Abstract: This study investigated the difference of photosynthetic capacity in three macroalgae species (Ulva lactuca, Enteromorpha clathrata, and Caulerpa mexicana) commonly used for nutrient removal in coral aquariums. The photochemical efficiency (F_v/F_m), parameters relevant to rapid light curve (RLC) and nonphotochemical quenching (NPQ) in the macroalgae were measured by underwater saturation pulse modulated chlorophyll fluorometer (Diving-PAM). The results showed that F_v/F_m was 0.808±0.004 for U. lactuca and 0.816±0.009 for E. clathrata, which were higher than that for C. mexicana. Higher maximum relative electron transfer rates (rETR_max) (17.52±2.92 and 19.59±4.43 μmol e·m^-2·s^-1) and halfstarved value of light intensities (I_k) (53.41±8.18 and 59.71±13.52 μmol photons·m^-2·s^-1) were observed in U. lactuca and E. clathrata than that in C. mexicana (13.72±5.41 μmol e·m^-2·s^-1 for rETR_max and 32.67±14.06 μmol photons·m^-2·s^-1 for I_k), indicating that U. lactuca and E. clathrata have stronger photosynthetic capacities, photoprotection capacities and tolerance to higher intense light than C. mexicana. A significantly lower RLC initial slope α in C. mexicana implied that this algal species has a higher photosynthetic capacity under weak light condition. With increasing the light intensity (0-373 μmol photons·m^-2·s^-1), however, C. mexicana had a limited increase of NPQ (0-0.2), the maximum of which was equivalent to 38.1% of that in U. lactuca and 62.5% of that in E. clathrata. These results indicate that the photosynthesis of E. clathrata may be more easily limited by intense light. Our study suggests that the selection of algal species for nutrient removal in a coral aquarium should be adapted to the light intensity. Single species or the combination of different species of macroalgae can be selected according to the illumination of the coral aquarium in order to maximize the efficiency of nutrient removal.

Key words: flue-cured tobacco, suitability., climate change