Daily course of photosynthesis and photoinhibition in marine macroalgae investigated in the laboratory and field

Photoinhibition of photosynthesis and its recovery was investigated in the laboratory and in the field with fluorescence and oxygen measuring devices. Photosynthetic efficiency measured at non-saturating fluence rates and the ratio of variable fluorescence to maximal fluorescence (FJF,) showed an approximately inverse course compared to the fluence rate of daylight measured continuously during the day. In the morning photosynthetic efficiency was high, but decreased with increasing fluence rate. Maximal photoinhibition of photosynthesis occurred around noon or in the early afternoon. During the afternoon photosynthetic efficiency increased again and full recovery was reached in the evening. These lunetics of recovery differ from those obtained in the laboratory under artificial conditions, where the red algae required up to 48 h to recover from a strong photoinhibition. Different species showed Mferent sensitivity to photoinhibition and different capability for recovery. The red alga Porphyra spp., living in the upper eulittoral, was able to cope with the high fluence rates at the water surface. The red alga Delesseria sanguinea, living in the subtidal zone, shows the highest sensitivity to photoinhibition. Thus, a relation between photoinhibitory sensitivity and the zonation of the algae in the littoral exists.