Microbial interactions are fundamental to nutrient cycling, ecosystem stability, and population dynamics in aquatic environments, with bacteria driving processes like organic matter decomposition and nutrient release. These bacteria form critical links in the food web and interact with viruses and protists, shaping biogeochemical cycles and ecosystem productivity. This study examines the roles of protists and viruses in regulating bacterial mortality across aerobic (oxygen-rich) and anaerobic (oxygen-depleted) zones in Siders Pond, a salt-stratified meromictic pond in Falmouth, Massachusetts. 

We hypothesize that protists dominate bacterial mortality in the aerobic zone due to their oxygen-dependent grazing activity, while viruses play a more prominent role in the anaerobic zone, where oxygen limitation reduces protist activity. This research aims to clarify these interactions and their significance for nutrient cycling and ecosystem health.

Field and laboratory methodologies were applied to assess microbial dynamics along the oxygen gradient. Water samples were collected at varying depths and measured for dissolved oxygen, temperature, salinity, pH, dissolved organic carbon (DOC), and nutrients (PO4, NO3/NO2) to determine how the environment affects microbial activity. Bacterial and grazer production were quantified using C14-leucine incorporation. Protist abundances were determined using DAPI staining, while bacterial and viral abundances were measured using SYBR Gold staining.

Preliminary findings suggest that bacterial and protist production decreases when transitioning from aerobic to anaerobic zones, while viral activity remains consistent. This study contributes to understanding how microbial interactions respond to environmental stressors such as eutrophication, pollution, and climate change, offering a model for future research and strategies for preserving aquatic ecosystem health amidst global environmental challenges.