“. . . wo jedes Thier zur Blume wird.” (Haeckel) General Considerations The beauty of color and form and the overwhelming variety of life on coral reefs are both legendary and real. Nowhere else in the seas is there such a bewildering range of living things, and perhaps nowhere else is the physical and biological pattern so uniform, characteristic, and widespread as in the coral reef. Reefs are scattered over an area of 190,000,000 square kilometers (68,000,000 square miles) wherever a suitable substratum lies within the lighted waters of the tropics beyond the influence of continental sediments, and away from the cool upwellings of the sea in the eastern parts of the ocean basins. Coral reefs are deterministic phenomena of sedentary organisms with high metabolism living in warm marine waters within the zone of strong illumination. They are constructional physiographic features of tropical seas consisting fundamentally of a rigid calcareous framework made up mainly of the interlocked and encrusted skeletons of reef-building (hermatypic) corals and calcareous red algae. The framework controls the accumulation of sediments on, in, and around itself. These sediments are derived from organic and physical degradation of the frame and organism associated with the reef constructors and have a bulk ten or more times as great as the frame itself. They are best developed where the mean annual water temperatures are approximately 23–25°C. No significant reefs occur where temperatures during the year fall below about 18°C, except for very short periods, although a few hermatypic corals...