Date

Summer 2021

Document Type

Master's Thesis (Open Access)

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Anthropogenic climate change is predicted to trigger large-scale changes in ocean chemistry over the next few decades. 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 further shifts in ocean chemistry could push individuals beyond their physiological thresholds. I examined the effects of future upwelling conditions by simulating fluctuating vs. static levels of combined high pCO2 and low dissolved oxygen (DO) on the gill transcriptomes of three juvenile rockfish congeners with different life histories: copper rockfish (Sebastes caurinus), gopher rockfish (S. carnatus) and black rockfish (S. melanops). Juveniles were collected and exposed to static-ambient (DO= 8mg/L; pH=8.0), staticmoderate (DO=4.0mg/L; pH=7.5), static-extreme (DO=2.0mg/L; pH=7.3), or two fluctuating treatments that alternated between ambient and extreme conditions every 8 days, simulating upwelling and relaxation cycles. Gill tissue was sampled from fish following 13 weeks of exposure to each treatment. De novo transcriptome assemblies were constructed for each species, and compared for quality, completeness, and mapping rates across all samples. The copper rockfish reference assembly was selected to map and compare differential gene expression for common orthologs across all species. I found significant changes in gene expression (edgeR, FDR<0.01) under all pairwise comparisons of static vs. fluctuating treatments, with fluctuating treatment responses containing larger overall numbers of differentially expressed genes. Likewise, significant changes in gene expression of fishes from fluctuating-relaxation conditions vs. static-ambient may reflect persistent evidence of stress response after “recovering” from upwelling, or acclimatory preparation for subsequent upwelling exposure. Highly species-specific transcriptional responses may be related to life history differences and suggest the possibility of greater tolerance to future ocean chemistry in black rockfish, which was not reflected in the other species. Likewise, correlations of physiological data to transcriptional profiles from the same copper and gopher rockfish suggest that these congeners rely on different molecular mechanisms to cope with environmental stressors and highlight a stronger molecular and physiological stress response in gopher rockfish. Comparing transcriptomic responses of rockfish exposed to static vs. more ecologically relevant, fluctuating future upwelling conditions provides insights into the ways in which climate change will impact an ecologically and economically important group of marine fishes in North America.

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