Irrigation dams threaten Brazilian biodiversity.

Brazil is among the main contributors to global biodiversity, which, in turn, provides extensive ecosystem services. Agriculture is an activity that benefits greatly from these ecosystem services, but at the same time is degrading aquatic and terrestrial ecosystems and eroding Brazilian biodiversity. This conflict is growing, as emerging unsustainable legislative proposals that will benefit the agricultural sector are likely to accelerate the decline of biodiversity. One such initiative (Bill 1282/2019) would change Brazil's "Forest Code" (Law 12,651/2012) to facilitate construction of irrigation dams in Permanent Preservation Areas, a category that includes strips (with or without vegetation) along the edges of watercourses. Two other similar bills are advancing through committees in the Chamber of Deputies. Here we provide details of these three bills and discuss their consequences for Brazil's biodiversity if they are approved. Expected negative impacts with changes in the legislation include: increased deforestation; siltation; habitat fragmentation; introduction of non-native species; reduction in the availability of aquatic habitats; and changes in biogeochemical process. These proposals jeopardize biodiversity and may compromise the negotiations for an agreement between Mercosur and the European Union.

Spatial segregation in the reproductive activity of Neotropical fish species as an indicator of the migratory trait.

This study focused on the distribution of fish with high reproductive activity along a basin, using a 430 km stretch of the Cuiabá River in Brazil as a model. The main objective of this study was to identify those fish that migrate long distances for reproduction, among all the basin species. Thus, a set of working criteria are proposed to classify species according to their reproductive behaviour (i.e., reproductive activity and distribution). Samplings were performed in the Cuiabá River basin, encompassing several environments (river, channels and lakes) during the reproductive periods (between October and February), from 2000 to 2004. Species occurrence (presence and absence - proxy of distribution) across the basin and index of reproductive activity values were used as criteria to identify the species that perform long-distance longitudinal migrations for reproduction. The study confirmed the classification of long-distance longitudinal migration species; nonetheless, some species were not classified as described in the literature. The proposed sequential criteria have proven to be effective in the classification of long-distance longitudinal migrations species and certainly contribute to filling some existing knowledge gaps of reproductive traits. This classification is of fundamental importance in planning new dam projects, in decision making and in the development of management and conservation actions for the ichthyofauna.

Changes in ecosystem functions generated by fish populations after the introduction of a non-native predator (Cichla kelberi) (Perciformes: Cichlidae)

The introduction of non-native predators is a matter of great concern, but their impacts on ecosystem functions remain poorly understood. We investigated how changes in fish diversity following the invasion of Cichla kelberi affected ecosystem functions generated by fish populations. Fish assemblages were sampled in macrophyte patches in a Neotropical impoundment over a 5-year period, before and after the introduction of the predator. We assigned seven ecosystem functions (26 trait-states) to each fish species, and examined how these functions behaved after the invasion. We collected 577 fish belonging to 25 species. Species richness, fish biomass and main species declined significantly over periods. The biomass of ecosystem functions changed significantly over time, and most trait-states declined. Few trait-states were lost, but all functions had at least one trait-state reduced by more than 85%. A null model analysis showed that changes in functions were not driven by species identities, while species richness correlated positively with total biomass and with most functions, suggesting that the loss of taxa and biomass drove observed changes in ecosystem functions. Our study provided evidence that community disassembly associated with the invasion of C. kelberi translated to the decline of several ecosystem functions, affecting energy mobilization and transference.(AU)

