algae beach cliff coastline eroded erosion Great Britain hillside natural nature Pembrokeshire rocks sand sea seaweed shore united kingdom view wales water welsh blue coastal danger edge island rock summer surf wild anchorage green moored Skomer yacht boat ferry ship animals Balanus barnacles coast creature crustacea limpet marine Mollusca Patella vulgata sealife auk beak bird feet fly Fratercula arctica puffin Skomer Island stretch unfold webbed wings estuary home house low manor Mawddach mudbanks peace promontory quality sandbanks scene shingle tidal tide cattle cows grass islands landscape mammals peaceful relax rest tranquil Barmouth bridge Causeway hills line mountains Mud railway resort angry beat dash fierce furious pound spray spume waves