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In the frame of the European Project on Ocean Acidification (EPOCA), the response of an Arctic pelagic community (pCO2 was investigated. For this purpose 9 large-scale in situ mesocosms were deployed in Kongsfjorden, Svalbard (78°56.2´ N, 11°53.6´ E), in 2010. The present study investigates effects on the communities of particle-attached (PA; >3 μm) and free-living (FL; < 3 μm > 0.2 μm) bacteria by Automated Ribosomal Intergenic Spacer Analysis (ARISA) in 6 of the mesocosms, ranging from 185 to 1050 μatm initial pCO2, and the surrounding fjord. ARISA was able to resolve, on average, 27 bacterial band classes per sample and allowed for a detailed investigation of the explicit richness and diversity. Both, the PA and the FL bacterioplankton community exhibited a strong temporal development, which was driven mainly by temperature and phytoplankton development. In response to the breakdown of a picophytoplankton bloom, numbers of ARISA band classes in the PA community were reduced at low and medium CO2 (~ 185–685 μatm) by about 25%, while they were more or less stable at high CO2 (~ 820–1050 μatm). We hypothesise that enhanced viral lysis and enhanced availability of organic substrates at high CO2 resulted in a more diverse PA bacterial community in the post-bloom phase. Despite lower cell numbers and extracellular enzyme activities in the post-bloom phase, bacterial protein production was enhanced in high CO2 mesocosms, suggesting a positive effect of community richness on this function and on carbon cycling by bacteria.

International audience; The response of respiration, photosynthesis, and calcification to elevated pCO2 and temperature was investigated in isolation and in combination in the Mediterranean crustose coralline alga Lithophyllum cabiochae. Algae were maintained in aquaria during 1year at near-ambient conditions of irradiance, at ambient or elevated temperature (+3 degrees C), and at ambient (ca. 400atm) or elevated pCO2 (ca. 700atm). Respiration, photosynthesis, and net calcification showed a strong seasonal pattern following the seasonal variations of temperature and irradiance, with higher rates in summer than in winter. Respiration was unaffected by pCO2 but showed a general trend of increase at elevated temperature at all seasons, except in summer under elevated pCO2. Conversely, photosynthesis was strongly affected by pCO2 with a decline under elevated pCO2 in summer, autumn, and winter. In particular, photosynthetic efficiency was reduced under elevated pCO2. Net calcification showed different responses depending on the season. In summer, net calcification increased with rising temperature under ambient pCO2 but decreased with rising temperature under elevated pCO2. Surprisingly, the highest rates in summer were found under elevated pCO2 and ambient temperature. In autumn, winter, and spring, net calcification exhibited a positive or no response at elevated temperature but was unaffected by pCO2. The rate of calcification of L.cabiochae was thus maintained or even enhanced under increased pCO2. However, there is likely a trade-off with other physiological processes. For example, photosynthesis declines in response to increased pCO2 under ambient irradiance. The present study reports only on the physiological response of healthy specimens to ocean warming and acidification, however, these environmental changes may affect the vulnerability of coralline algae to other stresses such as pathogens and necroses that can cause major dissolution, which would have critical consequence for the sustainability of coralligenous habitats and the budgets of carbon and calcium carbonate in coastal Mediterranean ecosystems.

International audience; Coralline algae are major calcifiers of significant ecological importance in marine habitats but are among the most sensitive calcifying organisms to ocean acidification. The elevated pCO(2) effects were examined in three coralline algal species living in contrasting habitats from intertidal to subtidal zones on the north-western coast of Brittany, France: (i) Corallina elongata, a branched alga found in tidal rock pools, (ii) Lithophyllum incrustans, a crustose coralline alga from the low intertidal zone, and (iii) Lithothamnion corallioides (maerl), a free-living form inhabiting the subtidal zone. Metabolic rates were assessed on specimens grown for one month at varying pCO(2): 380 (current pCO(2)), 550, 750 and 1000 mu atm (elevated pCO(2)). There was no pCO(2) effect on gross production in C. elongata and L. incrustans but L. incrustans respiration strongly increased with elevated pCO(2). L corallioides gross production slightly increased at 1000 mu atm, while respiration remained unaffected. Calcification rates decreased with pCO(2) in L. incrustans (both in the light and dark) and L. corallioides (only in the light), while C. elongata calcification was unaffected. This was consistent with the lower skeletal mMg/Ca ratio of C. elongata (0.17) relative to the two other species (0.20). L. incrustans had a higher occurrence of bleaching that increased with increasing pCO(2). pCO(2) could indirectly impact this coralline species physiology making them more sensitive to other stresses such as diseases or pathogens. These results underlined that the physiological response of coralline algae to near-future ocean acidification is species-specific and that species experiencing naturally strong pH variations were not necessarily more resistant to elevated pCO(2) than species from more stable environment. (C) 2013 Elsevier B.V. All rights reserved.

