Photosynthetic performance of the Atlantic brown macroalgae, Cystoseira abies-marina, Dictyota dichotoma and Sargassum vulgare, measured in Gran Canaria on site

Photosynthetic performance was determined in three common Atlantic brown ma croalgae, Cystoseria abies-marina. Dictyota dichotoma and Sargassum vulgare , in Gran Canaria, Canary Islands, on site. The photosynthetic quantum yiel d was measured with both a portable PAM instrument on site and a diving PAM under water in the habitat. In parallel, solar radiation was measured cont inuously above and under water by means of two three-channel dosimeters. EL DONET (Real Time Computer, Mohrendorf. Germany), in three wavelength ranges , UV-A, UV-B and PAR. The effective photosynthetic quantum yield decreased in all species in response to exposure to 15 min of solar radiation but rec overed in the subsequent shade conditions within several hours. A 30-min ex posure caused an even more profound photoinhibition from which the algae re covered only partially. Most of the effect was due to visible radiation, ho wever, the UV wavelength range, and especially UV-B, considerably enhanced the decrease in photosynthetic quantum yield. In all species except Sargass um a significant photoinhibition was detected at their growth sites at high solar angles in the water column, measured with the diving PAM. (C) 2001 E lsevier Science B.V. All rights reserved.