Shiye Zhao

Suspended microplastics in the surface water of the Yangtze Estuary System, China: first observations on occurrence, distribution.

Levels of microplastics (MPs) in China are completely unknown. This study characterizes suspended MPs quantitatively and qualitatively for the Yangtze Estuary and East China Sea. MPs were extracted via a floatation method. MPs were counted and categorized according to shape and size under a stereomicroscope. The MP densities were 4137.3±2461.5 and 0.167±0.138 n/m(3), respectively, in the estuarine and the sea samples. Plastic abundances varied significantly in the estuary. Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment. Plastic particles (>5mm) were observed with a maximum size of 12.46 mm, but MPs (0.5-5 mm) constituted more than 90% by number of items. The most frequent geometries were fibres, followed by granules and films. Plastic spherules occurred sparsely. Transparent and coloured plastics comprised the majority of the particles. This study provides clues in understanding the fate and potential sources of MPs.

Microscopic anthropogenic litter in terrestrial birds from Shanghai, China: Not only plastics but also natural fibers.

The level of contamination by microscopic anthropogenic litter (0.5-5mm) in terrestrial ecosystems is not well understood. After chemical digestion in 10% KOH, microscopic anthropogenic litter from the gastrointestinal tracts of 17 terrestrial birds was identified and categorized under a stereomicroscope based on its physical properties and melting tests. In total, 364 items from 16 birds were identified as microscopic anthropogenic litter, ranging in size from 0.5 to 8.5mm. No relationship between plastic load and body condition was found. Natural fibers, plastic fibers and fragmented plastics represented, respectively, 37.4% (136 items), 54.9% (200 items) and 7.7% (28 items) of total litter items. Small sample sizes limited our ability to draw strong conclusions about the metabolism of natural fibers, but the decline in the proportion of natural fibers from the esophagus to stomach to intestine suggested that they may be digestible. Particles smaller than 5mm represented more than 90% of the total number of pollutant items. Particles with colors in the mid-tones and fibrous shapes were overwhelmingly common particles. The results reflect pollution by microscopic anthropogenic litter in the terrestrial ecosystem of the study area. Microscopic natural fibers, which may disperse and adsorb chemical pollutants differently from microplastic and may pose an even greater risk, are in urgent need of further research.

Fitness benefits and costs of induced defenses in Daphnia carinata (Cladocera: Daphnidae) exposed to cyanobacteria

Induced defenses can shape the trophic interactions between prey and predators, but the presence, benefits, and costs of induced defenses against harmful algae in zooplankton are little known. Here, the hypothesis that a short-time exposure to harmful algae can induce defenses in zooplankton was tested by evaluating the fitness changes in a single clone of Daphnia carinata (Cladocera: Daphnidae) after the exposure to a bloom-forming cyanobacterium Microcystis aeruginosa. Life-table experiments revealed that the 1-day exposure to M. aeruginosa significantly enhanced the average life span, the net reproductive rate, and the intrinsic rate of population increase of D. carinata in the presence of cyanobacteria, compared to nonexposed individuals. Then, we tested the second hypothesis that the induced defense in zooplankton would carry a cost on fitness in the absence of cyanobacteria. The 1-day exposure to M. aeruginosa significantly depressed the average life span, the net reproductive rate, and the intrinsic rate of population increase of D. carinata when exclusively feeding on a green alga, Chlorella pyrenoidosa. The induced defense against M. aeruginosa in D. carinata after a short-time exposure explains some aspects of the interactions between harmful algae and zooplankton, and may provide new general insights into the predator–prey “arms race”.