A introdução de predadores não-nativos tem gerado grande preocupação, mas seus impactos sobre a geração de funções ecossistêmicas permanecem pouco investigados. O presente estudo investigou como mudanças na diversidade de peixes, associadas com a invasão de Cichla kelberi, afetaram funções ecossistêmicas geradas por populações de peixes. As assembleias de peixes foram amostradas em bancos de macrófitas em um grande reservatório Neotropical durante um período de cinco anos, antes e depois da introdução do predador. Um conjunto de funções ecossistêmicas (26 trait-states) foi atribuído a cada espécie de peixe, e examinamos como as funções se comportaram depois da invasão. Foram coletados 577 peixes pertencentes a 25 espécies. Registramos declínio significativo da riqueza de espécies, biomassa total e biomassa das principais espécies ao longo dos períodos. A biomassa das funções ecossistêmicas mudou significativamente ao longo do tempo, e a maioria dos trait-states declinou. Poucos trait-states foram perdidos, mas todas as funções tiveram pelo menos um trait-state reduzido em mais de 85%. Uma análise de modelos nulos mostrou que as mudanças nas funções não foram impulsionadas pela identidade das espécies, enquanto que a riqueza de espécies correlacionou positivamente com a biomassa total e com a maioria das funções, sugerindo que a perda de espécies e biomassa impulsionou as mudanças observadas nas funções ecossistêmicas. Nosso estudo apresenta evidências de que a desestruturação da comunidade, associada com a invasão de C. kelberi, se traduziu no declínio de várias funções ecossistêmicas, afetando a mobilização e transferência de energia.(AU)

Negative impacts of mining on Neotropical freshwater fishes

Mining activities have significantly affected the Neotropical freshwater ichthyofauna, the most diverse in the world. However, no study has systematized knowledge on the subject. In this review, we assembled information on the main impacts of mining of crude oil, gold, iron, copper, and bauxite on aquatic ecosystems, emphasizing Neotropical freshwater fishes. The information obtained shows that mining activities generate several different disturbances, mainly via input of crude oil, metals and other pollutants, erosion and siltation, deforestation, and road construction. Mining has resulted in direct and indirect losses of fish diversity in several Neotropical waterbodies. The negative impacts on the ichthyofauna may change the structure of communities, compromise entire food chains, and erode ecosystem services provided by freshwater fishes. Particularly noteworthy is that mining activities (legal and illegal) are widespread in the Neotropics, and often located within or near protected areas. Actions to prevent and mitigate impacts, such as inspection, monitoring, management, and restoration plans, have been cursory or absent. In addition, there is strong political pressure to expand mining; if - or when - this happens, it will increase the potential of the activity to further diminish the diversity of Neotropical freshwater fishes.(AU)

As atividades de mineração têm impactado significativamente a ictiofauna de água doce Neotropical, a mais diversa do mundo. Porém, nenhum estudo sistematizou o conhecimento sobre o assunto. Nesta revisão, reunimos informações sobre os principais impactos da mineração de petróleo, ouro, ferro, cobre, e bauxita sobre os ecossistemas aquáticos, com ênfase nos peixes de água doce Neotropicais. As informações obtidas mostram que as atividades de mineração geram diferentes distúrbios, principalmente por meio de petróleo bruto, metais e outros poluentes, erosão e assoreamento, desmatamento e construção de estradas. A mineração resultou em perda direta e indireta de diversidade de peixes de vários corpos d'água Neotropicais. Os impactos negativos sobre a ictiofauna podem alterar a estrutura das comunidades, comprometer cadeias alimentares inteiras, bem como degradar os serviços ecossistêmicos fornecidos pelos peixes de água doce. Particularmente importante é que as atividades de mineração (legais e ilegais) são generalizadas na região Neotropical, e frequentemente estão localizadas dentro ou perto de áreas protegidas. Ações de prevenção e mitigação de impactos, como planos de fiscalização, monitoramento, manejo e restauração, têm sido precárias ou ausentes. Além disso, há forte pressão política para expandir a mineração; se - ou quando - isso acontecer, aumentará o potencial da atividade em diminuir ainda mais a diversidade de peixes de água doce Neotropicais.(AU)

Negative effect of turbidity on prey capture for both visual and non-visual aquatic predators.

