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

this region should be comprehensively protected using the best available conservation mea- sures to ensure that the Salas y Go´ mez and Nazca ridges remain a globally unique biodiver- sity hotspot. Introduction As the largest habitat on Earth, the deep sea is remarkably underexplored and under-charac- terized [1, 2]. Consequently, many fundamental questions in deep-sea ecology remain unre- solved [3, 4]. Although knowledge of deep-sea community composition and ecosystem functioning has advanced rapidly in recent decades, both in terms of the scale of sampling [5, 6] and large-scale data syntheses [5, 7–10], fundamental ecological data for much of the deep sea is lacking [11]. For example, a recent three-year, deep-sea exploration campaign in the Pacific found that fewer than 20% of the taxa could be identified, highlighting our knowledge limits of the deep ocean [12]. Lack of fundamental ecological knowledge, including what lives in the deep sea and how biodiversity and community composition are distributed, hinders efforts to map current spe- cies distributions and predict future distributions in a changing climate [13, 14], information which is highly relevant to planning management and conservation efforts. For example, habi- tat heterogeneity is thought to drive global patterns of species diversity, but relationships between environmental drivers and biological responses are still uncertain [4]. Further, main- taining well-connected populations, communities, and ecosystems is critical to design effective

networks of marine protected areas (MPAs) [15, 16]. Lacking baseline knowledge and accurate modeling parameters hinders our ability to manage these ecosystems effectively [1, 3] and to meet the global conservation and sustainable development targets that define the next Decade of Ocean Science for Sustainable Development (2021–2030) [17]. Therefore, major questions to be addressed by the research community in support of conservation and sustainable devel- opment goals are to understand the diversity of life in the deep ocean, its distribution, and how populations and habitats are connected [3]. Bathyal and abyssal species diversity are among the highest of any ecosystem worldwide [18, 19]. Supporting this remarkably high biodiversity, the deep seafloor and water column is composed of a complex mosaic of physical, geological, and geochemical features [20, 21], including submarine mountain ranges. Though remote, these ecosystems are not isolated from anthropogenic impacts, which increasingly threaten the health of the deep ocean [20, 22– 24]. Empirical studies have shown that seamounts and submarine ridges frequently harbor reef- building corals [25–27], and these habitats are well known for their high food availability, high proportion of endemic species [28, 29], and exceptional diversity of marine life [30–33]. These heterogeneous features support ecosystem connectivity by facilitating the dispersion of larvae between distant geographic areas and by serving as stepping stones and navigational marks for

the movement of benthic and pelagic species and providing important feeding, resting, and spawning grounds [31–33]. The high variability of community composition within and among seamounts is related to environmental variation in these heterogeneous habitats [34, 35], pro- viding evidence that each seamount is unique. Seamounts are vulnerable to anthropogenic dis- turbance (e.g., trawling) [31, 36] and often do not recover from intensive fishing pressure [37– 39]; therefore, they are a high priority for conservation [27]. Due to the dense aggregations of seamounts that comprise the Salas y Go´mez and Nazca ridges in the southeastern Pacific, this region represents an important reservoir for global 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 2 / 27 provided support in the form of salaries for authors [AMF, WG, JG, EEE, DW], but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. Competing interests: The authors have declared that no competing interests exist.