Phylum: Rhodophyta   Family: Corallinaceae

Lithophyllum incrustans  Philippi, 1837

Pink Paint Seaweed

Some red seaweeds resemble corals because of the hard lime deposits in their cell walls. These coralline seaweeds, as they are known, also form pink crusts on tidal rocks. In recent years scientists have discovered that coralline seaweeds produce chemicals which encourage the larvae of some shellfish, crabs and crayfish to settle on them. Crust-forming coralline seaweeds are known collectively as pink paint

References: 
Fish & Fish (2011) - A Student's Guide to the Seashore;
Bunker, et al - Seaweeds of Britain and Ireland;
Te Ara - The Encyclopedia of New Zealand