SUMMARYUV‐absorbing mycosporine‐like amino acid compounds (MAA) were identified and quantified in 13 macroalgal Chlorophyceae, six Phaeophyceae and 28 Rhodophy‐ceae collected in the intertidal zone from the tropical island Hainan, People's Republic of China, as well as from tropical mangrove locations in America, Africa, Australia and Japan. All of these habitats receive naturally high solar ultraviolet (UV) irradiances. The study revealed that all Rhodophyceae contained several MAA, which are assumed to function as natural UV sunscreens. Within all species investigated eight distinct compounds were found, seven of which were identified as mycosporine‐glycine, shinorine, porphyra‐334, pal‐ythine, asterina‐330, palythinol and palythene. The unknown substance had an absorption spectrum with a maximum at 357 nm. This compound was restricted to two red algal species from Hainan. In contrast, the Chlorophyceae and Phaeophyceae did not contain MAA or exhibited only trace concentrations. Compared with data from the literature, the amount of all MAA in the tropical Rhodophyceae seemed to be higher than in temperate organisms, probably reflecting acclimation to the stronger solar radiation which is typical for lower latitudes. The data suggest that accumulation of MAA may represent a natural defence system against exposure to biologically harmful UV radiation.