UC Santa Barbara

This dissertation uses multiple case studies to examine the role of environmental disturbances and human activity on microbial physiology and community composition. In ecological theory, environmental disturbances, which govern species succession, adaptation, and evolution and can shift ecosystem function, are critical components of ecosystems. George Hutchinson postulated the so-called “paradox of the plankton” in which the highly diverse plankton communities present in marine and freshwater systems seemed inconceivable due to the relatively homogenous aquatic environment. The unfathomable spatial and temporal scales of marine microbes in their environments help explain this diversity and the role of relatively small-scale disturbances and gradients in marine ecosystems but it also makes it difficult to understand how a variety of large-scale human induced perturbations may shift the overall composition and function of ecosystems. In the modern world, understanding and being able to predict or anticipate how our actions will influence the inherent nature and diversity of the environment as well as how ecosystem services will be altered is extremely important for the survival of the human species and a sustainable future for the Earth. This far-reaching and broad topic is of considerable focus in the research community and is being addressed at both large and small spatiotemporal scales. In this dissertation, I explore three distinct cases in which environmental disturbance and anthropogenic impacts influence marine microbes. (1) The first case study explores the impacts of an oil spill in the marine environment on phytoplankton physiology. Through laboratory experimentation on representatives of two important phytoplankton groups, the coccolithophore, Emiliania huxleyi, and the diatom, Pseudo-nitzschia australis, results showed that oil exposure negatively impacted the growth of these species though E. huxleyi appeared to be more tolerant of oil exposure than P. australis. Additionally, exposure to oil increased cellular transparent exopolymer particle (TEP) production by both species, while the toxin production of P. australis cells increased and the formation of calcium carbonate liths by E. huxleyi appeared abnormal. (2) The second chapter investigates a novel connection between land and ocean through wildfire ash deposition in the marine environment and the effects on marine protist communities. Experimentation on natural microbial communities and the use of 18S rRNA sequencing and chemical analyses revealed significant enrichment of nutrients due to leaching of wildfire ash in seawater that promoted the growth of microbes. The variety of nutrients appeared to simultaneously enhance the growth of a diverse microbial assemblage rather than selecting for distinct groups. (3) Lastly, the third chapter focuses on microbial community dynamics in a rapidly changing and culturally and economically important sub-Arctic ecosystem. During two years with distinct sea ice influences in the eastern Bering Sea (EBS), physical and chemical conditions and protist communities were drastically different with the warmer, low sea ice year associated with a large fraction of putative parasites while the relatively cooler, average sea ice year was associated with a larger proportion of phytoplankton to non-phytoplankton protists. These results suggest that as the climate continues to warm and alter the EBS ecosystem, protist communities should be considered as they are likely major drivers of ecosystem function with significant impacts on higher trophic levels.