Effects of ultraviolet-B radiation on primary production along latitudinal transects in the South Pacific ocean

Ambient intensities of solar ultraviolet radiation inhibit photosynthesis in the upper layers of the oceans. In this study the effect of ultraviolet-B radiation (UVBR) (290–320 nm) on marine phytoplankton carbon fixation during two latitudinal transects through the South Pacific ocean were measured to determine a dose-response model for estimating UVBR effects in natural surface populations and to identify latitudinal variation in UVBR sensitivity. Photoinhibition increased linearly with increasing doses of UVBR as weighted by the DNA action spectrum, with no apparent threshold for effect. The dose-rate response was nearly constant at low latitudes but varied at higher latitudes. Ambient intensities of UVBR cause photoinhibition and it is likely that even small increases in surface UVBR will cause additional photodamage. A quantitative estimate of the long-term effect of UVBR on marine phytoplankton, however, cannot be made from short-term measurements of photoinhibition since factors such as vertical mixing, photorepair, and photoadaptation will modify the final expression of UVBR damage.