Ecotoxicology of microplastics in Daphnia: A review focusing on microplastic properties and multiscale attributes of Daphnia.

The ubiquitous presence of microplastics in aquatic environments is considered a global threat to aquatic organisms. Species of the genus Daphnia provide an important link between aquatic primary producers and consumers of higher trophic levels; furthermore, these organisms exhibit high sensitivity to various environmental pollutants. Hence, the biological effects of microplastics on Daphnia species are well documented. This paper reviews the latest research regarding the ecotoxicological effects of microplastics on Daphnia, including the: 1) responses of individual, population, and community attributes of Daphnia to microplastics; 2) influence of the physical and chemical properties of microplastics; and 3) joint toxicity of microplastics and other pollutants on responses of Daphnia. Our literature review found that the published literature does not provide sufficient evidence to reveal the risks of microplastics at the population and community levels. Furthermore, we emphasized that high-level analysis has more general implications for understanding how individual-level research can reveal the ecological hazards of microplastics on Daphnia. Based on this review, we suggest avenues for future research, including microplastic toxicology studies based on both omics-based and community-level methods, especially the latter.

Ecological impact of surfactant Tween-80 on plankton: High-scale analyses reveal deeper hazards.

The ecological risks of surfactants have been largely neglected because of their low toxicity. Multiscale studies have indicated that even if a pollutant causes no acute toxicity in a test species, it may alter interspecific interactions and community characteristics through sublethal impacts on test organisms. Therefore, we investigated the lethal and sublethal responses of the plankton species Scenedesmus quadricauda, Chlorella vulgaris, and Daphnia magna, to surfactant Tween-80. Then, high-scale responses in grazer life-history traits and stability of the D. magna-larval damselfly system were further explored. The results showed that discernible adverse effects on the growth or survival of the three plankton species were evident only at exceptionally high concentrations (≥100 mg L-1). However, 10 mg L-1 of Tween-80 notably affected the MDA concentration in grazer species, simultaneously displaying a tendency to diminish grazer's heartbeat and swimming frequency. Furthermore, Tween-80 reduced the grazer reproductive capacity and increased its predation risk by larval damselflies, which ultimately jeopardized the stability of the D. magna-larval damselfly system at much lower concentrations (10-100 fold lower) than the individual-scale responses. This study provides evidence that high-scale traits are far more sensitive to Tween-80, compared with individual-scale traits for plankton organisms, suggesting that the ecological risks of Tween-80 demand careful reassessment. SYNOPSIS: The concentration of Tween-80 needed to induce changes in community characteristics is markedly lower than that needed to produce individual-scale consequences. Thus, high-scale analyses have broad implications for understanding the hazardous effects of surfactants compared with an individual-scale analysis.

Microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions.

The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but relatively little is known about their potential adverse effects on the function and stability of aquatic ecosystems. We investigated here the effects of polyethylene (PE) microplastics on several aspects of plankton ecosystems, including Daphnia magna behavior, the grazing rate of D. magna on Chlorella vulgaris cells, trophic-cascade effects in the C. vulgaris-D. magna-larval damselfly food chain, the life-history of D. magna, and the stability and persistence of the D. magna-larval damselfly system. PE microplastics decreased the D. magna grazing rate as a result of reductions in their heart rate and hopping frequency. In the trophic-cascade experiment, PE microplastics increased the foraging success of larval damselflies on grazers due to hopping inhibition in grazers, which ultimately strengthened the trophic-cascade effect on algal growth. Long-term exposure to PE microplastics reduced the stability and persistence of the grazer population via increased predation risk and reduced reproductive capacity for grazer species. This study provides evidence that microplastics can affect the trophic cascade strength and stability of plankton ecosystems via behavior-mediated indirect interactions, suggesting that microplastics have more extensive impacts on aquatic ecosystems than presently recognized. ENVIROMENTAL IMPLICATION: The massive production and environmental releasing of microplastics have become ubiquitous in the global environment. The negative effects of microplastics on the normal growth of aquatic organisms have been well studied, but little is known about potential adverse effects on the function and stability of aquatic ecosystems. Here, we found that microplastics increased the positive impacts of larval damselflies on algal growth, and reduced the stability and persistence of plankton ecosystems via a behavior-mediated indirect interaction. To our knowledge, this is the first systematic study assessing the effects of microplastics on the community-level characteristics of a freshwater ecosystem. SYNOPSIS: PE microplastics affect trophic cascade strength and reduce the stability and persistence of plankton ecosystems via behavior-mediated indirect interactions.

Effects of microplastics pollution on plankton: A review.

Microplastics, a new class of environmental pollutants, accumulates in the environment at an uncontrollable rate, which threatens aquatic organisms. Plankton are the basis of food webs and play a significant role in the material circulation and energy flow of aquatic ecosystems. Plankton are sensitive to various environmental pollutants. It is necessary to investigate the impacts of microplastics on plankton. Here, we analzyed the sources and characteristics of microplastics, and the current state of microplastic pollution in aquatic ecosystem. The direct and indirect harmful effects of microplastics on aquatic organisms were elaborated. Then, we focused on the potential consequences of microplastics on phytoplankton and zooplankton species from different scales, ranging from individual, population, to community level. With respect to plankton organisms, few studies were carried out on genomics and proteomics from the microcosmic perspective, and on popu-lation and community responses from the macroscopic aspect. This review would provide references for further studies.

Effect of norfloxacin on algae-cladoceran grazer-larval damselfly food chains: Algal morphology-mediated trophic cascades.

Antibiotic norfloxacin (NOR) has recently been demonstrated to affect the swimming behavior of zooplankton species and phytoplankton-zooplankton interactions, which may further affect trophic cascades. To test this hypothesis, two food chains (Scenedesmus quadricauda-Daphnia magna-larval damselfly and Chlorella vulgaris-D. magna-larval damselfly) were used to examine the effect of NOR concentrations (0, 0.5, 5, and 25 mg L-1) on trophic cascades. In the absence of NOR, larval damselflies reduced grazer density and increased algal density, regardless of algal species. In the presence of NOR, increasing NOR concentration strengthened the positive effect of larval damselflies on the growth of C. vulgaris because larval damselflies suppressed grazer density more efficiently resulting from reduced swimming ability in the grazers. Conversely, increasing NOR concentration reduced the positive effect on the growth of S. quadricauda due to inhibited grazer-induced colony formation in S. quadricauda. Therefore, exposure to NOR altered the direction and strength of trophic cascades and showed species-specific differences, depending on algal morphology-mediated indirect interactions. These findings provide novel insights into how NOR affects aquatic food chains and reveal the importance of algal traits in determining trophic cascades.