Caroline Chaves Arantes

Objective: Reproduction and recruitment represent distinct demographic processes that may independently limit establishment and spread of an invasive species. We evaluated reproduction and recruitment success of Bighead Carp Hypophthalmichthys nobilis and Silver Carp H. molitrix in the Ohio River basin across multiple spatial and temporal scales to identify potential demographic bottlenecks. Methods: We assessed detection/nondetection data on Bighead Carp and Silver Carp eggs/larvae and young of the year (age 0) to provide information on these species’ reproduction and recruitment, respectively. Data were assessed at reach-level (i.e., pool) and site-level spatial scales and at annual and intra-annual temporal scales throughout the Ohio River basin, relating patterns of egg/larval and young-of-the-year occurrence to adult relative abundance, hydrologic conditions, and nursery habitat availability. Results: Estimated occurrence of Bighead Carp eggs/larvae and young of the year was inconsistent throughout the study area, suggesting limited establishment success in the Ohio River. Silver Carp egg/larval persistence probability was primarily associated with adult densities rather than variation in flow or temperature, and eggs were estimated to occur across a large portion of the basin. However, Silver Carp young-of-the-year occurrence appeared to be spatially restricted. Annual pool and intra-annual site young-of-the-year persistence probability was correlated with the availability of nursery habitat at both scales. Young of the year were consistently detected at only one location, a floodplain lake (Hovey Lake) in the John T. Myers pool, indicating the presence of a potential localized source population in this location. Conclusions: Silver Carp eggs/larvae were detected across much of the invaded portion of the Ohio River, suggesting that reproduction is widespread. However, young-of-the-year occurrence was most strongly associated with nursery habitat. In the Ohio River, the lack of widespread nursery habitat may be limiting the recruitment success of young-of-the-year Silver Carp into the population, potentially creating a demographic bottleneck that constrains their spread in this basin.

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Temperate streams are among the most well-studied ecosystems globally, yet there remains much uncertainty regarding the processes that regulate food web structure. Here we explore the relative contribution of food web composition and watershed factors on inter-stream variation in size spectra slopes (λ). Size spectra describe the decrease in abundance with increasing body size of individuals within a community (N∼M ^λ). We estimated λ for invertebrate, fish, and combined food webs to test effects of functional groups and watershed variables. The mean λ for combined and invertebrate food webs aligned well with theoretic predictions (mean = −2.04 and −2.02 respectively, range =−2.58 to −1.51). In contrast, the mean fish slope was shallower and more variable among sites (mean = −1.85, range = −2.71 to −1.33). Drainage area, a proxy for ecosystem size, was positively related to λ in all three data groupings. The fish-only λs were also positively related to agricultural land cover and negatively associated with the relative abundance of predators and omnivores. These results demonstrate the potential for drainage area to increase the relative abundance of large consumers and highlight the role of functional group dominance. Such insights are difficult to obtain without a size spectrum approach.

Forest cover is positively associated with fish biomass and fisheries yield in the Amazon River floodplain, and many species enter flooded forests to feed, spawn, or seek refuge from predation. Floating macrophyte beds, known as floating meadows, in Amazon floodplains support high fish diversity and serve as nursery habitat for many fishes of high commercial importance. We surveyed fish from floating meadows in floodplain lakes along the lower Amazon River to evaluate variation in fish abundance in relation to forest cover and local environmental variables. Species associations with forest cover were estimated with threshold indicator taxa analysis (TITAN2). The analysis identified taxa that gradually increased in abundance and occurrence as forest cover increased. Many species gradually increased at approximately 40% forest cover in the local landscape. Taxa that decreased as forest cover increased exhibited thresholds, whereby their abundance and occurrence declined rapidly when forest cover exceeded approximately 9% and when it was about 20%. Small‐bodied, sedentary species with equilibrium and opportunistic life‐history strategies (i.e. functional groups) and Cichlidae and Characidae (taxonomic groups) were indicators of high forest cover, whereas large‐bodied, migratory species with periodic and intermediate life‐history strategies and Serrasalmidae were indicators of low forest cover. Our findings could be used to predict how the taxonomic and functional structure of fish communities inhabiting floating meadows would respond to deforestation.

Floodplain agriculture is a practice that involves cultivating arable soils along riverbanks and reservoirs, which become submerged during the rainy season. This study aimed to analyze the socioeconomic aspects of floodplain farmers in the municipalities of Amarante, Floriano, and Uruçuí along the banks of the Parnaíba River in northeastern Brazil. We conducted semi-structured interviews using the rapport technique. Data were analyzed using generalized linear models with four distributions (gamma, inverse Gaussian, exponential, and Gaussian), with the aim of identifying patterns and relationships between socioeconomic variables and production system profiles. The average age of respondents was 49 years across the three communities, with a predominance of male farmers. Regarding the length of residence, communities in Uruçuí had lived in the area the longest. In terms of monthly income, 80% of farmers earned up to one minimum wage. Land size analysis indicated that properties in Amarante had the highest average land area in hectares. We conclude that agriculture in the region studied is dominated by manual planting, low adoption of technologies, and scarce use of soil conservation techniques, suggesting more sustainable agricultural practices, the development of management plans, and rural extension practices.

