Endolithic Algae in Stony Corals!

Far from being devoid of life, the skeleton of a coral harbors a wide array of algae, endolithic fungi, heterotrophic bacteria, and other boring eukaryotes, often forming distinct bands of color visible to the bare eye. Some functions of these endolithic microorganisms are critical in coral health, such as nutrient cycling and metabolite transfer, but they are poorly known, particularly by aquarists.