Salinity and Climate Variability Drive the Distribution of Perkinsus marinus in Eastern Oysters Across Texas Estuaries

Over the 20th and 21st centuries, eastern oyster (Crassostrea virginica) populations have experienced significant declines in distribution and abundance, with parasite proliferation driving significant declines across estuaries. This study examines trends of the protozoan parasite Perkinsus marinus (the causative agent of dermo disease) over a seven−year period (2005–2011) across five Texas bay systems (Galveston Bay, Matagorda Bay, San Antonio Bay, Aransas Bay, and Corpus Christi Bay) with an emphasis on the role of freshwater inflow, temperature, and salinity. Weighted prevalence was used as the overall parasite indicator. This is a useful parameter to identify disease−related mortalities in the Gulf of Mexico as it integrates prevalence and infection intensity into one metric. Bay–specific variation in weighted prevalence of P. marinus was present, suggesting that localized conditions strongly influence parasite dynamics. San Antonio Bay and Aransas Bay (south Texas coast) had peak levels of P. marinus early in the summer while the remaining bays experience peak levels in the fall. Modeled factors explained 73% of total variability in weighted prevalence of P. marinus and indicated that P. marinus was strongly associated with salinity, and to freshwater inflow and temperature to a lesser extent. Further, an additional focused analysis in Galveston Bay, a known hotspot for P. marinus, corroborated this finding and demonstrated higher weighted prevalence of P. marinus in zones of higher average salinities (> 15). These findings are particularly relevant under future modeling scenarios, which forecast climate−driven changes in salinity globally. By examining seasonal and multiyear trends of P. marinus within a narrow latitudinal band along Texas bays, this study offers insights for understanding the drivers of natural variability of P. marinus on oysters in other Gulf of Mexico estuaries.