The environmental microbial composition and pathogen reduction capability of temperate seagrass beds

Abstract

Marine pathogens present serious challenges to aquaculture, fisheries productivity, and marine conservation requiring novel solutions to identify, control, and mitigate their effects. Several ecological habitats, such as mangroves and wetlands can recycle wastes and serve as aquatic filtration systems. In chapter 1 I review how mangroves, shellfish beds, seagrasses, and constructed wetlands can reduce pathogen pressure in coastal ecosystems. I identified mechanisms responsible for pathogen reduction in these ecosystems including sedimentation, biological/chemical filtration, and desalination. Protecting and restoring coastal ecosystems is key to maintaining pathogen filtration capacity, benefiting conservation efforts of threatened host populations, and mitigating large disease outbreaks. In chapter 2 I examine fecal indicator bacteria abundance and microbial community composition when the temperate eelgrass (Zostera marina) is present and absent in Puget Sound, Washington, USA. In one Indonesian study, seagrasses reduced the abundance of fecal indicator bacteria, Enterococcus, suggesting their ability to act as a natural pathogen reduction system. Eelgrass (Zostera marina) is a temperate seagrass found around the globe that provides a variety of ecosystem services; however, it is not known whether eelgrass reduces bacterial abundance like its tropical counterparts. Additionally, it is not known how the bacterial community in the water column of eelgrass beds changes throughout the year. I found that there were strong differences in alpha and beta diversity between water samples collected during different seasons with higher alpha diversity in the spring and summer compared to the fall and winter. I did not find a consistent reduction of bacterial abundance associated with Z. marina beds or differences in microbial communities associated with Z. marina beds. I found that high Enterococcus abundance was correlated with high temperatures and low levels of pH, dissolved oxygen, salinity, and irradiance. We found the highest bacterial abundances during the summer months with several samples crossing the EPA single sample threshold of 104 CFUs/100mL. I detected Vibrio, Pseudomonas, and Enterobacter, potentially pathogenic bacteria that can all cause illness in human, fish, and marine mammals. My results suggest that seasonality, site, temperature, light and distance from shore are the best predictors of bacterial abundance and microbial community composition. This research has important implications for coastal management and human, animal, and environmental health.