Prior to 1994, the wide variability exhibited in the appearance of Montastraea annularis was attributed to the different environmental conditions in which it occurs (3). However, scientists have since discovered that it actually comprises a species complex that can be divided into three distinct species: the type specimen, M. annularis, together with two newly described species, M. faveolata and M. franksi (1) (3) (4).
Like other colony-forming corals, colonies of M. annularis are composed of numerous small polyps, which are soft-bodied animals, related to anemones. Each polyp bears numerous tentacles that direct food into a central mouth, where it is digested in a sac-like body cavity. One of the most remarkable and ecologically important features of corals is that the polyps secrete a hard skeleton, called a ‘corallite’, which over successive generations contributes to the formation of a coral reef. The coral skeleton forms the bulk of the colony, with the living polyp tissue comprising only a thin veneer (4). In M. annularis, the colonies are formed by long, thick columns, with only the top parts supporting living tissue. The colour of the living colonies is usually golden brown to tan, but sometimes appears grey or green (3).