Photosynthetic performance of Arctic macroalgae after transplantation fromdeep to shallow waters

Transplantation experiments conducted in the Arctic Kongsfjord (Spitsbergen ) in summer 1997 investigated the effects of various types of filtered natu ral radiation (solar, solar without UV-B, solar without UV-A/B) on photosyn thesis of various macroalgae. Two brown algal species (Laminaria solidungul a, Saccorhiza dermatodea) and four red algal species (Palmaria palmata, Phy codrys rubens, Phyllophora truncata, Ptilota plumosa) were collected from d eeper waters, kept in UV-transparent plexiglass tubes wrapped with differen t spectral cut-off filter foils and positioned at fixed depths in shallow w aters for 7-9 days. At regular intervals, chlorophyll fluorescence of photo system II (optimum quantum yield, F-v/F-m) was determined, as an indicator of photosynthetic performance. The data demonstrate that shallow-water spec ies such as P. palmata are much less affected by natural photosynthetically active radiation (PAR) and UV radiation near the surface than extremely se nsitive deep-water species such as Phyc. rubens which exhibited strong decr eases in photosynthetic performance, as well as photobleaching of part of t he thallus. The other species showed intermediate response patterns. In mos t species investigated inhibition of photosynthesis was mainly caused by th e UV-B wavelengths. Interpretation of the data clearly indicates species-sp ecific tolerances of photosynthesis to ambient solar radiation which can be explained by broad physiological acclimation potentials and/or,genetic ada ptation to certain (low or high) irradiances. The species-specific photosyn thetic performance under radiation stress is in good accordance with the ve rtical distribution of the macroalgae on the shore.