Coastal upwelling influences population structure of dusky grouper Epinephelus marginatus: An integrative approach based on otolith chemistry and muscle stable isotopes.

The dusky grouper (Epinephelus marginatus) is an overfished and threatened fish species with coastal distribution. In the Southwestern Atlantic, it occurs across a broad region influenced by two major oceanographic features: the Cabo Frio (23°S) and the Cabo Santa Marta (28°S) upwelling systems. Along the Brazilian coast, the species may present continuous or discrete populations, depending on the methodological approach used. In this study we combined otolith chemistry and muscle stable isotope analyses to examine the population structure of dusky groupers and its association with the two upwelling systems. Fish were collected in shallow coastal waters of the Southwest Atlantic Ocean, covering the southeastern and southern Brazilian coasts, among Macaé (22°S), Santos (24°S), Florianópolis (27°S), and in Rio Grande (32°S). The results show three statistically well-separated population groups along the region. We named these population groups as North (north of Cabo Frio); Center (between upwelling regions); and South (south of the Cabo Santa Marta system). Our findings allow to suggest that the upwelling systems may influence the distribution of E. marginatus stocks along the Brazilian south-western coast, even though a causal effect may not be attributed at this point. Overall, this combined approach, leveraging information from distinct natural tags, and reflecting variability of water chemistry and food webs with latitude, allowed us to enhance our understanding on how major upwelling systems influence the structuring of fish populations along the southwestern Atlantic Ocean.

Spatial analysis of mercury and stable isotopes in the vulnerable Dusky Grouper Epinephelus marginatus along the Brazilian coast.

Mercury (Hg) is a contaminant of global concern due to its damaging toxicological effects on organisms. For the vulnerable Dusky Grouper (Epinephelus marginatus) off the coast of Brazil, we investigated: i) spatial patterns in muscle tissue total mercury (THg) contamination; ii) the relationship between muscle THg concentrations and total length iii) the relationship between muscle THg and stable isotopes; and iv) THg concentrations among muscle, liver, and ovary tissues. Out of 134 fish sampled, 21.8 % were higher than 0.5 mg/kg wet weight (above the safe limit for human consumption). THg concentrations increased toward lower latitudes, but an opposite pattern was observed for δ13C and δ15N with decreased values toward lower latitudes. There were significant differences in THg concentration among the three tissues. Results of Hg concentrations are useful for understanding the potential adverse effects on the health of this vulnerable species and to serve as a guide to human consumers.

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)

Taxonomic and functional turnover of Amazonian stream fish assemblages is determined by deforestation history and environmental variables at multiple scales

High rates of deforestation, either in the past or the present, affect many of the ecological processes in streams. Integrating deforestation history and the current landscape structure enhances the evaluation of ecological effects of land-use change. This is especially true when contemporary landscape conditions are similar but the temporal path to those conditions differs. One approach that has shown promise for evaluating biodiversity responses over time and space is the β-diversity partitioning, which combines taxonomic and functional trait-based approaches. We tested hypotheses related to stream fish assemblages' turnover in watersheds with different environmental conditions and deforestation histories. We sampled fish from 75 watersheds in the Machado River basin, Brazil, and environmental factors were quantified at multiple scales. Taxonomic turnover was higher than expected by chance, whereas functional turnover was lower than expected by the observed taxonomic turnover, indicating that deterministic processes are structuring these assemblages. The turnover, and the environmental factors differed among watersheds with different deforestation histories. Besides being scale-dependent, turnover patterns are also likely dependent on land use dynamics and involve time-lags.(AU)

