Deep-sea biodiversity at the extremes of the Salas y Gómez and Nazca ridges with implications for conservation

fraction of its national waters (< 0.5%) and fallen short of achieving its Aichi Biodiversity Tar- get 11 commitment of protecting 10% of its national waters by 2020. While the recent efforts by Chile and Peru to establish or propose MPAs in the national waters of this region provide important advances, these efforts could be undermined if sur- rounding ecosystems in ABNJ cannot be properly conserved [53]. Over 73% of the ridges fall outside national jurisdictions, where they are unprotected and under threat from overfishing, climate change, plastic pollution, and potential seabed mining. This region has been recog- nized as one of the most important to protect on the high seas globally [27, 112–117]. While the surveys of our study all occurred within Chilean waters of the region, it is highly likely that high seas waters between our study subregions also provide critical habitats and ecological stepping stones for many of the species documented during our surveys. For example, seafloor topography data indicates that there are many seamounts in ABNJ of this region [21], which are well known to provide highly suitable habitats for many of the demersal fish, coral, and sponge taxa recorded in our surveys [69]. Furthermore, recently developed habitat suitability models, indicate that highly suitable habitat for VME taxa is widespread in ABNJ of the Salas y Go´mez and Nazca ridges [118]. Most large-scale features (e.g., seamounts, guyots, ridges, and escarpments) in this region provide suitable habitats for deep-water corals and sponges and all

our survey sites with VME taxa present (n = 20) were in areas of high habitat suitability based on these distribution models. Given the importance of VME taxa in deep-sea ecosystem func- tioning and their slow recovery rates from disturbance, these features should be proactively protected from bottom fishing and seabed mining. Caveats The deep ocean presents many challenges in exploration and assessment given the extreme environmental conditions, remote locations, and paucity of existing data on which to base tar- geted studies [1]. For example, determining habitat type a priori was not possible, resulting in an unbalanced sampling design in our study. Expanded development and accessibility of sea- floor mapping datasets would allow for more informed sampling design and enable more bal- anced representation of different habitat types [119]. Our study is based on opportunistic sampling to provide baseline observations at two remote and underexplored locations. Like all baited-camera methods, our deep-sea camera system is specialized to measure the relative abundance of mobile megafauna that are attracted to bait [61, 120, 121]. However, species’ absences may be less reliably measured by opportunis- tic point video surveys [122]. Further, our deep-sea camera system is designed to optimize the survey field of view and the ability to identify distinguishing characteristics of mobile taxa (e.g., pectoral and anal fins and head characteristics) [61]. However, without physical sam- pling, species-level identifications can be difficult or impossible to determine from video

alone. For example, in the Desventuradas, a new species of Squalidae may have been present, but a physical specimen would be required for confirmation. In most cases in our study, taxo- nomic resolution was achieved to the family level for fishes and order level for invertebrates, which was sufficient for statistical comparisons of assemblage-level differences among locations. Moreover, for baited camera methods, small sessile fauna (e.g., meiofanua, infauna) in the background of a frame can be difficult to confidently identify, therefore this method typically focuses on assessments of mobile megafauna [61, 120, 123]. However, our study recorded numerous VME taxa, therefore we included sessile fauna in our analyses of invertebrate assem- blages as these taxa indicate areas that are of high conservation value. PLOS ONE Deep-sea biodiversity along the Salas y Go´ mez and Nazca ridges PLOS ONE | https://doi.org/10.1371/journal.pone.0253213 June 30, 2021 20 / 27