Preliminary Survey of Modern Marine Environments of San Andres Island, Colombia

Abstract

The modern reef complex of San Andres Island, Colombia, can be divided into five major depositional environments on the basis of sediment type and biota. These are: fore-reef, reef crest, back-reef platform, lagoon, and near-shore. Dominant organisms of the reef crest are Millepora complanata (hydrozoan), Palythoa mammillosa (zoantharian), and calcareous algae. Windward, or the reef-complex environments, are characterized by abundant zoanthariar corals, and leeward environments are dominated by alcyonarians. Modern subtidal sediments from the San Andres area average 70% aragonite and 30% high Mg calcite with a maximum of 20 mole % MgCO3. High concentrations of MgCO3 were found only in sediments from the reef crest and near-shore (turtle grass) environments and are attributed to coralline algae.