Estrutura da assembleia de peixes recifais em costões rochosos da Ilha Grande, RJ: influência da complexidade topográfica, cobertura bêntica e atividade antrópica

Abstract

Understanding processes that determine spatial species distribution is important to establish effective management procedures to conservation of marine ecosystems. In coastal reefs, factors associated to habitat structure, such as topographic complexity, benthic cover and anthropogenic activities influence fish assemblages and are important to detect the relative contribution of each one for distribution of reef fishes. Fish sampling and measurement of habitat structure (benthic cover and topographic complexity), and factors associated to anthropogenic influences were carried out in the sheltered coastline of Ilha Grande Bay, southern of Rio de Janeiro State. The tested hypothesis is that there is a hierarchy on the influence of these groups of variables, and that the anthropogenic influences are the main factors to determine fish assemblage structure. Photos of the substrate were taken to characterize benthic cover and topographic complexity and quantify the percent of benthic groups, refugees and substrate height. Measurements of distance from the navigation channel distance from the Abraão town, and an index associated to tourism and fisheries were used as a proxy of anthropogenic influences in the study area. Relationship between potential predictors and responses variables (fish assemblage, richness, abundance, biomass, trophic groups and selected families) were investigated using the distance matrix based linear model (DistLM) to detect predictors that explained variability on response variables A total of 8294 individuals of 68 species, belonging to 30 families were observed in the 100 transects. The most important predictors to explain variability in the fish assemblage structure were the distance from the channel (19.8%), distance from Abraão town (7.1%) and sediment cover (4.4%). A spatial gradient of samples distribution was observed, with the costal reefs near to the channel having lower abundance of fishes with total length > 20 cm, and lower biomass and species richness, whereas those far from the channel had the opposite pattern, suggesting the effect of tourism and fisheries and from factors related to sediment re-suspension in the navigation channel. The distance from Abraão town was associated to fish assemblage structure, with the nearest sites having assemblages dominated by species of great plasticity to disturbance and gregarious behavior, whereas the farthest sites had more specialized trophic groups as carnivores and herbivores. Topographic complexity also influence structure of fish assemblage, mainly the substrate height and presence of small crevices (<30 cm). Benthic cover, dominated by Matrix of Epilitic Algae – MAE and by zooantids, was the factor with lesser influence on fish assemblage structure, but it was significantly related to increases in richness. The highest contribution of anthropogenic variables structuring ichthyofauna detected in this study is of great importance as subsides to protection measures in this area, such as control of vessels that use the navigation channel and of tourism, fisheries ban and creation of marine protected areas.