Effect of an antidepressant on aquatic ecosystems in the presence of microplastics: A mesocosm study.

Emerging pollutants, such as pharmaceuticals and microplastics have become a pressing concern due to their widespread presence and potential impacts on ecological systems. To assess the ecosystem-level effects of these pollutants within a multi-stressor context, we simulated real-world conditions by exposing a near-natural multi-trophic aquatic food web to a gradient of environmentally relevant concentrations of fluoxetine and microplastics in large mesocosms over a period of more than three months. We measured the biomass and abundance of different trophic groups, as well as ecological functions such as nutrient availability and decomposition rate. To explore the mechanisms underlying potential community and ecosystem-level effects, we also performed behavioral assays focusing on locomotion parameters as a response variable in three species: Daphnia magna (zooplankton prey), Chaoborus flavicans larvae (invertebrate pelagic predator of zooplankton) and Asellus aquaticus (benthic macroinvertebrate), using water from the mesocosms. Our mesocosm results demonstrate that presence of microplastics governs the response in phytoplankton biomass, with a weak non-monotonic dose-response relationship due to the interaction between microplastics and fluoxetine. However, exposure to fluoxetine evoked a strong non-monotonic dose-response in zooplankton abundance and microbial decomposition rate of plant material. In the behavioral assays, the locomotion of zooplankton prey D. magna showed a similar non-monotonic response primarily induced by fluoxetine. Its predator C. flavicans, however, showed a significant non-monotonic response governed by both microplastics and fluoxetine. The behavior of the decomposer A. aquaticus significantly decreased at higher fluoxetine concentrations, potentially leading to reduced decomposition rates near the sediment. Our study demonstrates that effects observed upon short-term exposure result in more pronounced ecosystem-level effects following chronic exposure.

Diversity, distribution and extinction risk of native freshwater fishes of South Africa.

Extinction risk for 101 valid species and 18 unique genetic lineages of native freshwater fishes of South Africa was assessed in 2016 following the IUCN Red List criteria. An additional five species (three new species that were described and two species that were revalidated subsequent to the 2016 assessments) were assessed in the present study. A synthesis of the outcome of the assessments of the 106 valid species and 18 genetic lineages indicates that 45 (36%) of South Africa's freshwater fish taxa are threatened (7 Critically Endangered, 25 Endangered, 13 Vulnerable). Of the remaining taxa, 17 (14%) are listed as Near Threatened, 57 (46%) are Least Concern and five (4%) are Data Deficient. More than 60% of the endemic taxa are threatened. The Cape Fold Ecoregion has the highest proportion of threatened taxa (67%) due to the existence of a unique assemblage of narrow-range endemic species. Galaxias and Pseudobarbus have the highest number of highly threatened taxa as most of the species and lineages in these genera are classified as either CR or EN. Major threats to the native freshwater fishes of the country are invasive fish species, deterioration of water quality, impoundments and excessive water abstraction, land use changes and modification of riverine habitats. Immediate conservation efforts should focus on securing remnant populations of highly threatened taxa and preventing deterioration in threat status, because recovery is rare. Accurate delimitation of species boundaries, mapping their distribution ranges, improved knowledge of pressures and long-term monitoring of population trends need to be prioritised to generate credible data for the 2026 IUCN threat status assessments and designation of important fish areas as part of the National Freshwater Ecosystem Priority Areas (NFEPA) initiative.

Swimming with the giant: coexistence patterns of a new redfin minnow Pseudobarbus skeltoni from a global biodiversity hot spot.

Ecological niche theory predicts that coexistence is facilitated by resource partitioning mechanisms that are influenced by abiotic and biotic interactions. Alternative hypotheses suggest that under certain conditions, species may become phenotypically similar and functionally equivalent, which invokes the possibility of other mechanisms, such as habitat filtering processes. To test these hypotheses, we examined the coexistence of the giant redfin Pseudobarbus skeltoni, a newly described freshwater fish, together with its congener Pseudobabus burchelli and an anabantid Sandelia capensis by assessing their scenopoetic and bionomic patterns. We found high habitat and isotope niche overlaps between the two redfins, rendering niche partitioning a less plausible sole mechanism that drives their coexistence. By comparison, environment-trait relationships revealed differences in species-environment relationships, making habitat filtering and functional equivalence less likely alternatives. Based on P. skeltoni's high habitat niche overlap with other species, and its large isotope niche width, we inferred the likelihood of differential resource utilization at trophic level as an alternative mechanism that distinguished it from its congener. In comparison, its congener P. burchelli appeared to have a relatively small trophic niche, suggesting that its trophic niche was more conserved despite being the most abundant species. By contrast, S. capensis was distinguished by occupying a higher trophic position and by having a trophic niche that had a low probability of overlapping onto those of redfins. Therefore, trophic niche partitioning appeared to influence the coexistence between S. capensis and redfins. This study suggests that coexistence of these fishes appears to be promoted by their differences in niche adaptation mechanisms that are probably shaped by historic evolutionary and ecological processes.

