Zooxanthellae densities are highest in summer months in equatorial corals in Kenya

Abstract

Coral bleaching (loss of zooxathellae) is an increasing problem for the health and persistence of corals, but the phenomenon can not be fully comprehended without understanding seasonal fluctuations in the field. Seasonal dynamics of coral zooxanthellae (population density and mitotic indices) of eleven scleractinian coral species (Acropora sp., Echinopora gemmacea, Favia sp., Galaxea fascicularis, Hydnophora microconos, Montipora aequituberculata, Pavona decussata, Pocillopora damicornis, Pocillopora eydouxi, Porites cylindrica and Porites lutea) were monitored in Mombasa Marine Park from 1998 to 2006. Direct tracking of mapped corals provided evidence that zooxanthellae densities were highest during the North-East Monsoon (NEM) season and displayed highest mitotic indices during transition periods directly preceding this season. The higher densities found during the northeast monsoon (when temperatures and light radiation levels are higher) are surprising as they are contrary to trends found at higher latitudes. It is possible that at higher latitudes seasonal variability of temperatures and light is so great that it dictates zooxanthellae density dynamics, while corals closer to the Equator are less influenced and other factors may have greater influence on zooxanthellae dynamics. The present study highlights the degree of variability of zooxanthellae dynamics that may exist among coral species and compares sites from widely different geographic locations.