Impact of UV-radiation on viability, photosynthetic characteristics and DNA of brown algal zoospores: implications for depth zonation

Measurements of photosynthesis, germination capacity and assessment of DNA damage were carried out in the laboratory to determine the effect of differ ent conditions of ultraviolet (UV) and photosynthetically active radiation (PAR) on zoospores of various large brown algae collected on Spitsbergen (S valbard, High Arctic) and Tarifa (Cadiz, southern Spain). Results were corr elated to in situ light conditions and indicated that zoospores suffer phot oinhibition of photosynthesis, loss of viability and DNA damage in relation to the growth depth of parental sporophytes. At both sites, germination ca pacity of zoospores in species collected in deep waters was more strongly i mpaired after exposure to the same UV doses than in species from shallower waters. In general, zoospores exposed to PAR+UVA+UVB showed higher mortalit y rates than after exposure to PAR+UVA or PAR alone. For Laminaria digitata from Spitsbergen, it was found that the loss of zoospore viability is the result of DNA damage and photodamage of the photosynthetic apparatus. UVB i rradiances occurring in southern Spain at water depths shallower than 7 m p revented the germination of spores of deep water Laminariales from this reg ion.