ABSTRACT

The coccolithophore Emiliania huxleyi is the most abundant calcifying phytoplankton species in the world's oceans. Due to its abundance and broad range of occurrence, deep-sea export of its CaC03 coccoliths plays a significant role in the oceans alkalinity balance, and in turn, air-sea CO2 exchange. Since the start of the industrial age, atmospheric partial pressure of CO2 (pCO2) has steadily increased due to fossil fuel combustion and land use change, and is projected to reach 750 ppm by the end of this century. As a consequence, both seawater pH and carbonate ion concentration are expected to drop significantly relative to pre-industrial times. Calcifying organisms are sensitive to changes in carbonate ion concentration, however, neither the extent of this sensitivity, nor its physiological basis, are well understood. The purpose of this project is to examine the mechanism (s) by which E. huxleyi physiologically acclimates and adapts to changes in its environment in order to understand the impact of changes in seawater carbonate chemistry on this important planktonic calcifying organism. Cells from two genetically distinct ecotypes will be cultured in chemostats at present day and projected year 2100 levels of pCO2 under nitrogen or phosphorus limitation. Both short- (2 week) and long-term (2 year) experiments will be conducted to investigate acclimation and adaptation responses to changes in carbonate chemistry, respectively. In each experiment, patterns of gene expression will be investigated using a microarray that has been developed by the E. huxleyi genome sequencing projects. Gene expression will be analyzed as a function of physiological performance (photosynthesis vs. irradiance), calcification rates and cellular nutrient content. The results of this project will generate a novel set of candidate biomarker genes for analysis of the environmental physiology of coccolithophorids and contribute to a better prediction of the role of E. huxleyi in air-sea CO2 exchange in the next century. Since E. huxleyi is a globally distributed organism that frequently forms massive blooms, there are numerous investigators studying it and this research will therefore be of broad interest to the scientific community. Graduate students, a postdoctoral investigator, and high school students will be trained during this project and underrepresented minorities will participate in this research project. Public outreach on this research will be conducted through the Romberg Tiburon Center and the NSF-funded Bay Area Discovery Museum.

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