Surveys of Sea Caves in Welsh Special Areas of Conservation (SAC) dataset https://portal.medin.org.uk/portal/start.php?tpc=007_NRW_DS110463 Inventorial survey as a first step for former Countryside Council for Wales (CCW), now part of Natural Resources Wales (NRW), to develop sensitivity management and monitoring for submerged or partially submerged caves. Submerged or partially submerged caves are an Annex 1 habitat listed under the Habitats directive. Caves vary in size, from only a few metres to more extensive systems, which may extend hundreds of metres into the rock. There may be tunnels or caverns with one or more entrances, in which vertical and overhanging rock faces provide the principal marine habitat. Sea cave communities vary considerably depending on the structure and extent of the cave system, their degree of submergence and of exposure to sand scour and wave-surge, and their geology. Caves are typically colonised by encrusting animal species but may also support shade-tolerant seaweeds near their entrances. Physical conditions, such as inclination, wave surge, scour and shade, change rapidly from cave entrance to the inner parts of a cave, and this often leads to a marked gradation in the communities present. Surveys were set up to identify a baseline and trial survey methodologies in order to establish surveillance and monitoring programmes for the feature. 24 caves (and tunnels) were described. They include caves that are wholly Intertidal, wholly subtidal and ones with both littoral and sublittoral elements. They range from caves that extend 1-3 meters into the cliff to ones that extend up to 100 meters into the cliff. Inventorial survey as a first step for CCW to develop sensitivity management and monitoring for submerged or partially submerged caves. 24 caves across Pembrokeshire Marine Special Area of Conservation (SAC), Cardigan Bay SAC, Pen Llyn a'r Sarnau SAC and Menai Strait and Colwyn Bay SAC. All measurements were taken to a standard protocol as described in the CCW Marine Monitoring Report no. 6. Specimens were fixed and preserved. 20030430