SEASONAL-CHANGES IN THE PHOTOSYNTHETIC CAPACITIES AND PIGMENT CONTENT OF ULVA-RIGIDA IN A MEDITERRANEAN COASTAL LAGOON

Photosynthetic capacities of Ulva rigida C. Agardh were tested at 4 stages of their in situ vegetative cycle in a Mediterranean coastal lagoon in 1993: during maximal density period, decreasing biomass period, winter low biomass period, and beginning of biomass production period. Unexpectedly in 1993, there was a relatively unusual in situ biomass development which started in the end of spring, was maximal in August and decreased until the end of autumn. Oxygen output and pigment content were measured under constant experimental conditions at the corresponding season temperature (respectively 25 degrees C, 15 degrees C, 7 degrees C and 18 degrees C). That same year, biomass density and some physical parameters were followed monthly in the lagoon. Experimental results suggest that photosynthetic capacities change depending on in situ biomass development, and seasonal trends of light and temperature in the lagoon: maximal in August, similar responses in October and February, and intermediate photosynthetic rate in May. Light appears to be a controlling factor of pigment content with a direct effect until self-shading phenomena appear as population density increases.