Clonal Variation in Growth Plasticity within a Bosmina longirostris Population: The Potential for Resistance to Toxic Cyanobacteria

Many aquatic organisms respond phenotypically, through morphological, behavioral, and physiological plasticity, to environmental changes. The small-size cladoceran Bosmina longirostris , a dominant zooplankter in eutrophic waters, displayed reduced growth rates in response to the presence of a toxic cyanobacterium, Microcystis aeruginosa , in their diets. The magnitude of growth reduction differed among 15 clones recently isolated from a single population. A significant interaction between clone and food type indicated a genetic basis for the difference in growth plasticity. The variation in phenotypic plasticity was visualized by plotting reaction norms with two diets. The resistance of each clone to dietary cyanobacteria was measured as the relative change in growth rates on the “poor” diet compared with the “good” diet. The enhanced resistance to M . aeruginosa in B . longirostris was derived from both the reduced slope of reaction norms and the increased mean growth rates with two diets. The large clonal variation within a B . longirostris population may contribute to local adaptation to toxic cyanobacteria and influence ecosystem function via clonal succession.

Effects of toxic and non-toxic Microcystis aeruginosa in different mixtures with Scenedesmus obliquus on growth of Brachionus calyciflorus

This study seeks to determine whether microcystins of unicellular Microcystis are the sole explanation for its adverse effects on rotifer growth. Brachionus calyciflorus were exposed to toxic and non-toxic strains of Microcystis aeruginosa separately and together with an edible alga (Scenedesmus obliquus) at different algal ratios and carbon compositions. Complete mortality was observed on B. calyciflorus cultured on toxic M. aeruginosa at all food concentrations (50, 100, and 400 μg C·L−1) and non-toxic M. aeruginosa at 400 μg C·L−1. Rotifers fed the pure non-toxic strain exhibited reduced viability at lower food concentrations. Overall, growth rate decreased with increased proportions of M. aeruginosa. In mixed-diet experiments, rotifers showed greater tolerance to the non-toxic M. aeruginosa. Diets composed of both toxic and non-toxic Microcystis combined with Scenedesmus slightly supported rotifer growth at 100 μg C·L−1. Due to the mixtures with sufficient S. obliquus at 400 μg C·L−1, nutritional deficiency could be excluded. Results are in agreement with the fact that unicellular M. aeruginosa cultured in the laboratory is a poor food for aquatic herbivores and might contain other toxic inhibiting substances to B. calyciflorus.

Temperature reaction norms of Daphnia carinata fitness: the effects of food concentration, population density, and photoperiod

Increasing concerns over climate change have renewed interest in temperature effects on aquatic organisms. The effects of temperature, food concentration, population density, and photoperiod on Daphnia carinata fitness were examined using life-table experiments in a full factorial design. The high temperature enhanced fitness at the high food concentration, but depressed it at the low food concentration. The temperature–food interactions were significant in the four combinations of two population densities and two photoperiods. The temperature–population density interactions were significant in the two combinations of two photoperiods and the high food concentration, in which the high population density masked the temperature effects. The temperature–photoperiod interaction was only significant in one combination with the low population density and the low food concentration, in which the long day length weakened the temperature effects. Such complicated interactions suggest that multiple ecological variables need to be taken into account simultaneously when assessing temperature effects on zooplankton in nature.

Limitations for Microplastic Quantification in the Ocean and Recommendations for Improvement and Standardization

Abstract Microplastics (MPs) in aquatic ecosystems, especially in the marine environment, represent an environmental issue of increasing scientific and societal concern. MPs have widespread adverse effects to the marine environment. However, the ecological effects of marine MPs, at regional and global scales, have remained poorly understood, which is partly due to the inconsistency of methodologies employed. In this chapter, we summarize and compare the analytic approaches utilized by the scientific community for numerating MPs in marine environments. Based on commonly used procedures for quantification of MPs in different marine matrices, this chapter is structured in four sections: (1) sample collection, (2) separation, (3) analysis, and (4) quality assurance/quality control. Amid the specific challenges in these four steps, cost-effective recommendations are provided to accelerate method standardization and harmonization for measuring MPs in different marine environments. The reliable and consistent methods are the imperative prerequisite for clarification of crucial questions about MPs in seas and thus for future risk assessment and reduction strategies. Furthermore, the analytic techniques discussed here are also applicable to other aquatic environments, such as freshwater and estuarine systems.