Photosynthetic fluorescence induction and oxygen production in two Mediterranean Cladophora species measured on site

Photoinhibition under solar radiation was measured in the green macroalgae Cladophora prolifera and C. pellucida, using pulse amplitude modulation fluorescence and oxygen production in situ. Photosynthetic oxygen production is inhibited within about 1 h and the quantum yield follows with similar time kinetics. Samples were collected from a habitat protected from exposure to direct solar radiation except for a few hours per day. Therefore, individuals of both species were adapted to low irradiance and readily inhibited by exposure to excessive radiation. Impairment occurred even at their natural habitat during the few hours of exposure to direct solar radiation of the day. Recovery from photoinhibition of both the photosynthetic quantum yield, defined as F-v'/F-m', and oxygen production took several hours and was not complete. Judging from both parameters indicated above, C. pellucida showed a higher degree of photoinhibition than C. prolifera. These results suggest that photoinhibition may be a significant factor in determining the spatial distribution of these benthic macroalgae.