Abstract
A growing body of evidence suggests that ocean acidification acting synergistically with ocean warming alters carbonate biomineralization in a variety of marine biota. Magnesium often substitutes for Ca in the calcite skeletons of marine invertebrates, increasing their solubility. The spatio-environmental distribution of Mg in marine invertebrates has seldom been studied, despite its importance for assessing vulnerabilities to ocean acidification. Because pH decreases with water depth, it is predicted that levels of Mg in calcite skeletons should also decrease to counteract dissolution. Such a pattern has been suggested by evidence from echinoderms. Data on magnesium content and depth in Arctic bryozoans (52 species, 103 individuals, 150 samples) are here used to test this prediction, aided by comparison with six conceptual models explaining all possible scenarios. Analyses were based on a uniform dataset spanning more than 200 m of coastal water depth. No significant relationship was found between depth and Mg content; indeed, the highest Mg content among the analyzed taxa (8.7 % mol MgCO3) was recorded from the deepest settings (>200 m). Our findings contrast with previously published results from echinoderms in which Mg was found to decrease with depth. The bryozoan results suggest that ocean acidification may have less impact on the studied bryozoans than is generally assumed. In the broad context, our study exemplifies quantitative testing of spatial patterns of skeletal geochemistry for predicting the biological effects of environmental change in the oceans.
Highlights
Ocean acidification is a decrease in pH in the oceans caused by the uptake of anthropogenic CO2 from the atmosphere (e.g., Orr et al 2005) and is recognized to have negative effects on many groups of planktonic and benthic marine invertebrates with calcareous skeletons
Maximum values of Mg in our dataset were unexpectedly found in the bryozoans from the deepest depth bin, while the lowest values were found in the shallowest bin (\50 m) (Table 1)
The fact that there is a lack of pattern locally as well as for the entire area covered by this study demonstrates that local differences in environmental conditions have no appreciable influence on the pattern of skeletal Mg with depth
Summary
Ocean acidification is a decrease in pH in the oceans caused by the uptake of anthropogenic CO2 from the atmosphere (e.g., Orr et al 2005) and is recognized to have negative effects on many groups of planktonic and benthic marine invertebrates with calcareous skeletons (for reviews see Hoegh-Guldberg et al 2007; Fabry 2008; Portner 2008; Fabry et al 2008; Rost et al 2008; Doney et al 2009; Pelejero et al 2010) It may have a biotic impact at various levels, from cells to larvae, mature individuals, populations and entire ecosystems/regions. The effect of elevated CO2 on marine biota is still being assessed and debated
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