Effects of UV-B-induced DNA damage and photoinhibition on growth of temperate marine red macrophytes: Habitat-related differences in UV-B tolerance

The sensitivity to UV-B radiation (UVBR: 280-315 nm) was tested for littora l (Palmaria palmata [L] O Kuntze, Chondrus crispus Stackhouse) and sublitto ral (Phyllophora pseudoceranoides S. G. Gmelin, Rhodymenia pseudopalmata [L amouroux] Silva, Phycodrys rubens [L.] Batt, Polyneura hilliae [Greville] K ylin) red macrophytes from Brittany, France. Algal fragments were subjected to daily repeated exposures of artificial UVBR that were realistic for spr ingtime solar UVBR at the water surface in Brittany, Growth, DNA damage, ph otoinhibition, and UV-absorbing compounds were monitored during 2 weeks of PAR + UV-A radiation (WAR) + UVBR, whereas PAR + UVAR and PAR treatments we re used as controls. The littoral species showed a higher UV tolerance than the sublittoral species. After 2 weeks, growth of P. palmata and C, crispu s was not significantly affected by UVBR, and DNA damage, measured as the n umber of cyclobutane-pyrimidine dimers per 10(6) nucleotides, was negligibl e. Photoinhibition, determined as the decline in optimal quantum yield, was low and decreased during the course of the experiment, coinciding with the production of UV-absorbing compounds in these species. In contrast, no UV- absorbing compounds were induced in the sublittoral species. Growth rates o f P. pseudoceranoides and R. pseudopalmata were reduced by 40% compared wit h the PAR treatment. Additionally, constant levels of DNA damage and pronou nced photoinhibition were observed after the UVBR treatments. Growth was co mpletely halted for Phycodrys rubens and Polyneura hilliae, whereas DNA dam age accumulated in the course of the experiment. Because Phycodrys rubens a nd Polyneura hilliae showed the same degree of photoinhibition as the other sublittoral species, it appears that the accumulation of DNA damage may ha ve been responsible for the complete inhibition of: growth. The results sug gest an important role of DNA repair pathways in determining the UV sensiti vity in red macrophytes.