Impact of Ocean Acidification on Species Adaptation Across 11 Degrees of Latitude

Upwelled coastal waters in the California Current system are naturally acidified, and already experience low pH levels not expected in the open ocean for another 50-100 years.  An NSF-supported team of researchers (Ocean Margin Ecosystem Group for Acidification Studies or OMEGAS) spread over 7 institutions and spanning 1600 km of coast is conducting oceanographic, ecological, physiological, and genetic studies to track responses of sea urchins and mussels to spatial and temporal variation in ocean acidification (OA).  We ask: How does OA vary along the coast? Do growth and survival of key species respond to changing carbonate chemistry?  How do larvae respond to present pH regimes and how will they respond to future changes? Can species adapt and evolve as OA, and consequent reduced abilities to calcify, increases with rising CO₂ emissions?  The first-ever time series of pH and pCO₂ at 7 sites from the central Oregon coast to Santa Barbara show that, as predicted, OA varies (1) latitudinally, (2) between sites within region, and (3) within sites on hourly to daily to weekly time scales.  Drivers of this variation include large-and regional-scale upwelling-driven currents, and regional- to local-scale biological processes.  Laboratory mesocosm studies have found that sea urchin larvae are smaller, and grow less skeletal material at future-scenario pH levels compared to present levels; these effects were most pronounced in southern urchins. Mussel larvae were even more strongly affected by future-scenario conditions, growing thinner, smaller, and more fragile shells.  The first genome-wide survey of evolutionary response to acidification shows that hundreds of sea urchin genes shift allele frequencies when cultured under elevated pCO₂ and that geographic patterns in important physiological genes seem to be directed by these selective changes.  Thus, as expected, OA in this highly dynamic and productive upwelling ecosystem varies naturally in concert with periodic intrusions of deep, high CO₂ water, with the intensity of how these intrusions vary alongshore, and with variation in algal photosynthesis and respiration.  Although larvae of key calcifiers show some resistance to this variability at present, they do poorly under future-scenario CO₂ levels. Pending analyses will reveal if these species have the capacity to adapt or acclimate to future OA conditions.