Are symbiotic algae in corals in northern parts of the Persian Gulf resistant to thermal stress?

One of the most important factors threatening the ecosystem today is global warming resulting from human-induced climate change. Coral dominated ecosystems sensitive to such stressors are negatively affected by an increase in sea surface temperatures which can lead to the deterioration of coral reef communities. This occurs following the break-down of the symbiosis between corals and their endosymbiotic zooxanthellae which play an important role in the corals' capacity to thrive in extreme conditions. Various Symbiodinium clades also exhibit differing resistance to such circumstances. The present study aimed to specify the zooxanthella types of coral reefs in northern parts of the Persian Gulf. For this purpose, different coral species were collected from several locations, i.e. from Larak, Farur and Hendourabi Islands. Throughout the study, partial 28S nuclear ribosomal (nr) DNA of Symbiodinium was amplified using polymerase chain reaction (PCR), and the resulting PCR products were analyzed. Results showed that Symbiodinium clade D was the most abundant symbiont in the sampled corals. Clade C was the next most common Symbiodinium at the studied sites, with the exception of Larak Island in the Strait of Hormuz, where clade C was not found and the rarer clade A occurred. The frequency with which clade D, A and C were found was 70%, 18.3% and 11.7%, respectively. The prevalent abundance of clade D may be due to its physiology which is best adapted to the specific conditions of the Persian Gulf and its bleaching history. Hence, with global temperatures continuously on the rise, the capacity of the host-symbiont combination to mitigate the effects of global warming could result in fewer bleaching events.