Award: OCE-1220648

This one-year renewal grant supported the continuation of a coast-wide consortium called OMEGAS (Ocean Margin Ecosystems Group for Acidification Studies), a group of 13 principal investigators spread across six West Coast institutions from Oregon to southern California. The OMEGAS consortium was the first, and most comprehensive, effort to study the patterns and impacts of ocean acidification (OA) at the scale of a large marine ecosystem using a combination of field studies, laboratory experiments, and a network of oceanographic sensors. OMEGAS addressed the effects of OA using an approach that integrated across levels of biological organization (i.e., genes, genomes, individuals, populations, communities, and ecosystems). Our prior results from OMEGAS (grant OCE-1041089) documented a mosaic of varying OA intensity along the US West Coast, and investigated the genetic and physiological mechanisms underlying ecological responses of sea urchins and mussels to these oceanographic conditions. In this one-year project, we sought to better understand the oceanographic drivers of this striking mosaic of coastal pH. We also conducted coordinated field and laboratory experiments to link this OA seascape to the physiological and ecological performance of a key member of rocky intertidal communities, the mussel Mytilus californianus. At field sites exposed to both low pH and low food levels (chlorophyll-a), we found juvenile mussels grew less, had thinner shells, had different respiration rates, and were sometimes more vulnerable to predation by drilling snails. Paradoxically, the northern sites that were exposed to the most frequent low pH events had mussels that grew faster, had thicker shells, and contained the most tissue. However, these northern sites also experienced frequent phytoplankton blooms and had chlorophyll-a levels that were much higher. Thus, it appears that abundant food may help ameliorate the negative impacts of OA on mussel growth. In a separate controlled laboratory experiment, we also found that moderate warming can offset some of the detrimental effects of OA on mussel growth through temperatureÆs effects on physiology and seawater chemistry. Data from our network of pH sensors on rocky shores and in adjacent shallow waters demonstrated that (1) periods of unexpectedly low pH are already occurring along the California Current System (CCS) and are induced by upwelling events, and that (2) surprisingly, these low pH events are more severe in the north (Oregon), where upwelling is weaker but where phytoplankton blooms are denser. Decay of dense phytoplankton blooms is known to release carbon dioxide, which ultimately drives down pH, making waters more acidic. It appears that, combined with the naturally low pH in upwelled water, this additional source of acidity can drive coastal pH to exceptionally low levels in some regions, such as the central Oregon coast. Overall, results from the OMEGAS consortium have vastly increased our understanding of current and future OA regimes in the CCS, and have set the stage for investigation of broader, ecosystem impacts of OA, which remain as perhaps the greatest challenge imposed on marine systems in an era of accelerating climate change. In addition to publishing results in scientific journals, OMEGAS scientists were actively engaged in training and outreach activities, and served on national committees and regional working groups. OMEGAS scientists forged strong connections with shellfish growers, and provided timely and accurate information on OA conditions. OMEGAS scientists routinely participated in outreach focused on OA through media interviews, short video micro-documentaries, and as speakers at events for school groups, teachers, and the general public. OMEGAS was a truly interdisciplinary consortium of scientists with expertise spanning from physiology to ecology to oceanography. This model provided a unique educational opportunity, and OMEGAS contributed to the ...