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Abstract Zooplankton composition and distribution influence prey quality and availability for higher trophic levels, yet ecological forces structuring communities are not often resolved on spatial scales relevant to predator–prey encounters (1–10 m). Because continental shelf water columns are often vertically stratified, fine-scale interactions may influence overall biological productivity. Using a towed imaging system, we measured meso- and macrozooplankton abundances (>2.2 mm equivalent spherical diameter) in the South Atlantic Bight between the 25 and 45 m isobaths in August 2021. Zooplankton were parsed into four key traits (size, carbon content, trophic strategy, and swimming speed), and buoyancy frequency was used to identify discrete vertical oceanographic zones. Trait diversity was less variable in mixed waters due to the dominance of low carbon content zooplankton or passive swimmers. Upwelling intrusions generated high chlorophyll-a and sharp stratification, which favoured high-carbon, fast swimming zooplankton. Trait group abundances were often higher in these deeper, sharply stratified waters, suggesting that intrusions generally favour secondary production, with gelatinous organisms gradually becoming more dominant as the pycnocline weakens. The distribution of size classes, however, did not change among water masses. Stratification and mixing generate distinct environments and consistent trait assemblages, potentially improving predictions of community responses to oceanographic structure. 

Overexposure to ultraviolet radiation (UVR) emitted by the sun can damage and kill living cells in animals, plants, and microorganisms. In aquatic environments, UVR can penetrate nearly 47 m into the water column, severely impacting many marine organisms. Jellyfish are often considered resilient to environmental stressors, potentially explaining their success in environmentally disturbed areas, but the extent of their resilience to UVR is not well known. Here, we tested resiliency to UVR by exposing benthic polyps of the moon jellyfish,Aureliasp., to UVA and UVB—the two types of UVR that reach Earth’s surface—both separately and in combination. We quantified asexual reproduction rates and polyp attachment to hard substrate, in addition to qualitative observations of polyp health. There were no differences in asexual reproduction rates between polyps exposed to isolated UVA and polyps that received no UVR. Polyps reproduced when exposed to short term (∼7–9 days) isolated UVB, but long-term exposure limited reproduction and polyp attachment to the substrate. When exposed to both UVA and UVB, polyps were unable to feed and unable to remain attached to the substrate, did not reproduce, and ultimately, experienced 100% mortality within 20 days. Although many studies only examine the effects of UVB, the combination of UVA and UVB here resulted in greater negative impacts than either form of UVR in isolation. Therefore, studies that only examine effects of UVB potentially underestimate environmentally relevant effects of UVR. These results suggest that polyps are unsuccessful under UVR stress, so the planula larval stage must settle in low-UVR environments to establish the success of the polyp stage.