Linking phytoplankton diversity in the North Atlantic to the annual cycle of ecological disturbance and recovery

Lee Karp-Boss1, Luis Manuel Bolanos2, Stephen J Giovannoni2, Jason Graff3, Consuelo Carbonell-Moore4, Nils Haëntjens5, Alison Chase5, Emmanuel Boss6 and Michael Behrenfeld3, (1)University of Maine, School of Marine Sciences, Orono, United States, (2)Oregon State University, Department of Microbiology, Corvallis, OR, United States, (3)Oregon State University, Corvallis, OR, United States, (4)Oregon State University, Department of Botany and Plant Pathology, Corvallis, OR, United States, (5)University of Maine, Orono, ME, United States, (6)University of Maine, Orono, United States
Abstract:
The spring phytoplankton bloom in the North Atlantic has been a topic of interest for over a century. Much focus has been given to the environmental conditions that promote the accumulation of biomass in the spring, in particular, the interplay between mixing and stratification. The role of these processes in shaping phytoplankton community composition and structure has been studied to a lesser extent and diversity patterns across the annual cycle remain largely unexplored. Deep winter mixing generates a strong annual disturbance to the North Atlantic pelagic ecosystem. According to one ecological theory, greater levels of disturbance will favor organisms with high specific growth rates, reducing overall diversity in a community. As the water column stratifies, diversity is expected to increase until community climax is reached and competitive interactions become prominent in reducing it. Thus, phytoplankton diversity is expected to be greatest in the spring when the frequency and intensity of vertical mixing has decreased but the water column has not yet been stratified for prolonged periods. To test this hypothesis, we characterized phytoplankton communities using genetic profiles (16S rRNA amplicon sequences), imaging and flow cytometry data collected during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). Four field campaigns were conducted along a latitudinal gradient, covering different periods in the annual cycle (early winter, early spring, late spring and fall). Initial results show that whole community diversity followed an annual pattern with lowest diversity in the fall and winter in the subtropical and subpolar sections of the study area, respectively. Diversity was highest in the spring with variations to this pattern observed when group-specific diversity was considered. These results will be discussed in the context of ecological disturbance hypotheses and their application to marine phytoplankton.
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