Coralline algae

Coralline algae are red algae in the Family Corallinaceae of the order Corallinales characterized by a thallus that is hard as a result of calcareous deposits contained within the cell walls. Unattached specimens (maerl, rhodoliths) may form relatively smooth compact balls to warty or fruticose thalli. Many are typically encrusting and rock-like, found in tropical marine waters all over the world. They play an important role in the ecology of coral reefs. Colors are most typically pink or some other shade of red, but may be purple, yellow, blue, white or gray-green. Sea urchins, parrot fish, limpets (molluscs) and chitons molluscs feed on coralline algae.

A close look at almost any intertidal rocky shore or coral reef will reveal an abundance of pink to pinkish-grey patches, splashed as though by a mad painter over rock surfaces. These patches of pink paint are actually living algae: crustose coralline red algae. The red algae belong to the division Rhodophyta, within which the coralline algae form a distinct, exclusively marine order, the Corallinales. Coralline algae are widespread in all of the world's oceans, where they often cover close to 100% of rocky substrata. Many are epiphytic (grow on other algae or marine angiosperms), or epizoic (grow on animals), and some are even parasitic on other corallines. Despite their ubiquity, the coralline algae are poorly known by ecologists, and even by specialist phycologists (people who study algae). For example, a recent book on the seaweeds of Hawai'i does not include any crustose coralline algae even though corallines are quite well studied there and dominate many marine areas.