Award: OCE-1220338

This project completed the first, and most comprehensive effort to study the patterns and impacts of ocean acidification at the scale of a large marine ecosystem using a combination of laboratory and field experiments, and remote sensing. The 2012 grant supported the continued research of the 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 OA 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. Here, the California Current system (CCS) flows from north to south, and during April-October each year, drives coastal upwelling. As is well known, this process injects cold, nutrient-rich, salty, and low pH water into the coastal zone. Infusions of high nutrients drive the high productivity of the CCS, but also have a downside. The dense phytoplankton blooms that are formed along some sectors of the CCS overwhelm 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 acidification 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. The discovery by R. Feely in 2007 that such acidified water occurs at the surface of the ocean over the continental shelf, and actually "shoals" on the shore was a surprise to most marine scientists. In OMEGAS 2012, we (1) maintained 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, (2) transplanted marked juvenile mussels, a key space occupier along the coast, to determine how their growth varied along the coastal ocean acidification (OA) mosaic, (3) transferred these field-exposed animals to a common-garden laboratory setting where experiments tested the ability of juvenile mussels to resist whelk predation, and (4) tested the growth of adult sea urchins to variable OA regimes in northern California and Oregon. We found that (1) periods of unexpectedly low pH are already occurring along the CCS and are induced by upwelling events, (2) that, surprisingly, these events reach lower levels to the north, where upwelling is weaker but where phytoplankton blooms are denser, (3) 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 (4), the current decreasing levels of pH along the CCS are attributable to anthropogenic-derived increases in CO2, (5) juvenile mussels grew fastest at sites with frequent exposure to low pH but high food levels and slowest at sites with persistent upwelling or warmer waters independent of pH regime, and (6) sea urchin growth was minimally affected by elevated OA. Further, because of 30-40 year time lags between the uptake of CO2,in the Western and Tropical 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 have set t...