Salinization and heavy metal cadmium impair growth but have contrasting effects on defensive colony formation of Scenedesmus obliquus

The Easily Overlooked Effect of Global Warming: Diffusion of Heavy Metals

Since industrialization, global temperatures have continued to rise. Human activities have resulted in heavy metals being freed from their original, fixed locations. Because of global warming, glaciers are melting, carbon dioxide concentrations are increasing, weather patterns are shifting, and various environmental forces are at play, resulting in the movement of heavy metals and alteration of their forms. In this general context, the impact of heavy metals on ecosystems and organisms has changed accordingly. For most ecosystems, the levels of heavy metals are on the rise, and this rise can have a negative impact on the ecosystem as a whole. Numerous studies have been conducted to analyze the combined impacts of climate change and heavy metals. However, the summary of the current studies is not perfect. Therefore, this review discusses how heavy metals affect ecosystems during the process of climate change from multiple perspectives, providing some references for addressing the impact of climate warming on environmental heavy metals.

Interference of two typical polycyclic aromatic hydrocarbons on the induced anti-grazing defense of Tetradesmus obliquus

Anthropogenic emissions of polycyclic aromatic hydrocarbons (PAHs) cause severe ecological impacts by contaminating natural water bodies, affecting various biological groups, and altering interspecies relationships and ecological functions. This study examined the effects of two typical PAHs, phenanthrene (Phe) and naphthalene (Nap), on the anti-grazing defense mechanisms of Tetradesmus obliquus, a primary producer in freshwater food chains. Four non-lethal concentrations (0.01, 0.1, 1, and 10 mg L-1) of Phe and Nap were tested and the population growth, photosynthetic capacity, pigment content, and morphological defense of T. obliquus were analyzed. The results indicated that Phe and Nap inhibited both the growth rate and formation of defensive colonies of T. obliquus induced by Daphnia grazing cues, and the inhibition ratio increased with concentration. Phe and Nap significantly shortened the defense colony formation time of T. obliquus. Phe and Nap significantly suppressed photosynthesis in the early stages; however, the photosynthetic efficiency recovered over time. These findings highlight the high sensitivity of grazing-induced colony formation in T. obliquus to Phe and Nap at non-lethal concentrations, which could affect the interactions between phytoplankton and zooplankton in aquatic ecosystems. Our study underscores the influence of Phe and Nap on the defense mechanisms of phytoplankton and the consequential effects on ecological interactions within freshwater ecosystems, providing insight into the complex impacts of pollutants on phytoplankton-zooplankton relationships. Therefore, it is necessary to consider interspecific interactions when assessing the potential negative effects of environmental pollutants on aquatic ecosystems.

Proposing Effective Ecotoxicity Test Species for Chemical Safety Assessment in East Asia: A Review

East Asia leads the global chemical industry, but environmental chemical risk in these countries is an emerging concern. Despite this, only a few native species that are representative of East Asian environments are listed as test species in international guidelines compared with those native to Europe and America. This review suggests that Zacco platypus, Misgurnus anguillicaudatus, Hydrilla verticillata, Neocaridina denticulata spp., and Scenedesmus obliquus, all resident to East Asia, are promising test species for ecotoxicity tests. The utility of these five species in environmental risk assessment (ERA) varies depending on their individual traits and the state of ecotoxicity research, indicating a need for different applications of each species according to ERA objectives. Furthermore, the traits of these five species can complement each other when assessing chemical effects under diverse exposure scenarios, suggesting they can form a versatile battery for ERA. This review also analyzes recent trends in ecotoxicity studies and proposes emerging research issues, such as the application of alternative test methods, comparative studies using model species, the identification of specific markers for test species, and performance of toxicity tests under environmentally relevant conditions. The information provided on the utility of the five species and alternative issues in toxicity tests could assist in selecting test species suited to study objectives for more effective ERA.

Freshwater salinization reduces vertical movement rate and abundance of Daphnia: Interactions with predatory stress

Contaminants in human-dominated landscapes are changing ecological interactions. The global increase in freshwater salinity is likely to change predator-prey interactions due to the potential interactive effects between predatory stress and salt stress. We conducted two experiments to assess the interactions between the non-consumptive effects of predation and elevated salinity on the abundance and vertical movement rate of a common lake zooplankton species (Daphnia mendotae). Our results revealed an antagonism rather than a synergism between predatory stress and salinity on zooplankton abundance. Elevated salinity and predator cues triggered a >50% reduction in abundance at salt concentrations of 230 and 860 mg Cl^-/L, two thresholds designed to protect freshwater organisms from chronic and acute effects due to salt pollution. We found a masking effect between salinity and predation on vertical movement rate of zooplankton. Elevated salinity reduced zooplankton vertical movement rate by 22-47%. A longer exposure history only magnified the reduction in vertical movement rate when compared to naïve individuals (no prior salinity exposure). Downward movement rate under the influence of predatory stress in elevated salinity was similar to the control, which may enhance the energetic costs of predator avoidance in salinized ecosystems. Our results suggest antagonistic and masking effects between elevated salinity and predatory stress will have consequences for fish-zooplankton interactions in salinized lakes. Elevated salinity could impose additional energetic constraints on zooplankton predator avoidance behaviors and vertical migration, which may reduce zooplankton population size and community interactions supporting the functioning of lake ecosystems.