Effect-based water quality assessment of rivers receiving discharges from legacy mines by using acute and chronic bioassays with two cladoceran species

Information about the ecotoxicological impacts of surface waters that receive discharges from legacy mines is valuable to infer the ecological impacts on natural environment for managing mine discharges. In this study, we investigated behavioural and reproductive responses of two cladoceran species Ceriodaphnia dubia and Daphnia magna to water samples collected from metal-contaminated and reference rivers near legacy mines in Japan. The toxicity identification evaluation (TIE) of water samples that caused D. magna immobility was conducted to evaluate the key metals causing acute toxicity. The results of our water quality assessment performed using two cladoceran species demonstrated modest to significant adverse effects on their behaviour and reproduction, suggesting the potential for ecotoxicological impacts on natural populations and communities at several contaminated sites that received mine drainage. The results of TIE of water samples that caused D. magna immobility indicated likely contributions of Zn and Cu. These results imply that effect-based water quality assessments such as ours can provide direct and unique evidence of the ecotoxicological impacts of metals in river waters, which will be useful for better understanding and predicting the ecological effects of these metals in the natural environment.

Experiments on invertebrate predation on cladocerans and its relationships with lake data

Until recently, knowledge of the impact of invertebrate predators on cladocerans in the Brazilian Lake Monte Alegre was limited to a few species. In order to assess the effects of predation on other cladoceran species, experiments were carried out with different pair-wise combinations of prey species. The experiments tested predation by fourth instar larvae of the dipteran Chaoborus brasiliensis Theobald on neonates and adults of the cladocerans Daphnia gessneri Herbst, Diaphanosoma birgei Kořínek, and Ceriodaphnia richardi Sars, and predation by the water mite Krendowskia sp. on neonates and adults of C. richardi and D. gessneri. In replicated treatments, the prey was offered alone or in combination with neonates and adults of two species and kept in bottles on a plankton wheel under controlled temperature, photoperiod, and light conditions. Chaoborus larvae preyed on neonates of D. birgei and D. gessneri and on adults of the former species. They preyed preferentially on neonates and adults of D. birgei over neonates and adults of C. richardi. The mite Krendowskia sp. preyed on only one species: neonates and adults of D. gessneri. Data on the distribution and strategies of prey in the lake are discussed in light of the experimental results, in an attempt to establish a link between laboratory data and field conditions.

Changes in Antibiotic-Resistance Genes Induced by the Grazing Effect in Three Cladoceran Species

The acquisition of Antibiotic-Resistance Genes (ARGs) by natural bacteria caused by antibiotic abuse is causing serious problems for human and animal welfare. Here, we evaluated the influence of three cladoceran species on Antibiotic-Resistant Bacteria (ARB) and tetracycline-resistance gene (tet(A)) copies, and discussed the effect of these biological interactions on the distribution and diffusion of ARGs in freshwater ecosystems. Bacterial community and tet(A) abundances in water samples collected from wetlands were strongly influenced by cladoceran presence. The presence of Daphnia obtusa dramatically decreased ARB and tet(A) abundance compared to that with other cladoceran species (Chydorus sphaericus and Simocephalus vetulus). Interestingly, we found a high abundance of Flavobacteriales in the microbiomes of cladoceran species. Considering that Flavobacteriales species are potential carriers of the tet(A) gene, their adsorption and assimilation with cladocerans could significantly impact the reduction of tet(A) in water. Field surveys also showed that tet(A) abundance could be low if the dominance of D. obtusa in each wetland was high. This study highlighted the need for ecological interactions and a broad range of niches in the food web when discussing the fate of ARGs in freshwater ecosystems.

Does habitat restoration disturb? A case study of a shallow urban water reservoir in western India using cladoceran zooplankton.

Anthropogenic stressors, including restoration activities, can have ecosystem wide impacts, reflecting in various biotic components, particularly the basal levels in the trophic webs. Functional traits link taxonomic diversity to ecosystem function, thereby enabling a better ecological assessment of ecosystem health. We studied the effects of restoration activities on the community structure and functional diversity of freshwater cladoceran zooplankton in an urban water reservoir. Samples were taken in the early and late phases of the restoration work. Cladoceran species community and functional composition was significantly different between the two phases. There was a considerable reduction in taxonomic richness, functional richness and redundancy in the late phase. Taxonomic beta diversity between the two phases was explained more by nestedness. Habitat degradation due to haphazard restoration measures such as destruction of littoral zone and arbitrary desilting in addition to the dumping of untreated sewage could have contributed to the decrease in species and functional richness within the reservoir.

