Abstract
BackgroundOcean acidification (OA), a change in ocean chemistry due to the absorption of atmospheric CO2 into surface oceans, challenges biogenic calcification in many marine organisms. Ocean acidification is expected to rapidly progress in polar seas, with regions of the Southern Ocean expected to experience severe OA within decades. Biologically, the consequences of OA challenge calcification processes and impose an energetic cost.ResultsIn order to better characterize the response of a polar calcifier to conditions of OA, we assessed differential gene expression in the Antarctic pteropod, Limacina helicina antarctica. Experimental levels of pCO2 were chosen to create both contemporary pH conditions, and to mimic future pH expected in OA scenarios. Significant changes in the transcriptome were observed when juvenile L. h. antarctica were acclimated for 21 days to low-pH (7.71), mid-pH (7.9) or high-pH (8.13) conditions. Differential gene expression analysis of individuals maintained in the low-pH treatment identified down-regulation of genes involved in cytoskeletal structure, lipid transport, and metabolism. High pH exposure led to increased expression and enrichment for genes involved in shell formation, calcium ion binding, and DNA binding. Significant differential gene expression was observed in four major cellular and physiological processes: shell formation, the cellular stress response, metabolism, and neural function. Across these functional groups, exposure to conditions that mimic ocean acidification led to rapid suppression of gene expression.ConclusionsResults of this study demonstrated that the transcriptome of the juvenile pteropod, L. h. antarctica, was dynamic and changed in response to different levels of pCO2. In a global change context, exposure of L. h. antarctica to the low pH, high pCO2 OA conditions resulted in a suppression of transcripts for genes involved in key physiological processes: calcification, metabolism, and the cellular stress response. The transcriptomic response at both acute and longer-term acclimation time frames indicated that contemporary L. h. antarctica may not have the physiological plasticity necessary for adaptation to OA conditions expected in future decades. Lastly, the differential gene expression results further support the role of shelled pteropods such as L. h. antarctica as sentinel organisms for the impacts of ocean acidification.
Highlights
Ocean acidification (OA), a change in ocean chemistry due to the absorption of atmospheric Carbon dioxide (CO2) into surface oceans, challenges biogenic calcification in many marine organisms
The advantages of comparative transcriptomics are valuable in marine systems, where differential gene expression analysis has been used to explore how organisms respond to their abiotic environment
We examined expression profiles for sets of genes involved in four physiological and cellular processes: (i) genes involved in shell formation, (ii) genes associated with the cellular stress response, (iii) genes associated with metabolism, and (iv) genes associated with neural function
Summary
Ocean acidification (OA), a change in ocean chemistry due to the absorption of atmospheric CO2 into surface oceans, challenges biogenic calcification in many marine organisms. We use the analysis of differential gene expression to examine the resistance of a key member of the zooplankton in the Southern Ocean, the shelled pteropod Limacina helicina antarctica, to the impacts of an advancing anthropogenic stress, ocean acidification Polar seas, such as the Southern Ocean, are predicted to be ‘first in time’ to experience the impacts of ocean acidification, the reduction of pH and saturation states for minerals such as aragonite as a result of the absorption of CO2 into surface waters [8,9,10]. This rapid rate of change for the Southern Ocean will present a physiological and energetic challenge to calcifying marine organisms such as the shelled pteropods
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