A joint mesocosm experiment will take place in February/March 2013 in the bay of Villefranche, nearby the Laboratoire d’Océanographie de Villefranche (LOV; http://www.obs-vlfr.fr/LOV/). Nine mesocosms (52 m3) will be deployed over a 30 days period and 6 different levels of pCO2 and 3 control mesocosms (~ 400 μatm), will be used, in order to cover the range of pCO2 anticipated for the end of the present century. During this experiment, the potential effects of these perturbations on chemistry, planktonic community composition and dynamics including: eucaryotic and prokaryotic species composition, primary production, nutrient and carbon utilization, calcification, diazotrophic nitrogen fixation, organic matter exudation and composition, micro-layer composition and biogas production will be studied by a group of ~ 20-25 scientists from 8 institutes and 6 countries.
Archive for February 7th, 2013
Tags: biological response, corals, multiple factors, temperature
Biological mediation of carbonate dissolution represents a fundamental component of the destructive forces acting on coral reef ecosystems. While ocean acidification can increase dissolution of carbonate substrates, the combined impact of ocean acidification and warming on the microbioerosion of coral skeletons remains unknown. Here, we exposed skeletons of the reef-building corals, Porites cylindrica and Isopora cuneata, to present day (Control: 400 μatm – 24°C) and future pCO2-temperature scenarios projected for the end of the century (Medium: +230 μatm – +2°C; High: +610 μatm – +4°C). Skeletons were also subjected to permanent darkness with initial sodium hypochlorite incubation, and natural light without sodium hypochlorite incubation to isolate the environmental effect of acidic seawater (i.e. Ωaragonite < 1) from the biological effect of photosynthetic microborers. Our results indicated that skeletal dissolution is predominantly driven by photosynthetic microborers, as samples held in the dark did not decalcify. In contrast, dissolution of skeletons exposed to light increased under elevated pCO2-temperature scenarios, with P. cylindrica experiencing higher dissolution rates per month (89%) than I. cuneata (46%) in the high treatment relative to control. The effects of future pCO2-temperature scenarios on the structure of endolithic communities were only identified in P. cylindrica and were mostly associated with a higher abundance of the green algae Ostreobium spp. Enhanced skeletal dissolution was also associated with increased endolithic biomass and respiration under elevated pCO2-temperature scenarios. Our results suggest that future projections of ocean acidification and warming will lead to increased rates of microbioerosion. However, the magnitude of bioerosion responses may depend on the structural properties of coral skeletons, with a range of implications for reef carbonate losses under warmer and more acidic oceans.