In situ photosynthetic performance of Laminaria digitata (Phaeophyceae) during spring tides in Northern Brittany

The ability of Laminaria digitata (Hudson) J.V. Lamouroux to cope with rapid and drastic changes in light was studied in the field by measuring photosystem II fluorescence, net oxygen roduction and pigment content. Experiments were conducted during two spring tides of late spring in Northern Brittany where low spring tides occur around noon. Daily patterns of the photosynthetic performance of Laminaria digitata were observed in relation to changes in incident under- water light. Photoinhibitory light exposure induced a sharp decrease of the optimal quantum yield (Fv/Fm), a decline of the net oxygen production in the first of the two spring tides investigated and a concomitant increase in the de-epoxidation ratio of the Violaxanthin pool. Photoinhibition persisted at a lower extent at the end of the day and complete recovery was achieved during the night. The implications of the photoinhibition of photosynthesis of Laminaria digitata are discussed in relation to the natural ambient conditions experienced in the field.