Calcification rates of a massive and a branching coral species were unrelated to diversity of endosymbiotic dinoflagellates

Background To explore the possibility that endosymbiotic dinoflagellates (Symbiodiniaceae) are associated with coral calcification rates, we investigated the diversity of symbiotic algae in coral colonies with different calcification rates within massive and branching corals ( Porites australiensis and Acropora digitifera ). Methods and results Genotyping symbiotic algae from colonies with different calcification rates revealed that all the colonies of both species harbored mainly Cladocopium (previously clade C of Symbiodinium ). The Cladocopium symbionts in P. australiensis were mainly composed of C15 and C15bn, and those in A. digitifera of C50a and C50c. We did not detect clear relationships between symbiont compositions and calcification rates within the two coral species. Conclusions Our results suggest that different coral calcification rates within species may be attributed to genetic factors of coral hosts themselves and/or within symbiont genotypes.