Acoustic Monitoring of the Extent of the North Llyn Modiolus Reef dataset https://portal.medin.org.uk/portal/start.php?tpc=007_NRW_DS109891 Biogenic horse mussel (Modiolus Modiolus) reef is an important feature of the Pen Llyn a'r Sarnau Special Area of Conservation (SAC). The reef has high biodiversity and is vulnerable to anthropogenic activities, such as benthic fishing. The mussel reef forms an undulating surface that is significantly different to the surrounding seabed and therefore acoustic monitoring methods can be used to monitor changes in extent and identity areas of potential damage. Work is carried out on the north Llyn horse mussel reef in Pen Llyn a'r Sarnau jointly by Countryside Council for Wales (CCW) and University of Wales Bangor. The purpose of this data capture was to: - Measure extent and temporal changes within the of the Modiolus reef in the Pen Llyn a'r Sarnau SAC. - Investigate the health of the reef and for signs of anthropogenic activity within the area. An area approximately 10km by 6km, adjacent to the Pen Llyn coast, south-west of Porth Dinllaen, approximately 1.5km off shore was surveyed. All data is processed to reduce errors (e.g. positional corrections). Acoustic data is subject to ground-truthing using drop down videos captured as part of a separate project. As of April 1st, 2013 data is held and managed by Natural Resources Wales (NRW). 20130401