Submerged Reefs of Eastern Caribbean

Abstract

Submerged early Holocene or late Pleistocene reefs up to 90 km long and with bottom relief commonly about 20 m were established in relation to preexisting lower sea levels on outer edges of terraces at 30-80-m depths off most islands in the eastern Caribbean Sea. Submerged reefs are far more impressive physiographic features than their modern counterparts and are in depths greater (below about 15-20 m) than those commonly associated with present reef-framework construction by hermatypic corals. Data from echo-sounder profiles, rock dredging, bottom photographs, and in situ observations indicate that off the Virgin Islands, St. Martin, St. Barthelemy, Montserrat, Guadeloupe, Martinique, St. Lucia, and the Grenadine Islands submerged reefs are dead and covered by only a few scattered living corals. Hermatypic corals below 15 m on these reefs cannot cope with skeletal destruction by boring organisms and cannot compete for substrate with other encrusting or attached organisms. Off the west coast of Barbados, however, reef-framework construction is still occurring below about 15 m. The age relations of these reefs are not known, but probably they are no older than late Pleistocene and started to grow no later than 8,000 years ago. Although the eastern Caribbean area is characterized by inner-shelf fringe reefs, the common occurrence of shelf-edge submerged reefs indicates that, during the latter stages of the Holocene transgression, reefs were generally adjacent to deep waters, as are modern Pacific barrier and atoll reefs.