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

Our study supports evidence that the biodiversity hotspot and role of ecosystem connectiv- ity extends beyond the shallow coastal waters, and into the deep sea surrounding RN/SyG and Desventuradas. For example, Chromis mamatapara is a recently described damselfish from around Rapa Nui and is believed to be endemic to the mesophotic ecosystems of Rapa Nui, Salas y Go´mez, and nearby seamounts. We recorded two individuals of Chromis mamatapara at Salas y Go´mez Island in 150 m (Fig 2). Several species are known to occur at both RN/SyG and Desventuradas islands, which highlights the connectivity between these emergent islands along the ridge. The moray eel Gymnothorax bathyphilus, which was previously known only from Rapa Nui and Desventuradas, was observed at Salas y Go´mez Island in 150 m. Similarly, Gay’s morwong (Nemadactylus gayi) is known only from the Desventuradas and Juan Ferna´n- dez islands and was observed at three sites around Desventuradas with up to 14 individuals in a single frame. The beardfish (Polymixia salagómeziensis) is endemic to the Salas y Go´mez Ridge and we recorded individuals at two locations near Salas y Go´mez Island between 640 and 644 m. Plectranthias nazcae is endemic to the Nazca Ridge and was recorded at Desven- turadas in 167 m. We observed several invertebrate species that are endemic to the region, including two crabs (Chaceon chilensis and Paromola rathbuni), one lobster (Jasus frontalis), and one sea urchin (Stereocidaris nascaensis). Collectively, these findings highlight that the

region is a global hotspot of endemic of species, and that the ridges are important for species connectivity. Threats Fishing. A number of commercially exploited fisheries species were observed during our study. These included two endemic decapods: the Juan Ferna´ndez lobster (Jasus frontalis), which was only observed at one station at Desventuradas in 156 m, and the Chilean golden crab (Chaceon chilensis), which was observed on 44% of the deployments around Desventura- das between 201 and 1,352 m. These species are currently harvested at sustainable levels by the small-scale artisanal fishers from the nearby Juan Ferna´ndez Archipelago [91, 92]. The recently created Nazca-Desventuradas Marine Park and Mar de Juan Ferna´ndez Marine Park were strongly promoted by the Juan Ferna´ndez community to preserve their traditional lobster fish- ing and to exclude industrial fishing [93]. In addition, the Juan Ferna´ndez trevally (Pseudocar- anx chilensis) and Gay’s morwong (Nemadactylus gayi) are both endemic to the Desventuradas and Juan Ferna´ndez archipelagos, where they are important bait for the lobster fishery [94]. However, these endemic species are not protected on the seamounts in adjacent ABNJ and are susceptible to overexploitation by industrial-scale fisheries. Immediate threats to the region are from large-scale foreign fishing fleets, primarily from China, who accounted for over 72% of the total fishing effort in this region between 2012 and 2020 [53]. Seamount habitats worldwide are often heavily impacted by fishing efforts as deep-

sea fish species aggregate and often spawn on seamounts and can be slow to recover from dis- turbance. For example, heavy fishing efforts in the 1960s to the 1980s on seamounts on the far northwestern Hawaiian Ridge and Emperor Seamount Chain resulted in the largest quantity of fish and invertebrate biomass removed from any documented seamount fishery in the world [38]. These fisheries collapsed by the early 1980s, and after 40 years of protection, the habitats are only showing signs of limited recovery [39]. Further, seamounts are often domi- nated by deep-sea corals and sponges that are generally slow growing and extremely long lived. For example, a black coral species taken at 450 m off O‘ahu, Hawai‘i is the oldest skele- tal-accreting marine organism known (4,265 yrs) and the oldest colonial organism yet found on Earth [95]. 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 18 / 27