Identifying mechanisms of ultraviolet radiation (UVR) tolerance is an important step in understanding the direct and indirect effects of UVR exposure on aquatic organisms. We used laboratory exposure experiments and a solar exposure experiment to evaluate mechanisms of UVR tolerance in the freshwater snail, Physa acuta. Survival following short-wavelength UVB exposure was higher in the presence of simultaneous exposure to longer-wavelength UVA and visible light than with UVB alone, indicating that P. acuta possessed photoenzymatic repair. Survival also increased as a function of body size and shell thickness, suggesting that the shell provides photoprotection. Last, snails actively selected locations further below the water surface in the presence than in the absence of solar UVR, suggesting behavioral avoidance as another mechanism of UVR tolerance. These defense mechanisms can be influenced by environmental conditions, so effects of UVR exposure may vary widely among populations and will be strongest in systems with a combination of low temperature, high transparency, and low Ca concentrations.
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Vol. 33 • No. 1