| Coral and coral reef development on the Pacific coast of Colombia were examined in relation to local environmental conditions. Surveys revealed that coral communities exhibited high levels of mono-specificity. Structural differences between the offshore (Gorgona Island) and the onshore fringing coral reefs (Ensenada de Utría and Tebada) were also observed. These differences were based on the following criteria: size and degree of coral reef development, percent of live coral cover, species richness and diversity, and the overall structural complexity, including the development of reef zones. Several kinds of environmental disturbances were identified to affect corals and coral reefs, including: El Niño-Southern Oscillation, terrigenous siltation, cold water spells and seasonal upwelling, extreme low tides, tectonism and freshwater discharge.; Alizarin staining and X-radiography showed that coral extension rates and skeletal density also exhibited spatial variability. During the study period, coral growth was highest and skeletal density lowest at Gorgona Island, probably due to the combination of warm stable sea surface temperatures (SSTs) and higher light levels. Sclerochronology also provided evidence of uninterrupted coral growth between ca. 1930–1982, indicating that the 1982–1983 El Niño-Southern Oscillation (ENSO) was probably the most severe environmental disturbance that occurred in the last seven decades.; Coral reef sedimentary deposits were studied based on sediment cores. Deposits were well preserved and indicated that uninterrupted coral reef accretion has occurred during the last ca. 2000–3000 years. Composition analyses indicated that both reefs are mainly built by Pocillopora damicornis , with a minor contribution by Psammocora sp. Coral reef stratigraphic sequences also provided evidence of increased terrigenous influx at Utría. It is proposed that the local physical and biological conditions, including climate, water circulation, colony morphology and the presence of mangrove forests, control the occurrence of a positively calcifying community under environmentally ‘poor’ conditions.; Based on coral reef community structure, skeletal chronologies and reef sedimentary sequences, the ecological and geological differences between coral reef communities of the Pacific coast of Colombia can be mainly attributed to El Niño-Southern Oscillation, terrigenous siltation and upwelling events associated with cold water and increased nutrients. (Abstract shortened by UMI.)... |
