The process of spectral attenuation of radiant energy in natural waters is well understood and straight forward to model. Bacteria play a vital role in mineralization of organic matter and provide a trophic link to higher organisms. New techniques have substantially changed our perception of the role of bacteria in aquatic ecosystems over the recent past and bacterioplankton productivity is far greater than previously thought, having high division and turnover rates. Bacterioplankton are more prone to UV-B stress than larger eukaryotic organisms and, based on one study, produce about double the amount of caeyclobutane dimers. Recently, the mechanism of nitrogen fixation by cyanobacteria has been shown to be affected by UV-B stress.
Wetlands constitute important ecosystems both in the tropics and at temperate latitudes.
In these areas, cyanobacteria form major constituents in microbial mats. The organisms optimize their position in the community by vertical migration in the mat which is controlled by both visible radiation and UV-B. Cyanobacteria are also important in tropical and subtropical rice paddy fields where they contribute significantly to the availability of nitrogen. Solar UV affects growth, development, and several physiological responses of these organisms. On a global basis, phytoplankton is the most important biomass producer in aquatic ecosystems. The organisms populate the top layers of the oceans and freshwater habitats where they receive sufficient solar radiation for photosynthetic processes.