Ocean Acidification at High Latitudes: Potential Effects onFunctioning of the Antarctic Bivalve Laternula elliptica

摘要

Ocean acidification is a well recognised threat to marine ecosystems. High latitude regions are predicted to be particularly affected due to cold waters and naturally low carbonate saturation levels. This is of concern for organisms utilising calcium carbonate (CaCO3) to generate shells or skeletons. Studies of potential effects of future levels of pCO2 on high latitude calcifiers are at present limited, and there is little understanding of their potential to acclimate to these changes. We describe a laboratory experiment to compare physiological and metabolic responses of a key benthic bivalve, Laternula elliptica, at pCO2 levels of their natural environment (430 µatm, pH 7.99; based on field measurements) with those predicted for 2100 (735 µatm, pH 7.78) and glacial levels (187 µatm, pH 8.32). Adult L. elliptica basal metabolism (oxygen consumption rates) and heat shock protein HSP70 gene expression levels increased in response both to lowering and elevation of pH. Expression of chitin synthase (CHS), a key enzyme involved in synthesis of bivalve shells, was significantly up-regulated in individuals at pH 7.78, indicating L. elliptica were working harder to calcify inseawater undersaturated in aragonite (ΩAr = 0.71),the CaCO3 polymorph of which their shells are comprised. The differentresponse variables were influenced by pH in differing ways, highlighting theimportance of assessing a variety of factors to determine the likely impactof pH change. In combination, the results indicate a negative effect of oceanacidification on whole-organism functioning of L. ellipticaover relatively short terms (weeks-months) that may be energetically difficultto maintain over longer time periods. Importantly, however, the observed changesin L. elliptica CHS gene expression provides evidence forbiological control over the shell formation process, which may enable somedegree of adaptation or acclimation to future ocean acidification scenarios.