Trace Metal Requirement of the Coral Symbiont Symbiodinium kawagutii: the Interactive Effects of Cu, Zn, Mn and Co

Coral reefs are ecologically and economically important but these ecosystems are increasingly threatened by coral bleaching, the discoloration caused by decline in population of the endosymbiotic algae Symbiodinium from the coral endoderm or loss of photosynthetic pigments in the symbiont. Survival of the coral-algal symbiosis in an environment susceptible to fluctuating stress is dependent on its capacity to mount antioxidative defenses, which includes antioxidative enzymes such as superoxide dismutases (SOD), catalases, and peroxidases. We studied the effect of trace metals, which are cofactors of different antioxidative ensymes, on S. kawagutii growth when the dinoflagellate is grown in 600 µE m^-2 s^-1 and 27 °C. We found that S. kawagutii requires trace metals as follows: Fe >> Cu/Zn > Mn >> Ni. We also observed that intracellular Mn and Co quotas in S. kawagutii were elevated at low Cu/Zn treatments and that the dinoflagellate required higher Fe when the other metals were not supplied in the growth medium. These results indicate that the dinoflagellate utilizes the different metals preferentially and suggest that Mn or Co may replace Cu or Zn when these are lacking supply in the growth medium. Our results represent the baseline study about the trace metal requirement for the growth of Symbiodinium and these could lead to a better understanding about the role of trace metals in the survival of corals in an environment largely influenced by anthropogenic activities.