Award: OCE-1131692

Eastern boundary current upwelling systems (EBUS) harbor a major portion of the marine fisheries that support humankind, and these sites are forecast to experience extreme (pH < 7.3) ocean acidification into the next century due to the combination of increasing atmospheric CO2 and a shallowing of organic matter remineralization. The more extreme pH changes in these productive waters than projected for most ocean surface waters likely will have impacts on trace metal (particularly iron) and nitrogen availability, causing potential shifts in phytoplankton species composition and physiology. One understudied aspect of ocean acidification is the stress related changes in the synthesis of total lipids and polyunsaturated fatty acids (PUFAs), particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA); essential fatty acids (EFAs) needed to support production at higher trophic levels where most organisms lack the ability to produce these compounds. We propose to evaluate the effect of extreme ocean acidification (OA) under iron replete and deplete upwelling conditions in terms of changes in species composition, total lipid production and the specific production of polyunsaturated fatty acids. The project will be guided by the following two hypotheses: H1 Extreme ocean acidification will increase lipid synthesis and EFA production in phytoplankton through the imbalance between increased carbon uptake and decreased nitrogen uptake. The degree of these changes will differ among taxonomic groups and cellular growth phases, and H2: Extreme ocean acidification in natural upwelling regions will change the amount and composition of PUFA and EFA produced due either to the direct effects of acidified ocean on cell physiology, or to marked shifts in phytoplankton community composition. The current Fe-replete and Fe-deplete upwelling zones in the California upwelling region will illustrate these impacts on PUFA and EFA concentrations, forecasting a trend towards lower food quality of primary production in EBUS. We will use well-controlled laboratory monoclonal, semi-continuous culture experiments to subject representative coastal phytoplankton isolates to varying pH and Fe availability to characterize their individual organism tolerance/success under extreme pH environmental conditions, and to quantify the cellular physiological response to these combined stressors in terms of the magnitude and food quality of PUFA production. These experiments will create a solid foundation for predicting specific outcomes of extreme OA in boundary current regions, which will be tested in the third year by examining community scale responses to the same stressors using deck--?board continuous cultures in the California Current upwelling region. The findings will provide critical insights to the effects that extreme OA will have on the comparative food quality of future phytoplankton communities in the EBUS. Ultimately, we provide critical information required by fisheries modelers who are concerned with understanding the quality of the links between phytoplankton communities and food chain success. We will offer EFA-production as a link between projected increases in atmospheric CO2 and marine food resources for future world populations. Last Modified: 12/16/2014 Submitted by: Robert R Bidigare