Variação espacial e temporal na estrutura de assembleias de peixes em um estuário tropical

Abstract

In tropical lagoons, environmental conditions may spatially change due to seasonal fluctuations. Such variability represents a potential regulator of abundance distribution and is critical to the permanence of specific fish species. The present study investigates how environmental variability controls the spatial structuring of the ichthyofaunal community of a tropical lagoon and how the functional structuring of this community is seasonally organized. Monthly standardized collections were conducted from November 2013 to October 2014 at sampling stations in the Mundaú lagoon, central coast of Alagoas. Fish were captured with a seine 1,000 m long by 3 m height (35 mm mesh). Physical and chemical parameters of the water at each station were also recorded. In the laboratory, fish were identified to species level and morphometric and ecomorphological measurements of individuals were taken. Grouping analyses (cluster) were performed among the points with the environmental variables, as well as with the fish composition considering functional groups based on a functional dendrogram. A total of 8,972 individuals (46 species) were collected. Differences in species abundance distribution between sites, seasons, and an interaction between these two factors were observed (PERMANOVA: p<0.05). Eight functional groups were identified by the cluster analysis based on ecomorphological functional traits. Functional diversity was similar among stations, indicating functional redundancy. The results suggest that distinct sets of environmental variables correlate with community structure seasonally, with the distance from the estuarine mouth and rainfall being the most significant variables in the dry season (BIOENV: r=0.56) and chlorophyll-a, distance from the estuarine mouth and salinity (BIOENV: r=0.33) in the dry season. Finally, the spatial and seasonal rearrangements of the species contribute to ecosystem stability, causing the trophic resources associated with habitat diversity to be better used by the species that make up the different functional groups, thus ensuring a certain degree of resilience to the studied ecosystem.