Baía de Sepetiba: avaliação espaço-temporal da ictiofauna e suas relações ambientais

Abstract

Shallow water estuarine environments have many habitats that favor colonization and use by different fish species. These coastal ecosystems are undergoing increasingly impacts resulting from industrial and urban developments in their surroundings, resulting in a growing loss of biodiversity, which may be accompanied by the losses of important ecological functions. Investigating the patterns and processes that act on biodiversity is essential to obtain a more view of the dynamics and roles of communities in the ecosystems, and for this, short and long-term studies are essential. Studies have mainly addressed the taxonomic structure, requiring a more integrated approach, aiming to understand the dynamics and roles of functional groups in space and time. The present study, divided into two chapters, aims to understand the spatiotemporal dynamics of the ichthyofauna of shallow areas in a tropical bay in a growing process of environmental change, exploring taxonomic and functional aspects. In chapter 1, we seek to describe the relationship between beta diversity and environmental heterogeneity, in order to test the hypothesis that environmental heterogeneity influences biodiversity. A weak positive relationship between environmental heterogeneity and beta diversity was detected, suggesting that more heterogeneous environments tend to have greater variations in biological composition. In Chapter 2, we assess temporal changes (1983-1985, 1999-2001, and 2017-2019) in taxonomic and functional indices. Previous studies have already reported a decline in the fish richness in the shallow areas of Sepetiba Bay, but the investigation of how the functional groups have been affected has not yet been investigated. We tested the hypothesis that functional diversity indices also changed over time, as a result of environmental changes in the recent decades. We found a substantial decrease in species richness and abundance in more recent periods compared to 1983-1985. However, the functional structure remained relatively stable, with the exception of functional richness, which showed a significant decrease, indicating an impact on the amount of functional space occupied by the local community, so that some of the resources potentially available to the community were no longer used. The stability observed in the functional descriptors can be explained by the fact that estuarine environments tend to have high functional redundancy due to the restrictions imposed by the marked environmental gradient, which can result in the convergence of functional traits between species, ensuring that, despite losses in richness and abundance of species, the main functions can be maintained. The information obtained in this study confirms that the use of functional indices is essential to complement taxonomic assessments, giving a detailed view of the extent of biodiversity loss in impacted environments.