Physiological Ecology of Marine Cyanobacterial Communities

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9633111 PALENIK This project will use an integrated multi-investigator approach to determine the extent and causes of cyanobacterial biodiversity in the marine environment. The project hypothesis is that stratification in the oceans, although often transient, has led to the development of a limited number of physiologically and genetically distinct and recognizable groups ("species") of cyanobacteria specifically adapted to the high light, low nutrient mixed layer and others adapted to the higher nutrient, low light life below it. Even this simple scenario is much more complex than the current oceanographic paradigm. There is currently little knowledge of the spatial or temporal variations in natural cyanobacterial diversity, and we can only guess at the factors that may be driving it. The importance this diversity may have in determining oceanographic rate processes, such as in situ growth or carbon fixation rates, is unknown, and its role cannot really be addressed until we understand the extent and patterns of cyanobacterial diversity. This project is the first step in being able to assay the growth rates and metabolic activities of individual physiological or genetic types. Since similar genetic and physiological processes probably also occur in other groups of phytoplankton, these questions are of general significance to biological oceanography. This project will also begin to look at not just the number of microbial "species" in an environment, but why that number? The microbiota of the marine environment are coming to be seen as remarkably diverse, and an understanding of the processes underlying this diversity will best be gained by examining the diversification of a related group of microorganisms in detail in relationship to physiochemical parameters. The marine environment is probably the best place to begin to understand these questions because there is also considerable experience in understanding the physiochemical gradients surrounding the o rganisms. RNA polymerase gene sequences from strains and bulk community samples, flow cytometric analyses, pigment analyses, antibody assays for motile Synechococcus and other strains, strain isolation techniques, physiological studies on nitrogen and light utilization, and physiochemical data will be the initial set of tools we will bring to these problems, with others under development. Three sites in the oligotrophic boundary of the Southern California Bight will be sampled at several depths for two consecutive years at the same season to ensure the reproducibility of our conclusions. A third cruise will focus on characterizing the same sites at a different season in order to begin to explore temporal variations in diversity. This focused sampling effort will ensure a tractable approach to understanding the importance of cyanobacterial diversity to marine ecosystems. ***