The Pembrokeshire coastline is geologically complex, in both the range of rock types and the complexity of faulting and folding and many sea caves can be found here.
Partially submerged, intertidal caves are widely distributed throughout the length of the rocky coast, with the largest known concentrations on St David’s peninsula, Ramsey Island, Skomer Island and the Castlemartin coast.
The distribution of submerged sea caves is poorly known; the few that have been documented have been the result of opportunistic discovery. Individual caves range in size from very small (little more than deep, enclosed overhangs) to extremely large; either very long (such as Ramsey Island, > 50 metres) or high and wide (such as South Pembrokeshire limestone).
Sea caves typically support species that are “out of place” because caves provide areas which are physically different, such as being darker and more sheltered, than immediately outside the cave. Cave species differ according to the rock type of the cave. They often need to be very tolerant of scour and of extreme wave surge.