6. Coral Reefs of the Cayman Islands

The three Cayman Islands of Grand Cayman, Cayman Brac and Little Cayman lie in the north-western part of the Caribbean Sea. All three are surrounded by a narrow shelf which acts as a base for the extensive development of coral reefs and lagoons. The shelf around each island has two gently-sloping terraces, a shallow one at 8–10 m depth and a deeper one at 15–20 m. The shallowest reefs, best developed around Grand Cayman and Little Cayman, are fringing reefs with an Acropora-Millepora thicket at or near sea level, behind which is a lagoon with a rubble zone, sands, patch reefs and grass beds. Seawards of the fringing reef is a barren rock pavement zone, succeeded by extensive development of coral reefs on the shallow terrace, where spur-and-groove structure is common, the spurs dominated by a coral assemblage of Diploria, Montastrea, Porites and Agaricia. A sand plain then leads to a second development of reefs at the edge of the deep terrace at about 20 m, beyond which is a steep drop-off down the fore-reef slope into deep water, to the limit of coral growth at about 70 m. Occasionally, as at Bloody Bay on Little Cayman, the deep terrace is absent and the drop-off occurs at the edge of the shallow terrace at 7 m as a spectacular, almost vertical wall.