Effects of human activities, environment, and time on eelgrass-associated epifaunal communities

Eelgrass (Zostera marina) is a coastal marine angiosperm found in the Northern Hemisphere and forms expansive meadows in sheltered estuaries and bays, providing habitat for a high diversity of organisms, including algae, invertebrates, microbes, fish, birds, and mammals. It also provides invaluable ecosystem services for humans, including coastal storm protection, carbon sequestration, and nutrient cycling. However, eelgrass meadows are threatened worldwide by numerous anthropogenic activities, including shoreline modification, overfishing, land-based nutrient loading, and climate change. In British Columbia, Canada, eelgrass ecosystems are vulnerable to human activities such as habitat destruction, fishing, and pollution, and warming waters, which can cumulatively lead to negative impacts on eelgrass and associated fauna. To understand how environmental variation and BC-specific human activities affect eelgrass ecosystems temporally and spatially, I used a three-year, monthly observational time series of two trophic groups, statistical modeling, and an experiment to study how eelgrass communities and species interactions vary at the micro and macro scales. I show that eelgrass and epiphytic algae biomass change seasonally, and the timing of their peak biomasses varies interannually and is driven by nutrient availability and mesograzer abundances. I also show that human activities have a negative effect on eelgrass biomass, epiphytic algae, and epifaunal invertebrate abundances and species richness. Lastly, I show the first experimental evidence that eelgrass leaves host a core microbiota, eelgrass leaf-associated microbial communities are primarily driven by their surrounding environment, yet there may be host influence because microbial communities are resistant to environmental change within short periods of time. This research provides new insight to how environmental variability and human activities shape eelgrass-associated epifauna communities. This information can be used to predict how eelgrass ecosystems may change over time, which can help inform management decisions for restoration and conservation practices. Implementing more regulations for coastal anthropogenic activities may help ensure that eelgrass, and the organisms and humans that depend on it, will be sustained well into the future.Science, Faculty ofZoology, Department ofGraduat