The Study Of Acute Orthogonal Stress Driven By Temperature, Salinity And Light Intensity On Qatari Porites Photosynthesis And Growth

ABSTRACT Coral ecosystems are very important as they provide a foundation habitat to many aquatic species. Laboratory experiments (microcosms: ecosystems under controlled conditions) were initiated to understand Qatari corals physiology. Coral samples were collected and nubbins were cultured in pre-acclimatized laboratory aquaria. Acute orthogonal experiments for two weeks were conducted to test the health of the 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. We were able to detect biological responses of the corals to stress stimuli using Imaging-PAM parameters Maximum Quantum Yield (Fv/Fm), Electronic Transfer Rate (ETR) and Non-Photochemical Quenching (NPQ). High levels of temperature and salinity caused damages to the corals, while light intensity did not have negative impact on the photosynthetic activity. OBJECTIVE To establish corals culture under laboratory controlled conditions and detect biological (growth)/ physiological (photosynthesis) responses in corals to different levels of stress stimuli: salinity, light intensity and temperature using Imaging-PAM and buoyant weight. METHODOLOGY Corals samples were collected from mother colonies from different location in Qatar (Umm Al-Arshan and Fuwayirt). Acclimatization process started immediately after reception at laboratory by adding collected corals gradually into pre-acclimatized laboratory aquarium. Corals were stressed for 12 days under 3 stress stimuli (separately): salinity, light intensity and temperature. PAM measurements were taken every 3 days until the end of the experiment. Weight of individual corals was measured at the beginning and at the end. RESULTS & DISCUSSION Results revealed that elevated levels of temperature and salinity have statistically significant effect on Symbidonuim photosynthetic activity; while light intensity did not. High level of salinity (50 psu) affected the corals photosynthetic efficiency (Fv/ Fm) by causing a drop to a very low range (0.28). As a result, corals weight dropped down too. In contrary to salinity, elevated light intensities showed normal regime of efficiency in ETR. Photoadaptive mechanisms of corals (NPQ) allowed them to cope with available light; these mechanisms allowed many coral species to maintain metabolic functions over a broad light rang. The growth rate on the other hand increased with increasing lights. Finally, Porites Symbidonuim are highly sensitive to increases in temperature up to 38°C, where they exhibited complete death "bleached" and PAM parameters Fv/Fm, ETR and NPQ dropped to zero value. CONCLUSION Salinity, light intensity and temperature are considered the most important ecological factors for corals growth. Using high-resolution fluorescence Imaging-PAM combined with its derived detailed image and gain percentage allowed us to identify the stress that is caused by elevated levels of these parameters. High salinities (50 psu) and temperatures (38°C) affect the photosynthetic activities of the in hospite Symbidonuim of Porites. Photosynthetic activity is completely shutoff under 38°C temperatures and an exposure of more than 6 days, damage was detected by PAM. FUTURE WORK PAM associated to genetic identification tools (transcriptomics) by correlating species tolerance to different stress stimuli sounds to be very promising to better understand coral response mechanism.