COMMUNITY RESPONSES TO UV-RADIATION - II - EFFECTS OF SOLAR UVB ON FIELD-GROWN DIATOM ASSEMBLAGES OF THE CARIBBEAN

The effects of ambient solar UV on community productivity and structur e were assessed during primary succession of benthic diatoms on artifi cial substrate in a coral reef of the Caribbean. Artificial substrates , partially enclosed by UV cutoff filters, were placed at a depth of 6 0 cm below surface. During the initial colonization stages, the assemb lages exposed to the full solar spectrum had a mean productivity 43.4% lower than the assemblages exposed to PAR + UVA only. Some difference s in species diversity of assemblages under the different UV treatment s were also observed. Sensitive species to UVB exposure were Mastogloi a angulata, M. ovata, M. paradoxa, Nitzschia longissima, Plagiogramma staurophorum, Rhopalodia musculus, and Surirella ovata. These UVB effe cts gradually diminished as succession proceeded; 5 to 6 weeks after t he placement of the substrates in the water, no significant difference s in productivity were observed between the different treatments, whil e after 6 weeks of growth, species diversity and evenness were higher, although not statistically significant, in the UVB-exposed assemblage s. During the first 2 weeks of growth, the productivity under PAR + UV A was significantly lower than that under PAR only.