Extremely sheltered shore on Menai Strait with typical dense algal cover. Sweeping movement of algal fronds inhibits barnacle establishment apart from on occasional steep surfaces which limpets keep free of alga by grazing sporelings. N. lapillus ,feeding on barnacles, are concentrated on such “oases”, and, if the barnacles are exhausted, may turn their predation onto the limpets if no Mytilus available.