Altas taxas de desmatamento, seja no passado ou no presente, afetam muitos processos ecológicos em riachos. Integrar o histórico do desmatamento à estrutura atual da paisagem melhora a avaliação dos efeitos ecológicos da mudança do uso do solo. Isto é especialmente verdadeiro quando as condições da paisagem contemporânea são semelhantes, mas seguiram trajetórias distintas. Uma abordagem promissora para avaliar as respostas da biodiversidade ao longo do tempo e espaço é a partição da diversidade-β, que combina abordagens taxonômica e funcional. Testamos hipóteses relacionadas à substituição das assembleias de peixes de riachos em microbacias com diferentes condições ambientais e histórias de desmatamento. Amostramos 75 microbacias na bacia do rio Machado, fatores ambientais foram quantificados em múltiplas escalas. A substituição taxonômica foi maior do que esperada pelo acaso, enquanto a substituição funcional foi menor do que o esperado pela substituição taxonômica, indicando que as assembleias são estruturadas por processos determinísticos. As substituições e fatores ambientais diferiram entre microbacias com históricos de desmatamento distintos. Além de serem escala-dependentes, os padrões de substituição provavelmente são dependentes da dinâmica do uso do solo, envolvendo defasagem temporal.(AU)

Threshold responses of Amazonian stream fishes to timing and extent of deforestation.

Deforestation is a primary driver of biodiversity change through habitat loss and fragmentation. Stream biodiversity may not respond to deforestation in a simple linear relationship. Rather, threshold responses to extent and timing of deforestation may occur. Identification of critical deforestation thresholds is needed for effective conservation and management. We tested for threshold responses of fish species and functional groups to degree of watershed and riparian zone deforestation and time since impact in 75 streams in the western Brazilian Amazon. We used remote sensing to assess deforestation from 1984 to 2011. Fish assemblages were sampled with seines and dip nets in a standardized manner. Fish species (n = 84) were classified into 20 functional groups based on ecomorphological traits associated with habitat use, feeding, and locomotion. Threshold responses were quantified using threshold indicator taxa analysis. Negative threshold responses to deforestation were common and consistently occurred at very low levels of deforestation (<20%) and soon after impact (<10 years). Sensitive species were functionally unique and associated with complex habitats and structures of allochthonous origin found in forested watersheds. Positive threshold responses of species were less common and generally occurred at >70% deforestation and >10 years after impact. Findings were similar at the community level for both taxonomic and functional analyses. Because most negative threshold responses occurred at low levels of deforestation and soon after impact, even minimal change is expected to negatively affect biodiversity. Delayed positive threshold responses to extreme deforestation by a few species do not offset the loss of sensitive taxa and likely contribute to biotic homogenization.

Dry season limnological conditions and basin geology exhibit complex relationships with δ13C and δ15N of carbon sources in four Neotropical floodplains.

Studies in freshwater ecosystems are seeking to improve understanding of carbon flow in food webs and stable isotopes have been influential in this work. However, variation in isotopic values of basal production sources could either be an asset or a hindrance depending on study objectives. We assessed the potential for basin geology and local limnological conditions to predict stable carbon and nitrogen isotope values of six carbon sources at multiple locations in four Neotropical floodplain ecosystems (Paraná, Pantanal, Araguaia, and Amazon). Limnological conditions exhibited greater variation within than among systems. δ15N differed among basins for most carbon sources, but δ13C did not (though high within-basin variability for periphyton, phytoplankton and particulate organic carbon was observed). Although δ13C and δ15N values exhibited significant correlations with some limnological factors within and among basins, those relationships differed among carbon sources. Regression trees for both carbon and nitrogen isotopes for all sources depicted complex and in some cases nested relationships, and only very limited similarity was observed among trees for different carbon sources. Although limnological conditions predicted variation in isotope values of carbon sources, we suggest the resulting models were too complex to enable mathematical corrections of source isotope values among sites based on these parameters. The importance of local conditions in determining variation in source isotope values suggest that isotopes may be useful for examining habitat use, dispersal and patch dynamics within heterogeneous floodplain ecosystems, but spatial variability in isotope values needs to be explicitly considered when testing ecosystem models of carbon flow in these systems.

Mercury concentrations in dusky grouper Epinephelus marginatus in littoral and neritic habitats along the Southern Brazilian coast.

