Florações de macroalgas e seus efeitos sobre a pesca e macrofauna em uma região neotropical

Abstract

Macroalgae play important ecosystem functions in aquatic ecosystems: they contribute to primary production and nutrient cycling, generate complex environments, act as shelter and provide food and nesting surfaces for many species. However, environmental changes related to anthropic activities have been causing the eutrophication of aquatic ecosystems due high nutrient inputs in the water bodies. Eutrophic environments favor the massive algae proliferation, commonly known as blooms. Blooms can cause impacts on ecosystems by oxygen depletion and toxins releases, consequently generating social and economic issues. In this thesis, we aim to verify the impacts caused by macroalgae blooms encompassing the environmental, social, and economic effects. In the first chapter, we evaluate the Ulva lactuca blooms in a hypersaline estuary on the semiarid coast. We analyzed macroalgae abundance in relation to physical-chemical factors during dry and rainy seasons. Our results support greater abundance during dry season, mainly concentrated in the upstream region of the estuary. During dry seasons, the river exhibits slower currents and less turbid waters while nutrients are accumulated, providing the ideal scenario for U. lactuca development. In the second chapter, we intend to list possibilities for macroalgae biomass uses. As a bioaccumulator species, we also verified the metal concentration on its tissues. Macroalgae exhibited high levels of metal concentration, limiting its use for biomanipulation, biofuels agents. In the third chapter, we aimed to better understand the impacts of U. lactuca blooms on fishery using the local ecological knowledge provided by fishermen. Fishermen information’s indicated that blooms mainly occur during the dry period in the estuarine region. Net gears were heavily impacted by macroalgae blooms and fishes were the mainly impacted resource. Finally, in the fourth chapter, we evaluate the impacts of macroalgae on comercial shrimps and other benthic macroinvertebrates of bottom trawling fishery in two distinct climatic zones: tropical zone and dry zone. The dry zone showed greater algae biomass than in tropical zone. On the other hand, shrimp productivity was higher in the tropical zone. Shrimp diversity indexes were negatively related to algae richness, indicating that algal banks are usually avoided by the species. The benthic macrofauna density, on the other hand, exhibited a positive relationship with macroalgae biomass. However, when evaluating the relations for each species, the influences were positive and negative dependending on the species diet and preferential habitat.