International audience; Marine organisms inhabiting environments where pCO(2)/pH varies naturally are suggested to be relatively resilient to future ocean acidification. To test this hypothesis, the effect of elevated pCO(2) was investigated in the articulated coralline red alga Corallina elongata from an intertidal rock pool on the north coast of Brittany (France), where pCO(2) naturally varied daily between 70 and 1000 mu atm. Metabolism was measured on algae in the laboratory after they had been grown for 3 weeks at pCO(2) concentrations of 380, 550, 750 and 1000 mu atm. Net and gross primary production, respiration and calcification rates were assessed by measurements of oxygen and total alkalinity fluxes using incubation chambers in the light and dark. Calcite mol % Mg/Ca (mMg/Ca) was analysed in the tips, branches and basal parts of the fronds, as well as in new skeletal structures produced by the algae in the different pCO(2) treatments. Respiration, gross primary production and calcification in light and dark were not significantly affected by increased pCO(2). Algae grown under elevated pCO(2) (550, 750 and 1000 mu atm) formed fewer new structures and produced calcite with a lower mMg/Ca ratio relative to those grown under 380 mu atm. This study supports the assumption that C. elongata from a tidal pool, where pCO(2) fluctuates over diel and seasonal cycles, is relatively robust to elevated pCO(2) compared to other recently investigated coralline algae.

International audience; Primary production and calcification responses to irradiance were investigated in Lithophyllum cabiochae, a crustose coralline alga from Mediterranean coralligenous communities, collected at c. 25m depth in the Bay of Villefranche. Algae were maintained in aquaria at temperature and irradiance levels close to in situ conditions. Physiological measurements were performed using incubation chambers in the dark and in the light at different irradiance levels within the range of those measured in situ. Both photosynthesis and calcification rates in L. cabiochae were strongly related to irradiance. Dark respiration averaged 0.20.3 mu molcm(2) thallus h(1) in terms of both O-2 consumption and CO2 release and maximal gross photosynthesis averaged 1.0 mu molcm(2) h(1) in terms of both O-2 production and CO2 uptake. Mean rate of net calcification was 0.1 mu mol CaCO3 cm(2) h(1) in the dark and reached 0.4 mu mol CaCO3 cm(2) h(1) in the light. Diel net and gross organic C productions were estimated to be 3 and 7 mu molC cm(2) thallus d(1,) respectively. Diel net inorganic C production was estimated to be 3 mu mol CaCO3 cm(2) thallus d(1). Despite the low light conditions experienced by the algae at c. 25m depth, L. cabiochae can be considered as a major contributor to primary productivity and calcium carbonate deposition, making coralligenous communities a major carbon and carbonate producer in the Mediterranean Sea.

International audience; Over the next century, elevated quantities of atmospheric CO2 are expected to penetrate into the oceans, causing a reduction in pH (-0.3/-0.4 pH unit in the surface ocean) and in the concentration of carbonate ions (so-called ocean acidification). Of growing concern are the impacts that this will have on marine and estuarine organisms and ecosystems. Marine shelled molluscs, which colonized a large latitudinal gradient and can be found from intertidal to deep-sea habitats, are economically and ecologically important species providing essential ecosystem services including habitat structure for benthic organisms, water purification and a food source for other organisms. The effects of ocean acidification on the growth and shell production by juvenile and adult shelled molluscs are variable among species and even within the same species, precluding the drawing of a general picture. This is, however, not the case for pteropods, with all species tested so far, being negatively impacted by ocean acidification. The blood of shelled molluscs may exhibit lower pH with consequences for several physiological processes (e.g. respiration, excretion, etc.) and, in some cases, increased mortality in the long term. While fertilization may remain unaffected by elevated pCO(2), embryonic and larval development will be highly sensitive with important reductions in size and decreased survival of larvae, increases in the number of abnormal larvae and an increase in the developmental time. There are big gaps in the current understanding of the biological consequences of an acidifying ocean on shelled molluscs. For instance, the natural variability of pH and the interactions of changes in the carbonate chemistry with changes in other environmental stressors such as increased temperature and changing salinity, the effects of species interactions, as well as the capacity of the organisms to acclimate and/or adapt to changing environmental conditions are poorly described.

