Abstract
Coral reefs are in rapid decline on a global scale due to human activities and a changing climate. Shallow water reefs depend on the obligatory symbiosis between the habitat forming coral host and its algal symbiont from the genus Symbiodinium (zooxanthellae). This association is highly sensitive to thermal perturbations and temperatures as little as 1°C above the average summer maxima can cause the breakdown of this symbiosis, termed coral bleaching. Predicting the capacity of corals to survive the expected increase in seawater temperatures depends strongly on our understanding of the thermal tolerance of the symbiotic algae. Here we use molecular phylogenetic analysis of four genetic markers to describe Symbiodinium thermophilum, sp. nov. from the Persian/Arabian Gulf, a thermally tolerant coral symbiont. Phylogenetic inference using the non-coding region of the chloroplast psbA gene resolves S. thermophilum as a monophyletic lineage with large genetic distances from any other ITS2 C3 type found outside the Gulf. Through the characterisation of Symbiodinium associations of 6 species (5 genera) of Gulf corals, we demonstrate that S. thermophilum is the prevalent symbiont all year round in the world's hottest sea, the southern Persian/Arabian Gulf.
Highlights
Symbiodinium thermophilum sp. nov., a thermotolerant symbiotic alga prevalent in corals of the world’s hottest sea, the Persian/Arabian Gulf
Through the characterisation of Symbiodinium associations of 6 species (5 genera) of Gulf corals, we demonstrate that S. thermophilum is the prevalent symbiont all year round in the world’s hottest sea, the southern Persian/Arabian Gulf
Denaturing gradient gel electrophoresis (DGGE) of the nrDNA ITS2 region was used to identify predominant Symbiodinium types associated with the corals
Summary
Symbiodinium thermophilum sp. nov., a thermotolerant symbiotic alga prevalent in corals of the world’s hottest sea, the Persian/Arabian Gulf. In a number of locations in the Persian/Arabian Gulf (hereafter referred to as ‘the Gulf’) corals are able to cope with exceptionally high seasonal temperature maxima (34–36uC) as well as large (,20uC) annual fluctuations[18,19,20,21]. The existence of these coral communities indicates that at least some coral-Symbiodinium associations can survive under conditions that are predicted to occur in coral reef containing waters elsewhere in the 100 years. The physiological basis for this stress resilience is not yet understood[24]
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