Spatial Variability and Seasonal Patterns of Co-Occurrence between two Marine Biotoxins in the Puget Sound and Implications for Public Health Management

Abstract

Shellfish are of utmost cultural, recreational, and commercial importance in Washington State. However, the accumulation of marine algal biotoxins in shellfish can pose severe health risks to shellfish consumers. While Paralytic Shellfish Toxins (PSTs) have been well monitored in the state for decades, Diarrhetic Shellfish Toxins (DSTs) were only recently detected in Washington but are now widespread throughout the Puget Sound and neighboring marine basins. This study investigates the frequency, intensity, and variability of PSTs, DSTs, and their co-occurrence across various marine basins in Washington State's Puget Sound during the first decade of co-monitoring. Biotoxin monitoring data for PST and DST were sourced from the Washington Department of Health and were used to identify when and where toxin co-occurrence was observed from 2012 to 2022. Additionally, Bayesian Hierarchical autoregressive models were created to parse out the effects of month, year, and marine subbasin on PST and DST concentrations. The findings reveal distinct geographic patterns in toxin occurrences, indicating basin-specific environmental influences on toxin concentration. Additionally, concentrations of both toxins showed seasonal variation, though temporal peaks were not often synchronous, resulting in back-to-back toxin events and prolonged shellfish harvesting closures. This thesis provides a baseline assessment of toxin co-occurrence during the first decade of co-monitoring for PSTs and DSTs and characterizes patterns underlying toxin co-occurrence, highlighting the need for further study into the human health effects of co-exposure to these toxins.