A reef's primary producers Sargassum Photo courtesy of the UH Botany Dept. EcoMasters web page. Some species are indicators of high nutrient content in the water, usually a sign of pollution, especially along developed coastlines. Many types of algae are inhabitants of coral reefs whose abundance are kept in check by grazing fish, molluscs, and other animals.
Some algae can calcify, secreting skeletons composed of calcium carbonate.
Both coralline algae and the calcareous green alga Halimeda are significant producers of sediment in shallow waters around the Hawaiian Islands. Only a few types of algae found on Hawaiian reefs are shown here. Contributions and suggestions are welcome.