Effects of Fluctuating vs. Static Exposure to Hypoxia and High pCO2 on Gill Transcriptomes in Three Rockfish Species

Anthropogenic climate change is predicted to trigger large-scale changes in ocean chemistry over the next few decades, resulting in ocean acidification and hypoxia. These conditions may be exacerbated in coastal upwelling regions where strong, seasonal increases in pCO₂ and hypoxia are expected to intensify under climate change. Nearshore rockfishes (genus Sebastes) may already be adapted to fluctuating upwelling environments along the West coast of North America, but intensified conditions could push individuals beyond their physiological thresholds. We examined the effects of fluctuating vs. static levels of combined high pCO₂ and low dissolved oxygen (DO) on gill transcriptomes of three juvenile rockfish congeners with different life histories: copper (S. caurinus), gopher (S. carnatus) and black rockfishes (S. melanops). Juveniles were collected and exposed to control (DO= 8mg/L; pH=8.0), moderate-static (DO=4.0mg/L; pH=7.5), extreme-static (DO=2.0mg/L; pH=7.3), or two fluctuating treatments that alternated between control and extreme conditions every 8 days. Gill tissue was sampled from each treatment at the end of 13 weeks, including the “fluctuating-upwelling” and “fluctuating-relaxation” treatments sampled after a final 8-day exposure to either extreme or control conditions. De novo transcriptome assemblies were constructed for each species, and differential gene expression (DGE) analysis performed using edgeR. Preliminary findings show significant changes in DGE of fishes treated under fluctuating-relaxation conditions vs. control, that may reflect recovery from upwelling or acclimatory preparation for subsequent upwelling exposure. Previous physiological data from the same fishes also suggest the possibility of greater tolerance in black rockfishes not reflected in the other species. Species-specific DGE responses and those shared across species will be discussed in context of life history differences and possible mechanistic underpinnings of conserved physiological responses. Comparing rockfish responses to static vs. fluctuating conditions provides insights into effects of intensified upwelling in an ecologically and economically important group of marine fishes in North America.