Impactos antropogênicos sobre comunidades de macroalgas marinhas

Abstract

Human activities have been causing environmental alterations with consequences to marine biological communities. These changes have been occurring at local scale, such as urbanization and coastal pollution, and globally, throught climate change and ocean acidification caused by higher CO2 concentrations in the atmosphere. Coastal urbanization is rapidly expanding worlwide. This phenomenon has been leading to the contamination of the marine environment by a variety of pollutants, such as heavy metals. However, the effects of coastal urbanization on marine macroalgae communities still need further studies that consider their latitudinal limits of distribution. Likewise, studies on the effects of climate change, such as temperature increases and ocean acidification, on macroalgal communities are recent and still relatively limited. Thus, the aims of the present study were: 1) Evaluate the impacts of urbanization on marine macroalgae communities within different phycogeographycal regions along the Brazilian coast; 2) Assess the physiological effects of heavy metal contamination at concentrations observed in polluted regions within the temperature ranges of distribution of the seaweed Halimeda cuneata Hering in the SW Atlantic; 3) Evaluate the effects of increased temperatures and CO2 driven ocean acidification on the photosynthesis of marine macroalgae. For the first, a significant fraction of the Brazilian coast was studied, including sampling areas on the three phycogeographycal regions (warm temperate, tranzition zone, and tropical) where the structure and composition of the communities were determined in urban and reference areas. For the second, an experiment of metal enrichment was performed in laboratory, assessing the effects of metals at temperatures that occur within the limits of distribution of H. cuneata on the Brazilian coast and its recovery potential at the different temperatures. The third consisted of performing experiments in a reef mesocosms in a tropical region on the Brazilian coast, using calcified macroalgae species, evaluating the effects of temperature increases and CO2 driven acidification on the macroalgae photosynthetic performance. The results are presented here in three chapters. The first shows that urbanization leads to substantial declines in species number and causes drastic changes on marine macroalgae communities. The second provides evidence of the negative effects of heavy metals on the physiology of H. cuneata, which showed no photosynthetic recover at temperatures that occur on its limit of distribution in the south Atlantic. The third indicates a high photosynthetic adaptability of the studied macroalgae in face of temperature increases and acidification, which can be related to the possibilities of utilization of different inorganic carbon species by these algae.