Our study incorporated a comprehensive suite of parameters (i.e., body size, age, diet and trophic position) to investigate mercury concentration in dusky groupers Epinephelus marginatus. This study was carried out in rocky bottoms in littoral and neritic habitats along the Southern Brazilian coast. We also determined spatial variation in mercury concentrations in individuals inhabiting both zones, which may provide insights into how dietary differences or potential pollution sources affect bioaccumulation. A total of 244 dusky groupers was analyzed to determine total mercury concentrations. Our study revealed that when considering similar body sizes, individuals inhabiting littoral rocky habitats had higher concentrations of mercury probably due to proximity to pollution sources associated with human activities in the estuary and its drainage basin. Furthermore, large individuals (>650mm and >8years old) showed mercury contamination levels that are potentially harmful for this endangered fish species and above the acceptable limits for human consumption.

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.

Aquatic food webs in mangrove and seagrass habitats of Centla Wetland, a Biosphere Reserve in Southeastern Mexico

Mangrove and seagrass habitats are important components of tropical coastal zones worldwide, and are conspicuous habitats of Centla Wetland Biosphere Reserve (CWBR) in Tabasco, Mexico. In this study, we examine food webs in mangrove- and seagrass-dominated habitats of CWBR using stable isotope ratios of carbon and nitrogen. Our objective was to identify the importance of carbon derived from mangroves and seagrasses to secondary production of aquatic consumers in this poorly studied conservation area. Carbon and nitrogen isotope ratios of basal sources and aquatic consumers indicated that the species-rich food webs of both habitats are dependent on riparian production sources. The abundant Red mangrove Rhizophora mangle appears to be a primary source of carbon for the mangrove creek food web. Even though dense seagrass beds were ubiquitous, most consumers in the lagoon food web appeared to rely on carbon derived from riparian vegetation (e.g. Phragmites australis). The introduced Amazon sailfin catfish Pterygoplichthys pardalis had isotope signatures overlapping with native species (including high-value fisheries species), suggesting potential competition for resources. Future research should examine the role played by terrestrial insects in linking riparian and aquatic food webs, and impacts of the expanding P. pardalis population on ecosystem function and fisheries in CWBR. Our findings can be used as a baseline to reinforce the conservation and management of this important reserve in the face of diverse external and internal human impacts.

Manguezais e pradarias de gramíneas são importantes componentes das zonas costeiras tropicais em todo o mundo, sendo habitats comuns nos ''Pântanos de Centla'', uma Reserva da Biosfera localizada em Tabasco, México. Nesse trabalho, são investigadas as teias alimentares de habitats dominados por manguezais e pradarias de gramíneas, através de isótopos estáveis de carbono e nitrogênio, tendo como objetivo identificar a importância do carbono derivado desses produtores para a produção aquática secundária nessa unidade de conservação tão pouco estudada. As razões isotópicas de carbono e nitrogênio das fontes basais e dos consumidores aquáticos indicam que as teias alimentares, ricas em espécies, de ambos os habitats, são dependentes da produção ripária. O abundante mangue-vermelho Rhizophora mangle parece ser a fonte primária de carbono no habitat dominado por manguezais. Em contraste, muito embora as pradarias de gramíneas sejam conspícuas no ambiente lagunar estudado, muitos dos consumidores da teia alimentar nessa região parecem depender do carbono oriundo da vegetação ripária (e.g. Phragmites australis).A espécie de bagre exótica Pterygoplichthys pardalis possui assinaturas isotópicas que se sobrepõem a das espécies nativas (incluindo algumas de elevado valor comercial na pesca), sugerindo competição potencial por recursos. Novas investigações deveriam avaliar o papel dos insetos terrestres como elo de conexão entre as teias alimentares da mata ripária e do ambiente aquático, bem como os impactos da expansão da população de P. pardalis sobre o funcionamento do ecossistema e das pescarias no ''Pântano de Centla''. Considerando os múltiplos impactos antrópicos na região, os resultados obtidos no presente trabalho podem ser utilizados como uma base de referência em programas de gerenciamento e conservação da diversidade nessa importante Reserva da Biosfera.

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.