coral bleaching is a phenomenon characterized by the lack of pigmentation in the coral tissue due to the loss of the existing relationship between corals and their symbiotic zooxanthellae, resulting in loss of zooxanthellae and/or of its photosynthetic pigments. the purpose of the present work was to evaluate if bleaching of siderastrea spp. colonies from the tidal pools of the guarajuba reef top, occurred as a result of seasonal variations of sea water parameters such as temperature, salinity and ph. the evaluation was based upon measurement of the density of zooxanthellae in the coral samples, which were collected in the tidal pools during low spring tides, from march 2005 to march 2006. amongst the analyzed parameters, sea water temperature varied more significantly. considering the density of the symbiotic zooxanthellae, the results indicated that it was higher in the colonies collected in the coldest month (june/05) of the studied period than in the other months, when water temperature in the tidal pools was warmer, thus characterizing a seasonal influence in the bleaching of coral colonies.