I’ve noticed the grazing marks of limpets on the sea defences before, but today was struck by the small grazed areas higher up. On inspection, these proved to be small bubbles in the concrete that were colonised by tiny periwinkles, several in each bubble, and each with its own little territory. There are always large colonies of adult winkles (Littorina littorea) on the limestone platforms on the beach, but I had noticed lots of tiny ones on my last couple of expeditions, and perhaps those up the wall were taking advantage of the shelter provided away from the waves.
The photo above shows where two or three limpets, lurking in the drain, venture out to eat the algae growing on the wall. Close up, you can see the tiny serrations from their radulae (toothed tongue-like organs).