In addition to growth rates in quartz test tubes under the different light regimes, we examined pigmentation changes, as some pigments are probably much more vulnerable to UV-B than others, while production of photoprotective pigments may be enhanced. These were analyzed by high performance liquid chromatography. Although there is considerable variation within phylogenetic groups, the cyanobacteria, red algae, and dinoflagellates are, overall, most sensitive to UV-B radiation. Diatoms are the most variable as a group, with some extremely sensitive and others not affected at all at the highest UV-B intensities tested. Other species will be affected, however, so changes in species composition can be expected.
Many large species are also as sensitive to UV-B as the small celled species.
The results of the pigmentation studies reveal that phytoplankton respond to exposure to UV-B radiation by altering the concentrations of some, but not all, of their pigments. The most striking changes seem to occur in some of the carotenoids. The same was true for the coccolithophores. The most dramatic changes in pigment ratios were observed in the chlorophyte Dunaliella tertiolecta whose growth rate did not seem to be affected by UV-B radiation. In general there will be a decrease in cyanobacteria and dinoflagellates.