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

Islands (Fig 1). Both expeditions resulted in the first systematic survey of these subregions, including its deep waters, using National Geographic Society Exploration Technology Lab’s deep-sea camera system [55]. These surveys provided a rare opportunity to visually examine the deep waters of the region at subregions that bookend the eastern and western portion of the Salas y Go´mez Ridge, as well as the western portion of the Nazca Ridge (Fig 1). The objectives of this research were to characterize biodiversity and community composi- tion of deep-sea demersal fauna at seamounts surrounding Rapa Nui, Salas y Go´mez Island, and the Desventuradas Islands to better understand deep-ocean biogeography and its environ- mental drivers in the region. We tested the hypotheses that biodiversity and faunal assemblage composition vary with location and environmental variables (e.g., depth, ocean chemistry, habitat complexity, geology). Our study represents the first characterization of deep-sea biodi- versity spanning the east and west ends of the Salas y Go´mez seamount chain, as well as the west end of the Nazca Ridge. By surveying remote deep-sea locations in a region of high con- servation value, we provide important insights into patterns in biodiversity, connectivity, and its drivers for deep-sea ecosystem science and conservation, thereby advancing the global knowledge base for effective conservation and sustainable use. Methods Ethics statement Data were collected by all authors in a collaborative effort. Non-invasive research was con-

ducted, which included photographs and videos as described in the methods below. The Republic of Chile granted all necessary permissions to conduct this research. No vertebrate sampling was conducted and therefore no approval was required by any Animal Care and Use Committee. Our data are publicly available at Data Dryad: doi.org/10.5061/dryad.c866t1g6j. Study region The Salas y Go´mez and Nazca ridges are two adjacent volcanic seamount chains in the south- eastern Pacific that stretch across more than 2,900 km of seafloor (Fig 1). The Nazca Ridge is adjacent to South America and stretches across approximately 1,100 km of seafloor between the eastern edge of the Salas y Go´mez Ridge and the subduction zone off the Peruvian coast (Fig 1). A small northeastern section of the Nazca Ridge is in Peruvian national waters, whereas the majority of this ridge lies in areas beyond national jurisdiction (ABNJ). Stretching across roughly 1,600 km between the Nazca Ridge and Rapa Nui, the central portion of the Salas y Go´mez Ridge lies within ABNJ. Both the western end around the islands of Rapa Nui and Salas y Go´mez and the eastern end around San Fe´lix and San Ambrosio (Desventuradas Islands) fall within Chile’s exclusive economic zone (EEZ) (Fig 1). The Easter Island Ecoregion consists of Rapa Nui, Salas y Go´mez, and the nearby sea- mounts [56]. Salas y Go´mez Island (SyG) is considered part of Polynesia, making it the east- ernmost landmass of Polynesia and the most southeastern coral reef in the Pacific. Rapa Nui

(RN) is considered one of the most isolated inhabited islands globally [57]. The island (total area of 166 km2) is located ~ 2,000 km east of Pitcairn Island, and ~3,700 km west of continen- tal Chile. SyG is a small, emergent rock 0.15 km2 in area and 770 m in total length, with the highest point 30 m above sea level [58]. It is located ~390 km east of RN, and 3,210 km west of the Chilean mainland. These two islands are a part of the Salas y Go´mez Ridge, and are the only places where the submarine mountain range rises above sea level [59, 60]. The several dozen seamounts in the Easter Island Ecoregion extend 2,232 km eastward where the Salas y Go´mez Ridge joins the Nazca Ridge. 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 4 / 27