Evaluation of in vivo thallus absorptance and chlorophyll fluorescence as biomarkers of UV-B exposure and effects in marine macroalgae from different tidal levels

A field survey and an outdoor experiment were conducted to evaluate the potential of chlorophyll fluorescence and in vivo absorptance spectra as biomarkers of short-term experimental and long-term solar UV radiation exposure in macroalgae. The eulittoral macroalga Porphyra umbilicalis (L.) (Rhodophyta) and the sublittoral macroalga Palmaria palmata (L.) (Rhodophyta) were collected at three different sites along a vertical transect on the beach and in the water column. Significant decreases in the absorptance spectra at 497 and 569 nm (consistent with the presence of R-phycoerythrin and/or carotenoids and phycoerythrobilin, respectively) occurred in P. palmata after exposure to elevated UV-B (2.7 Wm−2). Furthermore, depth-dependent decreases in thallus absorptance at specific wavelengths were found after all exposures, indicating that in vivo thallus absorptance may be a useful general indicator of UV exposure in conjunction with other biomarkers. Also, a depth-dependent decrease in Fv/Fm was detected in P. palmata. A 60% decrease in thallus absorptance and lack of recovery in chlorophyll fluorescence Fv/Fm ratio indicated irreversible damage to accessory pigments, chlorophyll a and photosystem II after exposure to elevated UV-B. Moreover, a depth-dependent increase in thallus absorptance between 290 and 325 nm was observed in P. palmata in response to short-term experimental elevated UV-B exposure and between 290 and 380 nm in response to long-term solar UV-B. In contrast, the eulittoral alga Porphyra umbilicalis exhibited a greater degree of tolerance of UV-B exposure. The results highlight the potentially damaging effects of high irradiances of photosynthetically active radiation and UV and the necessity of utilising several biomarkers when assessing the biological effects of UV-B irradiation associated with ozone depletion.