Seawater carbonate chemistry and larval growth rates of sea urchin Strongylocentrotus droebachiensis

Ocean acidification (OA) is increasing due to anthropogenic CO2 emissions, and poses a threat to marine species and communities worldwide. To better project the effects of acidification on organisms' health and persistence an understanding is needed of (1) the mechanisms underlying developmental and physiological tolerance, and (2) the potential populations have for rapid evolutionary adaptation. This is especially challenging in non-model species where targeted assays of metabolism and stress physiology may not be available or economical for large-scale assessments of genetic constraints. We used mRNA sequencing and a quantitative genetics breeding design to study mechanisms underlying genetic variability and tolerance to decreased seawater pH (-0.4 pH units) in larvae of the sea urchin Strongylocentrotus droebachiensis. We used a gene ontology-based approach to integrate expression profiles into indirect measures of cellular and biochemical traits underlying variation in larval performance (i.e., growth rates). Molecular responses to OA were complex, involving changes to several functions such as growth rates, cell division, metabolism, and immune activities. Surprisingly, the magnitude of pH effects on molecular traits tended to be small relative to variation attributable to segregating functional genetic variation in this species. We discuss how the application of transcriptomics and quantitative genetics approaches across diverse species can enrich our understanding of the biological impacts of climate change.