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Agricultural runoff and biological invasions alter native species interactions with implications for the management of pests. Here, we used live larvae of common house mosquito Culex pipiens to test the efficiencies of the invasive fish Gambusia holbrooki and the IUCN endangered fish Aphanius iberus to manage mosquitoes at three ecologically relevant concentrations of algae and clay. Both species reduced mosquito abundance in aquaria and outdoor mesocosms though A. iberus reduced it at a slower pace. However, G. holbrooki preferentially captured larger larvae at all fish sizes, whereas smaller individuals of A. iberus captured higher number of smaller larvae. Algal turbidity, but not clay, reduced the efficiency of both species, probably because of an adaptation to inorganic turbidity. Fish efficiency was not reduced in mesocosms where fish captured mosquito larvae interacting with natural invertebrate assemblages. Managers should maintain algal turbidity at < 10 FTU based on the visual detection threshold for both species. Our study shows that algal turbidity threatens the potential of waterbodies to naturally control mosquitoes and discusses why the faster foraging rates of alien species such as G. holbrooki should not be used to justify more introductions. [ABSTRACT FROM AUTHOR]

Agricultural intensification and shifts in precipitation regimes due to global climate change are expected to increase nutrient concentrations in aquatic ecosystems. However, the direct effects of nutrients widely present in wastewaters, such as nitrate, are poorly studied. Here, we use multiple indicators of fish health to experimentally test the effects of three ecologically relevant nitrate concentrations (<10, 50 and 250 mg NO3-/l) on wild-collected mosquitofish (Gambusia holbrooki), a species widely introduced for mosquito biocontrol in often eutrophic waters. Overall, biomarkers (histopathology, feeding assays, growth and caloric content and stable isotopes as indicators of energy content) did not detect overt signs of serious disease in juveniles, males or females of mosquitofish. However, males reduced food intake at the highest nitrate concentration compared to the controls and females. Similarly, juveniles reduced energy reserves without significant changes in growth or food intake. Calorimetry was positively associated with the number of perivisceral fat cells in juveniles, and the growth rate of females was negatively associated with δ15N signature in muscle. This study shows that females are more tolerant to nitrate than males and juveniles and illustrates the advantages of combing short- and long-term biomarkers in environmental risk assessment, including when testing for the adequacy of legal thresholds for pollutants. [ABSTRACT FROM AUTHOR]

The aquarium hobby is popular worldwide, but it has positives and negatives for freshwater fish conservation. The most damaging impacts of the aquarium trade on ecosystems are overharvesting and invasive species. Consequently, many conservationists and academics have the perception that aquarium hobbyists are generally harmful to species conservation. Without overlooking these major drawbacks of the aquarium hobby, we aim to establish common ground between hobbyists and conservationists by correcting some misconceptions and showing the benefits of serious aquarium hobbyists in the conservation of freshwater fishes and their habitats. Our overview illustrates that the aquarium hobby is not insensitive to the pernicious effects of this enduring hobby on natural systems and that serious aquarists and their associations can directly assist and fund scientific research, increase conservation awareness among the general public and even participate in ex situ and in situ conservation programmes for native fish species at national or international levels. Whilst the relationship between conservationists and the aquarium hobby has often been antagonistic in recent years, ultimately most biologists and aquarists share a love of the species they study or maintain, and this common interest could be the basis for a more positive and productive relationship. [ABSTRACT FROM AUTHOR]

Functional traits are growing in popularity in modern ecology, but feeding studies remain primarily rooted in a taxonomic-based perspective. However, consumers do not have any reason to select their prey using a taxonomic criterion, and prey assemblages are variable in space and time, which makes taxon-based studies assemblage-specific. To illustrate the benefits of the trait-based approach to assessing food choice, we studied the feeding ecology of the endangered freshwater fish Barbus meridionalis. We hypothesized that B. meridionalis is a selective predator which food choice depends on several prey morphological and behavioral traits, and thus, its top-down pressure may lead to changes in the functional composition of in-stream macroinvertebrate communities. Feeding selectivity was inferred by comparing taxonomic and functional composition (13 traits) between ingested and free-living potential prey using the Jacob's electivity index. Our results showed that the fish diet was influenced by 10 of the 13 traits tested. Barbus meridionalis preferred prey with a potential size of 5-10 mm, with a medium-high drift tendency, and that drift during daylight. Potential prey with no body flexibility, conical shape, concealment traits (presence of nets and/or cases, or patterned coloration), and high aggregation tendency had a low predation risk. Similarly, surface swimmers and interstitial taxa were low vulnerable to predation. Feeding selectivity altered the functional composition of the macroinvertebrate communities. Fish absence favored taxa with weak aggregation tendency, weak flexibility, and a relatively large size (10-20 mm of potential size). Besides, predatory invertebrates may increase in fish absence. In conclusion, our study shows that the incorporation of the trait-based approach in diet studies is a promising avenue to improve our mechanistic understanding of predator-prey interactions and to help predict the ecological outcomes of predator invasions and extinctions. [ABSTRACT FROM AUTHOR]

