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

The Desventuradas Archipelago is located ~ 200 km southeast of the junction of the Salas y Go´mez and Nazca ridges, rising from a depth of 4,000 m at just over 850 km from the Chilean coast. This archipelago consists of the islands of San Ambrosio, with a surface area of 2.2 km2, San Fe´lix with a surface area of 1.4 km2, and the Gonza´lez and Roca Catedral islets (Saint Peterborough) (Fig 1). In total, the Chilean EEZ around the Desventuradas covers an area of 449,805 km2. Data collection. Remote autonomous benthic landers with baited camera systems [55, 61] were used to conduct stationary video surveys at RN/SyG and the Desventuradas (Fig 1). These systems include high-definition cameras (Sony Handycam HDR-XR520V 12 megapixel) encased in a borosilicate glass sphere that are rated to 11,000 m depth. The camera is fixed at a 45˚ declination from the horizontal plane and has a 35 mm equivalent focal length of 29.8 mm, which results in a horizontal 62.27˚ and a vertical 37.53˚ angular field-of-view. Lighting at depth was achieved through a high-intensity LED array directed using external reflectors, and lighting intensity was constant among all deployments. Depth gauging was conducted using an external pressure sensor. The anchor line extended 2 m from the seafloor to optimize the field of view to both capture large mobile scavenging megafauna and allow for identification of organisms. The deep-sea camera system is positively buoyant, resulting in an ascent rate of 0.5 ms−1, and weighted with a 22 kg external weight, resulting in a descent rate of 1.5 ms−1. The weight

is released by burn wire, activated using onboard battery voltage, and the camera system was located for recovery by communication of an onboard VHF transmitter and locating antennae, with backup location via communication with the ARGOS satellite system. Up to three deep-sea camera systems were simultaneously deployed between 22 February– 4 March, 2011 at 20 stations between 150–1,850 m depth (�X = 1,104.6 ± 433.6) along the island slopes of SyG and RN and the slopes of two seamounts west of SyG (Fig 1). At Desventuradas, 27 successful deployments were conducted between 10–26 February, 2013 at 75–2,363 m depth (�X = 755.8 ± 649.2) (Fig 1). Cameras were deployed with a minimum distance of 500 m from another deployment location, and each camera was baited with chopped frozen fish and deployed for 1 to 5 hours with an average footage per deployment of 112 min at Desventuradas and 129 min at RN/SyG. Deployments targeted geological features and specific depths based on available bathymetry. Sampling design aimed to represent a gradient of depths away from a feature (e.g., island, seamount), and thus deployments generally occurred in a line radiating out from the shallow depths of a feature to deeper waters. The substrata for each camera deployment were classified as hard or soft, based on video footage. Seafloor type was defined as soft if the seafloor observed during the deployment con- sisted of �80% sediment (sands and muds), and hard if <80% of the seafloor observed during the deployment was composed of sediment. Hard habitats included rock, cobbles, pebbles,

gravel, biogenic material (including live coral), coral rubble, and shell material. Biological data processing. Annotations were made from the video footage based on standardized taxonomic nomenclature according to the World Register of Marine Species (WoRMS). Video files were stored in Tator, which is a cloud-based collaborative video annota- tion platform developed by CVisionAI (http://cvisionai.com/). Frame grabs of representatives of each species were taken in Tator for archival and identification purposes. Individuals were identified to the lowest possible taxonomic level using the Hawaii Under- water Research Laboratory (HURL) database ([62]; http://www.soest.hawaii.edu/HURL/ HURLarchive/guide.php), the NOAA Office of Ocean Exploration Benthic Deepwater Animal identification Guide (https://oceanexplorer.noaa.gov/okeanos/animal_guide/animal_guide. html), FishBase [63], regional guides and reports of trawl data from the Salas y Go´mez and 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 5 / 27