Turbidity plays an important role in aquatic predator-prey interactions. Increases in turbidity are expected to reduce prey capture rates, especially for visually oriented predators. However, there is also evidence indicating that turbidity may have little or no effect on predation rates. Here, we conducted a systematic review and meta-analysis of the relationship between turbidity and capture rate. We explored possible sources of heterogeneity in the effect sizes (capture strategy, predator's body size, relative eye size and turbidity range in the experiments) while controlling for the dependence among effects sizes and phylogenetic relationships among predator species. We found a consistent negative effect of turbidity on prey capture and that turbidity range (manipulated in the experiments) was the main factor accounting for between-study variation in effect sizes. Also, capture rates of both visually and non-visually oriented predators decreased with an increase in turbidity. In addition, for visually oriented fish predators, the relative eye size did not influence the effect sizes. Despite the paucity of studies for some groups of aquatic predators (mainly in tropical regions), we provide corroborative evidence that turbidity is a critical environmental factor controlling predator-prey interactions. This result is especially relevant considering that changes in turbidity is a human-induced pervasive environmental alteration resulted from, among other mechanisms, runoff after deforestation, eutrophication or oligotrophication in reservoir cascades, which imply changes in predator-prey interactions.

Two sides of a coin: Effects of climate change on the native and non-native distribution of Colossoma macropomum in South America.

Climate change and species invasions interact in nature, disrupting biological communities. Based on this knowledge, we simultaneously assessed the effects of climate change on the native distribution of the Amazonian fish Colossoma macropomum as well as on its invasiveness across river basins of South America, using ecological niche modeling. We used six niche models within the ensemble forecast context to predict the geographical distribution of C. macropomum for the present time, 2050 and 2080. Given that this species has been continuously introduced into non-native South American basins by fish farming activities, we added the locations of C. macropomum farms into the modeling process to obtain a more realistic scenario of its invasive potential. Based on modelling outputs we mapped climate refuge areas at different times. Our results showed that a plenty of climatically suitable areas for the occurrence of C. macropomum occurrence are located outside the original basins at the present time and that its invasive potential is greatly amplified by fish farms. Simulations of future geographic ranges revealed drastic range contraction in the native region, implying concerns not only with respect to the species conservation but also from a socio-economic perspective since the species is a cornerstone of artisanal and commercial fisheries in the Amazon. Although the invasive potential is projected to decrease in the face of climate change, climate refugia will concentrate in Paraná River, Southeast Atlantic and East Atlantic basins, putting intense, negative pressures on the native fish fauna these regions. Our findings show that short and long-term management actions are required for: i) the conservation of natural stocks of C. macropomum in the Amazon, and ii) protecting native fish fauna in the climate refuges of the invaded regions.

Using long-term data to predict fish abundance: the case of Prochilodus lineatus (Characiformes, Prochilodontidae) in the intensely regulated upper Paraná River

Populations show spatial-temporal fluctuations in abundance, partly due to random processes and partly due to self-regulatory processes. We evaluated the effects of various external factors on the population numerical abundance of curimba Prochilodus lineatus in the upper Paraná River floodplain, Brazil, over a 19-year period. Panel data analysis was applied to examine the structure of temporal and spatial abundance while controlling auto-regressive processes and spatial non-homogeneity variances that often obscure relationships. As sources of population variation, we considered predation, competition, selected abiotic variables, construction of a dam upstream of the study area, water level and flood intensity during the spawning period. We found that biological interactions (predation and competition) were not significantly related to variations in curimba abundance; specific conductance was a space indicator of abundance, apparently linked to the biology of the species; intensity of floods determined inter-annual variation in abundances; Porto Primavera Dam negatively impacted the abundances at sites in the floodplain directly affected by discharges from the dam. Panel data analysis was a powerful tool that identified the need for intense flooding to maintain high abundances of curimba in the upper Paraná River. We believe our results apply to other species with similar life strategy.(AU)

