Dissertation Abstract

Little is known about the magnitude and the relative importance of chemosynthesis (CS) in marine ecosystems. The main goal of this study was to evaluate the importance of CS in relation to bacterial production (BP) and its main regulatory factors in the following marine ecosystems: South Atlantic Ocean (Brazil-Africa transect and around Vitória-Trindade seamount chain), Southern Ocean (in the Western Antarctic Peninsula) and Guanabara Bay (eutrophic and polluted estuarine system). Temporal and spatial variations, as well as the effect of the climate change conditions and the influence of the seamounts on both microbial processes were evaluated. The microbial community structure and its relation to CS and BP were investigated in the Western Antarctic Peninsula. Dark 14C-bicarbonate and 3H-leucine incubations were used to determine the microbial production rates, and the pyrosequencing was used for microbial diversity. The results indicate a significant temporal variation of CS in Guanabara Bay, and higher rates of BP in more polluted and shallower waters. Chemosynthetic rates were higher than BP rates for all pelagic provinces in the oceanographic regions. Surface samples from South Atlantic and Vitória-Trindade seamount chain were apparently more influenced by higher temperature and salinity, while deep-water samples, by higher concentrations of nitrate, silicate and phosphate. The seamounts influenced only the BP rates, probably due to the organic matter supply. The addition of humic compound and CO2 in a mesocosm treatment did not affect CS, but BP showed a tendency of decreasing under lower pH conditions. Among the groups identified in the Southern Ocean, Thaumarchaeota (Nitrosopumilus), Gammaproteobacteria (Oceanospirillales and related to Thiotrichales and Thiohalorhabdus), Deltaproteobacteria (SAR 324) and Planctomycetes are likely to have contributed to the measured chemosynthetic production and in general may contribute to carbon fixation in deep waters. A combination of environmental factors drives the microbial community structure in Antarctic waters. This study showed for the first time that CS is a relevant process also in the open ocean, contributing to the organic matter production, being sometimes one order of magnitude higher than the heterotrophic BP. The main contribution of this study was to demonstrate the relevance of CS and add new data in new areas to our small but growing knowledge of CS in marine ecosystems, by using different approaches (temporal and spatial) and relating it to BP and environmental parameters.