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Abstract :
[en] Understanding the physiological response of hermatypic scleractinians
to global changes is critical to predict the future of coral reefs. Coral holo- bionts are complex symbiotic associations where multiple biochemical re- actions involving carbon fluxes and pH balance occur concurrently (respi- ration, photosynthesis, calcification, nitrogen assimilation and (de)nitrification, ...).
In this context, growth and physiology of Seriatopora hystrix are stud- ied in contrasting pCO2 conditions, focusing on accurate quantification of pCO2 fluxes as well as metabolic activity of symbionts. The conditions are selected to match (1) current conditions (385ppm.) and (2) future conditions estimated for 2100 (750ppm; prepared by CO2 addition) as proposed by Riebesell et al. (2010). These studies are performed in origi- nal, small-scale chemostats (total volume: 1.25L). They allow to maintain S.hystrix in controlled environment (temperature 26.9 ± 0.1 àC, 12h/12h light/dark phases, 250 μE.m-1.s-2). Main physico-chemical parameters in- cluding dissolved oxygen concentration, pH in total scale, pCO2, total alkalinity and nutrients concentration are monitored. Each organism is successively placed in current and future conditions (randomly) during 24h, to take into account individual variability. In this poster we compare gross/net photosynthesis, respiration, growth, calcification, nutrients ab- sorption of S.hystrix in each pCO2 condition, and total balance of pCO2 is quantified (source or sink) every 4 h. Effects of light and dark phases on physiological activities are also investigated. The chemostats and protocol can be easely adjusted to investigate the impact of other (or combined) stresses on S.hystrix physiology or other marine organisms.
