Underwater surveys reveal deep-sea corals in newly explored regions of the southwest Atlantic

Abstract

Deep-sea coral distribution and composition are unknown in much of the global ocean, but repurposing ocean industry surveys can fill that gap. In Santos Basin, southeast Brazil, areas (241–963 m depth) were surveyed during seven Petrobras cruises, mapping bottom topography with multibeam sonar, then collecting video with remotely operated vehicles. Here, we defined deep-sea coral species distribution and richness, using these surveys, correlating them to physical oceanographic properties. Solenosmilia variabilis was the most prevalent colonial species in coral mounds. Overall, 67% of species were Octocorallia. Coral assemblage structure, abundance, and richness varied among sites both within and among depths, with higher density and richness in the northernmost Santos basin. Depth was the strongest predictor for scleractinian coral distribution, with depth ranges varying by species. Assemblage differences corresponded to changes in water mass. Desmophyllum pertusum was more abundant in South Atlantic Central Water and S. variabilis in Antarctic Intermediate Water influenced areas.

Deep-water seafloor geomorphic features of the Santos Basin, Southeastern Brazilian Margin, shown by analyses and integration of an exten-sive 3-D seismic data set

“…The southern plateau shows two NW-SE welldeveloped valleys from the 2600 m isobath that flow into a depocenter below 3200 m. These 105-165 km long and 12-15 km wide valleys have talweg depths varying from 100 to 300 m and are connected upward to the Cananéia canyon (Figures 5 and 12). Carvalho et al (2023) characterized the diversity and distribution of cold-water corals in five sites in the upper/middle slope (200-1000 m depth) of the northeastern domain (III) using multibeam bathymetric data, remotely operated vehicle images, and bottom samples (Figure 17). The coral assemblage structure, abundance, and richness varies among sampled sites and across depths, with increasing coral abundance and richness toward the northern end of the Santos Basin, near Cape Frio, in which the known eddyinduced upwelling phenomenon probably provides higher food availability to the benthos.…”