Since the Persian Gulf is a semi-closed water ecosystem, climate change has more severe impacts on organisms, especially on non-motile ones. The harmful effects on organisms can be studied at all biological levels of morphology, anatomy, physiology, to cellular and molecular levels. The collapse of the symbiotic relationship between coral and its symbiont algae can result in bleaching and it is the first effect of changing favorable conditions on hard coral. The cells produce Heat Shock Proteins (hereinafter referred to as HSP) in response to heat stress. The rate and way of HSP production in corals depend on the expression of the genes encoding these proteins. In this study, we investigated the expression of heat shock gene HSP70 in response to elevated temperature in Acropora downingi (Wallace, 1999) coral reef. After sampling hard corals in March 2018 and adapting them to laboratory conditions, their ambient water temperature increased to 9 °C (from 25 °C to 34 °C). The samples were adapted to laboratory conditions for 2 weeks after being transferred to the laboratory. The water temperature was 25 °C under control conditions, which was increased to 34 °C to create thermal stress. The expression of the gene Hsp70 was evaluated at control time and also 24 h and 48 h after temperature rise. The study showed that gene expression was significantly increased 24 h after stress and it decreased at 48. However, the corals were bleached, which could be due to the deterioration and reduced resistance to heat shock.

Keywords: Heat shock protein, coral, global warming, climate change, Thermal stress

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