EXPERIMENTAL STUDY ON THE IMPACT OF OCEAN ACIDIFICATION ON PHOTOSYNTHESIS EFFICIENCY IN SYMBIOTIC ZOOXANTHELLAE OF CORALS
ZHOU Jie;YU Ke-Fu;SHI Qi;South China Institute of Oceanology,CAS;Hainan Tropical Marine Biology Research Station,CAS;
Ocean acidification as a phenomenon of lowering pH in the ocean is believed caused by the increase in concentration of CO2 at atmosphere, and it has become a global concern on the environmental threat in recent year. Ocean acidification has already threatened coral reefs and calcifying organisms. Indicated by latest forecast models and field data, the consequences caused by ocean acidification may be much more severe than forecast previously. The objectives of this short-term study are to investigate the viability of three ecologically important reef-building coral species, Acropora valida, Galaxea astreata, and Favites abdita. Corals were exposed to high pCO2 conditions, during which changes in physiological parameters were monitored. Fragments of corals were kept for 10 days under controlled aquarium conditions characterized by elevated pCO2 conditions, i.e. pCO2 values at 450, 650, and 750 μatm. Fluorescence spectra show that the gross photosynthetic efficiency was highest at 650 μatm of pCO2 in seawater. During 10-day experiments, with the time lasting in the acidified seawater, parameters of fluorescence presented a tendency of decrease in diverse degrees, although the responses of the three corals are not consistent with each other. When pCO2 was low, acidification that controlled the changes of zooxanthellae was stronger than fertilization induced by increasing CO2. As the pCO2 increases, the fertilization became apparent, coral assemblage started to fight against acidification for survival, leading to the variations of fluorescence parameters.