Seabed habitat mapping using available regional bathymetric data along the Eastern Brazilian Margin

In understudied and underexplored marine areas, low-resolution regional available data becomes an important asset for any research planning in the area. The Brazilian Margin, especially the continental shelf, is an underexplored area in terms of high-resolution bathymetric surveys. A regional single beam bathymetric data collected by the Navy Hydrographic Office are still the main bathymetric information available. Continental slope and rise are areas of great interest for the oil industry and high-resolution bathymetric data is not open-source. Here, we propose the use of regional available bathymetric data as a first approach to map seabed habitats along the eastern Brazilian shelf, including the Abrolhos Shelf, the greatest coralline reef complex of the South Atlantic. The analysis is based on a produced digital terrain model with 2km resolution in the continental slope and rise and 500m along the continental shelf. Seabed habitat classes were derived using morphometric tools, including the Benthic Terrain Model, a tool at ArcGIS. Available sediment distribution maps were also used to produce regional seascape benthic habitats. 15 physical habitat classes were defined based on their water depth, slope and bed position index (BPI). Analysis showed that shelf morphology controls the pattern of habitat distribution, combined with major sedimentary processes acting in different time-scales: riverine sediment input, carbonate sedimentation and deglaciation-related morphology. Flat bottoms, rough/irregular beds, shelf-incised valleys and a shelf depression were recognized as the most conspicuous habitats along the shelf, increasing seabed complexity and biodiversity. The integration of sediment type with seabed morphology showed the dominance of carbonate sedimentation in the shelf, with the presence of an extensive rhodolith bed habitat. Slope and Rise habitats were also distinguished along the study area due to variations in shelf-slope sediment transfer sources and carbonate sedimentation domains. The eastern and northern Abrolhos slope/rise show steeper gradients habitats, being dominated by a carbonate sedimentation, while the southern Abrolhos and Espirito Santo slope/rise present canyons and a more gentle relief habitat associated with submarine fans.