The organization of life on coral reefs was a mystery to scientists for many years. The first ecologists, scientists who study ecosystems, to visit coral reefs were surprised to identify only a few types of producers. Because phytoplankton in seawater supports most marine ecosystems, scientists expected to find it in large quantities around reefs. The lack of phytoplankton mystified them.
Today, scientists realize that the reef is rich in producers, but not in the form of phytoplankton. Chief among reef autotrophs are the zooxanthellae, green protists found in the cells of corals and a few other species of animals. Studies have demonstrated that zooxanthellae are responsible for at least half of the productivity in a reef system.
Coralline seaweeds are major contributors to the reef structure. In some reef ecosystems, they provide as much calcium carbonate as the coral animals. Porphyra is a typical coralline algae found on the reef crests. Although it is a slow grower, Porphyra can withstand a lot of wave action, drying conditions, and grazing by predators.
Several species of cyanobacteria and macroalgae are responsible for providing food for reef residents. The secondary pigments found in these organisms ensure their ability to trap the Sun’s energy in the photosynthetic process, increasing their efficiency. All macroalgae are highly adapted for life in the sea, with flexible, slime-coated thalli that are secured to the ocean floor by holdfasts.
The reef producers, one-celled algae, macroalgae, and vascular plants, are an incredibly diverse group. All are highly adapted specialists capable of life in a harsh and highly competitive environment. This group of organisms is the key to the riches of coral reef ecosystems and the reason for their unrivaled success.