Macroinvertebrados bentônicos e a estrutura do habitat em um rio intermitente do semiárido brasileiro

Interactions between the habitat structure and physical and chemical parameters generate environmental conditions that influence the distribution and abundance of macroinvertebrate species and their assemblages. This study describes the habitat structure and its effects on macroinvertebrate composition in an intermittent stream in the Brazilian semi-arid. Collections of benthic invertebrates were performed in three reaches along the Ipanema River during the dry and wet seasons using a “D” shaped net (40 cm wide and 250 ?m mesh). A total of 23 taxa was recorded, Insecta being the most representative with 12 families and an average density of 168.1 ind/m². Correlations between environmental variables and CCA axes showed that substrate composition (sand and mud), macrophytes, litter and altitude were the main variables explaining benthic macroinvertebrate composition in the study stream. Canonical correlations between macroinvertebrate and physical and chemical variables were not significant. This study shows that the habitat structure contributes to the persistence and stability of macroinvertebrate communities in a Brazilian semi-arid stream, by creating refugia for organisms and contributing to the physical structures available for colonization.Key words: hydrological disturbances, patch dynamics, drylands.As interações entre a dinâmica do habitat e os parâmetros químicos e físicos criam condições ambientais que influenciam fortemente a distribuição e a abundância de macroinvertebrados. Este estudo descreve a estrutura do habitat ao longo de um rio intermitente do semiárido brasileiro, quantifica variações na composição da fauna bentônica e avalia associações de variáveis físicas e químicas e da estrutura física do habitat com a fauna de macroinvertebrados. Foram realizadas coletas em três trechos ao longo do rio Ipanema, durante os períodos seco e chuvoso. Macroinvertebrados bentônicos foram amostrados usando uma rede tipo “D” com 40 cm de abertura e malha de 250 ?m. Foram registrados 23 táxons, sendo a classe Insecta a mais representativa com 12 famílias e uma densidade média de 168.1 ind/m². As correlações entre as variáveis ambientais e os eixos da CCA mostraram a composição do substrato (areia e lama), percentual de macrófitas e folhiço, e altitude como variáveis explicativas para a composição da fauna de macroinvertebrados. A associação entre as variáveis físicas e químicas e a composição de macroinvertebrados não foi significativa. Este trabalho mostra que a estrutura do habitat tem o potencial de contribuir para a persistência e a estabilidade das comunidades de macroinvertebrados nos rios do semiárido por criar refúgios para a diversidade e contribuir para a estrutura física disponível para colonização destes organismos.Palavras-chave: perturbação hidrológica, distribuição em manchas

Checklist of zooplankton from the upper Ipanema River (Pernambuco), an intermittent river in semi-arid Brazil

The present study aimed to survey the zooplankton composition (Rotifera, Cladocera and Copepoda) in the upper Ipanema River, an intermittent river affluent of the São Francisco River in semi-arid Brazil. Sampling was performed during the wet (April and July 2007) and dry (October 2007 and January 2008) periods. Thirty species were recorded, Rotifera being the richest with 25 species. Among the Rotifera families recorded, Brachionidae and Lecanidae showed greater number of species, in contrast with lower richness of Cladocera and Copepoda

Relação peso-comprimento de duas espécies de peixes em um rio intermitente no nordeste do Brasil