An Assessment of the Effect of Rotenone on Selected Non-Target Aquatic Fauna.

Rotenone, a naturally occurring ketone, is widely employed for the management of invasive fish species. The use of rotenone poses serious challenges to conservation practitioners due to its impacts on non-target organisms including amphibians and macroinvertebrates. Using laboratory studies, we investigated the effects of different rotenone concentrations (0, 12.5, 25, 37.5, 50, 100 µg L-1) on selected invertebrate groups; Aeshnidae, Belostomatids, Decapods, Ephemeroptera, Pulmonata and zooplankton over a period of 18 hours. Based on field observations and body size, we hypothesized that Ephemeropterans and zooplankton would be more susceptible to rotenone than Decapods, Belostomatids and snails. Experimental results supported this hypothesis and mortality and behaviour effects varied considerably between taxa, ranging from no effect (crab Potamonuates sidneyi) to 100% mortality (Daphnia pulex and Paradiaptomus lamellatus). Planktonic invertebrates were particularly sensitive to rotenone even at very low concentrations. Future research should investigate the recovery time of invertebrate communities after the application of rotenone and conduct field assessments assessing the longer term effects of rotenone exposure on the population dynamics of those less sensitive organisms.

Biomarker responses and morphological effects in juvenile tilapia Oreochromis mossambicus following sequential exposure to the organophosphate azinphos-methyl.

Pesticides are contaminants of aquatic environments. Such ecosystems in the Western Cape, South Africa are at risk as most organophosphates are highly toxic to fish and other aquatic organisms. The objective of this experimental study was firstly to determine the acute toxicity of azinphos-methyl (AZP) to juvenile fish (Oreochromis mossambicus) and, secondly, to investigate the effects of repeated exposure of fish to an array of sublethal concentrations on morphological parameters such as growth, condition factor and organ-somatic indices. Food consumption and feeding response time were investigated as ecologically relevant behavioral endpoints which could affect growth, reproduction and survival and subsequently causes impacts at the population and/or community level. Finally, acetylcholinesterase (AChE) was used as biomarker to investigate effects at sub-organismal level following sequential exposure to AZP. The aim was to determine how sequential spraying procedures, using different exposure concentrations and intervals, affected fish as reflected by their responses at different organizational levels. A dose-dependent effect on feeding impairment was observed in the feeding response experiment. The correlation found between growth impairment, feeding activity and AChE inhibition therefore indicates that frequency of exposure can play an important role regarding the severity of impacts to non-target organisms. This study provides evidence that AZP has harmful effects on non-target aquatic organisms, such as fish which can be manifested in the early developmental stages. Sequential exposures showed that dosage and frequency of spraying and spraying interval could exacerbate harmful effects. AChE inhibition and organosomatic indices can be used effectively to measure effects.

Acute and sublethal effects of sequential exposure to the pesticide azinphos-methyl on juvenile earthworms (Eisenia andrei).

The use of organophosphate pesticides is an integral part of commercial farming activities and these substances have been implicated as a major source of environmental contamination and may impact on a range of non-target fauna. The extent to which soil dwelling non-target organisms are affected by exposure to the organophosphate azinphos-methyl was investigated through monitoring selected biomarker responses and life cycle effects under laboratory conditions in the earthworm Eisenia andrei. Standard acute toxicity tests were conducted followed by a sequential exposure regime experiment, in order to assess the effects of multiple pesticide applications on biomarker (cholinesterase activity and neutral red retention time), life-cycle (growth and reproduction) and behaviour (avoidance and burrowing activity) responses. The present study indicates that the time between exposure events was a more important variable than concentration and that a longer interval between exposures may mitigate the effects of pesticide exposure provided that the exposure concentration is low. Additionally, it was shown that E. andrei was unable to avoid the presence of azinphos-methyl in soil, even at concentrations as high as 50% of the LC(50) value, indicating that the presence of azinphos-methyl in the soil pose a realistic threat to earthworms and other soil dwelling organisms. The ChE inhibition test showed a high percentage inhibition of the enzyme in all exposure groups that survived and NRR times of exposed organisms were lower than that of the controls. The present study yielded important results that contribute to the understanding of biological impacts of pesticide pollution on the environment. Extrapolating these results can aid in optimising pesticide application regimes to mitigate the environmental effects thereof and thus ensuring sustained soil biodiversity in agricultural areas.