As populações apresentam flutuações espaço-temporais em abundância devido a processos aleatórios e auto-regulatórios. Nesse trabalho avaliamos efeitos de vários fatores sobre a abundância da curimba, Prochilodus lineatus, em cinco ambientes da planície de inundação do alto rio Paraná, Brasil, durante 19 anos. A análise de dados em painel foi utilizada por examinar variações espaço-temporais na abundância considerando processos auto-regressivos e variâncias espacialmente heterogêneas, que por vezes dificultam a identificação das relações. Como fontes de variação na abundância da curimba foram consideradas: predação, competição, variáveis abióticas selecionadas, construção da barragem de Porto Primavera, nível da água do rio Paraná e intensidade de cheia no período reprodutivo. Foi identificado que predação e competição não foram significativamente associadas às abundâncias da curimba; condutividade específica foi indicadora espacial da abundância; intensidade das cheias foi determinante de variações interanuais na abundância; barragem de Porto Primavera influenciou, negativamente, a abundância em corpos d'água diretamente afetados. A análise de dados em painel mostrou ser uma poderosa ferramenta preditiva, que possibilitou identificar a necessidade de cheias intensas para manutenção de elevadas abundâncias de curimba no alto rio Paraná. Acreditamos que o mesmo seja válido espécies de peixes que apresentam estratégia de vida similar.(AU)

Fish passages in South America: an overview of studied facilities and research effort

River regulation has fragmented fluvial ecosystems in South America, affecting fish migration and dispersion dynamics. In response, authorities have installed fish passage facilities (FPF) to mitigate impacts. However, little is known about the geographical distribution of these facilities, and no synthesis of the research effort applied to understanding their functioning and limitations exists. To address this issue, our study gathered the available scientific literature about fishways in South America to provide an overview of studied FPF and associated research effort. We found 80 studies that investigated 25 FPF, mostly ladders installed in the upper reaches of large rivers, particularly in the Paraná River Basin. One important finding is that most facilities do not lead to upstream and/or downstream sites due to the presence of other dams with no FPF. Though the number of studies has increased over the past 10 years, there is no consistent trend towards increased research effort. Overall, studies have focused on the fishway itself (i.e. upstream passage), and rarely evaluated broader issues (i.e. habitat distribution, population dynamics, conservation and management success). Our research therefore identified technical limitations of past studies, and revealed important gaps in the knowledge of FPF as a management tool.(AU)

A implantação de barragens tem perturbado e fragmentado os ecossistemas fluviais da América do Sul, afetando a migração dos peixes e dinâmicas de dispersão. Sistemas de transposição de peixes (STPs) têm sido instalados na tentativa de atenuar esses impactos. No entanto, pouco se sabe sobre a distribuição geográfica desses dispositivos, bem como o esforço de pesquisa aplicado para entender seu funcionamento e limitações. Nosso trabalho reuniu a literatura disponível com a finalidade de fornecer um panorama sobre os mecanismos investigados na América do Sul, bem como revelar o esforço e perfil das pesquisas. Encontramos 80 estudos que investigaram 25 STPs, a maioria escadas instaladas nos trechos superiores de grandes rios, particularmente na bacia do rio Paraná. Um resultado interessante é que a maior parte dos STPs está desconectada de trechos a montante e jusante devido à presença de outras barragens sem STPs. Embora o número de estudos tenha aumentado na última década, não registramos tendência consistente de incremento ao longo dos anos. No geral, os estudos abordam aspectos do próprio STP, especificamente a passagem ascendente, ignorando temas mais abrangentes (i.e. distribuição de habitats, dinâmica populacional). Além disso, o foco da pesquisa se direciona especialmente às questões de eficiência da passagem e raramente ao contexto da conservação e sucesso do manejo. Nossa avaliação, portanto, indicou que os estudos pretéritos são tecnicamente limitados, revelando importantes lacunas sobre o conhecimento dos STPs como medida de manejo.(AU)

Is coexistence between non-native and native Erythrinidae species mediated by niche differentiation or environmental filtering? A case study in the upper Paraná River floodplain

