Seasonality and Salinity Shape Parasite Prevalence in an Estuarine Crab Host

Parasite-host dynamics in marine ecosystems are strongly influenced by spatial and temporal conditions. We aimed to investigate how spatiotemporal factors such as salinity and seasonality influenced the prevalence of macroparasites - the entoniscid Cryptocancrion brevibrachium, the rhizocephalan Loxothylacus panopaei, and digenean trematode cysts - in the estuarine crab host, Rhithropanopeus harrisii. Crabs (N=912) were collected from the Chesapeake Bay across a salinity gradient of 10.5ppt-20ppt from August 2024-May 2025. Crabs were dissected, and crab and parasite species were recorded. Linear modeling showed that salinity significantly influenced L. panopaei prevalence but had no effect on C. brevibrachium, cysts, or coinfection prevalence. Trematode cyst prevalence was scarce throughout the year, but prevalence of L. panopaei, C. brevibrachium, and coinfections was higher during warmer months (e.g., summer through early fall). The high prevalence of C. brevibrachium (13%), L. panopaei (40%), and coinfections (12%) found in warmer months is likely associated with high parasite reproduction during this time. Understanding the role that salinity and seasonality play in determining the prevalence of these parasites within this host is important because R. harrisii is an invasive species around the globe and can be used as a vector for these parasites to spread.