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The aim of this thesis is to characterize the shallow gas deposits of the inner area of the Bahía Blanca estuary and to evaluate the effect of the gas-bearing sediments on the associated subtidal benthic communities. For this purpose, the distribution of shallow gas in the estuary was mapped through the analysis of highresolution seismic records. Based on this map, two study sites were selected (with gas and control) that only differed in the presence of gas in contact with the surface of the seabed. Acoustic methods were used to determine the stratigraphy and morphology of the site with gas and the adjacent area. In addition, the gas sediments were evaluated by means of the following analyses: grain size, organic matter content, X-rays and HPLC head space measurement. The benthic organisms of both sites were compared in terms of abundance, biomass, diversity, evenness, species richness, taxonomic and functional structure. The gas was found widely distributed in the estuary, both near and in contact with the surface of the seabed of the inner area of the Bahía Blanca estuary. It was evidenced in the form of acoustic turbidity and acoustic blanking. The seismo-stratigraphic column presented five seismic sequences of the late Pleistocene-Holocene. It was established that the gas origin is biogenic, being associated with a Middle Holocene deposit, from which it migrated until it was in contact with the surface of the seabed due to the permeability of the overlying strata. The gas in the surface of the seabed was evidenced in sonograms by means of the attenuation of the acoustic signal, which evidences a low cohesion Índice Dedicatoria…………………………………………………………………………………………………….I

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We examined spatial variations in the biological descriptors of macrobenthic assemblage in relation to environmental parameters and metal distribution in the sediments along a channel of Bahía Blanca estuary affected by non-treatment sewage effluents. Along the channel, metal concentration values were higher than those in the internal estuary area, a sector considered as a reference site. The highest values of water turbidity and metal content in sediments were observed in the effluent discharge zone and at the site where sediments from dredging activities were deposited two years ago. The density of macrobenthic assemblages decreased towards the effluent discharge zone, but the richness and diversity reached to minimum values in both disturbed areas. Only two species of polychaetes were associated with these areas: Laeonereis acuta and Aphelochaeta sp.; the former being found in the effluent discharge zone, where Cd and Pb were most abundant, and the latter being the dominant species in the site characterized by dredging material and high concentrations of Cr and Ni. This study is the first approach to explore the impact of anthropogenic activities over the macrobenthic assemblage of the Bahía Blanca estuary, providing background data to use future management decisions.

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The deep ocean comprises complex ecosystems made up of numerous community and habitat types that provide multiple services that benefit humans. As the industrialization of the deep sea proceeds, a standardized and robust set of methods and metrics need to be developed to monitor the baseline conditions and any anthropogenic and climate change-related impacts on biodiversity, ecosystem function, and ecosystem services. Here, we review what we have learned from studies involving offshore-energy industries, including state-of-the-art technologies and strategies for obtaining reliable metrics of deep-sea biodiversity and ecosystem function. An approach that includes the detection and monitoring of ecosystem services, with open access to baseline data from multiple sectors, can help to improve our global capacity for the management of the deep ocean.

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