Natural and anthropogenic disturbances are key forces governing the structure and functioning of aquatic communities. Understanding how these factors shape organism performance can help to identify the most vulnerable species and develop effective management strategies. This is particularly important for ichthyofaunas with high endemicity and low diversity, such as those of the Iberian Peninsula., We explored the suitability of a novel and simple condition index, the scaled mass index (SMI), based on mass-length relationships, for analysis of the effects that abiotic and biotic pressures have on the body condition of four fish taxa widely distributed in Mediterranean rivers in north-eastern Spain: brown trout ( Salmo trutta), Iberian redfin barbel ( Barbus haasi), Ebro barbel ( Luciobarbus graellsii) and minnows ( Phoxinus spp.). The SMI performed better in explaining spatial variation in body condition than the Fulton Index, a traditional method for fish studies., For all taxa, anthropogenic stressors influencing water quality and physical habitat explained more variance in SMI than other factors. Variation partitioning and GLM approaches consistently showed that SMI increased with altitude, reduced concentrations of toxic nitrogenous compounds, and well-preserved riparian canopy and natural channel morphology, despite the fact that three of the study taxa are in expansion and generally considered 'tolerant'. In addition, the application of SMI to an independent fish data set showed that SMI provides a novel indicator of ecosystem health, which performs better than the current index of biotic integrity developed in this region., We discuss the likely mechanisms behind the strong effects of habitat quality on SMI and the implications for our understanding of tolerance. Incorporating SMI into studies of fish monitoring is likely to improve the value of fish studies as indicators of river quality and ecological change. Further studies should compare the response of SMI to specific fish health indicators such as parasite load, haematological assays and pollutant bioaccumulation to improve our understanding of the value of SMI as a non-lethal diagnostic procedure. [ABSTRACT FROM AUTHOR]

The current freshwater fish fauna crisis is such that natural resource managers urgently need to identify priorities and understand the management consequences of actions aimed at maximizing the preservation of biodiversity. Freshwater research is often poorly linked to conservation ecology; and interdisciplinary studies illustrating examples of freshwater ecosystem conservation are scarce. The Iberian Peninsula has a long history of anthropogenic disturbance that has led to the poor conservation status of its ichthyofauna, with 52 % of species now catalogued as critically endangered, endangered or vulnerable, according to UICN criteria. This paper gives an overview of the main threats (habitat degradation, hydrological alterations and exotic species) that have altered the function and connectivity of Iberian rivers. Case-study examples are provided to analyse the repercussions of these threats and the management actions planned or already performed in these systems. The interaction of many threats is responsible for native fish decline. However, freshwater managers and researchers should not let the trees prevent them from seeing the overall wood, when seeking to achieve practical solutions with the best balanced cost benefit and the collaboration of all ecosystem researchers and stakeholders. Conservation efforts should be focused on the preservation of ecological processes, in order to achieve the goals of the Water Framework Directive and guarantee the conservation of Iberian native fish species. [ABSTRACT FROM AUTHOR]

1. North-eastern Spain is a hot spot for the introduction of alien fish species, and its native fish fauna is one of the most endangered worldwide. We used an extensive data set from 2002 to 2003 and historical information from the area to characterize fish diversity and establish conservation priorities in river catchments. 2. Diversity indices were used to characterize fish diversity at the basin scale. An index of conservation status was applied for each species, which considers the occurrence, abundance and endemicity of each taxon. We used indirect ordination methods to test the relationship among basin features and to identify those variables most correlated with each other. To identify physical, biotic and environmental characteristics that seem to make a basin particularly susceptible to invasion, we performed a step-wise multiple regression to examine the relationship between the number of native, translocated and introduced fish species (including the original native species richness of each basin), and landscape variables. 3. Over a period of approximately 50 years, the mean range size of native fish species has decreased by 60%. The greatest decline occurred in Gasterosteus gymnurus, Anguilla anguilla and Salaria fluviatilis, for which species over 75% of the original distribution area has been lost. The species with the highest conservation index were Gasterosteus gymnurus and Salaria fluviatilis. 4. Basin area and the catchment type explained 70% of variation in native species richness, whereas the number of dams and basin area accounted for more than 80% of variation in the number of introduced species. 5. The original native species richness and the number of introduced species at basin scale were not related, and thus there was no evidence of “biotic resistance” to invasion. The restoration of natural hydrologic processes and the development of specific management tools to protect native species, such as the prioritization of areas for fish conservation and the eradication of local populations of exotic species, are required to restore native fish fauna in these catchments. [ABSTRACT FROM AUTHOR]

