This project will specifically support achieving the overarching goal of the University of South Carolina Center (USC Center) and its overall Specific Aim, which includes assessing the effects of climate change (through alterations in temperature, salinity, pH and biogeochemical cycling of trace metals and microplastics) on the antibiotic resistance and/virulence of Vibrio bacteria and the growth and toxins production by cyanobacteria that adversely affect drinking water, contact recreation and seafood safety exposure to humans, which may lead to increases in Vibrio infections, increased inflammation and disease (e.g., Non Alcoholic Liver Disease) in humans. Though we have known for decades that nutrient enrichment of surface waters can lead to excessive algal growth, including the development of harmful algal blooms (HABs), the causes and consequences of toxins produced by these blooms has recently received heightened attention from environmental public health practitioners. Nutrient enrichment, primarily from phosphorus (P) and nitrogen (N), increases the frequency and magnitude of blooms along the freshwater to marine continuum. However, less is known about how the stoichiometric interactions between N and P across environmentally relevant gradients, particularly in combination with salinity, may influence the growth, toxins production and comparative toxicity of cyanobacteria HABs. Climate change can affect incidents of HABs and salinity, which can be altered by both changes in precipitation (droughts or floods) and sea level rise. Whereas ecological studies and monitoring activities have previously examined ?toxicity,? these efforts are routinely limited by absence of robust analytical quantitation of diverse toxins produced by specific HAB species and comparative toxicity exerted through multiple mechanisms of action including major alterations in water quality conditions resulting in differential risks to human health and ecosystems. This represents a critical consideration for management of water resources and protection of human health because algae growth does not necessarily predict toxins production, yet routine monitoring and surveillance activities, an essential environmental public health service, when these efforts do exist, use microscopic methods for cyanobacteria and thus do not quantify the presence of toxins. If toxins analysis occurs, it most commonly uses ELISA techniques to check for presence of microcystins. Further, commonly used water quality models lack inputs for toxins production, which inherently limits predictive capacity of HAB events. Some species of cyanobacteria have evolved unique adaptations to promote their growth under N-deficient conditions, but it remains unknown whether or not these traits actively exist simultaneously with toxins production. Developing predictive growth, toxins production and comparative toxicity models, proposed through the Specific Aims of this project, for cyanobacteria that commonly dominate toxic HAB events across relevant environmental gradients is thus imperative for forecasting, diagnosing and preventing human health risks presented by algal toxins, which appear to represent a transformative threat to water resources assessment and management.