Abstract
Coral bleaching and mortality events have recently increased in frequency and severity in the whole world. Combined effects of natural and anthropogenic impacts were assumed to be the cause for coral’s health degradation. Sedimentation, urban waste, sewage discharge and agricultural activities are among the nutrient input for Malaysian waters, which can affect the coral reefs indirectly. In this study, photosynthetic performance of tropical corals under stresses were studied by exposing three common tropical scleractinian corals, Stylophora pistillata, Montipora digitata and Seriatopora hystrix to combination of different levels of high and ambient temperature and in a laboratory condition. Quantum yield fluorescence before, after stress and after recovery stage were recorded using a dark-adapted photochemical efficiency (Fv/Fm) methodology with a pulse-amplitude-modulation (PAM) chlorophyll fluorometer (WATER-PAM, Walz, Germany). Physical appearance of the corals were after the post-stress stages. The results showed that nutrient enrichment not have a synergistic effect, and that high temperatures alone significantly impact Fv/Fm values (three-way ANOVA, p > 0.05) for all coral species. Slow growing corals (S. pistillata) appeared to cope better with the high temperatures than the fast-growing corals (M. digitata and S. hystrix). Hence, that a nitrate concentration contributed as an intial response of the symbiont’s physiological changes, which can give more understanding on studying specific coral species resistance towards coral bleaching issues.
Highlights
Coral-zooxanthellae symbioses have the ability to survive in a low-nutrient environment, unlike any other organisms [1]
M. digitata showed a recovery after ambient temperature level and high nitrate level of stress
4.1 Coral species response towards high temperature The results indicate that high temperature is the dominant stressor to the coral species and the corals are more susceptible to high temperatures (30°C) than the high nitrate levels
Summary
Coral-zooxanthellae symbioses have the ability to survive in a low-nutrient environment, unlike any other organisms [1]. Experimental protocol for photochemical efficiency measurement Experiments were performed in the laboratory using nubbins (4-5 cm) of three species of scleractinian corals, S. pistillata, M. digitata and S. hystrix They were chosen because of their high and moderate susceptibility to bleaching, fast growth and abundance in Malaysian waters [21] [22]. All experimental aquaria were aerated by spreader bars to keep the water evenly heated In this experiment, nitrate was added to the nutrient enriched treatments as NaNO3. (a) ambient control (27oC, 2 μM NO3−) (b) high nitrate (27oC, 15 μM NO3−) (c) high temperature (30oC, 2 μM NO3−) (d) high temperature + high nitrate (30oC, 15 μM NO3) After the stress-experiments, corals were brought to a shallow black water-filled container under a black canvas Both black container and canvas allowed the corals to dark-adapt and made successive measurements of the Fv/Fm parameter of the samples [26]. The post-hoc Tukey is used for multiple comparison of means at P
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