Impact of Short-Term Ultraviolet (UV) Radiation Exposure on Paramecium Behavior, Viability, Proliferation and Implications for Freshwater Ecosystem Health

Paramecium caudatum, a well-established freshwater protozoan model, was employed to assess the sub-lethal and lethal effects of ultraviolet (UV) radiation exposure at 254 nm. Paramecia were exposed to varying durations of UV light ranging from 1 to 5 minutes, and observed for behavioral and physiological changes over a period of 96 hours. Short-term exposure (1-3 minutes) resulted in no mortality and retained normal motility and morphology. However, 4-minute exposure induced noticeable stress responses, including reduced swimming speed, disrupted locomotion patterns, and partial loss of cellular activity, with approximately 50% of individuals becoming inactive. The most severe effects were recorded following 5-minute exposure, where paramecia exhibited pronounced morphological deformities such as swelling, elongation, and loss of symmetry, along with pigmentation changes such as darkening and spotting of cytoplasm, loss of shape and structure, impaired coordination, and complete mortality by 24 hours post-exposure. Due to its ecological importance and sensitivity to UV radiation Paramecium serves as a valuable bioindicator for assessing the environmental impacts of increasing UV radiation associated with climate change. Additionally, it contributes to SDG 14 (Life below Water) by emphasizing that the UV sensitivity of freshwater protozoa reflects broader risks to aquatic microbial communities.