Species-Specific Responses of Juvenile Rockfish to Elevated pCO2: From Behavior to Genomics.

In the California Current ecosystem, global climate change is predicted to trigger large-scale changes in ocean chemistry within this century. Ocean acidification-which occurs when increased levels of atmospheric CO2 dissolve into the ocean-is one of the biggest potential threats to marine life. In a coastal upwelling system, we compared the effects of chronic exposure to low pH (elevated pCO2) at four treatment levels (i.e., pCO2 = ambient [500], moderate [750], high [1900], and extreme [2800 µatm]) on behavior, physiology, and patterns of gene expression in white muscle tissue of juvenile rockfish (genus Sebastes), integrating responses from the transcriptome to the whole organism level. Experiments were conducted simultaneously on two closely related species that both inhabit kelp forests, yet differ in early life history traits, to compare high-CO2 tolerance among species. Our findings indicate that these congeners express different sensitivities to elevated CO2 levels. Copper rockfish (S. caurinus) exhibited changes in behavioral lateralization, reduced critical swimming speed, depressed aerobic scope, changes in metabolic enzyme activity, and increases in the expression of transcription factors and regulatory genes at high pCO2 exposure. Blue rockfish (S. mystinus), in contrast, showed no significant changes in behavior, swimming physiology, or aerobic capacity, but did exhibit significant changes in the expression of muscle structural genes as a function of pCO2, indicating acclimatization potential. The capacity of long-lived, late to mature, commercially important fish to acclimatize and adapt to changing ocean chemistry over the next 50-100 years is likely dependent on species-specific physiological tolerances.

Loss of genetic diversity as a consequence of selection in response to high pCO2.

Standing genetic variation may allow for rapid evolutionary response to the geologically unprecedented changes in global conditions. However, there is little known about the consequences of such rapid evolutionary change. Here, we measure genetic responses to experimental low and high pCO 2 levels in purple sea urchin larvae, Strongylocentrotus purpuratus. We found greater loss of nucleotide diversity in high pCO 2 levels (18.61%; 900 µatm) compared to low pCO 2 levels (10.12%; 400 µatm). In the wild, this loss could limit the evolutionary capacity of future generations. In contrast, we found minimal evidence that purple sea urchin larvae physiologically respond to high pCO 2 through alternative splicing of transcripts (11 genes), despite a strong signal of alternative splicing between different developmental stages (1193 genes). However, in response to high pCO 2, four of the 11 alternatively spliced transcripts encoded ribosomal proteins, suggesting the regulation of translation as a potential response mechanism. The results of this study indicate that while the purple urchin presently may have enough standing genetic variation in response to rapid environmental change, this reservoir of resilience is a finite resource and could quickly diminish.