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

Abstract

The Salas y Gómez and Nazca ridges are underwater mountain chains that stretch across 2,900 km in the southeastern Pacific and are recognized for their high biodiversity value and unique ecological characteristics. Explorations of deep-water ecosystems have been limited in this region, and elsewhere globally. To characterize community composition of mesophotic and deep-sea demersal fauna at seamounts in the region, we conducted expeditions to Rapa Nui (RN) and Salas y Gómez (SyG) islands in 2011 and Desventuradas Islands in 2013. Remote autonomous baited-cameras were used to conduct stationary video surveys between 150–1,850 m at RN/SyG (N = 20) and 75–2,363 m at Desventuradas (N = 27). Individual organisms were identified to the lowest possible taxonomic level and relative abundance was quantified with the maximum number of individuals per frame. Deployments were attributed with associated environmental variables (temperature, salinity, dissolved oxygen, nitrate, silicate, phosphate, chlorophyll-a, seamount age, and bathymetric position index [BPI]). We identified 55 unique invertebrate taxa and 66 unique fish taxa. Faunal community structure was highly dissimilar between and within subregions both for invertebrate (p < 0.001) and fish taxa (p = 0.022). For fishes, dogfish sharks (Squalidae) accounted for the greatest dissimilarity between subregions (18.27%), with mean abundances of 2.26 ± 2.49 at Desventuradas, an order of magnitude greater than at RN/SyG (0.21 ± 0.54). Depth, seamount age, broad-scale BPI, and nitrate explained most of the variation in both invertebrate (R2 = 0.475) and fish (R2 = 0.419) assemblages. Slightly more than half the deployments at Desventuradas (N = 14) recorded vulnerable marine ecosystem taxa such as corals and sponges. Our study supports mounting evidence that the Salas y Gómez and Nazca ridges are areas of high biodiversity and high conservation value. While Chile and Peru have recently established or proposed marine protected areas in this region, the majority of these ridges lie outside of national jurisdictions and are under threat from overfishing, plastic pollution, climate change, and potential deep-sea mining. Given its intrinsic value, this region should be comprehensively protected using the best available conservation measures to ensure that the Salas y Gómez and Nazca ridges remain a globally unique biodiversity hotspot.

Benthic Assemblage Composition of South Atlantic Seamounts

“…Ascension and St. Helena are connected to other ridge systems (MAR and Guinea seamount chain, respectively) and therefore similar effects may be felt should MPAs/fisheries closures be designated in the northern southeast Atlantic. Investment in furthering our understanding on the health and connectivity of VME populations across EEZs and ABNJ in South Atlantic will facilitate incorporation of these principles into broadscale sustainable management, and ultimately make management plans more robust (sensu Friedlander et al, 2021). It will also allow insight into the conservation significance of the existing large MPAs in the South Atlantic and allow for assessment of the ecological coherence of the South Atlantic MPA network as a whole (Foster et al, 2017;Ross et al, 2017).…”

The Habitat Persistence Hypothesis: a new perspective on the distribution of coral-reef organisms

“…The bathymetry of Rapa Nui, Pitcairn and Rapa is sloped, so shallow-reef habitats are more likely to persist across glacial cycles than shallowreef habitats within the Tuamotu Archipelago. Several recent studies have focused on marine biodiversity and associated biogeographic implications at Rapa Nui, including species inhabiting MCEs (Easton et al 2017, Delrieu-Trottin et al 2019, Hoeksema et al 2019, Mecho et al 2019, Friedlander et al 2021, Liggens et al 2021, Mah 2021). The results of these studies reveal patterns that are consistent (or, at least, not inconsistent) with the predictions of the HPH.…”

First Ecological Characterization of Whip Black Coral Assemblages (Hexacorallia: Antipatharia) in the Easter Island Ecoregion, Southeastern Pacific

“…Further studies at these depths are needed to understand their true distribution. Nevertheless, this first characterization presents a fundamental basic knowledge of the whip corals and environment in this relatively poorly studied region of the Pacific Ocean, with high conservation value (Friedlander et al, 2021;Georgian et al, 2021;Wagner et al, 2021).…”

“…Furthermore, recently developed habitat-suitability models indicate that these high seas seamounts provide highly suitable habitat for various deep-sea corals and sponges (Georgian et al, 2021). Given the slow recovery rates of these taxa, they should be proactively protected from destructive practices such as bottom trawling and seabed mining (Rogers, 2018;Friedlander et al, 2021;Wagner et al, 2021).…”