Phytoplankton Under Pressure: Temperature, Precipitation and Cyanobacterial Blooms as Drivers of Chytrid Infections

The area of fungal parasitism is attracting growing attention because of its great importance for aquatic organisms and their community dynamics. Despite increasing interest in this area, few studies have addressed baseline data on occurrence and environmental factors associated with chytrid parasite infections in natural ecosystems. This work provides insights into occurrence, prevalence, and dynamics of parasitic infections by studying three freshwater reservoirs over a period of 6 years. Chytrid infections were detected in each of the studied water bodies, infecting species of cyanobacteria, green algae and diatoms. However, recurring and prevalent infections were observed in only one water body, which is classified as a natural aquatic ecosystem. The recorded infection prevalence (IPC) ranged between 0% and 20%, while the mean infection severity remained low. Infection rates were highest in summer and most prominent during cyanobacterial blooms. Yet, the most infected group of phytoplankton consisted of green algae. GLM revealed a significantly positive correlation between IPC and water temperature and precipitation. Overall, these results demonstrate the dynamic nature of chytrid infections, which are shaped by multiple environmental factors across space and time.