Collaborative Research: Seasonal bloom dynamics: Synechococcus-grazer interactions as a model system

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Cyanobacteria in the genus Synechococcus are minute, but ubiquitous phytoplankton of temperate oceans that contribute a large amount of the biomass produced at the base of marine food webs. Seasonal blooms of Synechococcus are a remarkably consistent feature of coastal water of both the Atlantic and Pacific oceans. However, new molecular techniques have revealed that underlying the consistency of these blooms is a wealth of genetic variation that exhibits rapid dynamical turnover. This has led to a hypothesis that genetic diversity within Synechococcus is ecologically important to sustaining seasonal blooms, and to predicting marine ecosystem response to longer term environmental change. This project will combine ecological and genomic approaches to understand how genetic diversity interacts with the physical and food web processes that drive seasonal cycles of Synechococcus blooms. The genetic diversity of Synechococcus and co-occurring microbes will be quantified on a weekly basis during bloom periods in Booth Bay, Gulf of Maine and Scripps Pier, Southern California. Flow cytometric cell sorting in combination with molecular approaches will be utilized to investigate the diversity of bloom assemblages using a three-tiered approach including: DNA and RNA analysis of the whole unsorted community, DNA analysis of flow-sorted communities, and single cell genomics of Synechococcus and their protist grazers. Ecological processes that cause Synechococcus blooms to end will be investigated through experiments designed to measure the relative importance of mortality from protist grazers versus from viruses on various Synechococcus ecotypes. These results will yield insights into bloom dynamics and how genetic diversity interacts with ecosystem processes.This project will develop methods and resources that will be generally useful for quantifying variability of the seasonal bloom of phytoplankton, which is likely to be an early indicator of ecosystem responses to longer term climate change. Quantitative PCR methods will be designed for rapid quantification of diversity in Synechococcus and in Synechococcus grazers in marine waters. Numerous protist and Synechococcus single amplified genomes will be produced and cryo-preserved to enable future studies. This project will also support the research training of a graduate student and several undergraduate students, who will be intimately involved with individual projects. Results will be translated to formal courses held at Bigelow Laboratory and to the public through presentations at a successful weekly Café Scientifique series held in Boothbay Harbor each summer.