LAUSR

Abstract The knowledge of the astonishing diversity of intracellular, photosynthetic dinoflagellates in the family Symbiodiniaceae, which have crucial symbioses with scleractinian corals, is essential to anticipate the adaptive response of corals to environmental stressors. Coral reefs in the northern Persian Gulf (nPG) and Gulf of Oman (nGO) experience a wide range of natural (e.g., high and low water temperature, high salinity) and anthropogenic (e.g., different levels of turbidity) disturbances, and so are excellent models to study the effects of these conditions on the biogeography of symbiotic alga. In this regard, the algal component of an acroporid coral was genotyped using chloroplastic 23S, nuclear 28S and the internal transcribed spacer 2 of ribosomal DNA across the nPG and nGO. Two genera (three distinct taxa) were detected, all of which corresponded to previously reported phylogenetic lineages. Durusdinium trenchii was found to be widely distributed in nearly all examined locations in the nPG and nGO. The turbid waters of the nGO and the harsh conditions in the eastern nPG may to some extent explain the ecological success of D. trenchii in these areas. However, in the westernmost nPG (Kharkoo Island), Acropora sp. solely harbored Cladocopium thermophilum. The occurrence of this thermotolerant species only at the westernmost nPG (with higher salinity and water clarity) may reveal the potency of low salinity and excessive turbidity as distribution barriers for the association of these symbiont lineages and corals (at least acroporids) outside the Persian Gulf.