Eurythenes atacamensis sp. nov. (Crustacea: Amphipoda) exhibits ontogenetic vertical stratification across abyssal and hadal depths in the Atacama Trench, eastern South Pacific Ocean

Johanna N J Weston,William D K Reid,Liliana Espinosa-Leal,Carolina E González,Rubén Escribano,Pamela Hidalgo,Alan J Jamieson,Eva C D Stewart,Marcelo E Oliva,Osvaldo Ulloa,Ronnie N Glud,Thomas D Linley,Frank Wenzhöfer,Jennifer A Wainwright

doi:10.1007/s12526-021-01182-z

Abstract

Eurythenes S.I. Smith in Scudder, 1882 (Crustacea: Amphipoda) are prevalent scavengers of the benthopelagic community from bathyal to hadal depths. While a well-studied genus, molecular systematic studies have uncovered cryptic speciation and multiple undescribed lineages. Here, we apply an integrative taxonomic approach and describe the tenth species, Eurythenes atacamensis sp. nov., based on specimens from the 2018 Atacamex and RV Sonne SO261 Expeditions to the southern sector of the Peru-Chile Trench, the Atacama Trench (24–⁠21°S). Eurythenes atacamensis sp. nov. is a large species, max. observed length 83.2 mm, possesses diagnostic features, including a short gnathopod 1 palm and a chelate gnathopod 2 palm, and a distinct genetic lineage based on a 16S rRNA and COI phylogeny. This species is a dominant bait-attending fauna with an extensive bathymetric range, spanning from 4974 to 8081 m. The RV Sonne SO261 specimens were recovered along a 10-station transect from abyssal to hadal depths and further examined for demographic and bathymetric-related patterns. Ontogenetic vertical stratification was evident across the trench axis, with only juveniles present at abyssal depths (4974–6025 m). Total length-depth analysis revealed that the size of females was unrelated to depth, whereas juveniles followed a sigmoidal relationship with a step-up in size at depths >7200 m. Thus, these bathymetric trends suggest that juveniles and females employ differing ecological strategies in subduction trench environments. This study highlights that even dominant and ecologically important species are still being discovered within the abyssal and hadal environments. Continued systematic expeditions will lead to an improved understanding of the eco-evolutionary drivers of speciation in the world’s largest ecosystem.

Highlights

The deep ocean is the Earth’s largest ecosystem, extending from the edge of the continental shelf (200 m) to the bottom of the subduction trenches (~11,000 m; Thiel 2003, Stewart and Jamieson 2019), covering approximately 1.4 × 109 km3 (Charette and Smith 2010)
The relationship between total length and coxa 4 (t = 132.281, p < 2e-16, r2 adjusted = 0.9694) followed a linear relationship (Fig. 9b): This study described a scavenging amphipod endemic to the Peru-Chile Trench, Eurythenes atacamensis sp. nov., by applying an integrative taxonomic approach
Analysis of the Atacamex and RV Sonne SO261 Expeditions specimens expanded the bathymetric range of E. atacamensis sp. nov. from

Summary

Introduction

The deep ocean is the Earth’s largest ecosystem, extending from the edge of the continental shelf (200 m) to the bottom of the subduction trenches (~11,000 m; Thiel 2003, Stewart and Jamieson 2019), covering approximately 1.4 × 109 km (Charette and Smith 2010). Smith in Scudder, 1882 are prevalent members of the deep ocean, benthopelagic community (Stoddart and Lowry 2004; Havermans 2016) This genus inhabits every ocean across an extensive bathymetric range—observed in polar waters (Ainley et al 1986; Bowman and Manning 1972), on the abyssal plains (Barnard 1961; Brandt et al 2012; Havermans 2016), and at hadal depths (Thurston et al 2002; Fujii et al 2013; Eustace et al 2016; Weston et al 2020a, 2021). At least five distinct genetic lineages are awaiting formal description (France and Kocher 1996; Havermans et al 2013; Eustace et al 2016; Horton et al 2020) and more are likely to be discovered via expansion of sampling programs (Havermans 2016)

Methods

Results

Conclusion