Marine coralline algae are calcifying red algae, which have a hard skeleton resulting from the precipitation of calcium carbonate within their cell walls. Coralline algae are abundant and widespread in coastal areas throughout the world, from polar regions to the tropics. They grow from the surface to depths of more than 100 meters; some under intense illumination, others with very dim lighting.

Lythophyllum cabiochae, an example of a non-geniculate coralline. (Photo: Amélie Charnoz)

Coralline algae belong to the family Corallinaceae (see Classification) and are divided into two general types based on their morphology: geniculate corallines and non-geniculate corallines.

Classification

• Kingdom: Protista
• Division: Rhodophyta (Red algae)
• Class: Rhodophyceae
• Subclass: Florideae
• Order: Corallinales
• Family: Corallinaceae (Coralline algae)

Geniculate corallines

Jania rubens, an example of a geniculate coralline. (Photo: Sophie Martin)

The geniculate or articulated corallines are branched and flexible due to the presence of flexible uncalcified joints called genicula, between calcified segments. They grow as individual plants on rocks or granular substrates, but can also grow as epiphytes on shells or other algae. They primarily occupy intertidal and subtidal coastal areas.

Non-Geniculate corallines

Lithothamnion corallioides, an example of a non-geniculate coralline. (Photo: Marie-Dorothée Castets)

The non-geniculate or non-articulated corallines may form crusts attached to rock, pebbles, coral skeletons, shells, or other algae, or they may live unattached on the hard or (mostly) soft substrate, growing as nodules, rhodoliths or as branched structures. They develop in the intertidal zone and in the deep subtidal.

Coralline algae are of ecologic and economic importance. Their rigid structure contributes to the formation of numerous habitats such as coral reefs in the tropics or coralligenous habitats in the Mediterranean Sea. When unattached, coralline algae can accumulate at high concentration over a large area, forming Rhodolith beds, which provide habitats for a very high diversity of associated organisms. Coralline algae are also thought to induce settlement and recruitment of invertebrates. Coralline algae are used for various economic purposes such as soil conditioner, treatment for acid drinking water, animal food additive or pharmaceutical products. However, their intensive extraction, especially for unattached coralline algae, causes the reduction and the degradation of their community.

Further Reading

• Johansen, H.W. 1981. Coralline algae, a first synthesis. CRC Press, Boca Raton, FL, 239 pp.