Intellectual Merit. This project will investigate the impacts of ocean acidification (OA) 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 OA. 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 OA 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
We used a unique combination of field collections, experimental laboratory culture, and genetic data to address for the first time issues that are at the forefront of modern climate biology: Will organisms be able to evolve in response to rapidly changing climate conditions? If so, what will be the molecular mechanisms of adaptation? In our work, we take the next step by using newly developed DNA sequencing methods to measure natural selection in action in response to experimental ocean acidification. This is a first in the field of genomics: we measure selection due to climate change in a single generation from the standing genetic variation in natural populations. We measure genetic change at over 19,000 places in the sea urchin genome to report a remarkable finding. Sea urchin larvae maintain normal growth in low pH conditions by means of natural selection acting on specific genes that give them improved performance in stressful environmental conditions. These results are the first to link resistance to the negative effects of acidification to genetic changes across the genome. The presence of these adaptive alleles is likely due to the high environmental variation in this coastal upwelling ecosystem, high dispersal among regions, and high mutation rate. These characteristics are common to many other highly dispersing organisms, such as many plant and migratory animal species, suggesting such organisms may have some scope for adaptation to future climate conditions. Last, we note the pivotal point that adaptive capacity is a double-edged sword: it may allow future evolution, but only at a significant demographic cost to the evolving population. Populations that are already at low numbers because of climate or other anthropogenic stresses may not have the demographic scope to respond
