Repurposing offshore industry surveys in deep-sea coral sites of the Southwest Atlantic

Industry-university partnership probes uncharted deep-sea coral zones and ecosystems off SE Brazil. Robotics capture vital video in tech-demanding, costly areas. Economically challenged nations' universities often lack resources. Using existing data and cruises may presents a practical solution.
Repurposing offshore industry surveys in deep-sea coral sites of the Southwest Atlantic
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Studying the deep ocean is typically a privilege of wealthy nations, while poor and developing countries often lack access to the high technology required for exploring deep areas. Industry-science partnerships play a crucial role in advancing knowledge about poorly understood deep areas adjacent to these less affluent countries. However, numerous large industries are already conducting exploration in their rich seafloor territories. Notably, areas off the African continent and Brazil extensively exploit offshore deep areas for oil and gas production, with well-established companies using highly capable vessels and robotic technology for surveying, maintaining and servicing pipes, and collecting environmental data to support their models. In Brazil, Petrobras, the main Brazilian energy company, collaborates with Brazilian universities and research centers to conduct ecosystem surveys and assess potential adverse effects of its activities on the biota. Surprisingly, the ROV (Remotely Operated Vehicle) data from these activities possess significant intrinsic value and global coverage, outweighing any potential limitations related to non-standardized sampling strategies for scientific purposes.

Our study focuses on the energy company areas off SE Brazil, which coincide with deep-sea coral habitats. In partnership with Petrobras, our objective was to enhance our comprehension of these systems within the Santos Basin. This region holds comparable importance to the Campos Basin in terms of exploration and production. Analyzing hundreds of hours of video footage collected during environmental surveys and regular inspections, we sought to determine the distribution and diversity of these corals and the cohabiting organisms. Despite the larger number of ROV surveys and the occasional lack of standardized methodology in offshore operations, which could compromise data analyses, the provided database allowed us to establish a crucial baseline for this yet poorly known region.

We have made remarkable discoveries, uncovering an incredible abundance of both stony and soft corals, fostering a rich community of fish and invertebrate species (Intended to be published shortly) at depths between 200 and 1000 m (Figure 1). Dense deep-sea coral reef sites were observed on the upper slope under the influence of the South Atlantic Central Water (SACW), while deeper sites, below 600 m, featured coral carbonate mounds, predominating under the influence of the Antarctic Intermediate Water (AAIW).

Figure 1. Images depicting three distinct morphological features of coral sites in the study areas (left panel) and reference images of some deep-sea coral taxa (middle and right panels) presented in the manuscript.

 Although some species exhibited broad distributions, most of them inhabited the middle slope. Coral assemblage structure and richness varied with depth, reflecting the presence of different water masses stacked atop each other, each carrying distinct physical-chemical properties and varying food loads. For example, Solenosmilia variabilis was the most abundant stony coral and never formed large reefs, preferring the AAIW. The well-known hard coral Desmophylum pertusum predominantly inhabited shallower areas bathed by the SACW, where it formed larger reef structures in some places (Figure 2). 

Figure 2. a) Distribution patterns of the best match units taxa in the trained SOM (self-organizing map) based on the frequency of occurrence of deep-sea coral, and b) Distribution of sampling depths on the SOM. Each map corresponds to one taxon; these can be superimposed onto the map representing the cluster distribution of depths to show at which depths they are more frequently observed.

Understanding the factors influencing coral assemblage structure in the SW Atlantic remains a significant challenge, as it involves a complex interplay of ecological and physical processes that overlap. These corals substantially alter their environment and surroundings, attracting a diverse array of other organisms seeking partners, food, shelter, and associations. This delicate ecosystem is highly vulnerable and currently faces potential threats from trawling,  ocean acidification, littering, and exploration & production. Overall, our research highlights the value of repurposing industry surveys to gain insights into the deep sea, whether it involves slope sediments, cold seeps, or the fascinating deep-sea coral habitats studied here. Our study has shed light  on the poorly understood habitats in the Santos basin, raising public awareness about the presence of these colorful organisms in deep, dark waters, out of sight, out of mind, identifying some factors influencing their distribution, and providing valuable information for future conservation efforts in the Santos Basin and similar regions.

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Ecology
Life Sciences > Biological Sciences > Ecology

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