UC San Diego

Marine microbial communities are crucial to ecosystem function and productivity, but their spatial and temporal distributions are highly variable. Microbes exhibit unique environmental preferences, called niches, that drive observable distribution patterns across space and time. However, it’s not well understood how much and at what scales external biotic and abiotic influences, such as competition and dispersal affect microbial distributions. It's expected that microbial distributions are going to change as a result of anthropogenic climate changes, such as increase sea surface temperatures and increased water column stratification. However, current predictive models rely on some assumptions about niches, such as niche stability over time, that have not been broadly tested or observed. This thesis aims to elucidate the mechanisms that shape spatial and temporal variability in marine microbial niches across three distinct chapters. The first chapter asks how the laboratory expectations and observations of niches in the field compare for a globally important genus of cyanobacteria Prochlorococcus. The second chapter asks how temporal variability and dispersal shape microbial realized niches across a latitudinal gradient by utilizing a simplified metacommunity model. The final chapter asks if and how microbial niches have adapted to spatial and temporal environmental change in the California Current Ecosystem. Understanding the mechanisms behind microbial distributions can influence our mitigation and management of broader ecosystem changes such as food web dynamics and carbon export.