EFFECTS OF SOLAR UV-RADIATION ON DIATOM ASSEMBLAGES OF THE MEDITERRANEAN

Three UV treatments (PAR; PAR + UVA; PAR + UVA + UVB) were performed b y placing different W-absorbing filters over communities developing on ceramic tiles in a natural marine habitat near Korinthos, Greece, The experiment was repeated at three depths (0.5 m, 1 m, 1.5 m) below the surface of the sea, Differences in community structure due to UV radi ation exposure were more pronounced during the early stages of communi ty development. After the first 3 weeks of growth, the productivity of the PAR + UVA + UVB treatment was significantly lower than the PAR UVA but not than the PAR treatment, This difference did not persist th ereafter, At 5 weeks of growth, the productivity at 0.5 m was signific antly lower that at 1.0 m, No other significant differences were obser ved. The findings of the present study suggest that periphytic communi ties occurring at the upper layers of the euphotic zone may be capable of adjusting to changes in environmental stresses such as by increase d solar UVB irradiance.