Fish species richness is associated with the availability of landscape components across seasons in the Amazonian floodplain.

Understanding environmental biodiversity drivers in freshwater systems continues to be a fundamental challenge in studies of their fish assemblages. The present study seeks to determine the degree to which landscape variables of Amazonian floodplain lakes influences fish assemblages in these environments. Fish species richness was estimated in 15 Amazonian floodplain lakes during the high and low-water phases and correlated with the areas of four inundated wetland classes: (i) open water, (ii) flooded herbaceous, (iii) flooded shrubs and (iv) flooded forest estimated in different radius circular areas around each sampling site. Data were analyzed using generalized linear models with fish species richness, total and guilds as the dependent variable and estimates of buffered landscape areas as explanatory variables. Our analysis identified the significance of landscape variables in determining the diversity of fish assemblages in Amazonian floodplain lakes. Spatial scale was also identified as a significant determinant of fish diversity as landscape effects were more evident at larger spatial scales. In particular, (1) total species richness was more sensitive to variations in the landscape areas than number of species within guilds and (2) the spatial extent of the wetland class of shrubs was consistently the more influential on fish species diversity.

Mercury bioaccumulation in fish of commercial importance from different trophic categories in an Amazon floodplain lake

Thirty-two species of commercially important fish from three trophic levels and nine trophic categories were sampled at a floodplain lake of the Solimões River (Lago Grande de Manacapuru). The fish were analyzed to determine their Hg level and the bioaccumulation, bioconcentration, and biomagnification of this element. The observed increase in mean concentration of mercury (49.6 ng.g-1 for omnivores, 418.3 ng.g-1 for piscivores, and 527.8 ng.g-1 for carnivores/necrophages) furnished evidence of biomagnification. Primary, secondary, and tertiary consumers presented biomagnification factors of 0.27, 0.33, and 0.47, respectively. Significant differences in the bioconcentration and concentration of total Hg occurred between the categories of the third trophic level and the other categories. Plagioscion squamosissimus (carnivorous/piscivorous) and Calophysus macropterus (carnivorous/ necrophagous) showed levels of total Hg above those permitted by Brazilian law (500 ng.g-1). Six other species also posed risks to human health because their Hg levels exceeded 300 ng.g-1. Fifteen species showed bioaccumulation, but only eight presented significant correlations between the concentration of Hg and the length and/or the weight of the fish.

Trinta e duas espécies de peixes de importância comercial de três níveis tróficos e nove categorias tróficas foram amostradas em um lago de várzea do rio Solimões (Lago Grande de Manacapuru). Os peixes foram analisados para determinar seu nível de contaminação por mercúrio e a bioacumulação, bioconcentração e biomagnificação desse elemento. O aumento na concentração média de mercúrio (49,6 ng.g-1 para os onívoros, 418,3 ng.g-1 para os piscívoros e 527,8 ng.g-1 para os carnívoros/necrófagos) representa evidência de biomagnificação. Consumidores primários, secundários e terciários apresentaram fatores de biomagnificação de 0,27, 0,33 e 0,47, respectivamente. Houve diferença significativa na bioconcentração e na concentração de mercúrio total entre as categorias do terceiro nível trófico e as demais. Plagioscion squamosissimus (carnívoros / piscívoros) e Calophysus macropterus (carnívoros / necrófagos) apresentaram níveis de mercúrio acima do permitido por lei (500 ng.g-1). Seis outras espécies também apresentam riscos para a saúde humana porque seus níveis de mercúrio ultrapassaram 300 ng.g-1. Quinze espécies apresentaram bioacumulação, mas apenas oito apresentaram correlações significativas entre a concentração de mercúrio e o tamanho e/ou o peso do peixe.

Factors controlling Hg levels in two predatory fish species in the Negro river basin, Brazilian Amazon.

A number of environmental factors have been shown to influence the dynamics of Hg in aquatic ecosystems. Here we investigate the influence of fish size, pH, dissolved organic carbon (DOC), and the availability of potential methylation sites (floodplain forests and hydromorphic soils) on the concentration of total Hg in two carnivorous fishes: Cichla spp. and Hoplias malabaricus in the Negro River, Brazil. Fish and water samples for chemical analysis were collected from 33 sites in the Negro basin. The percentage of alluvial floodplains and hydromorphic soils (potential methylation sites) in the drainage basin upstream from each sampling point was estimated from radar imagery and existing soil maps with GIS. The average of Hg concentrations were 0.337 ppm (SD=0.244) in Cichla spp. and 0.350 ppm (SD=0.250) in H. malabaricus. Although the study area was geographically isolated from most major anthropogenic Hg sources, over 18% of Cichla spp. and 29% of H. malabaricus had Hg concentrations above 0.5 ppm, indicating naturally high background levels of Hg. Hg concentrations increased with size in both Cichla spp. (r(2)=0.664, p=0.000) and H. malabaricus (r(2)=0.299, p=0.000). Hg concentrations in H. malabaricus also increased with percent floodable area (p=0.006), pH (p=0.000) and DOC (0,063). In Cichla spp, Hg increased only in relation to percent floodable area (p=0.000). Hydromorphic soils did not influence fish Hg.

Composição da comunidade de diatomáceas periféricas do rio Jaú, Amazonas, Brasil / Composition of the periphytic diatom community of the Jaú river, Amazonas, Brazil

Foi realizado um estudo da flora perifítica de diatomáceas (Bacillariophyceae) existente no Rio Jaú, tributário do Rio Negro, Amazônia (2º57'S e 61º49'W). As coletas foram realizadas manualmente nas cheias de 1995, 1996 e 1997, e as lâminas permanentes encontram-se depositadas no Herbário FLOR, Universidade Federal de Santa Catarina. Foram identificados 60 táxons específicos e infra-específicos, distribuidos em 16 gêneros e 13 famílias. Eunotiaceae foi a família melhor representada, com 43,3 por cento do total dos táxons inventariados, seguida de Pinnulariaceae com 21,6 por cento e Surirellaceae com 11,6 por cento. O gênero Eunotia destacou-se dentre os demais com 20 táxons. Eunotia e Pinnularia foram os gêneros mais abundantes da flora diatomológica e os que apresentaram maior variação morfológica. Para cada táxon identificado foi feita uma revisão de literatura que incluem diversos aspectos ecológicos.

The periphytic diatom flora of the Jaú River, a tributary of the Negro River, in Amazonia (2º 57' S; 61º49' W) was studied. Algae were collected manually during the high water periods of 1995, 1996 and 1997 and permanent slides prepared from this material were deposited in the FLOR Herbarium of the Federal University of Santa Catarina. Sixty specific and infra-specific taxa were identified, distributed among 16 genuses and 13 families. Eunotiaceae was the best represented family, with 43.3 percent of all taxa inventoried, followed by Pinnulariaceae with 21.6 percent and Surirellaceae with 11.6 percent. Accounting for 20 taxa. Eunotia and Pinnularia were the dominant genuses and showed the broadest morphological variation. Eunotia was the best. The relevant literature for each taxon was reveiwed and discussed.