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      <i>δ</i><sup>11</sup>B as monitor of calcification site pH in divergent marine calcifying organisms

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      Biogeosciences
      Copernicus GmbH

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          Abstract

          <p><strong>Abstract.</strong> The boron isotope composition (<i>δ</i><sup>11</sup>B) of marine biogenic carbonates has been predominantly studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. However, a number of assumptions regarding chemical kinetics and thermodynamic isotope exchange reactions are required to derive seawater pH from <i>δ</i><sup>11</sup>B biogenic carbonates. It is also probable that <i>δ</i><sup>11</sup>B of biogenic carbonate reflects seawater pH at the organism's site of calcification, which may or may not reflect seawater pH. Here, we report the development of methodology for measuring the <i>δ</i><sup>11</sup>B of biogenic carbonate samples at the multi-collector inductively coupled mass spectrometry facility at Ifremer (Plouzané, France) and the evaluation of <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> in a diverse range of marine calcifying organisms reared for 60 days in isothermal seawater (25<span class="thinspace"></span>°C) equilibrated with an atmospheric <i>p</i>CO<sub>2</sub> of ca. 409<span class="thinspace"></span>µatm. Average <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> composition for all species evaluated in this study range from 16.27 to 35.09<span class="thinspace"></span>‰, including, in decreasing order, coralline red alga <i>Neogoniolithion</i> sp. (35.89<span class="thinspace"></span>±<span class="thinspace"></span>3.71<span class="thinspace"></span>‰), temperate coral <i>Oculina arbuscula</i> (24.12<span class="thinspace"></span>±<span class="thinspace"></span>0.19<span class="thinspace"></span>‰), serpulid worm <i>Hydroides crucigera</i> (19.26<span class="thinspace"></span>±<span class="thinspace"></span>0.16<span class="thinspace"></span>‰), tropical urchin <i>Eucidaris tribuloides</i> (18.71<span class="thinspace"></span>±<span class="thinspace"></span>0.26<span class="thinspace"></span>‰), temperate urchin <i>Arbacia punctulata</i> (16.28<span class="thinspace"></span>±<span class="thinspace"></span>0.86<span class="thinspace"></span>‰), and temperate oyster <i>Crassostrea virginica</i> (16.03<span class="thinspace"></span>‰). These results are discussed in the context of each species' proposed mechanism of biocalcification and other factors that could influence skeletal and shell <i>δ</i><sup>11</sup>B, including calcifying site pH, the proposed direct incorporation of isotopically enriched boric acid (instead of borate) into biogenic calcium carbonate, and differences in shell/skeleton polymorph mineralogy. We conclude that the large inter-species variability in <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> (ca. 20<span class="thinspace"></span>‰) and significant discrepancies between measured <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> and <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> expected from established relationships between abiogenic <i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> and seawater pH arise primarily from fundamental differences in calcifying site pH amongst the different species. These results highlight the potential utility of <i>δ</i><sup>11</sup>B as a proxy of calcifying site pH for a wide range of calcifying taxa and underscore the importance of using species-specific seawater-pH–<i>δ</i><sup>11</sup>B<sub>CaCO<sub>3</sub></sub> calibrations when reconstructing seawater pH from <i>δ</i><sup>11</sup>B of biogenic carbonates.</p>

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          Ocean acidification: the other CO2 problem.

          Rising atmospheric carbon dioxide (CO2), primarily from human fossil fuel combustion, reduces ocean pH and causes wholesale shifts in seawater carbonate chemistry. The process of ocean acidification is well documented in field data, and the rate will accelerate over this century unless future CO2 emissions are curbed dramatically. Acidification alters seawater chemical speciation and biogeochemical cycles of many elements and compounds. One well-known effect is the lowering of calcium carbonate saturation states, which impacts shell-forming marine organisms from plankton to benthic molluscs, echinoderms, and corals. Many calcifying species exhibit reduced calcification and growth rates in laboratory experiments under high-CO2 conditions. Ocean acidification also causes an increase in carbon fixation rates in some photosynthetic organisms (both calcifying and noncalcifying). The potential for marine organisms to adapt to increasing CO2 and broader implications for ocean ecosystems are not well known; both are high priorities for future research. Although ocean pH has varied in the geological past, paleo-events may be only imperfect analogs to current conditions.
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            Impacts of ocean acidification on marine organisms: quantifying sensitivities and interaction with warming

            Ocean acidification represents a threat to marine species worldwide, and forecasting the ecological impacts of acidification is a high priority for science, management, and policy. As research on the topic expands at an exponential rate, a comprehensive understanding of the variability in organisms' responses and corresponding levels of certainty is necessary to forecast the ecological effects. Here, we perform the most comprehensive meta-analysis to date by synthesizing the results of 228 studies examining biological responses to ocean acidification. The results reveal decreased survival, calcification, growth, development and abundance in response to acidification when the broad range of marine organisms is pooled together. However, the magnitude of these responses varies among taxonomic groups, suggesting there is some predictable trait-based variation in sensitivity, despite the investigation of approximately 100 new species in recent research. The results also reveal an enhanced sensitivity of mollusk larvae, but suggest that an enhanced sensitivity of early life history stages is not universal across all taxonomic groups. In addition, the variability in species' responses is enhanced when they are exposed to acidification in multi-species assemblages, suggesting that it is important to consider indirect effects and exercise caution when forecasting abundance patterns from single-species laboratory experiments. Furthermore, the results suggest that other factors, such as nutritional status or source population, could cause substantial variation in organisms' responses. Last, the results highlight a trend towards enhanced sensitivity to acidification when taxa are concurrently exposed to elevated seawater temperature.
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              Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms.

              Ocean acidification is a pervasive stressor that could affect many marine organisms and cause profound ecological shifts. A variety of biological responses to ocean acidification have been measured across a range of taxa, but this information exists as case studies and has not been synthesized into meaningful comparisons amongst response variables and functional groups. We used meta-analytic techniques to explore the biological responses to ocean acidification, and found negative effects on survival, calcification, growth and reproduction. However, there was significant variation in the sensitivity of marine organisms. Calcifying organisms generally exhibited larger negative responses than non-calcifying organisms across numerous response variables, with the exception of crustaceans, which calcify but were not negatively affected. Calcification responses varied significantly amongst organisms using different mineral forms of calcium carbonate. Organisms using one of the more soluble forms of calcium carbonate (high-magnesium calcite) can be more resilient to ocean acidification than less soluble forms (calcite and aragonite). Additionally, there was variation in the sensitivities of different developmental stages, but this variation was dependent on the taxonomic group. Our analyses suggest that the biological effects of ocean acidification are generally large and negative, but the variation in sensitivity amongst organisms has important implications for ecosystem responses. © 2010 Blackwell Publishing Ltd/CNRS.
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                Author and article information

                Journal
                Biogeosciences
                Biogeosciences
                Copernicus GmbH
                1726-4189
                2018
                March 08 2018
                : 15
                : 5
                : 1447-1467
                Article
                10.5194/bg-15-1447-2018
                ce847d0d-d1d9-4fe7-a3f5-c022e34e9bd5
                © 2018

                https://creativecommons.org/licenses/by/3.0/

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