The limiting similarity theory predicts that divergence in the functional traits of native and introduced species is an essential component in species establishment, as introduced species must occupy a niche that is unoccupied by resident species. On the other hand, the environmental filtering hypothesis predicts convergence between introduced and native species, as both possess traits that make them adapted to the local abiotic environment. Morphology, spatial co-occurrence, diet, feeding selectivity, and niche breadth and overlap of Erythrinidae were evaluated to detect possible mechanisms acting in the coexistence between non-native and native species. Native (Hoplias sp. B and Hoplias cf. malabaricus) and non-native (Hoplerythrinus unitaeniatus and Hoplias mbigua) species presented differences in morphological traits, spatial co-occurrence, diet, selectivity, and niche breadth and overlap. The mechanisms mediating species coexistence seem to vary according to species. The absence of spatial and feeding overlap suggests that non-native species H. unitaeniatus occupy a different niche than native species, supporting its successful establishment without eliminating the native species. However, low feeding overlap and similar morphologies between non-native and native species of Hoplias point to environmental filters; in this case, the non-native H. mbigua is able to establish due to similarities in functional traits.(AU)

Teorias sobre nicho ecológico afirmam que divergência em traços funcionais entre espécies nativas e introduzidas são essenciais ao estabelecimento da espécie introduzida, pois estas devem ocupar um nicho não utilizado pelas espécies residentes. Por outro lado, a teoria de filtros ambientais afirma a convergência entre espécies introduzidas e nativas, pois ambas possuem traços funcionais que fazem com que essas espécies estejam mais adaptadas as variáveis ambientais. Foram avaliadas a morfologia, ocorrência espacial, dieta, seletividade alimentar, sobreposição e largura de nicho em Erythrinidae para detectar possíveis mecanismos atuando na coexistência de espécies nativas e não nativas. Espécies nativas (Hoplias sp. B e Hoplias cf. malabaricus) e não nativas (Hoplerythrinus unitaeniatus e Hoplias mbigua) apresentaram diferenças em todos os atributos testados. Os mecanismos mediando a coexistência de espécies nativas e não nativas parecem variar de acordo com a espécie considerada. A ausência de sobreposição espacial e na dieta sugere que a espécie não nativa H. unitaeniatus ocupa um nicho distinto que as espécies nativas, favorecendo seu estabelecimento sem eliminar as espécies nativas, apontando para segregação de nicho. Por outro lado, morfologias similares, porém com diferentes dietas foram observadas para as espécies de Hoplias, sugerindo que as espécies coexistem devido à filtros ambientais, assim, neste caso, a espécie não nativa H. mbigua é capaz de se estabelecer no novo ambiente devido à similaridades em traços funcionais.(AU)

The metabolic theory of ecology convincingly explains the latitudinal diversity gradient of neotropical freshwater fish.

In the context of diversity gradients, the metabolic theory of ecology (MTE) posits that the logarithm of species richness should decrease linearly with the inverse of temperature, resulting in a specific slope. However, the empirical validity of this model depends on whether the data do not violate certain assumptions. Here, we test the predictions of MTE evaluating all of its assumptions simultaneously. We used Neotropical freshwater fish and tested whether the logarithm of species richness varied negatively and linearly with temperature, resulting in the slope value specified by the MTE. As we observed that the assumption of the energetic equivalence of populations was not achieved, we also analyzed whether the energetic nonequivalence of populations could be responsible for the possible lack of fit to the MTE predictions. Our results showed that the relationship between richness and the inverse of temperature was linear, negative and significant and included the slope value predicted by the MTE. With respect to the assumptions, we observed that there was no spatial variation in the average energy flux of populations or in the body size and abundance of species. However, the energetic equivalence of populations was not achieved and the violation of this assumption did not affect the predictive power of the model. We conclude that the validity of the assumptions (spatial invariance in the average flux energy of populations and spatial invariance in the body size and abundance, especially) is required for the correct interpretation of richness patterns. Furthermore, we conclude that MTE is robust in its explanation of diversity gradients for freshwater fish, proving to be a valuable tool in describing ecological complexity from individuals to ecosystems.

Loss of rare fish species from tropical floodplain food webs affects community structure and ecosystem multifunctionality in a mesocosm experiment.

