Inhibition of algal photosynthesis by a symbiotic coral

When symbiotic dinoflagellate algae (Symbiodinium sp,), isolated from the scleractinian coral Plesiastrea versipora were incubated in homogenized host tissue, carbon fixation was usually lower than in seawater only (43 cases of of 54), and this inhibition occurred throughout the year, Algae incubated in homogenized host tissue fixed a mean of 78.84% +/- 22.6% of the amount fixed by algae in seawater (n = 54, range 33-142%). The difference between rates of fixation in seawater (mean +/- SD of 61.300 +/- 22.71 nmol C/10(5) cells) and in homogenates (mean +/- SD of 47.377 +/- 21.42 nmol C/10(5) cells) in individual experiments, was highly significant (p<0.0001, paired t-test). Homogenized host tissue from populations of P. versipora separated by 4000 km inhibited photosynthesis in algae from both their own and the distant coral population, Inhibition of photosynthesis, was not observed when isolated algae from the anemone, Aiptasia pulchella were incubated in homogenate from P. versipora. An inhibitor of photosynthesis was isolated from a low molecular weight Fraction of homogenized host tissue of P. versipora by cation-exchange chromatography and further purified by HPLC. This is the first natural inhibitor of photosynthesis that has been found in an invertebrate with symbiotic algae.