The effects of human-induced stressors on riverine fish assemblages are still poorly understood, especially in species-poor assemblages such as those of temperate South American rivers. In this study we evaluated the effects of human-induced stressors on the taxonomic and functional facets of fish assemblages of two central-southern Chilean rivers: the Biobío River (flow regulated by multiple dams) and the Valdivia River (free-flowing). The study design considered reference condition, urban polluted, and urban-industrial polluted sites. To evaluate the effects of stressors on fish assemblages we assessed: (i) components of beta diversity; (ii) spatial and temporal patterns of fish structure using a multivariate approach; and (iii) functional diversity (specialization, originality, dispersion, and entropy) using linear models. We found a strong association between taxonomic and functional fish assemblage facets with a predominance of natural processes in the Valdivia River reflected in marked temporal dynamics. In contrast, the Biobío River showed a clear loss of association with seasonal pattern, and both taxonomic and functional facets appeared to respond significantly to pollution zones. Implementation of stricter environmental policies and integrated river basin management are instrumental for conserving species-poor fish assemblages in Chilean temperate rivers characterized by low functional traits redundancy. [ABSTRACT FROM AUTHOR]

• Traditional forest management may reduce the abundance of SWD in chestnut forests. • Degraded riparian vegetation may help SWD to spread along stream margins. • No overall association between 31 families of insects and SWD captures. • Stream distance may be an important factor to predict SWD captures in dry summers. Protected native-forested areas may be occupied by fruit pests, and so, studies exploring the biotic and abiotic determinants of fruit-pest abundance in forested areas may reduce damages in crops and wild forest frugivores. The Spotted Wing Drosophila (SWD) Drosophila suzukii is an economically important fruit pest in many temperate regions around the world. During the dry summer in northwestern Spain, we assessed 24 native riparian and 32 non-riparian chestnut forest patches as non-crop habitats for the SWD. We surveyed chestnut forests in 2017 and found a positive association between spatial proximity of forest patches to streams and SWD captures, which led us to study in 2019 the stream-SWD associations in greater detail. We explored whether native-insect communities and changes in vegetation structure related to rural abandonment were associated with variation in SWD captures, while accounting for the effects of covariates, including stream distance. There were no significant associations in the riparian and non-riparian-habitat surveys between the captures of SWDs and those of native insects, including 22 families of flies and 10 families of parasitic wasps. However, captures of SWDs and of other drosophilid flies were positively related to each other and the direction of the association was reversed by stream distance, which suggests the potential role of streams in regulating interactions among non-riparian insects, including SWD. We also found correlative evidence that degraded riparian forests and the abandonment of traditional forest practices in chestnut forests may be contributing to the spread of SWD. Given the numbers of SWDs in our forest samples were similar to values in August in crop areas, it is advisable that future studies address the impacts of SWD invasion on native forest frugivores, which have been overlooked in studies of this widely distributed invasive species. [ABSTRACT FROM AUTHOR]

• Food-chain length is an important property of food-webs in forests. • Three hypothesis might explain variation in FCL in forests. • We found support for the disturbance hypothesis arising from wild boar rooting. • Increased soil nutrient concentrations may reduce FCL in chestnut forests. • Promoting understory plant richness may increase FCL in chestnut forests. Food-chain length, or the trophic level of an apex predator, is among the most important properties of food-webs with implications for community structure, ecosystem processes and pollutant accumulation in forests. Three main hypotheses (ecosystem-size, productivity, and disturbance) have been erected to explain variation in food-chain length in freshwater ecosystems, yet the support for these hypotheses in less spatially restricted terrestrial ecosystems has not been extensively studied. Here, we used nitrogen (δ15N) and carbon (δ13C) stable isotopes to explore variation in the realized trophic positions (δ15N) of a beetle Carabus lineatus lateralis and a wasp Vespula vulgaris in 32 chestnut woodland patches in northwestern Spain, while accounting for the insects' relative mobility by using inferences based on δ13C. We used five potential predictors of ecosystem-size productivity, seven of disturbance and six covariates in anticipation that biological assemblages in woodlands might be influenced by ecosystem-size productivity, and from a change from the human management to a much-increased activity of ecosystem engineers, especially wild boar. Our results provided support for the disturbance hypothesis and suggested that the beetle FCL seems to be more affected by wild boar disturbance than by human-forest management, possibly due to increased forest cover and to rural abandonment in recent decades. Moreover, we found a negative association between the wasp FCL and the ecosystem-size productivity hypothesis, as indicated by the plant Ellengberg's indicator value for nitrogen, which contrasts to the hypothesis that ecosystem-size productivity should increase FCL. Our findings are discussed in relation to: (1) differences in intensity and frequency between human- and wild boar-induced disturbances; (2) the diets and mobilities of the two predators; and (3) the near lack of hard ecological boundaries in terrestrial ecosystems, such as chestnut woodlands. [ABSTRACT FROM AUTHOR]