Copepod Mortality due to Short-Term Exposure to Natural Ultraviolet Radiation at Subtropical Latitudes

Zooplankton, particularly copepods, are key components in aquatic food webs. However, the effects of ultraviolet (UV) radiation on copepods in marine systems, especially at tropical and subtropical latitudes, are not well understood. Incubations in UV and non-UV treatments during outdoor solar experiments at a subtropical latitude where copepods dominated the zooplankton community demonstrated that UV exposure led to 40%-50% higher mortality than in non-UV treatments after 4 h of exposure. In outdoor plankton migration tower experiments, most copepods avoided surface waters regardless of radiation treatment. While adaptations to avoid UV damage, such as the accumulation of photoprotective compounds, were observed in copepods, they were insufficient to fully mitigate UV-induced harm. Thus, surface avoidance is likely the primary adaptation employed by copepods and other zooplankton to evade UV exposure. This study expands upon existing UV research, which has largely focused on high-latitude and high-altitude ecosystems, suggesting that UV is a major environmental threat factor for low-latitude zooplankton. Hence, projected future climate-change related or geoengineering-driven increases in UV levels in subtropical and tropical systems may lead to higher mortality rates in zooplankton populations.