On the significance of solar ultraviolet radiation for the ecology of microbial mats

The shortest wavelengths of the solar spectrum reaching the ground, known as the solar ultraviolet (UV, 280–400 nm), amount to only a small percentage of the total incident irradiance (Table 1). However, they may produce disproportionately large biological effects because they activate many photochemical reactions involving molecules of central biological importance. The consequence of these photoreactions is usually detrimental to the cellular metabolism. Mutation and lethal DNA and RNA damage, lipid peroxidation, photoinhibition of photosynthesis and respiration, and specific enzyme inactivation can all be a result of exposure to UV (Jagger 1985). These physiological effects are not always a laboratory curiostity but have ecological implications under natural conditions: the solar UV has been recognized as an important environmental stress factor in a variety of microbially dominated ecosystems. UV has been shown to cause sustained inhibition of both primary productivity and bacterial production in planktonic communities and to drive marked changes in species composition in periphyton communities (see Worrest 1982), but not much is known about the significance of ultraviolet radiation in benthic ecosystems. We have gathered some direct experimental evidence, as well as strong indirect inference from ecophysiological studies in diverse mat communities, suggesting that UV may be of importance, at least for the top phototrophic layers.