Algae

This picture taken through a microscope shows a soft coral polyp (Lobophytum compactum) Green shows the polyp tissue, while the red represents the zooxanthellae.

Marine algae have been part of the marine ecosystem for more than 2 billion years. They are often not very conspicuous because they lack roots, stems leaves and even the green colour with which we are familiar - marine algae generally come in brown, red, and only occasionally, green.

Zooxanthellae support coral

As in most ecosystems, plants form the basis of the Reef's ecosystem. Some, like the single-celled zooxanthellae, live within the tissue of marine animals directly supplying their host's nutritional requirements.

Algae build reefs

In addition to being the Reef's primary producers, many marine algae contribute to its overall structure. Coralline algae are like the Reef's mortar, secreting limestone and by growing between coral fragments and rubble, they help to bind the reef together.

Red algae	Coralline algae	Halimeda algae

Limestone-producing algae also make up a major component of the sand. Even though they may not be visually striking, marine plants dominate the Reef - as builders, consolidators and sediment producers.

How algae feed

Like other plants, algae obtain nourishment through a process of photosynthesis, where the energy of the sun converts carbon dioxide and water in oxygen and carbohydrates.

Human impacts

The increased nutrients such as phosphorus and nitrogen being released onto the reef through human activity has lead to an increase in the amount of marine algae in several areas. These 'over-fed' algae can out-compete corals, robbing them of the light they need to survive.