Experiments with realistic scenarios of species loss from multitrophic ecosystems may improve insight into how biodiversity affects ecosystem functioning. Using 1000 L mesocoms, we examined effects of nonrandom species loss on community structure and ecosystem functioning of experimental food webs based on multitrophic tropical floodplain lagoon ecosystems. Realistic biodiversity scenarios were developed based on long-term field surveys, and experimental assemblages replicated sequential loss of rare species which occurred across all trophic levels of these complex food webs. Response variables represented multiple components of ecosystem functioning, including nutrient cycling, primary and secondary production, organic matter accumulation and whole ecosystem metabolism. Species richness significantly affected ecosystem function, even after statistically controlling for potentially confounding factors such as total biomass and direct trophic interactions. Overall, loss of rare species was generally associated with lower nutrient concentrations, phytoplankton and zooplankton densities, and whole ecosystem metabolism when compared with more diverse assemblages. This pattern was also observed for overall ecosystem multifunctionality, a combined metric representing the ability of an ecosystem to simultaneously maintain multiple functions. One key exception was attributed to time-dependent effects of intraguild predation, which initially increased values for most ecosystem response variables, but resulted in decreases over time likely due to reduced nutrient remineralization by surviving predators. At the same time, loss of species did not result in strong trophic cascades, possibly a result of compensation and complexity of these multitrophic ecosystems along with a dominance of bottom-up effects. Our results indicate that although rare species may comprise minor components of communities, their loss can have profound ecosystem consequences across multiple trophic levels due to a combination of direct and indirect effects in diverse multitrophic ecosystems.

Temporal variability of fish larvae assemblages: influence of natural and anthropogenic disturbances

Natural and induced disturbances greatly influence the temporal distribution of ichthyoplankton abundance. This study assesses and compares the temporal variability of fish larvae assemblages in controlled and free environments to determine the influence of environment variables on the main taxa in these systems. The study was conducted at the Chapecó (without dam impact) and Ligeiro (with dam impact) river mouths, which are located in the upper Uruguay River. Samples were made between October 2001 and March 2004 during three reproductive periods. The larvae assemblages were composed of small and medium-sized Characiformes and Siluriformes. The variation in the distribution of larvae was mainly temporal (>85%). When the three reproductive periods were compared, it was observed in the second period, characterized by a larger water flow and a lower temperature, that there was a reduction in abundance, a lower number of taxa, an absence of stages in post-flexion and a high dissimilarity in larvae assemblage structure. In general, the environmental variables of water flow and temperature most influenced the distribution of egg and larvae abundance. In the studied area, a smaller temporal variability was observed in the structure of larvae assemblages at the sampling sites in the Chapecó River mouth than in in the Ligeiro River mouth under the influence of dams.

Os distúrbios naturais e induzidos têm notável influência na distribuição temporal da abundância do ictioplâncton. Este estudo visa avaliar e comparar a variabilidade temporal das assembleias de larvas de peixes, entre ambientes regulados e ambientes livres, bem como, determinar a influência das variáveis ambientais sobre os principais táxons presentes nestes ambientes. O trabalho foi conduzido na foz dos rios Chapecó (sem impacto de barramento) e Ligeiro (impactado por barragens), ambos localizados no alto rio Uruguai. As coletas foram realizadas entre outubro de 2001 e março de 2004 durante três períodos reprodutivos. As assembléias de larvas estiveram compostas principalmente por Characiformes e Siluriformes de pequeno e médio porte. A variação na distribuição de larvas foi principalmente temporal (>85%). Quando comparados os três períodos reprodutivos, foi observado que no segundo período, caracterizado por uma maior vazão da água e menor temperatura, houve redução na abundância, menor número de táxons, ausência de estágios em pós-flexão e elevada dissimilaridade na estrutura da assembléia de larvas. Em geral, as variáveis ambientais vazão e temperatura da água foram as que mais influenciaram a distribuição da abundância de ovos e larvas. Nos ambientes estudados, foi observado que existe uma menor variabilidade temporal na estrutura das assembléias de larvas das estações presentes na foz do rio Chapecó do que naquelas presentes na foz do rio Ligeiro, o qual esta sob influência dos barramentos.

