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The geochemical and biological study of corals
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Effects of elevated temperature and eutrophication on Acropora samoensis
P-G3-08-S
Adam Wang* , Chinese International School
Inga Elizabeth Conti-Jerpe, The University of Hong Kong
Johnny Lyons Richards, The University of Hong Kong
Phil Thompson, The University of Hong Kong
David Micheal Baker, The University of Hong Kong
Presenter Email: adamw5954@gmail.com |
| In the Anthropocene, corals face multiple stressors from different human activities including coastal development and climate change. Eutrophication from runoff negatively affects corals by slowing calcification rates and fueling algal growth that can smother corals. More recently, global climate change has warmed the oceans, resulting in a disruption in coral-algal symbiosis where zooxanthellae algae are expelled from the coral host's a phenomenon known as coral bleaching. Previous studies have identified that some genes are upregulated in response to stressors, including the 70 Kilodalton Heat Shock Protein (HSP70), a chaperone protein involved in refolding proteins during heat and heavy metal stress. While a large amount of research has been conducted on the effects of eutrophication and increased temperatures on different aspects of coral physiology, these two factors are predominantly studied independently, even though they act in tandem in the field. Here we present preliminary results from an experiment investigating the effect of high temperature combined with eutrophic conditions on the expression of HSP70 in a hermatypic coral. Four genotypes of the branching coral Acropora samoensis were subjected to four different treatments for five days: ambient conditions (28©bC, 2mM NO3, 0.01 mM PO4), high temperature (32©bC, 2mM NO3, 0.01 mM PO4), high nutrients (28©bC, 8mM NO3, 0.3 mM PO4), and high nutrients and temperature together (32©bC, 8mM NO3, 0.3 mM PO4). In the final three days of the experiment, we measured physiological changes in the coral symbiont with Pulse Amplitude Modulated (PAM) Fluorometry to quantify photosystem stress (photoinhibition). At the end of the experiment, treatments with only elevated temperature or nutrients were not significantly different from the control, however the combined high nutrient and high heat treatment had significantly lower Quantum Yield. Total RNA from the corals was immediately extracted and reverse transcribed. Gene expression for HSP70 was quantified using Real Time Quantitative Polymerase Chain Reaction (RT-qPCR). While there were slight differences in gene expression across treatments, they were not significant. These data suggest that magnitude and duration of heat stress was not enough to cause physiological changes in the host, but was enough to impact the photosystems in the symbionts. We plan to explore this hypothesis by investigating the relative expression of genes associated with oxidative stress (Catalase, Ferritin) and apoptosis (Survivin) that results from photoinhibition. Furthermore, we will also target a gene involved in calcification (Galaxin) that may be down-regulated in the presence of excess nutrients.
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