ANNUAL SKELETAL EXTENSION OF TWO REEF-BUILDING CORALS FROM THE COLOMBIAN CARIBBEAN SEA

The skeletal growth of the scleractinian corals Diploria labyrinthiformis (Linnaeus 1758) and Montastraea annularis (Ellis and Solander 1786) from Isla Grande (north of Rosario islands), Colombian Caribbean, was determined from annual extension increments revealed by X-radiography of 4-6 mm thick slabs obtained along the axis of maximum growth. The skeletal extension average rate for the last 22 years for D. labyrinthiformis was 3.8 mm year-1 (SE 0.10; N = 87). The correlation between growth of D. labyrinthiformis and hours of sunlight was significantly negative. The annual variances of sunlight enhanced annual statistically significant differences of growth in this species. M. annularis showed an average extension growth of 10.6 mm year -1 (SE 0.32; N = 55) during the last 14 years. The increase of M. annularis growth was coincident with the end of nearby dredging activities as well as the decrease of nutrient levels. Nevertheless, the growth rate of this species showed no statistically significant differences through the years and no correlation with variation in sunlight. A low density annual band, wider than high density band in D. labyrinthiformis and narrower in M. annularis, seems to form approximately during April and May in both species, which is coincident with the end of dry season (increase of sea surface temperature, decrease of hours of sunlight and high influence of Dique Channel waters over Rosario islands). The annual bands forming on both species at the study site might be highly related with time of reproduction of each species. Further investigation will permit a better understanding of how some local conditions or coral physiology are related with coral growth at Rosario islands.