EFFECTS OF NATURAL UV RADIATION ON ANTARCTIC CYANOBACTERIAL MATS

Abstract: Microbial mats dominated by cyanobacteria are the most abundant living forms in non-oceanic Antarctic ecosystems. The ultraviolet radiation increase may affect drastically the organisms living in the polar regions and especially those of terrestrial ecosystems exposed to full sunshine. The aim of this work was to investigate the effect of UV radiation on terrestrial Antarctic communities. Dominant species in these microbial assemblages belonged to the filamentous, non-heterocystous cyanobacteria group (e.g. Phormidiurn, Lyngbya, Oscillatoria, etc). Heterocystous (e.g. Noduluria) and coccoid (e.g. Synechococcus) cyanobacteria were subdominant although very abundant. We studied the effect of natural UV radiation on cyanobacterial mats, using a series of narrow band UV filters. After two weeks of differential exposure to UV (PAR, PAR +UVA, PAR +UVB, PAR +UVA + UVB) population structure, pigment composition and physiological activities were analyzed. Although statistical analyses revealed that mats under the four UV regimes assayed were not significantly different in community structure nor in pigment composition, surface appearance of mats was different between treatments. Phys-iological analyses indicated that the photosynthesis/respiration balance might be affected by UV radiation. The apparent contradiction between analytical data of pigments and surface appearance can be explained by considering that UV regime might have induced changes in the position of the microrganisms of the mat by mean of migration. This process is suggested to be one of the responses of escaping from an increasing UVB radiation environment. key words: Antarctica, cyanobacteria, McMurdo Sound, mycosporine-like-ami-noacids. UV