Award: OCE-1041075

This project was the first, and most comprehensive effort to study the patterns and impacts of ocean acidification, a decrease in ocean pH associated with the uptake of fossil fuel-derive CO2, at the scale of a large marine ecosystem using a combination of laboratory and field experiments, and remote sensing. The collaborative project enabled the formation of a coast-wide consortium, OMEGAS (Ocean Margin Ecosystem Group for Acidification Studies), a group of 15 PIs spread across six west coast institutions from Oregon to southern California. OMEGAS addressed the problems induced by lower pH using an approach that integrated across levels of biological organization (e.g. genes, genomes, individuals, populations, communities and ecosystems), with laboratory experiments investigating the molecular, genetic, and physiological mechanisms underlying ecological responses of mussels and sea urchins across the varying oceanographic conditions along the US west coast. The California Current system (CCS) flows from north to south, and during April-October each year, drives coastal upwelling. This process injects cold, nutrient-rich, salty, and low pH water into the coastal zone. The high nutrients drive high productivity in the CCS, but also have a downside. The dense phytoplankton blooms that are formed along some sectors of coast swamp the ability of planktonic grazers to control them, and after a short life, these microalgae die and begin to sink. The decomposition process uses oxygen, leading to hypoxia, and in some locations and times, anoxia. Phytoplankton decay also releases carbon dioxide, which ultimately drives down pH, making waters more acidic. Combined with the naturally low pH in the upwelled water, this additional source of acidity can drive coastal ocean pH to exceptionally low levels and interfere with precipitation of calcium carbonate structures in marine organisms that form hard parts such as shells, or incorporate CaCO3 into their body walls. In OMEGAS, we (1) developed novel sensors for deployment in the rocky intertidal, (2) established a network of pH sensors on the rocks and in shallow waters adjacent to rocky shores at 7-13 sites from central Oregon to southern California, (3) transplanted marked mussels, a key space occupier along the coast, to determine how their growth varied along the coastal ocean acidification (OA) mosaic, (4) carried out laboratory experiments testing the effects of present and future levels of OA on the performance of mussel and sea urchin larvae, and (5) sequenced the genomes of lab-reared larvae to identify those genes affected by elevated OA. We found that (1) mussel larvae grew less, had weaker shells, and lower tissue content when raised under elevated OA conditions, (2) sea urchin performance (growth, physiology) was minimally affected by elevated OA but (3) displayed rearrangements in their transcriptome that reflected responses to high OA, (4) adult mussel growth was positively, not negatively associated with lower pH conditions along the CCS, (5) periods of unexpectedly low pH are already occurring along the CCS and are induced by upwelling events, (6) that, surprisingly, these events reach lower levels to the north, where upwelling is weaker but where phytoplankton blooms are denser, (7) as a result, sectors of the shore differ in their intensity of OA, and thus, that refuges for organisms from intense OA may exist, and (8), the current decreasing levels of pH along the CCS are attributable to anthropogenic-derived increases in CO2. Further, because of 30-40 year time lags between the uptake of CO2, in the Northwest Pacific Ocean and the arrival of such waters to the CCS, we are committed to changes in carbonate chemistry that will result in substantial increases in the severity and frequency of corrosive conditions along the US West Coast. Thus our work vastly increased the depth and extent of our understanding of current and likely future OA regimes in the CCS, and ha...