Linking thallus morphology with P-I curves of 50 macrobenthic algae from Bolinao, Pangasinan, Philippines

Abstract

This study demonstrated that thallus morphology could affect a species' capacity to utilize light for photosynthesis and, hence, will affect its productivity. Fifty (50) macroalgal species collected from an intertidal habitat in Bolinao, Pangasinan, Philippines were grouped into five "functional-forms" based on their inferred productivity: functional-form group (FFG) A: very thin tubes/sheets/strips, FFG B: thin sheets/delicately branched, FFG C: medium-thick blade/coarsely branched with dense ramuli, FFG D: heavily thick branches/segments or with moderate calcification, and FFG E: heavily calcified. Their photosynthesis-irradiance (P-I) curves were determined through the measurement of oxygen evolved in a closed system after 1-h incubation under six different light treatments. P-I curve parameters such as P n max , I k , I c , α, and R d were assessed to determine the groups' physiological responses to light. The thickness of thallus blades, coarseness of branches, complex branching, and calcification appeared to lessen photosynthetic capacity, as shown by the significantly decreasing trend of P n max from FFGs A-E. FFG A also showed the steepest slope (highest mean α value) compared with the rest of the functional-form groups, indicating their efficiency to utilize low light for photosynthesis. Light saturation and compensation values were less distinct in differentiating the functional form groups, probably because the seaweeds examined were all collected from the same shallow intertidal zone, suggesting their acclimation to similar photon flux densities. Results from this study fit the prediction of the function form hypothesis for seaweeds quite well.