The Nutritional Physiology of Phytoplankton Mixotrophs: Eecological and Evolutionary Ramifications

点击翻译按钮获取中文摘要

The objectives of the proposed project are to determine key physiological and ecological processes that allow algal bloom species to out-compete other, co-occurring phytoplankton and bacteria. Shifts in phytoplankton community structure and increases in the frequency and duration of algal blooms in coastal waters around the world have been attributed to cultural eutrophication. For example, the Chesapeake Bay system has experienced decreases in species diversity and increases in the biomass of bloom producers over the last 50 years. Dissolved organic matter (DOM) may promote the growth of harmful algal species and initiate algal blooms. Algal bloom species can absorb and utilize dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) thereby contributing to eutrophication. Since DON and DOP also contain carbon (C), uptake can also provide a substantial heterotrophic subsidy to autotrophic photosynthesis. The ability of organisms to "swap" between autotrophic and heterotrophic metabolisms may offer clear evolutionary advantages as coastal areas become increasingly impacted by nutrient enrichment from anthropogenic activities. A major limitation to understanding algal blooms and ecological impacts of shifts in community structure is the lack of basic knowledge on the physiology of dinoflagellates and other bloom-forming organisms. The proposed research will contribute to the basic understanding of the physiological factors that allow algal mixotrophs to form monospecific blooms in the environment. The research will focus on field experiments in the lower Chesapeake Bay, near the mouth of the James River. Uptake of organic compounds by phytoplankton (relative to bacteria) will be evaluated in natural communities during bloom events. Autoradiography and antibiotic treatments will be used to manipulate species diversity and algal biomass. Nutrient enrichment bioassays will be conducted to determine competitive outcomes and shifts in trophic mode (e.g., shifting from photoautotrophy to osmotrophy) in natural assemblages in response to changes in the nutrient and light environment. The information derived from this study will be useful to the Chesapeake Bay Program (CBP) and the Virginia Department of Environmental Quality and Centers for Disease Control. This project will provide support for 2 graduate students. Funds will support research for ODU's undergraduate programs including the REU Minority Undergraduate Scholarship and Training (MUST) Program. A scholar from the Hall-Bonner Program for Minority Doctoral Scholars in Ocean Sciences will conduct research as part of this project. ODU is a minority serving institution and results from this project will be incorporated into the curriculum of undergraduate and graduate classes taught by Mulholland.