Photoinhibition of photosynthesis in the red alga Chondrus
crispus from different shore levels was investigated under laboratory
and field
conditions. The underwater light climate at Roscoff (French Atlantic
coast), characterized by transmittance spectra, was shown to be
intermediate between Jerlov coastal type 1 and oceanic type III.
Chondrus crispus thalli were collected at four depths
(3·5–8·5 m below
high tide level) and exposed to daily courses of artificial and natural
light. Filters were used to discriminate between the effects of
photosynthetically active radiation (PAR) and ultraviolet radiation (UVR)
under the photoinhibitory treatments. In the presence of natural
UVR, photoinhibition at midday was increased by up to 60%. Recovery from
photoinhibition was measured at different times throughout
the light stress. Recovery kinetics differed between morning and early
afternoon in all treatments, and were dependent on the light dose.
Whereas biphasic kinetics were observed in all treatments in the morning,
the
recovery in early afternoon was significantly slower. The
influence of UVR on recovery was apparent after exposure to higher light
doses. In all investigations, sensitivity to photoinhibition
corresponded to zonation of the algae, with deeper-growing algae showing
a
greater depression of fluorescence yield, and slower
recovery (indicating acclimation to the growth irradiance). An increase
in the phycoerythrin content and increasing photosynthetic
efficiency with increasing growth depth were observed.