Low‐head dams are widespread in river ecosystems around the globe, but due to their effects, removals have become a major mechanism for river restoration. Investigations of fish responses to dam removals have been mostly conducted in the short term and have shown mixed assemblage responses (e.g., increased or decreased species richness following removal). Here, we examined the effects of low‐head dam removals on taxonomic composition and functional diversity at a relatively long term (6 years post dam removal). We hypothesised that differential responses of fish assemblages to dam removal are driven by suites of guild and morphological traits and that removal impacts functional complexity, with free‐flowing sites having greater distributions of functional diversity than impounded sites. We conducted our study in the West Fork River, West Virginia, where three low‐head dams were removed in 2016. Boat electrofishing surveys were conducted 1 year before the removal (2015) focusing on species of recreational fisheries importance. Then, we conducted surveys in the same sites 6 years after the removal (between September and October 2022). These electrofishing surveys were conducted at sites that were previously impounded but are now free‐flowing and those that currently remain impounded by low‐head dams. Results from our univariate and multivariate analyses indicated that current impounded sites and free‐flowing sites have statistically distinct taxonomic and functional fish assemblages. Free‐flowing sites were associated with overall higher taxonomic richness and greater biomass of some recreationally important species, including muskellunge, smallmouth bass and channel catfish. Conversely, currently impounded sites were associated with lower taxonomic richness and greater biomass of some recreationally important fishes, including green sunfish, bluegill and largemouth bass. Furthermore, functional diversity indices showed high functional richness (FRic) at free‐flowing sites, while less evident changes were observed for functional evenness (FEve) and functional divergence (FDiv). Our findings suggest that long‐term changes in the fish assemblages following the dam removals led to greater taxonomic and functional diversity while maintaining fisheries of high recreational importance. While some previous short‐term assessments suggested decreased functional complexity shortly after removals, our results suggest increases in functional complexity in the long term. Though dam removals may have high upfront socioeconomic costs, the long‐term effects in this study appeared to lead to greater ecosystem function and enhanced recreational opportunities that may outweigh initial costs.

Microplastic pollution levels and potential sources of contamination in North Central Appalachia are evaluated to fill a major knowledge gap regarding microplastics in freshwater systems, which lead to negative consequences for the sustainability of healthy freshwaters. Fifty-five northern hogsucker fish were sampled from nine sites throughout seven freshwater streams in the region. Microplastic particles were extracted from the gastrointestinal (GI) tracts via 10% KOH digestion and identified visually. A total of 2185 particles were identified, ranging between 8 and 274 particles/individual and an average of 39.73 particles/individual. The most particles were found in fish within the Cheat watershed, particularly at the Big Sandy Creek downstream site, followed by tributaries of the Monongahela and Ohio Rivers. The most identified particle type was fiber (96.61%). There was a positive relationship between the total length of fish and number of particles. Agricultural land use and E. coli abundance were both positively correlated with microplastic abundance. Agricultural land use and sewage input both appear to be important drivers of microplastic pollution in these streams, although we cannot rule out the influence of atmospheric deposition. These results point to widespread levels of microplastic contamination in freshwater ecosystems in North Central Appalachia.

Neotropical freshwater ecosystems harbor some of the world’s most diverse fish communities, playing a fundamental role in ecosystem functionality and providing essential and free services to human societies. However, this exceptional biodiversity faces escalating threats from multiple and widespread anthropogenic pressures, particularly small-scale engineering activities such as channelization, damming, road crossings, water extraction, and mining, which remain insufficiently assessed despite their cumulative and synergistic impacts. This Special Issue, Impacts of Small-Scale Engineering Projects on Neotropical Freshwater Fish Diversity compiles eleven studies to assess how small-scale interventions affect fish diversity and ecosystem processes. Collectively, these studies consistently demonstrate ecological trends including habitat simplification, loss of sensitive species, predominance of tolerant or generalist taxa, and disturbances on reproductive and trophic dynamics. Hydrological alterations and reduced habitat heterogeneity are key drivers of biotic homogenization and simplification of functional diversity. Overall, these publications emphasize that both local and regional disturbances synergistically compromise the structural and functional integrity of fish assemblages. Maintaining ecological connectivity and functional diversity is essential for maintaining integrity and resilience of Neotropical freshwater ecosystems, and findings underscore the urgent need to integrate small-scale impacts into basin management and conservation, recognizing their cumulative and often underestimated influence on biodiversity and ecosystem functioning.