The first biological survey of the Royal Charlotte Bank (SW Atlantic) reveals a large and diverse ecosystem complex

The Southwestern Atlantic harbors unique reef environments with high proportions of endemic species. The most prominent reefs are located in the Abrolhos Bank, a 46,000 km2 extension of the South American continental shelf. However, just 100 km north of Abrolhos is the Royal Charlotte Bank (RCB), an area still poorly investigated. From a biological perspective, the only scientific information available is the historical record of lobster fisheries in the region. Hence, we performed an expedition to investigate what macrohabitats are found in the RCB and perform a preliminary biodiversity assessment. A dropcam was deployed in 67 sites and recorded images of macrohabitats and associated biodiversity. Four different macrohabitats were detected: rhodolith beds, macroalgal forests associated with rhodolith beds, calcareous sand deposits and coral reefs. The former two were the most frequent, and both rhodolith and macroalgae densities were higher on the outer shelf. A total of 83 species of fish, invertebrates and algae were identified, which comprises a comparatively high diversity for visual reef biodiversity assessments in the Southwestern Atlantic. Our findings show that the RCB is a large and diverse ecosystem complex mostly composed of rhodoliths, and also that it may be already undergoing anthropogenic impacts associated with climate change and fisheries. Therefore, further investigations are necessary to understand the extent of biodiversity and its main threats and evaluate the possible need of conservation and management measures.