A transcriptomic analysis of the response of the arctic pteropod Limacina helicina to carbon dioxide-driven seawater acidification

Ocean acidification from the uptake of anthropogenic carbon dioxide (CO₂) is regarded as a critical threat particularly to marine calcifying organisms. The arctic pteropod Limacina helicina may be one of the first polar organisms that are expected to display early sensitivity to ocean acidification, but a molecular approach as a foundation for understanding the effect of ocean acidification on this pteropod has rarely been reported. In this study, we examined the sublethal effects of CO₂-driven seawater acidification at the transcriptome level in L. helicina. cDNAs, treated under control (pH 8.2), high-CO₂ (pH 7.5), and extreme-CO₂ (pH 6.5) conditions, generated a total of 31,999,474 reads, comprising a total of 2,271,962,654 bp, using the Illumina platform. De novo assembly yielded 53,121 transcripts comprising 31.79 Mbp. Among the upregulated genes, 346 (0.7 %) and 655 (1.2 %) genes responded to extreme-level CO₂ (pH 6.5) and high-level CO₂ (pH 7.5), respectively. Also, 76 (0.1 %) transcripts were commonly upregulated in both conditions. Among the downregulated genes, 690 (1.3 %) and 739 (1.4 %) genes were in response to extreme-level CO₂ and high-level CO₂, respectively. Also, 270 downregulated genes (0.5 %) were affected in both acidic stress conditions. Moreover, 504 transcripts (1 %) of biomineralization-related genes were identified; 16 of these genes showed differential expression in response to acidified seawater. The dataset provides the first comprehensive overview of changes in transcript levels in the arctic pteropod L. helicina in response to increased CO₂, emphasizing the potential impact of future environmental change and ocean acidification on Arctic species with external calcified structures.