Temperature correlates with annual changes in Hematodinium perezi prevalence in blue crab Callinectes sapidus in Florida, USA.

Blue crabs Callinectes sapidus were monitored biannually throughout Florida, USA, for 2 yr using a highly sensitive, quantitative polymerase chain reaction (qPCR) to determine the spatial and temporal changes in prevalence and intensity of Hematodinium perezi infections during drought years. Despite persistent drought conditions, H. perezi infections were not universally found. Overall prevalence was 25.3% (95% CI: 22.8-28.1%) in 1066 crabs sampled from 6 locations (Jacksonville, Ormond Beach, Everglades City, Tampa Bay, Steinhatchee, and Panama City) from 2011 to 2012. Presence of H. perezi was consistently highest in winter season samples, ranging from 4.2-51.1% (3 locations) in 2011, to 32-83% (5 locations) in 2012. The highest prevalence and intensities were observed in the winter samples from Everglades City. Previous studies have found that the prevalence of H. perezi in C. sapidus in temperate regions of the US East Coast shows seasonal peaks in early winter in Maryland and South Carolina and in fall and spring in Georgia. The seasonality of infections in the subtropical waters of Florida reinforces the concept that temperature is a strong factor that may override other drivers, such as drought. Seasonal H. perezi infections in Florida appear to be triggered by the parasite responding to an optimal temperature during the annual rise from the low temperature of winter when salinity is elevated. However, salinity alone is not sufficient to trigger an increase in prevalence of H. perezi in Florida.