Patterns of interactions of a large fish-parasite network in a tropical floodplain.

1. Describing and explaining the structure of species interaction networks is of paramount importance for community ecology. Yet much has to be learned about the mechanisms responsible for major patterns, such as nestedness and modularity in different kinds of systems, of which large and diverse networks are a still underrepresented and scarcely studied fraction. 2. We assembled information on fishes and their parasites living in a large floodplain of key ecological importance for freshwater ecosystems in the Paraná River basin in South America. The resulting fish-parasite network containing 72 and 324 species of fishes and parasites, respectively, was analysed to investigate the patterns of nestedness and modularity as related to fish and parasite features. 3. Nestedness was found in the entire network and among endoparasites, multiple-host life cycle parasites and native hosts, but not in networks of ectoparasites, single-host life cycle parasites and non-native fishes. All networks were significantly modular. Taxonomy was the major host's attribute influencing both nestedness and modularity: more closely related host species tended to be associated with more nested parasite compositions and had greater chance of belonging to the same network module. Nevertheless, host abundance had a positive relationship with nestedness when only native host species pairs of the same network module were considered for analysis. 4. These results highlight the importance of evolutionary history of hosts in linking patterns of nestedness and formation of modules in the network. They also show that functional attributes of parasites (i.e. parasitism mode and life cycle) and origin of host populations (i.e. natives versus non-natives) are crucial to define the relative contribution of these two network properties and their dependence on other ecological factors (e.g. host abundance), with potential implications for community dynamics and stability.

Fish colonization of artificial reefs in a large neotropical reservoir: material type and successional changes.

Artificial reefs have barely been used in Neotropical reservoirs (about five studies in three reservoirs), despite their potential as a fishery management tool to create new habitats and also to understand fish ecology. We experimentally assessed how reef material (ceramic, concrete, and PVC) and time modulated fish colonization of artificial reefs deployed in Itaipu Reservoir, a large reservoir of the mainstem Paraná River, Brazil. Fish richness, abundance, and biomass were significantly greater in the reef treatments than at control sites. Among the experimental reefs, ceramic followed by the concrete treatments were the materials most effectively colonized, harboring the majority of the 13 fish species recorded. Although dependent on material type, many of the regularities of ecological successions were also observed in the artificial reefs, including decelerating increases in species richness, abundance, mean individual size, and species loss rates with time and decelerating decreases of species gain and turnover rates. Species composition also varied with material type and time, together with suites of life history traits: more equilibrium species (i.e., fishes of intermediate size that often exhibit parental care and produce fewer but larger offspring) of the Winemiller-Rose model of fish life histories prevailed in later successional stages. Overall, our study suggests that experimental reefs are a promising tool to understand ecological succession of fish assemblages, particularly in tropical ecosystems given their high species richness and low seasonality.

Fish migration, dams, and loss of ecosystem services in the Mekong basin.

The past decade has seen increased international recognition of the importance of the services provided by natural ecosystems. It is unclear however whether such international awareness will lead to improved environmental management in many regions. We explore this issue by examining the specific case of fish migration and dams on the Mekong river. We determine that dams on the Mekong mainstem and major tributaries will have a major impact on the basin's fisheries and the people who depend upon them for food and income. We find no evidence that current moves towards dam construction will stop, and consider two scenarios for the future of the fisheries and other ecosystems of the basin. We conclude that major investment is required in innovative technology to reduce the loss of ecosystem services, and alternative livelihood strategies to cope with the losses that do occur.

Effects of river impoundment on ecosystem services of large tropical rivers: embodied energy and market value of artisanal fisheries.

