DISTRIBUTION OF CORAL REEFS IN THE PEARL ISLANDS (GULF OF PANAMA) IN RELATION TO THERMAL CONDITIONS1

Abstract

The hypothesis that coral reefs are largely confined to the north and east sides of islands because of favorable thermal conditions was tested and confirmed in the Pearl Islands, Panamá. The growth rate of Pocillopora damicornis , the chief reef‐building species, declined markedly or ceased on shores exposed to temperatures in the range 20‐21°C, when median growth rates dropped to below 1.0 mm month ‐1 and a variety of alien benthic species invaded and overgrew the branch tips of corals. High rates of bedload sedimentation on exposed shores and a high organic matter content of sediments on reefs did not affect coral growth. Differences in coral growth preceding and following upwelling were correlated with seasonal variations in sky cover. Other factors affecting coral growth and reef development include the ability of corals to feed and reproduce at low temperatures, the influence of turbulent conditions, the capacity of a reef structure to modify the surrounding thermal regime, and the effects of attrition due to corallivores.