Arthrocardia species maybe

A seaweed is a marine plant belonging to the group called Algae. Some are permanently submerged in the sea and commonly seen when washed up on the coast after storms. The better-known ones are those growing in the intertidal range, i.e. attached to some object between the low tide and high tide lines and therefore more available for inspection.

The plant in picture is thought to be a Coralline species, a red seaweed that deposits lime upon its surfaces. Corallines are common along the South African coast, found in pools and gullies. In warmer waters the Corallines contribute to the formation of coral reefs.

The plant in picture may belong in the Arthrocardia genus, its segments flattened. Plants growing near the high tide line tend to become bleached on the side facing the sun, the other side remaining brownish pink. Arthron is a Greek word meaning joint and cardo is a Latin word meaning hinge (Seagrief, 1967; http://southafrseaweeds.uct.ac.za).