International audience; Boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water Mediterranean coral Cladocora caespitosa. The corals are from a range of seawater pH conditions (pH(T) similar to 7.6 to similar to 8.1) and environmental settings: (1) naturally living colonies harvested,from normal pH waters offshore Levanto, (2) colonies transplanted nearby a subsea volcanic vent system, and (3) corals cultured in aquaria exposed to high (700 mu atm) and near present day (400 mu atm) pCO(2) levels. BiCa compositions measured using laser ablation inductively coupled mass spectrometry (LA-ICPMS) show that boron uptake by C caespitosa cultured at different pCO(2) levels is independent of ambient seawater pH being mainly controlled by temperature-dependent calcification. In contrast, the boron isotope compositions (delta(11)B(carb)) of the full suite of corals determined by positive thermal ionisation mass spectrometry (PTIMS) shows a clear trend of decreasing delta(11) B(carb) (from 26.7 to 22.2%.) with decreasing seawater pH. reflecting the strong pH dependence of the boron isotope system. The delta(11)B(carb) compositions together with measurements of ambient seawater parameters enable calibration of the boron pH proxy for C caespitosa, by using a new approach that defines the relationship between ambient seawater pH (pH,) and the internally controlled pH at the site of calcification (pH(biol)). C. caespitosa exhibits a linear relationship between pH(sw) and the shift in pH due to physiological processes (Delta pH = pH(biol) - pH(sw)) giving the regression Delta pH(clad) = 4.80 - 0.52 x pH(sw) for this species. We further apply this method (''Delta pH-pH(sw)'') to calibrate tropical species of Porites, Acropora, and Stylophora reported in the literature. The temperate and tropical species calibrations are all linearly correlated (r(2)> 0.9) and the biological fractionation component (pH) between species varies within similar to 0.2 pH units. Our ``Delta pH-pH(sw)'' approach provides a robust and accurate tool to reconstruct palaeoseawater pH, for both temperate and tropical corals, further validating the boron fractionation factor (alpha(B3)-(B4) = 1.0272) determined experimentally by Klochko et al. (2006) and the boron isotope pH proxy, both of which have been the foci of considerable debate. (C) 2011 Elsevier B.V. All rights reserved.

SUMMARYOcean acidification is predicted to have significant effects on benthic calcifying invertebrates, in particular on their early developmental stages. Echinoderm larvae could be particularly vulnerable to decreased pH, with major consequences for adult populations. The objective of this study was to understand how ocean acidification would affect the initial life stages of the sea urchin Paracentrotus lividus, a common species that is widely distributed in the Mediterranean Sea and the NE Atlantic. The effects of decreased pH (elevated PCO2) were investigated through physiological and molecular analyses on both embryonic and larval stages. Eggs and larvae were reared in Mediterranean seawater at six pH levels, i.e. pHT 8.1, 7.9, 7.7, 7.5, 7.25 and 7.0. Fertilization success, survival, growth and calcification rates were monitored over a 3 day period. The expression of genes coding for key proteins involved in development and biomineralization was also monitored. Paracentrotus lividus appears to be extremely resistant to low pH, with no effect on fertilization success or larval survival. Larval growth was slowed when exposed to low pH but with no direct impact on relative larval morphology or calcification down to pHT 7.25. Consequently, at a given time, larvae exposed to low pH were present at a normal but delayed larval stage. More surprisingly, candidate genes involved in development and biomineralization were upregulated by factors of up to 26 at low pH. Our results revealed plasticity at the gene expression level that allows a normal, but delayed, development under low pH conditions.