Homogeneity of photosynthetic features in canopy-forming macroalgae of the order Fucales from shallow and sheltered environments

Photosynthetic features of different canopy-forming macroalgae of the order Fucales (Phaeophyceae) living in shallow and sheltered environments show a high homogeneity when compared with other morphologically similar species living across a depth gradient. Photosynthesis at saturation (situated around 5 mg O-2 gAFDM(1)h(1)) and photosynthetic efficiency [around 0.4 mg O-2.m(2)s (mu mol photon.gAFDM.h)(-1)] are relatively low, while dark respiration (around 1 mg O-2 gAFDM(1)h(1)) and light at compensation (around 24 mu mol photon.m(-2).s(-1)) are relatively high, as it corresponds to the characteristics of "sun" plants. C:N and C:P ratios suggest a strong nutrient limitation for growth and photosynthesis, in agreement with the low dissolved nutrient levels usually found in shallow Mediterranean waters. Homogeneity in photosynthetic features points to a good local adaptation of the different species to the prevailing light conditions but opens the question of which are the factors allowing the coexistence of different species of Fucales in sheltered and shallow Mediterranean environments.