Energetics, but not development, is impacted in coral embryos exposed to ocean acidification

Abstract

In light of the chronic stress and mass mortality reef-building corals face under climate change, it is critical to understand the processes driving reef persistence and replenishment, including coral reproduction and development. Here we quantify gene expression and sensitivity to ocean acidification across a set of developmental stages in the rice coral, Montipora capitata. Embryos and swimming larvae were exposed to pH treatments 7.8 (Ambient), 7.6 (Low) and 7.3 (Xlow) from fertilization to 9 days post-fertilization. Embryo and larval volume, and stage-specific gene expression were compared between treatments to determine the effects of acidified seawater on early development. While there was no measurable size differentiation between pH treatments at the fertilized egg and prawn chip (9 hours post-fertilization) stages, early gastrulae and larvae raised in reduced pH treatments were significantly smaller than those raised in ambient seawater, suggesting an energetic cost to developing under low pH. However, no differentially expressed genes were found until the swimming larval stage. Notably, gene expression patterns of larvae developing at pH 7.8 and pH 7.3 were more similar than those developing at pH 7.6. Larvae from pH 7.6 showed upregulation of genes involved in cell division, regulation of transcription, lipid metabolism, and response to oxidative stress in comparison to the other two treatments. While low pH appears to increase energetic demands and trigger oxidative stress in larvae, the developmental process is robust to this at a molecular level, with the swimming larval stage reached in all pH treatments.

Gene expression response under thermal stress in two Hawaiian corals is dominated by ploidy and genotype

“…Thermal stress is a leading cause of coral mass mortality worldwide, resulting in dysbiosis between algal endosymbionts and the coral host, which can lead to the expulsion of algae from coral tissues (i.e., “bleaching”; Hughes et al., 2017 ). Ocean acidification, alternatively, places a chronic energetic strain on the coral host by increasing the cost of maintaining homeostatic processes under altered acid–base balance (Chille et al., 2022 ). A recent meta‐analysis shows that the interactive effects of ocean acidification and thermal stress on corals are primarily additive, resulting in increasing bleaching severity and mortality (Klein et al., 2022 ).…”