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

Over 73% of the Salas y Go´mez and Nazca ridges are in ABNJ without protections from fishing. Globally, ABNJ account for only 4.2% of annual marine capture fisheries production, with most species destined for upscale markets in developed, food-secure countries, such as Japan, the European Union, and the United States, suggesting high seas fisheries play a negligi- ble role in ensuring global food security [96]. Deep-sea and high seas fishing often produces net economic benefits only due to subsidies as most of the world’s largest fishing fleets would be unprofitable without subsidies and low labor costs [97]. Closing the high seas would be catch-neutral, while reducing inequality in the distribution of fisheries benefits among the world’s maritime countries by 50% [98]. Climate change It is predicted that in the next 20–40 years, the seafloor of this region will experience increases in temperature, acidification, decreases in dissolved oxygen, and declining export of particu- late organic carbon [24, 99]. Portions of this region are already extremely nutrient [100] and oxygen-poor [51], so the global threat of climate change is especially heightened in this region and in need of management intervention to protect ecosystem structure and function. The numerous endemic species in this region are at high risk of extinction from climate change, as they have limited ranges, small thermal safety margins, and unique habitat and environmental requirements [29, 101, 102]. In addition, primary productivity and fisheries production are

projected to decline throughout the region over the next several decades due to climate change [103], and these changes will impact the entire ecosystem and require a precautionary approach to management of human use. Conservation opportunities Numerous previous studies have noted the exceptional natural and cultural significance of the Salas y Go´mez and Nazca ridges (reviewed in [53]). In 2014, at the 12th Meeting of the Confer- ence of the Parties [104], the Salas y Go´mez and Nazca ridges were recognized as an ecolog- ically or biologically significant marine area (EBSA). The eastern part of the Nazca Ridge is part of the most productive marine ecosystem in the world and is one of the region’s most unique underwater habitats [29, 105]. Seamounts on the Salas y Go´mez and Nazca ridges host a high abundance and diversity of unique organisms and provide important habitat and migration corridors for protected megafauna such as blue whales, leatherback turtles, and sharks; important fisheries species such as swordfish (Xiphias gladius) and Chilean jack mack- erel (Trachurus murphyi); and a diversity of other ecologically important species such as habi- tat-forming deep and shallow-water corals [27, 41, 106–110]. The results of this study provide additional evidence that the Salas y Go´mez and Nazca ridges are of high natural significance and conservation value. Our surveys documented numerous VME and endemic taxa. In addi- tion, some of the endemic taxa were documented on both ends of the Salas y Go´mez Ridge,

supporting previous conclusions that the ridges are important for connectivity as they provide migration corridors and ecological stepping stones for many species [104]. Chile has already protected the portions of the Salas y Go´mez and Nazca ridges that fall within its jurisdictions through various MPAs, including the Rapa Nui Multiple-Use Coastal Marine Protected Area, the Motu Motiro Hiva Marine Park, and the Nazca-Desventuradas Marine Park. While these conservation efforts represent important conservation advances for the region, collectively they only cover 23.8% of the area recognized as an EBSA. Although the portion of the Nazca Ridge that lies within Peru’s national waters has been proposed for increased protections [111], it remains unprotected, highlighting an immediate opportunity for Peru to expand its ocean conservation efforts. To date, Peru has protected only a small 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 19 / 27