Coralline algae play an important role in building and consolidating tropical reefs — structures projecting toward the water surface in turbulent areas and made up of communities which include lime-producing plants and animals. The temporally changing nature of reef systems suggests that their stage of evolution is reflected by their structure and by the kinds of reef-building organisms most prominent in particular localities. From the ecological point of view coralline algae in tropical areas play three roles: (1) primary producers of photosynthate, (2) contributors of sediment, and (3) consolidators and cementers of reefs. An important factor helping to determine the dominance of Porolithon onkodes and other crustose coralline algae on algal ridges or reef flats is grazing. W. A. Setchell argued that coralline algae are important reef builders and consolidators in the Indian and Pacific Oceans. Most Caribbean algal ridges originate by the fusion of mushroom-shaped cup reefs which represent earlier stages of development.