The algal population consists of turf algae, coralline algae and macro algae. Since coralline algae contain calcium carbonate, they fossilize fairly well. Carbonates and calcium are essential for all growth of corals, coralline algae, clams, and invertebrates. These include coralline algae and some sponges. Corals probably competed mainly with red and coralline algae for space on the seafloor. Thallophytes resembling coralline red algae are known from the late Proterozoic Doushantuo formation. Algal ridges are carbonate frameworks constructed mainly by nongeniculate coralline algae (after Adey, 1978). They are scavengers and also may feed on algae, including coralline algae. The particles can also be biological in origin, such as mollusc shells or coralline algae. It also describes a habit of coralline red alga. Algae, including beneficial types such as coralline algae, were viewed negatively and were generally removed. Most of the coralline structures of the Chagos are submerged reefs. Areas of ancient coralline limestone are found on Bougainville. It is often found on stabilised dunes formed of coralline sand and limestone. In the oceans, modern coralline algae appeared for the first time.