Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits 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. Only one species lives in freshwater. 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 marine order, the Corallinales. There are over 1600 described species of nongeniculate coralline algae.
The corallines are presently grouped into two families on the basis of their reproductive structures.
Coralline algae are widespread in all of the world's oceans, where they often cover close to 100% of rocky substrata. Only one species, Pneophyllum cetinaensis, is found in freshwater. 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 Hawaii does not include any crustose coralline algae, even though corallines are quite well studied there and dominate many marine areas.
Corallines have been divided into two groups, although this division does not constitute a taxonomic grouping:
the geniculate (articulated) corallines;
the nongeniculate (nonarticulated) corallines.
Geniculate corallines are branching, tree-like organisms which are attached to the substratum by crustose or calcified, root-like holdfasts. The organisms are made flexible by having noncalcified sections (genicula) separating longer calcified sections (intergenicula). Nongeniculate corallines range from a few micrometres to several centimetres thick crusts. They are often very slow growing, and may occur on rock, coral skeletons, shells, other algae or seagrasses. Crusts may be thin and leafy to thick and strongly adherent. Some are parasitic or partly endophytic on other corallines. Many coralline crusts produce knobby protuberances ranging from a millimetre to several centimetres high. Some are free-living as rhodoliths (rounded, free-living specimens).
Thalli can be divided into three layers: the hypothallus, perithallus and epithallus. The epithallus is periodically shed, either in sheets or piecemeal
Corallines live in varying depths of water, ranging from periodically exposed intertidal settings to 270 m water depth (around the maximum penetration of light). Some species can tolerate brackish or hypersaline waters, and only one strictly freshwater coralline species exists. (Some species of the morphologically similar, but non-calcifying, Hildenbrandia, however, can survive in freshwater.) A wide range of turbidities and nutrient concentrations can be tolerated.
Photos Ayia Napa,,,9 mts deep,11.12.2016 by Costas Constantinou