to 10th July 2009. Data quality and confidence considered high as all surveys were completed by professional and experienced marine field surveyors. 20100731