Part 2: How are coral reefs structured?

Coral reefs form in regions of the world where there are warm currents, mainly between the Tropics of Cancer and Capricorn. There are four main reef types: fringing, barrier, atolls, and patch reefs.

Fringing (or apron) reefs directly border shorelines:

Barrier reefs are similar to fringing reefs except that they are separated from the shoreline by lagoons that are often deep and wide:

Atolls are circular-shaped reefs that form on the rim of submerged volcanic islands; patch reefs are small, isolated formations that are not attached to a major reef structure:

Figures source: Mann, K. H., 1982, Ecology of Coastal Waters - A Systems Approach, Chapter 6: Coral Reefs, 160-182, Berkeley and Los Angeles: University of California Press (as modified).