Molecular indicators of warming and other climate stressors in larval Pacific cod

Pacific cod (Gadus macrocephalus) populations have declined in recent years in Alaska. Decreased recruitment estimates following marine heat waves suggest that warming directly impacted early life stages. This study applied transcriptomics to investigate mechanisms of Pacific cod larval mortality at suboptimal temperatures and co-occurring acidification. Gene expression analysis revealed that heightened immune systems paired with lipid dysregulation may be mechanisms of warming-associated mortality. Acidification may slow/impair digestion which could reduce larval condition. With the exception of possible effects to hemoglobin, acidification does not exacerbate effects of warming. Increased expression of a gene (ZP3) with possible antifreeze properties that is associated with population structure suggests that some populations may tolerate poleward shifts in spawning locations, but slower growth and condition could reduce larval survival. The overwhelming effect of warming on the transcriptome (and survival) substantiates the theory that marine heat waves severely impacted, and will continue to impact, Pacific cod larval physiology. This information will ultimately inform recruitment forecasts in years with conditions similar to those tested here.