ABSTRACT: HPLC analysis of pigments of the symbiotic algae of the coral Goniastrea aspera (Verrill) showed the presence of the chlorophylls a and c₂ (chl a and c₂) and the carotenoids peridinin,diadinoxanthin, diatoxanthin and β-carotene. Increased production of diatoxanthin was seen in algae extracted from the western surfaces of corals, exposed to high levels of solar radiation, during a solar bleaching event. Inaddition, an increase in the ratio of diatoxanthin to the total xanthophyll pool was observed in bleached tissues, together with a progressive increase in the total xanthophyll pool (relative to total chlorophyll levels) over the bleaching period. Theseresults support a potential photoprotective function for xanthophylls in the coral/algal symbiosis. Chlorophyll breakdown products, phaeophytin a and pyrophaeophytin a, were recognised in considerable quantities only in bleached tissues.Computation of a simple chlorophyll budget showed that 45% of chl a was lost in partially bleached tissues and approximately 62% in fully bleached tissues, indicating a very rapid photodegradation of chlorophyll 24 h after exposure to highirradiance.