The shallow water canopy-forming alga Ericaria brachycarpa (J.Agardh) Molinari-Novoa & Guiry shows higher photosynthetic efficiency (α), maximum photosynthetic rates (P_max), light at compensation (I_c) and dark respiration (R_d) in individuals collected at the lower depth limit of distribution of the species (20 m) than at shallower depths (2 and 10 m). Photosynthesis at saturation light levels (P_sat) does not change in crossed transplants from 3 to 20 and from 20 to 3 m neither after 11 or 90 days. However, production at low light levels (P_b) increased in transplants from 3 to 20 m and decreased in transplants from 20 to 3 m after 90 days. Photosynthesis, both at high and low light levels increased from June to September. Seasonality explained most of the variance (70%) in the values of P_sat, whilst transplantation explained 47% of the variance for P_b and R_d. Thus, E. brachycarpa is able to adapt its photosynthetic performances across its depth distribution limits and easily cope with sudden variations in the light environment associated or not with seasonality.