Given the context of high hydrological uncertainties and stress in dryland streams, the evaluation of length-weight relationships and condition factors of fish becomes of chief concern for the understanding of these systems. Length-weight relationships were estimated for two fish species, Astyanax fasciatus (Cuvier 1819) and Astyanax bimaculatus (Linnaeus 1758), from temporary pools in a dry river bed. Length-weight relationship information was compared between dry and rainy seasons. Sampling was performed using gillnets, manual trawls and cast nets at different reaches of the river. Estimates for the values of b of the length-weight relationship were 2.63 for A. fasciatus, and 2.78 for A. bimaculatus, indicating a negative allometric growth. The condition factor ranged between 0.0180 and 0.0187 for both species, without significant difference between seasons, and meaning a greater investment in growth rather than weight gain. Results indicated that fishes tended to be larger during the rainy season, likely representing the result of a higher frequency of immature and smaller individuals during the previous dry season as a consequence of reproductive activity of adults. Keywords: Astyanax fasciatus, Astyanax bimaculatus, temporary pools, condition factor.Dado o contexto de stress hídrico e alta variabilidade temporal em rios de regiões secas, o entendimento da relação peso-comprimento e fator de condição de peixes se apresenta como importante mecanismo para a compreensão desses sistemas. Relações pesocomprimento foram estimadas para duas espécies de peixes, Astyanax fasciatus (Cuvier 1819) e Astyanax bimaculatus (Linnaeus 1758), em poças temporárias de um rio intermitente. A relação peso-comprimento é comparada entre as estações seca e chuvosa. A amostragem foi realizada usando redes de espera, arrastos manuais e tarrafas em diferentes trechos do rio. Estimativas para os valores de b da relação peso-comprimento foram de 2,63 para A. fasciatus e 2,78 para A. bimaculatus, indicando crescimento alométrico negativo. O fator de condição variou entre 0,0180 e 0,0187 para ambas as espécies, não apresentando diferença sazonal significativa, dessa forma indicando maior investimento em crescimento em vez de ganho de peso. Os resultados indicaram que os peixes tendem a ser maiores durante a estação chuvosa, provavelmente decorrente de uma maior frequência de indivíduos juvenis e imaturos durante a estação seca precedente, causada por maior atividade reprodutiva dos adultos.Palavras-chave: Astyanax fasciatus, Astyanax bimaculatus, poças temporárias, fator de condição

Zooplankton community of Parnaíba River, Northeastern Brazil

Aim:The objective of the present work is to present a list of species of zooplankton (Rotifera, Cladocera and Copepoda) from the Parnaíba River. Additionally, we provide comments on their distribution along the river, and between dry and wet seasons.MethodsZooplankton was collected with a plankton net (60 µm mesh) and concentrated into a volume of 80 mL for further analysis, during the dry (October 2010) and wet (April 2011) seasons. Sampling was restricted to the marginal areas at depths between 80 and 150 cm.ResultsA total of 132 species was recorded among the three zooplankton groups studied. During the dry season a total of 82 species was registered and 102 species was registered for the wet season. Rotifera contributed with 66.7% of the species, followed by Cladocera (26.5%) and Copepoda (6.8%).ConclusionsThe richness of species observed was high compared to other large rivers in Brazil. In the context of current policies for water management and river diversions in northeastern Brazil, the present study highlights the importance of this river system for biodiversity conservation

Implications of low food availability on resource partitioning among three species of Cichlidae (Pisces: Perciformes) in a Brazilian semi-arid reservoir

AimResource partitioning has been recognized as a major driver affecting fish communities, with the potential to reduce interespecific competition. This is the result of differences in feeding apparatuses and feeding mode, location of the fish species in the water column and swimming ability, as well as type and size of prey and its availability. The present study surveys a highly limited aquatic system in semi-arid Brazil with regard to habitat and food availability, with very low diversity of fish, and poor in underwater habitat structures and prey, with the objective of understanding resource partitioning among fish species under such conditions.MethodsThree species of Cichlidae (Pisces: Perciformes) were sampled during the dry and wet seasons and had their stomach contents analyzed to evaluate food consumption. The resource partition among fish species was evaluated based on Pianka’s niche overlap index and tested for significance against null models.ResultsIt was observed a low overlap among the study species in food resource use, with individuals tending to specialize to select some food items. This is likely the result of low natural variation in abundance of specific food items associated with fish preferences (both morphological and behavioral).ConclusionsThese results support evidence that, in Brazilian semi-arid aquatic systems, coexistence of fish species seems to be enhanced by the partition of food items at specific trophic levels. Within this context, flow variability would have a key hole in fish coexistence by promoting a high diversity of aquatic habitat elements available for colonization of fish and their prey. Furthermore, food resources available to fish play an important role in this dynamics since prey foods are expected to vary in abundance as the habitat changes