Macrobenthic assemblages across deep-sea pockmarks and carbonate mounds at Santos Basin, SW Atlantic

Abstract

Ocean and Coastal ResearchThe SE Brazilian continental margin is rich in geomorphological features that create different seascapes, where diverse benthic communities thrive. The seafloor is composed of a mixture of pockmarks of different sizes and shapes and tall carbonate mounds that may form extensive chains. Mounds are colonized by deep-water corals which are the main responsible organisms promoting growth over geological time. Depressions and mounds affect the benthic ecosystem in multiple ways owing to water flow, sedimentation rates and food availability. This paper presents new data on macrofaunal composition and community structure associated with deep-sea coral habitats and pockmark areas along the upper continental slope of Santos Basin. Ten sites were sampled using a 0.25 m2 box corer on board R/V Alpha-Crucis, totaling 27 sediment samples. A total of 182 taxa were found, including new records for the Southwestern Atlantic, as well as several potential new species to science. In general, we observed an association of the macrobenthic fauna with the geomorphology of the area and the most important variables, mainly substrate composition and water flux. The abundance, taxonomic composition and also the feeding modes varied across the deep-water coral sites and pockmarks, reflecting in a mosaic of benthic habitats. As deepsea corals and pockmarks are extremely sensitive to anthropogenic influence and natural shifts, in addition to the economic value associated to fisheries, this study provides baseline information on these special habitats in Santos Basin that can be used for future research, monitoring activities, and conservation strategies.

Deep sea ecosystem exploration and ‘health check’: sampling strategy and methods applied during the iAtlantic_BR10_Petrobras cruise in the Santos Basin, Southwest Atlantic

“…Seafloor sediment sampling with box corer produced a large set of biological samples that can support qualitative studies on the local fauna diversity, adding information to previous studies (e.g., Carrerette et al, 2022). Also, the collected coral fragments supported earlier inferences about the distribution of coral banks (Sumida et al, 2004).…”

“…The iAtlantic_BR10-Petrobras cruise was the first initiative to apply the iAtlantic Project approach in the South Atlantic (Roberts et al, 2023). It included a chance to image the seafloor which would enable the visualization of habitats and megafauna communities, adding new elements to the characterization of benthic communities from previous studies (e.g., Carrerette et al, 2022;Santos et al, 2022 and other). Thus, the sampling plan that was originally developed for the expedition was severely impacted by the inoperability of the towcam system.…”

“…The interest in describing these communities has increased in the past 20 years as the region is associated with the extension of presalt oil fields (Cavalcanti et al, 2017) and was, from 2000 to 2008, subjected to intense bottom fishing (Perez et al, 2009). Significant advances in our understanding of the biological, geological, and geochemical aspects of these benthic ecosystems have derived from recent initiatives of the oil and gas industry, especially focused on exploring potential gas seepages in the region and its associated chemosynthetic communities (Bendia and Carrerette, 2022;Carrerette et al, 2022;Sumida et al, 2022, and others). Adding to these efforts and to the need to provide environmental baselines for the sustainable development of oil and gas exploration in the region, the 'iAtlantic_BR10-Petrobras' expedition was a joint iAtlantic -Petrobras enterprise conducted on board the research vessel 'NPqHOc Vital de Oliveira' of the Brazilian Navy, which focused on mapping the local seafloor and characterizing its deep ecosystem structure and functioning.…”