EFFECTS OF SOLAR-RADIATION ON PHOTOSYNTHESIS AND PHOTOINHIBITION IN RED MACROPHYTES FROM AN INTERTIDAL SYSTEM OF SOUTHERN SPAIN

The effects of solar radiation on photosynthesis, chlorophyll content and photoinhibition of the red macrophytes Asparagopsis armata, Gelidi um sesquipedale, Plocamium cartilagineum and Feldmannophycus rayssiae from an intertidal system of southern Spain were estimated by means of pulse amplitude modulated fluorometer (PAM), by measurement of the O- 2 exchange, and by quantification of the chlorophyll content of the th alli. The effective quantum yield (Delta F/F-m') decreased in all the experimental organisms after 60 min of exposure to solar radiation; mo reover, photoinhibition seemed to be more pronounced and long-lasting in shade-type plants. Secondly, all macrophytes from this study suffer ed more or less pronounced photoinhibition during some hours of the da y at their natural living site. Photoinhibition was maximal around noo n and the early afternoon, but almost complete recovery of photosynthe sis was achieved by dusk. Similarly, oxygen production and chlorophyll a content were minimal around noon. The ratio (1-qP)/qN was lower in shade than in sun algae indicating a lower electron flow rate, and a l ower rate of protective energy dissipation in shade than in sun-grown algae. This ratio is suggested as a good indicator of light stress, to compare different algal species with different pigment content, i.e. sun- and shade-type algae.