Padrões de distribuição de assembleias ictioplanctônicas em dois estuários tropicais do semiárido

Abstract

Understanding the processes that lead to the formation of local communities from the regional pool of species has been one of the main objectives of community ecology. Species that occupy available habitats are filtered through environmental constraints (environmental filters) that select species by segregating niches and favoring speciation and species turnover. In addition, biotic interactions (biotic filters) influence variations in species composition, such as assemblages dominated by species that have competitive advantages. These filters can act on hierarchical scales, partitioning species diversity according to the components α (local diversity), β (variation of diversity between locations) to γ (regional diversity). The present study aimed to: 1) to assess the variation of the ichthyoplankton, the abiotic environment (local and landscape environmental variables) and the availability of food resources; and 2) to analyze the effect of local environmental and landscape variables on the patterns of beta diversity of the local communities of two tropical estuaries with different anthropic pressures: one located in a densely populated urban area, and the other located in an area of environmental protection. The study was carried out in three zones, according to the salinity gradient (upper, intermediate and lower), along the main channel of the estuaries of the Paraíba do Norte and Mamanguape – PB rivers. The results showed that the variables at local scale, as well as the availability of food resources were environmental filters, which were responsible for the formation of the assemblies along both estuaries. In the most impacted estuary (Paraíba do Norte), the influences of the trophic gradient provided by high nutrient concentrations from sewage disposal, agricultural activities and a shrimp farming, in addition to other anthropic impacts, may have resulted in the reduced number of species, low abundance of species and consequently a lower beta diversity, in addition to interfering with their nursery functions for fish species. On the other hand, for the less impacted

estuary (Mamanguape), the environmental gradient driven by variations in temperature, transparency and chlorophyll-a, as well as food availability, were responsible for the spawning processes and formation of distinct larval assemblages between the estuarine zones. Which were directed through species substitution, suggesting the importance of environmental heterogeneity for fish diversity in this estuary.