The Arabian Gulf is well known as being probably the most extreme environment in which zooxanthellate coral reef communities occur. A combination of both extremely high and low temperatures as well as high salinities, combined with shallow profile of the coastal waters (high luminosity) imply high stress for coral physiology that may explain much of the coral bleaching events observed during the last decade. We proposed to investigate corals Symbiodinium response to different levels of those three elements. Among the different available methods; fluorescence technique (Imaging Pulse Amplitude Modulation - PAM) and buoyant weight were used to assess photosynthetic activity and health stress. Porites sp. samples were collected from two Qatari marine areas and exposed to high levels of the three essential elements in controlled laboratory conditions. Our results suggested that Imaging-PAM parameters (Maximum Quantum Yield Fv/Fm, Electronic Transfer Rate ETR, and Non-Photochemical Quenching NPQ) and growth gain percentage provided useful routine tools to detect stress situation in hospite Symbiodinium in Porites sp. Moreover, the high resolution images derived from PAM were able to capture the stress before it become visible to observer eyes. Elevated levels of temperature (38 °C) and salinity (50 psu) negatively influenced corals health and caused death events. Coral bleaching started after the sixth day of exposure suggesting that coral are affected only when extreme conditions persists for more than one week. With regards to raised light intensity, no stress was detected; in contrary growth and photosynthetic efficiency increased.

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