Light response curves for Gelidium sesquipedale from different depths, determined by two methods: O-2 evolution and chlorophyll fluorescence

Photosynthesis-light response curves of Gelidium sesquipedale from the west coast of Portugal (Cape Espichel) were determined at four different depths , 3, 10, 15 and 22 m. Data acquisition using chlorophyll a fluorescence met hodology and oxygen electrode measurements were compared. Response curves w ere determined over an increasing range of irradiance values (I), from dark ness to 900 mu mol photon m(-2) s(-1) PAR. In general, light response curve s obtained for G. sesquipedale showed a similar pattern whether determined by the chlorophyll fluorescence method or by oxygen evolution. The photosyn thetic capacity of G. sesquipedale decreased with depth, as expected, revea ling a 'sun' and 'shade' acclimation pattern, between shallow and deeper wa ters.