The effects of distinct components of the solar spectrum (ultraviolet A, ultraviolet B, and photosynthetically active radiation) on Gracilaria dentata, Hypnea musciformis, and Centroceras clavulatum were investigated under laboratory conditions. Thalli of the samples were exposed to either unfiltered solar radiation or solar radiation filtered through WG 295, WG 320, and GG 400 cut-off filters. Photosynthetic pigments were quantified using spectrophotometry, and gas exchange was measured using a Clark electrode. Pigments were significantly (P<0.05) bleached by all components of solar radiation used. Phycobilins were bleached even after short exposure, followed by carotenoids and then chlorophyll a, which was hardly affected. Photosynthetic oxygen production declined by 35-60% across species after 60 min of exposure, with ultraviolet B causing the highest inhibition. Respiration rates increased by 10-25%. H. musciformis exhibited greater resilience, maintaining a photosynthetic rate of 2.1 ± 0.3 µmol O? g?¹ FW h?¹ compared to G. dentata or C. clavulatum.  The ultraviolet B component, despite its lower intensity, had the most inhibitory effect on photosynthesis, likely due to oxidative stress and photobleaching of pigments. The findings highlight the differential susceptibility of red algae to solar radiation, emphasizing the need for further investigation into the mechanisms underlying ultraviolet-induced stress responses.

 

Key words: Absorption spectra, gas exchange, photobleaching, photoinhibition, photosynthetic pigments, solar radiation.