SEASONAL LIGHT AND TEMPERATURE RESPONSES OF CAULERPA-TAXIFOLIA FROM THE NORTHWESTERN MEDITERRANEAN

Seasonal light requirements and temperature tolerance of the Mediterra nean green alga Caulerpa taxifolia (Vahl) C. Agardh were examined by m eans of photosynthetic assays. Highest photosynthetic rates (P-max) we re obtained ih late fall (17.9 mg O-2 g(-1) organic dry weight h(-1)), while low values were observed from January to April (7.2-4.0 mg O-2 g(-1) organic dry weight h(-1)). Caulerpa taxifolia displayed low satu ration and compensation points (68-166 mmol m(-2) s(-1) and 1.8-11.5 m mol m(-2) s(-1) respectively) and high efficiency at low incoming phot on flux densities (0.077-0.197 mg O-2 g(-1) organic dry weight h(-1)/m u mol m(-2) s(-1)). Estimated potential depth-limits of colonisation f or this species are around 80 m in the extremely clear waters of the c entral Mediterranean and 50 m in the more turbid waters of the Gulf of Lions (northwestern Mediterranean). Photosynthesis at saturating phot on flux densities (P-max) was positive in the range of temperatures fr om 10 to 35 degrees C, but negative at 40 degrees C. In summer, P-max values were similar from 20-30 degrees C (10.7 mg O-2 g(-1) organic dr y weight h(-1)), while in winter a maximum of 16 mg O-2 g(-1) organic dry weight h(-1) was observed at 25 degrees C. These results indicate that Caulerpa taxifolia is well adapted to light and temperatures that are typical of the infralittoral and upper circalittoral zone in the Mediterranean. Its annual productivity pattern seems less affected by seasonal fluctuations in light and temperature than has been reported for endemic seaweeds. This particular response may enable Caulerpa tax ifolia to outcompete endemic species and explain its potentially high invasive capacity.