Red coralline alga

Natural History

Since these algae deposit calcium carbonate (limestone) in most of their cell walls, red corallines have the appearance and rough texture of coral. Grazing on these calcified algae would be like eating marble, so most hungry herbivores feed elsewhere.

Coralline algae take two different forms. Articulated species grow upright and have "branches" with flexible, uncalcified joints that withstand strong water motion. Crustose species encrust mostly on rocks, although they may also grow on plants or animals. All the different kinds of crustose algae cover more surface area than any alga species in the world.


Seaweeds—like the coralline algae—live in many ocean habitats. To protect seaweed species, we must learn more about the habitats they depend on and how we can preserve and protect their ocean homes. For instance, red articulated corallines growing in intertidal zones are vulnerable to trampling and other damage, so it's important to tread carefully when you visit tide pools.

Cool Facts

Since calcification—the process that makes these plants hard—takes a lot of energy, corallines grow slowly. An eight-inch articulated coralline may be more than nine years old.

Most seaweed grazers shun these stony red algae. However, a few animals with special hardened mouth parts—like juvenile abalone, some marine snails and a chiton species (Tonicella lineata)—actually prefer to munch on corallines.

In coral reefs, a tropical genus of crustose coralline, Porolithon is an important cementing and bonding agent. It's contributed more to the building of reefs than the corals have—so perhaps the name coral reefs might properly be changed to algal reefs.