Coral reefs are very important as they provide a foundation habitat for many aquatic species. Corals are marine invertebrates that exist as communities of polyps. Occasionally when corals experience physical stresses, the polyps expel their symbiotic zooxanthellae resulting in a white appearance. This is commonly described as “coral bleaching”. The Arabian Gulf is well known as one of the most extreme environments 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 and mortality events observed during the last decade. We initiated a series of laboratory experiments (microcosms: ecosystems under controlled conditions) to understand the impact of specific environmental parameters on Qatari coral health under controlled lab conditions. To draw a conclusion about optimum conditions and tolerance range for corals in Qatari waters, Porites sp. nubbins, collected from natural coral reefs North of Qatar, were cultured in pre-acclimatized laboratory aquaria. Orthogonal experiments were conducted to test the physiological response of corals under 3 stress stimuli: salinity, light intensity and temperature. Imaging-Pulse Amplitude Modulation Fluorometry (Imaging-PAM) and buoyant weight were utilized during experiment to measure photosynthetic performance and growth of the corals. Results revealed that elevated levels of temperature and salinity have a statistically significant effect on Symbiodinium photosynthetic activity; while light intensity did not. High level of salinity (50 psu) affected the corals’ photosynthetic efficiency. As a result, corals’ weight dropped down causing partial bleaching which was noticed at day 10 of the experiment with faded spots that covered the corals’ body and allowing other algae to overgrow. The decrease in photosynthetic activities of the in-hospite Symbiodinium under acute salinities and temperature levels were effectively observed through Imaging-PAM only after the 6th day of exposure. This suggests that in-hospite Symbiodinium of Porites sp. are affected only in relatively prolonged extreme conditions. A fast and comprehensive recovery of Porites sp. health could; therefore, be possible for short exposure to extreme temperature or salinity conditions. These results are very important to address the coral mortality and bleaching events occurring in Qatari coastal waters and may help establish guidelines for coral relocation efforts in Qatar marine environment or the identification of potential impacts of thermal pollution on coral reefs in Qatari waters due to industrial discharges from power or desalination plants.


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  • Received: 07 December 2015
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