Los efectos del disturbio de cuatro aberturas de la barra de arena en la laguna costera Imboassica, localizada en el municipio de Macaé, estado de Río de Janeiro, Brasil, en la comunidad de peces fueron evaluados en un estudio a largo plazo. Entre los años 1993 y 2004, colectas de peces y valores de salinidad fueron obtenidos con el objetivo de caracterizar la estructura y los efectos de las aberturas de barra sobre esta comunidad, como medidas de resiliencia y resistencia. Durante las aberturas de la barra realizadas entre los años de 1993 y 1996, el tiempo de resiliencia de la comunidad no fue identificado debido a los cortos intervalos de aberturas, a la magnitud del disturbio y a la discontinuidad de los muestreos de peces. Estudios realizados entre 1993 y 2004 indicaron que los factores que estructuran la ictiofauna de la laguna Imboassica son consecuencia de las variaciones de la salinidad, influenciadas por las aberturas de la barra a que este ambiente es sometido. Estos eventos fueron indicados por la recolonización de las especies primarias de agua dulce, valores de salinidad oligohalinos y bajas alteraciones en la composición y abundancia de la comunidad de peces. Debido a la magnitud y frecuencia de los disturbios, las poblaciones evaluadas de peces que entran en la laguna provenientes del océano adyacente, más la resistencia de este ambiente a las variaciones de salinidad, determinan la resiliencia y resistencia de la fauna de peces en la laguna. Así, la resiliencia de la fauna íctica en la laguna Imboassica fue indicada por el conjunto de: a) valores de probabilidad de Spearman menores de 0. 05 entre los pares de comunidades pre y pos disturbio; b) presencia de especies de peces de agua dulce indicadoras de resiliencia; c) intervalos de salinidad variando entre 0 y 5; y d) bajas alteraciones en la abundancia de las poblaciones de peces.

The effects of a disturbance by sandbank opening on the fish fauna community were evaluated through a long-term study in the Imboassica coastal lagoon, Rio de Janeiro State, Brazil. The fish and salinity samples were conducted between 1993 and 2004, with the goal of characterizing the structure and effects of four sandbank openings on this community, such as resilience and resistance measurements. During three sandbank openings, between the years of 1993 and 1996, the resilience time of the fish community could not be identified due to the short time period between openings, their magnitude and the discontinuity of the fish sampling. Monitoring studies previously conducted between 1993 and 2004, indicated that factors structuring the fish fauna of Imboassica lagoon are due to salinity fluctuations, influenced by the sandbank openings to which this environment is subjected. These events were indicated by the recolonization of primary freshwater species, oligohaline salinity values, and small variations in the composition and abundance on the fish community. Due to the magnitude and frequency of the disturbance, the ichthyic populations available that enter the lagoon from the adjacent ocean plus the resistance of this environment to salinity variations, determined the resilience and resistance of the ish fauna in the Imboassica lagoon. Thus, the resilience of the ish fauna in this lagoon was indicated in groupings of: a) Spearman probability values lower than 0. 05 between the pairs of communities pre and post-disturbance; b) presence of freshwater species that indicate resilience; c) salinity values varying between 0 and 5; and d) small alterations in the abundance of fish populations.

A ecologia alimentar de Leporinus taeniofasciatus no alto rio Tocantins foi caracterizada antes (fase rio) e após (fase reservatório) seu represamento pela Usina Hidrelétrica Serra da Mesa. A importância de cada item alimentar foi dada pelo Índice Alimentar (IAi), que combina os métodos de freqüência de ocorrência e volumétrico. Uma diferença sazonal significativa na dieta de L. taeniofasciatus durante a fase rio, que não foi mantida durante a formação do reservatório, foi detectada através de uma análise de variância multivariada. A atividade alimentar, verificada pela porcentagem de estômagos com diferentes graus de repleção, não foi afetada pelo represamento. L. taeniofasciatus foi capaz de incorporar itens alimentares terrestres a sua dieta quando estes se tornaram abundantes no começo da formação do reservatório. Apesar desta plasticidade, fatores secundários tais como predação ou competição podem ter afetado sua adaptação no ambiente novo e mais homogêneo. Sua dieta não foi significativamente diferente nas localidades lóticas entre as fases distintas, sugerindo que os ambientes lóticos remanescentes à montante ainda provêem condições favoráveis para esta espécie. Este fato reforça a necessidade de preservar estes ambientes, uma vez que L. taeniofasciatus, aparentemente endêmica à bacia do Tocantins, pode estar ameaçada.

The feeding ecology of Leporinus taeniofasciatus in the upper rio Tocantins was characterized before (river phase) and after (reservoir phase) its impoundment by the Serra da Mesa Hydroelectric Dam. The importance of each food item was given by the Alimentary Index (IAi), which combines the frequency of occurrence and volumetric methods. A significant difference in the diet of L. taeniofasciatus between seasons in the river phase, detected by a multivariate analysis of variance, was not kept when the reservoir was formed. Its feeding activity, verified through the percentage of stomachs with different degrees of fullness, was not affected by the impoundment. Leporinus taeniofasciatus was able to incorporate terrestrial food items to its diet when they became abundantly available at the beginning of reservoir formation. Despite this plasticity, secondary factors such as predation and competition might have affected its adaptation in the new, more homogeneous environment. Its diet was not significantly different in the lotic sites between the distinct phases, suggesting that the remaining upstream lotic environments still provide favorable conditions for this species, reinforcing the need to preserve those habitats, as L. taeniofasciatus, which is apparently endemic to the Tocantins basin, may be threatened.