The encrusting filaments trap sediments of sand, as well as cement the particles of sand together. In this way, coralline algae strengthen and support the coral reef structure. Even after a storm hits and many coral colonies have been broken, coralline algae quickly bind the pieces back together. Unlike the encrusting quality of coralline algae, calcareous algae, on the other hand, tend to grow upright. As a result, about fifty percent of the sand found on our beaches is created.
Many fish feed on the algae, which helps the reef when there is an overproduction of algae.
Parrotfish, for example, were once thought to be destructive, feeding on large areas of the reef, but now it is understood that Parrotfish actually help keep the algae production of the reef in check. In another relationship with algae, male Damselfish use red algae to prepare a nest on the reef on which the female can lay her eggs. Everything is the sea strives to live in balance with each other. This applies to algae as well. If there is not enough algae, the coral will die because it will not be able to acquire food and oxygen.