A Tale of Two Metrics: The EPA Risk Quotient Approach versus the Delay in Population Growth Index for Determination of Pesticide Risk to Aquatic Species

The risk that two closely related insecticides, spinetoram and spinosad, posed to three Cladoceran species, Ceriodaphnia dubia, Daphnia pulex, and D. magna was determined using two approaches, the USEPA Risk Quotient method and the Delay in Population Growth Index (DPGI). Results of the RQ method showed that spinetoram posed a risk to all three species, but spinosad posed a risk only to C. dubia. The DPGI analysis showed that exposure to spinetoram resulted in populations of all three species being delayed > 3 generation times. Exposure to the LC50 and the lower 95% CL resulted in delayed populations while exposure to the upper 95% CL concentration of spinetoram resulted in no recovery of any of the three species over the course of the modeling exercise (88 d). Exposure to the lower and upper 95% Cl and the LC50 of spinosad resulted in C. dubia populations being delayed > 3 generations. D. pulex populations were not negatively affected after exposure to spinosad. D. magna populations were delayed > 3 generations, but only after exposure to the upper 95% Cl of spinosad. These results illustrate that although the EPA risk quotient method indicated that spinetoram posed a risk to all three species and that spinosad only posed a risk to C. dubia, the DPGI showed that D. magna would be negatively affected by spinosad and none of the three species would recover after exposure to the upper 95% CL of spinetoram. Because the DPGI uses the 95% Cl as well as the LC50 in its calculation and produces a measure of population growth and recovery or lack thereof, it provides more detailed information in terms of the potential risk of pesticides to populations than the RQ method.

Interactions between a planktivorous fish and planktonic microcrustaceans mediated by the biomass of aquatic macrophytes

Habitat complexity is recognized to mediate predator–prey relationships by offering refuge or not. We investigated the availability of planktonic microcrustaceans and the diet of a planktivorous fish (Hyphessobrycon eques) at different levels (low, intermediate and high) of aquatic macrophyte biomass. Sampling was carried out in a river with low flow speed, located in a Neotropical floodplain. We collected fish and microcrustaceans in macrophyte stands with variations in biomass. There were no differences in microcrustacean density in the water among the levels of macrophyte biomass, but microcrustacean richness and diet composition of H. eques differed. Microcrustacean richness and trophic niche breadth of the planktivorous fish were higher in high biomass stands. There was high consumption of a small cladoceran species in low macrophyte biomass, which was replaced by larger species, such as copepods, in intermediate and high biomass. Thus, the selection of some species was different among the biomass levels. These results suggest that plant biomass plays an important role in the interaction between fish and microcrustaceans, and prey characteristics such as size, escape ability and energy value make them more or less subject to predation by fish according to habitat structuring.

Spatio-temporal variation in the distribution and abundance of marine cladocerans in relation to environmental factors in a productive lagoon (Güllük Bay, SW Aegean Sea, Turkey)

In order to understand the effects of some physical (temperature and salinity) and chemical (dissolved oxygen, nitrate and chlorophyll a) factors on the abundance and distribution of cladoceran species, zooplankton samples were seasonally collected between August 2015 and July 2016 from three stations near the entrance to the Boğaziçi Lagoon in Güllük Bay (Aegean Sea, Turkey) using a WP2 plankton net with a mesh size of 200 μm. Four cladoceran species – Penilia avirostris, Pseudevadne tergestina, Evadne spinifera and Pleopis polyphemoides – were found during all sampling events throughout the study period. They showed high abundance in August (4774 ind. m−3) and October (10 706 ind. m−3) as the dominant zooplankton group. The abundance of Penilia avirostris – the dominant cladoceran at all sampling locations – was estimated up to 10 871 ind. m−3 in October. Pseudevadne tergestina was the second dominant cladoceran. In September, only Pseudevadne tergestina and Pleopis polyphemoides were found in samples in small numbers. The abundance of cladocerans varied significantly throughout the seasons. Two physicochemical factors, temperature and dissolved oxygen, were the main drivers of changes in the cladoceran composition.

Differences in the Vertical Distribution of Two Cladoceran Species in the Nakdong River Estuary, South Korea

As cladocerans are a primary food source for fish, predator avoidance is important to sustain cladoceran populations. We hypothesized that Bosmina longirostris and Daphniaobtusa would show different vertical distributions that depend on environmental variables and their life cycle phase. Quarterly monitoring was implemented in three water column layers (upper, middle, and bottom) in the Nakdong River Estuary. Cladocerans were mostly observed during summer; B. longirostris and D.obtusa were most abundant and exhibited different vertical distributions. Large (>600 μm) D.obtusa individuals were mainly distributed in the bottom layer (9–11 m) during the daytime and in the upper layer (1–3 m) at night. Utilization of the bottom layer by large D. obtusa was possibly a defense strategy to avoid fish predation. Although the bottom layer was not supported by lower water temperatures and dissolved oxygen than the upper or middle layers, as suggested in the previous study, we assumed that high turbidity replaced this role as a place shunned by fish (and thus a refuge for Daphnia obtusa). In contrast, smaller individuals remained in the upper layer at all times because of the low predation risk. The consumption of B. longirostris by fish was low, as the largest B. longirostris (411 μm) was smaller than the small-sized Daphnia. From this finding, we suggest that the vertical distribution of cladocerans likely depends on selectivity feeding based on fish size rather than the presence/absence of fish. We considered that these results are an important advance in understanding distribution patterns of cladocerans related to environmental features, as well as their key predators.