Dinâmica da comunidade fitoplanctônica em dois estuários tropicais sujeitos a diferentes usos do solo: Estuários Paraíba e Mamanguape

Abstract

The phytoplankton community is composed of microorganisms that are excellent environmental bioindicators, since they respond quickly to environmental disturbances. In this sense, the study aimed to apply diversity indexes (taxonomic and functional), as well as to explore the functional groups along the environmental gradients of two estuaries (Paraíba and Mamanguape) in two seasonal periods (dry = November/2013 and wet = July/2014) and to relate to the physical and chemical variables of water, in order to understand how this community responds to the different environmental and seasonal conditions. Thus, in the 1st chapter, the taxonomy of the Chlorophyta group was verified, since this group was the second most representative in this study. In estuarine environments, these green algae are common in low salinity, especially in periods of less rainfall and in the upstream segments. Twelve taxa were divided into two classes, three orders and 11 genera. In the 2nd chapter we compare the phytoplankton community's responses in terms of structure (abundance, richness and diversity) in relation to the environmental variables in estuaries with different uses and occupation of the soil. Biomass and abundance were higher when nutrient loads were higher, contributing to low diversity and dominance of the species Cyclotella meneghiniana, Thalassionema nitzschioides and Thalassiosira gravida associated to the different degrees of impacts observed in both ecosystems and seasonal periods. In the 3rd chapter, functional complementarity (CWM), redundancy and functional composition indexes (functional richness, functional diversity and quadratic entropy of RAO) were analyzed through functional groups based on combinations of different traits. In both systems, the main dominant functional group was diatoms, characterized by lack of mobility and high sink rates due to siliceous walls, including small and larger individuals, and freshwater to more cosmopolitan species. The presence of this group and the change in the categories of traces along the spatial and seasonal gradient were associated with the environmental condition, for example, river flow, low light conditions and changes in salinity. Overall, this study combining different approaches to taxonomic and functional diversity has improved our understanding of the changes occurring in both estuaries, pointing to efforts that should be directed towards more effective conservation measures that can be used in conservation programs systems.