Southern Ocean Acidification impacts: Calcifying vs non-calcifying species

Abstract

Southern Ocean organisms are thought to be particularly vulnerable to ocean acidification (OA), as they inhabit cold waters where calcite-aragonite saturation states are naturally low. It is also generally assumed that calcifying animals would be more affected by the OA. In this context, we proposed to study the impacts of low-pH on two dominant species from an Antarctic fjord, one non calcifying, the ascidia Cnemidocarpa verrucosa and the bivalve Yoldia eightsii. We report results of ~2 months of experiment, comparing the molecular mechanisms underlying responses under two pCO2 treatments (ambient and low-pH). Enzymatic activity (spectrophotometry) and RNAseq using mass sequencing techniques were performed. Significant effects were found in caspase (Mann-Whitney; W=26.00; p=0.02) in C. verrucosa at 2 months in low-pH condition. There was an increase in the regulation of 224 genes and a decrease in the expression of 111 (FC≥2; p-value≤0.05). Particularly, low-pH caused an up-regulation of genes involved in the immune system and antioxidant response. While in the infaunal bivalve Y. eightsii less differentially expressed genes were observed, an up-regulation of 34 genes and a decrease in the expression of 69 genes were found (F ≥2; pvalue≤0.05). This work addresses the effect of OA in two abundant species from Potter Cove and surprisingly showed a more pronounced response in the non-calcifying species. The present approach is being carried out in other species, such as corals, limpets and snails, which in turn will allow us to increase the understanding of the response capacity of Antarctic coastal ecosystems to climate change.