Within the next century, Eastern Boundary Current upwelling systems, which are home to some of the major fisheries that support humans worldwide, are expected to undergo extreme acidification (pH falling to 7.3 or lower) because of increasing atmospheric CO2. Impacts on trace metal (especially iron) and nitrogen bioavailability are likely, and consequently changes in phytoplankton species composition and physiology are also to be expected. One understudied aspect of ocean acidification is its impact on the production of phytoplankton lipids and polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) and other essential fatty acids (EFA) upon which higher trophic levels depend.
In this project a research team from San Francisco State University, University of Hawaii, and University of Maine will study the effect of extreme ocean acidification (OA) under iron replete and deplete upwelling conditions in regard to changes in species composition, total lipid production, and the specific production of PUFAs. There are two guiding hypotheses: (1) Extreme ocean acidification will increase lipid synthesis and EFA production in phytoplankton through the imbalance between carbon uptake and decreased nitrogen uptake; and (2) Extreme ocean acidification in natural upwelling regions will change the amount and composition of PUFA and EFA produced due either the direct effects of acidified seawater on cell physiology or to marked shifts in phytoplankton community composition. Current Fe-replete and Fe-deplete upwelling zones in the California upwelling region will be investigated to illustrate these impacts. The team will use controlled laboratory monoclonal, semi-continuous culture experiments to subject representative coastal phytoplankton isolates to varying pH and Fe availability to characterize tolerance/success under extreme pH environmental conditions and to quantify cellular physiological response to the combined stressors. In the third year of the project, community-level responses to the same set of stressors will be studied.
Broader Impacts: Because of the global importance of marine fisheries and the as-yet modest understanding of the potential threats of ocean acidification, the topic of this study spans a variety of disciplinary, institutional, academic-government, and national boundaries. Researchers at all three participating institution will lead a variety of public educational outreach activities for the benefit of K-12 students and for society at-large. Graduate and undergraduate students will also be an important part of the research effort.
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.