Why is Red Algae Important to Coral Reefs

Red algae are a type of multicellular, marine algae, which contain the red pigment, phycobiliprotein. They cover the surface of coral reefs and cement the reefs together. The crustose type growth of red algae forms a thin mat on coral reefs, trapping the sediments on the coral reefs. The coralline algae, which consist of calcium carbonate in their cell walls, grow upright on coral reefs. Both crustose type and coralline algae help the coral reef to grow and provide support to the coral colony. 

Key Areas Covered

1. What are Red Algae
     – Definition, Facts
2. Why is Red Algae Important to Coral Reefs
     – Relationship Between Red Algae and Coral Reefs

Key Terms: Coral Reefs, Coralline Algae, Crustose, Red Algae

Why is Red Algae Important to Coral Reefs - Infograph

What are Red Algae

Red algae represent a large group of multicellular algae that are mainly red in color. They are classified in the phylum Rhodophyta under the kingdom Protista. They are found all over the seabed, attached to hard surfaces. Approximately 6,500 to 10,000 species of marine algae and over 160 species of freshwater algae have been identified so far. Red algae can be either microscopic or large fleshy algae.

Why is Red Algae Important to Coral Reefs

Figure 1: Red Algae on a Coral

Red algae store sugars in the form of glycogen. However, both brown and green algae store sugars in the form of starch. Besides cellulose, the cell wall of red algae contains three important chemicals: agar, carrageenan and gelans (mucusy sugars).

Why is Red Algae Important to Coral Reefs

Some red algae deposit calcium carbonate in their cell walls. This type of red algae are called coralline algae. The calcium deposits prevent the algae from being eaten. Furthermore, they provide them strength and support. The coralline algae make an important contribution to the growth of coral reefs.

Why is Red Algae Important to Coral Reefs_Figure 2

Figure 2: Lithothamnion sp.

Some red algae can grow as a thin mat over coral reefs. This form of growth is called a crustose. Both coralline algae that grow upright and crustose forms of red algae bind to the coral reefs and infill the coral skeletons, forming massive sedimentary structures. The thread-like filaments of red algae on the coral reefs trap the sediments of sands and cement the particles of sands. This helps the growth of coral reefs and provides support to the coral skeleton. The resultant red algae structures are strong enough to resist wave-action and erosion. If the coral colony is broken by a storm, the red algae quickly bind the pieces back together.


Two forms of red algae help the growth of coral reefs. Crustose red algae form a thin mat on the coral reefs by their filament-like growth. The sediments of sand are trapped within the crustose structure. This helps the growth of the coral reef. Moreover, the coralline algae grow upright on the coral reefs. This provides the support to the coral reef.


1. “Red Algae (Rhodophyta).” Marine Algae, Available here.

Image Courtesy:

1. “Helicase” By Phoebus87 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia 
2. “EukPreRC” By Lsanman – Own work (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Lakna

Lakna, a graduate in Molecular Biology & Biochemistry, is a Molecular Biologist and has a broad and keen interest in the discovery of nature related things

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