Adaptive specialization and constraint in morphological defences of planktonic larvae

The response of aquatic ecosystems to the interactive effects of stratospheric ozone depletion, UV radiation, and climate change

Variations in stratospheric ozone and changes in the aquatic environment by climate change and human activity are modifying the exposure of aquatic ecosystems to UV radiation. These shifts in exposure have consequences for the distributions of species, biogeochemical cycles, and services provided by aquatic ecosystems. This Quadrennial Assessment presents the latest knowledge on the multi-faceted interactions between the effects of UV irradiation and climate change, and other anthropogenic activities, and how these conditions are changing aquatic ecosystems. Climate change results in variations in the depth of mixing, the thickness of ice cover, the duration of ice-free conditions and inputs of dissolved organic matter, all of which can either increase or decrease exposure to UV radiation. Anthropogenic activities release oil, UV filters in sunscreens, and microplastics into the aquatic environment that are then modified by UV radiation, frequently amplifying adverse effects on aquatic organisms and their environments. The impacts of these changes in combination with factors such as warming and ocean acidification are considered for aquatic micro-organisms, macroalgae, plants, and animals (floating, swimming, and attached). Minimising the disruptive consequences of these effects on critical services provided by the world's rivers, lakes and oceans (freshwater supply, recreation, transport, and food security) will not only require continued adherence to the Montreal Protocol but also a wider inclusion of solar UV radiation and its effects in studies and/or models of aquatic ecosystems under conditions of the future global climate.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595-828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.

UV radiation affects antipredatory defense traits in Daphnia pulex

In aquatic environments, prey perceive predator threats by chemical cues called kairomones, which can induce changes in their morphology, life histories, and behavior. Predator-induced defenses have allowed for prey, such as Daphnia pulex, to avert capture by common invertebrate predators, such as Chaoborus sp. larvae. However, the influence of additional stressors, such as ultraviolet radiation (UVR), on the Daphnia-Chaoborus interaction is not settled as UVR may for instance deactivate the kairomone. In laboratory experiments, we investigated the combined effect of kairomones and UVR at ecologically relevant levels on induced morphological defenses of two D. pulex clones. We found that kairomones were not deactivated by UVR exposure. Instead, UVR exposure suppressed induced morphological defense traits of D. pulex juveniles under predation threat by generally decreasing the number of neckteeth and especially by decreasing the size of the pedestal beneath the neckteeth. UVR exposure also decreased the body length, body width, and tail spine length of juveniles, likely additionally increasing the vulnerability to Chaoborus predation. Our results suggest potential detrimental effects on fitness and survival of D. pulex subject to UVR stress, with consequences on community composition and food web structure in clear and shallow water bodies.

Costs and compensation in zooplankton pigmentation under countervailing threats of ultraviolet radiation and predation

Evolutionary responses to opposing directions of natural selection include trade-offs, where the phenotype balances selective forces, and compensation, where other traits reduce the impact of one selective force. Zooplankton pigmentation protects from ultraviolet radiation (UVR) but attracts visual predators. This trade-off is understudied in the ocean where planktonic larvae in surface waters face ubiquitous UVR and visual predation threats. We tested whether crab larvae can behaviorally reduce UVR risk through downward swimming or expansion of photoprotective chromatophores. Then we examined whether more pigmented larvae are more heavily predated by silverside fish under natural sunlight in the tropics in three UVR treatments (visible light, visible + UVA, visible + UVA + UVB). Lastly, we tested the behavioral chromatophore response of larvae to predation threats in two light treatments. Armases ricordi avoided surface waters after exposure to sunlight with UVR. Armases ricordi, Armases americanum, and Eurypanopeus sp. consistently expanded chromatophores in UVR or visible light, while Mithraculus sculptus and Mithraculus coryphe showed no response. Fish preferred pigmented larvae on sunnier days in visible light lacking UVR. Lastly, both M. coryphe and M. sculptus unexpectedly expanded chromatophores in fish cues, but responses were inconsistent over trials and across light treatments. The more consistent larval responses to UVR than to predator cues and the lack of predator preferences in natural light conditions suggest that UVR may have a stronger influence on pigmentation than predation. This study improves our understanding of planktonic adaptation to countervailing selection caused by visual predation and exposure to UVR.