Algal reefs are biological and algae-formed reefs. They are formed when coralline algae accumulate calcium carbonate and attract other organisms, after which they slowly evolve into a unique terrain structure. Coralline algae grow remarkably slowly, increasing approximately 1 cm in thickness every ten years. Coralline algae resemble coral reefs, are highly “productive” with high biodiversity, and possess a 3D space and porous environment that enable organisms to grow, hide, and forage.
 
   Large-scale algal reefs are distributed across the coasts of Taoyuan City and are mainly found in the intertidal zone between south of the Xiahai River (in Dayuan District) and the Yongan Fishing Harbor (in Xinwu District). In this intertidal zone, an algae area measuring approximately 7 km long and containing baiyu algal reefs, datan algal reefs, and guanxin algal reefs can be found. Said area is a relatively healthy algal reef area rich in crustose coralline algae (aka. hermatypic coral red algae). Other areas containing crustose coralline algae (albeit considerably less in number) include Shimen and Sanzhi Districts in New Taipei City, Kenting in Pingtung County, and Sanxiantai and Shanyuan in Taitung County.
 
   Animals found around algal reefs include various small fish, crustaceans, shellfish, and polychaeta. Algal reefs also provide shelter for birds and are a place for them to forage and breed. For migratory birds such as anatidae, Chinese egrets, and terns, algal reefs are their main food supply stations and resting places. Most importantly, because living crustose coralline algae attach themselves to aging calcified algal reefs, they ultimately protect the algae reefs from wave-led erosion, serving the role of protectors in marine ecosystems.