Photosynthetic performances of two deep-water canopy-forming fucoid algae across a depth gradient: Interspecific variability and short-term adaptation to the light environment

Abstract

Deep-water canopy-forming algae Gongolaria montagnei var. compressa and Ericaria zosteroides (Fucales: Ochrophyta) co-exist in mixed populations, the first taxa dominating at the upper limit of distribution (20 m) and the second at the lower limit (40 m). This depth distribution pattern is consistent with the photosynthetic performances of both taxa, with E. zosteroides showing higher photosynthetic efficiency (α) and lower light at saturation (Ik) and compensation (Ic) than G. montagnei var. compressa. Neither photosynthesis at saturation (Pmax) nor dark respiration showed any significant change at the species level. G. montagnei v. compressa showed higher Pmax and α at 20 and 40 m, but E. zosteroides did not follow the same trend, although both Ik and Ic decreased with depth in this species, pointing to an increased capacity of E. zosteroides to show photo-adaptation. Each species maintained its Psat values when transplanted from the depth where it was dominant to the depth where it was secondary, but in the case of G. montagnei var. compressa it decreased its Psat when transplanted from 40 to 20 m and in the case of E. zosteroides it increased its Psat when transplanted from 20 to 40 m. These results point to a better photosynthetic performance of E. zosteroides than G. montagnei var. compressa at low-light conditions, information that can be used to improve success in restoration action plans.