Applying the ecosystem services concept to conservation initiatives or in managing ecosystem services requires understanding how environmental impacts affect the ecology of key species or functional groups providing the services. We examined effects of river impoundments, one of the leading threats to freshwater biodiversity, on an important ecosystem service provided by large tropical rivers (i.e., artisanal fisheries). The societal and economic importance of this ecosystem service in developing countries may provide leverage to advance conservation agendas where future impoundments are being considered. We assessed impoundment effects on the energetic costs of fisheries production (embodied energy) and commercial market value of the artisanal fishery of the Paraná River, Brazil, before and after formation of Itaipu Reservoir. High-value migratory species that dominated the fishery before the impoundment was built constituted a minor component of the contemporary fishery that is based heavily on reservoir-adapted introduced species. Cascading effects of river impoundment resulted in a mismatch between embodied energy and market value: energetic costs of fisheries production increased, whereas market value decreased. This was partially attributable to changes in species functional composition but also strongly linked to species identities that affected market value as a result of consumer preferences even when species were functionally similar. Similar trends are expected in other large tropical rivers following impoundment. In addition to identifying consequences of a common anthropogenic impact on an important ecosystem service, our assessment provides insight into the sustainability of fisheries production in tropical rivers and priorities for regional biodiversity conservation.

Population structure, growth and fishery yield of Leporinus acutidens (Valenciennes, 1837) (Teleostei: Anostomidae) in Yacyretá Reservoir (Argentina)

The population structure and dynamics of Leporinus acutidens (Valenciennes, 1837), upstream from Yacyretá Dam (Upper Paraná River, Argentina) were analyzed for their relation to age, condition factor, growth, mortality and fishery yield. The pre- (1990-94) and post- (1995-98) filling phases of the reservoir were compared with regard to age structure, condition factor, and the length/weight relationship of fish. Fish sampling was carried out at four sampling sites following a longitudinal gradient along the river. The catches took place monthly using eight monofilament gillnets (mesh 40 to 160 mm). The growth marks on the scales were annual (9-year maximum). The study of the variation in the monthly averages of the scale marginal increments revealed that the period of the growth ring formation shifted from winter to spring in the post-filling phase. The length/weight relationship coefficient (b) was higher after dam closing. The condition factor increased before the reproduction period and during late summer, reaching maximum values in the post-filling phase, and especially at the sampling site placed within the reservoir region. The von Bertalanffy growth coefficient k for both sexes was 0.16, and the asymptotic length L" reached 338 mm. Natural mortality during the whole study period, according to Pauly's equation, was 0.25 years -1 and total mortality was 0.37 years -1. The Beverton-Holt yield per recruit (Y/R) model attained 57.23 g, with a maximum sustainable yield (MSY) of 70.75 g. Low total mortality was associated with the lack of commercial exploitation of the species.

A população de Leporinus acutidens (Valenciennes, 1837), a montante da barragem de Yacyretá (Alto Paraná, Argentina) foi analisada em relação à idade, crescimento, condição nutricional, mortalidade e rendimento da pesca, sendo realizadas comparações na estrutura etária, condição nutricional e relação peso-comprimento nos períodos pré (1990-94) e pós (1995-98) represamento. As amostragens foram conduzidas em quatro localidades ao longo do rio. As capturas foram realizadas mensalmente com oito redes monofilamento (malhagens de 40 a 160 mm). Os anéis de crescimento nas escamas são formados anualmente (máximo 9 anos). A análise das variações mensais na média do incremento marginal das escamas revelou que o período de formação dos anéis de crescimento alterou do inverno para a primavera após o represamento. Já o coeficiente da relação peso/comprimento (b) foi maior, para ambos os sexos, após o represamento. O fator de condição apresentou-se mais elevado antes do período reprodutivo e no final do verão, alcançando valores máximos após o represamento, especialmente em locais dentro do reservatório. O valor do coeficiente k da curva de crescimento de von Bertalanffy foi 0.16 e o comprimento assintótico L" alcançou 338 mm. A mortalidade natural, estimada a partir da equação de Pauly, foi de 0.25 year-1 e a mortalidade total de 0.37 year-1. O rendimento por recruta, estimado pelo modelo de Beverton-Holt (Y/R) atingiu 57.23 g, com um rendimento máximo sustentável (RMS) de 70.75 g. A baixa mortalidade total foi associada com a inexistência de uma exploração comercial relevante do estoque.