Diel patterns of UVBR-induced DNA damage in picoplankton size fractions from the Gulf of Aqaba, Red Sea.

This study focuses on the impact of natural levels of UVBR (ultraviolet-B radiation: 280 to 315 nm) on bacterio- and phytoplankton (<10 μm) from the Gulf of Aqaba, Red Sea. Incident biologically effective doses (BEDs) and attenuation of biologically effective radiation in the water column were measured using a DNA biodosimeter. UVBR-induced DNA damage was measured as cyclobutane pyrimidine dimers (CPDs), using an antibody directed to CPDs followed by chemiluminescent detection. Depth profiles of DNA damage were determined in two plankton size fractions (0.2 to 0.8 μm and 0.8 to 10 μm) collected down to 50 m depth. Furthermore, accumulation and removal of CPDs were monitored in surface plankton samples during several daily cycles. Small plankton (plankton <10 μm) composition was determined by flow cytometry. The plankton community in the Gulf of Aqaba was dominated by nonphototrophic bacteria and the free-living prochlorophyte Prochlorococcus spp. (<0.8 μm). In general, no DNA damage could be detected in dosimeter DNA below 15 m. In contrast, DNA damage (up to 124 CPD Mnucl