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Photosynthesis of cyanobacteria is well characterized under laboratory conditions. We present a detailed study of photosynthetic capacity of cyanobacterial communities measured under natural conditions using chlorophyll fluorescence techniques. Cyanobacteria of extensive and diverse communities grow epi- and endolithically on the bare rock of inselbergs in the tropics where they are exposed to extreme and rapid fluctuations in irradiance, temperature and water availability. Extreme and rapidly changing environmental conditions impose various stresses on cyanobacteria and lead to small-scale niches of different communities along the furrows of an inselberg in French Guiana. These different cyanobacterial communities can easily be separated from each other by their species composition. Moreover, cyanobacteria of these zonal areas show significantly different rates of apparent quantum yield of photosystem II (PSII), are differently adapted to utilize early morning light energy and have different strategies to face rapid cycles of desiccation. These different physiological strategies have led to the development of different cyanobacterial communities in distinct zones which are determined by different resistance to dehydration, water transport and storage capacity. In spite of the extreme environmental conditions with very high solar radiation, predawn measurements of potential quantum yield of PS II showed that they are not photoinhibited. We describe the manifold photosynthetic strategies that have developed in cyanobacteria under these extreme and highly fluctuating natural conditions. [ABSTRACT FROM AUTHOR]