The swiss-cheese rocks of the Dolphin Coast. Weird or what?

While on holiday just north of Durban, in a little town called Salt Rock (complete with ‘Salty’s’ – the hard drinking bar for salted types) we came across a small area of these rocks.

They were just under a headland, so I assume the odd patterning is a result of multiple currents in the undertow and some pumice-like lava rock. I can’t find anything online which explains this kind of wear (primarily on the land-facing side of each rock), but it certainly looks cool.