UVB RADIATION AND DEPTH INTERACTION DURING PRIMARY SUCCESSION OF MARINE DIATOM ASSEMBLAGES OF GREECE

Exposure to UVB radiation caused shifts in the species composition of diatom assemblages developing on ceramic tiles in a natural marine hab itat near Korinthos, Greece. These differences in community structure were more pronounced during the first month of community development. The diatom species Mastogloia crucicula and Nitzschia constricta were sensitive to both UVA and UVB radiation, while Amphora delicatissima, Amphora veneta, Opephora olsenii, Synedra baccilaris, and Synedra robu sta were excluded by exposure to UVB but not to UVA. Amphora robusta, Cocconeis fluminensis, Mastogloia erythraea, and Mastogloia ovalis wer e absent from 0.5 m while Nitzschia bilobata was present only in 1.0 m . Mastogloia badjikiana, Mastogloia labuensis, Nitzschia lanceolata, a nd Synedra laevigata were present during different stages of successio n. The fact that differences in community structure do not persist at later successional stages suggests that periphytic communities of the upper euphotic zone possess adjustment mechanisms to the stress posed by increased solar ultraviolet radiation.