Intellectual Merit. This project will investigate the impacts of ocean acidification (O-A) on two ecologically important, calcification-dependent marine invertebrates in relation to local-to-coastal variation in carbonate chemistry (e.g., pH and aragonite saturation) in the California Current Large Marine Ecosystem (CCLME). An interdisciplinary team of investigators with expertise in physical and chemical oceanography, marine ecology, biochemistry, molecular physiology, and molecular genetics will carry out an integrated, lab and field, multi-site investigation of the ecological, physiological, and evolutionary responses of sea urchins and mussels to spatial and temporal variation in O-A. The research will take place in the context of a mosaic of variable oceanography, including recently documented latitudinal variation in carbonate chemistry along the upwelling-dominated US west coast. Variation in upwelling regimes from Washington to southern California generates spatial and temporal gradients in concentration of CO2 that shoal to surface waters during upwelling events, extending shoreward into the inner shelf region. Through well-known chemical pathways, influxes of CO2 cause present-day declines in pH in coastal ecosystems that are lower than values forecast for the ocean in general in the year 2200. Lower than "normal" pH can influence organisms by altering intracellular biochemistry, and especially, for calcification-dependent marine organisms, interfere with formation of hard parts as the aragonite saturation state falls near or below 1.0. Because calcifiers in the upwelling-dominated CCLME have historically experienced persistent regional variation in pH, populations are likely differentially acclimatized and/or adapted to a variable carbonate chemistry environment. The new challenge to these organisms is that with global change and the resulting increase in seawater CO2, they already may be close to their acclimatization or adaptational capacity, and thus may have limited ability to respond to additional increases in CO2. It is this challenge, the mechanistic ability of calcifying invertebrates to acclimate or adapt to increasing CO2 and aragonite saturation states < 1.0 that we address here.
Preliminary results from NSF-funded, local-scale studies of sea urchin and oyster larvae (by PIs included in the present team) has made inroads into this question, but the response of these widely-ranging species to ocean acidification across the full range of conditions in the CCLME remains unclear. This project includes five integrated elements. (1) To document the oceanographic context in which the study organisms live, the team of PIs will build upon two local-scale NSF-funded networks of sensors (in Oregon and northern California) to quantify carbonate chemistry in four regions of the CCLME with contrasting upwelling regimes, and thus, likely a wide range of differences in carbonate chemistry. Based on NOAA surveys, OA should be most intense in northern California and Oregon, less intense in central California, and least intense in the Santa Barbara channel, east of Point Conception. (2) To examine physiological, genomic, and genetic mechanisms underlying acclimatization and adaptation to O-A conditions, the investigators will carry out coordinated and integrated studies of adults and larvae of sea urchins and mussels collected from each of two sites within each of the four regions. In common-garden experiments using NSF-funded laboratory mesocosms at UCSB and UCD-BML, the researchers will culture sea urchins and mussels under different CO2 and temperature regimes, and use genomics techniques
This project was 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 grant 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 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. The 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 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. 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, we (1) 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, (2) transplanted marked mussels, a key space occupier along the coast, to determine how their growth varied along the coastal ocean acidification (OA) mosaic, (3) carried out laboratory experiments testing the effects of present and future levels of OA on the performance of mussel and sea urchin larvae, and (4) 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 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, although funding cuts have ended OMEGAS, our work vastly increased the depth and extent of our understanding of current and likely future OA regimes in the CCS, and have set the stage for investigation of broader, ecosystem impacts, which remains as perhaps the greatest challenge imposed on marine systems as the climate inevitably changes.
