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

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 marineorder, the Corallinales. There are over 1600 described species of nongeniculate coralline algae.^[5]

The corallines are presently grouped into two families on the basis of their reproductive structures.^[6]

Coralline algae are widespread in all of the world’s oceans, where they often cover close to 100% of rocky substrata. Many areepiphytic (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 Hawaii does not include any crustose coralline algae, even though corallines are quite well studied there and dominate many marine areas.

Corallines live in varying depths of water, ranging from periodically-exposed intertidal settings to 270 m water depth (around the maximum penetration of light).^[11] Although some species can tolerate brackish^[11] or hypersaline^[12]waters, no freshwater species exist. (Some species of the morphologically-similar, but non-calcifying,Hildenbrandia, however, can survive in fresh water.) A wide range of turbidities and nutrient concentrations can be tolerated.^[11]

(From Wikipedia, May 31st, 2012)