In reality, one type of algae is the foundation of the coral reef. Tiny unicellular algae called zooxanthellae live within the coral animal polyps. The algae tends to be green or yellow in color and gives the coral polyps their pigment. In addition, this algae partner provides a specialized boundary layer that allows corals to add calcium skeletons by establishing an alkaline environment on the coral cell surfaces that is necessary for the deposit of the mineral. In the realm of minerals, there are other algae that are important contributors to the structure of tropical reefs.
Coralline algae are abundant on the reef, both in encrusting and branching forms.
Unlike zooxanthellae, coralline algae are brightly colored in hues of red, pink, white, and yellow. These colorful algae are helpful cementing agents along the coral reef because they deposit calcium carbonate within their cell walls. This leafy green macroalgae is abundant here in the Keys, both on the reef and on hardbottom areas. It provides a sturdy mat on shallow hardbottom areas that helps stabilize sediment. If you pick up a handful of sand you may notice an abundance pure white, flat, round pieces.