Short-term mechanisms, long-term consequences: transcriptomic insights into ocean acidification tolerance and stress in juvenile snow crab

Understanding how marine species tolerate ocean acidification (OA) is critical for predicting biological responses to ocean change, as well as impacts on the ecosystems and industries that rely upon them. Snow crab (Chionoecetes opilio) are both a major fishery resource in the Bering Sea and an important component of high-latitude marine food webs. Experimental work suggests that snow crab are relatively tolerant of OA, but that this tolerance has limits. In a recent study, juveniles maintained growth and molting during a year-long exposure to moderate OA (pH 7.8) and severe OA (pH 7.5), while survival declined in the severe OA treatment after 250 days. In this companion study, we applied RNA-seq to characterize transcriptomic responses to OA using individual whole-body juvenile snow crab. Expression profiles were characterized in OA treatments (pH 7.8, pH 7.5) at two time points: after 8 hours to identify molecular mechanisms underlying short-term tolerance; and after 88 days to understand chronic effects of severe OA (10–14 crabs per treatment and time point). The 8 h transcriptional response involved strong activation of genes associated with mitochondrial protein repair, cuticle maintenance, and immune modulation, processes shared between OA treatments but of substantially greater magnitude under severe OA (616 versus 148 differentially expressed genes). After 88 days of OA exposure, differential expression among the two OA treatments (186 genes) revealed sustained upregulation of stress- and damage-mitigation pathways in severe OA (pH 7.5). These findings suggest that juvenile snow crab tolerate OA through flexible molecular responses that maintain energy production capacity, cellular, and protective barrier function. However, persistent activation of these pathways under severe OA indicates a chronic stress state that precedes outward physiological effects and likely contributes to increased mortality under long-term exposure. We further highlight potential early indicators of chronic acidification stress in snow crab, among which a gene likely coding for carbonic anhydrase 7 (CA7) appears to be the most promising biomarker candidate.