Scavenging amphipods from the Wallaby-Zenith Fracture Zone: Extending the hadal paradigm beyond subduction trenches

Abstract

Our understanding of the ecology of the hadal zone (> 6000 m depth) is based solely on subduction trenches, leaving other geomorphological features, such as fracture zones, troughs, and basins, understudied. To address this knowledge gap, the Wallaby-Zenith Fracture Zone, Indian Ocean (WZFZ; ~ 22°S, 102°E; maximum depth 6625 m measured during Expedition SO258) was studied using free-fall baited landers. We assessed the amphipod distribution and community assemblage of this non-subduction hadal feature and compared it to subduction hadal features. Eleven species were identified across the abyssal-hadal transition zone using a paired morphological and DNA barcoding approach. The community composition was found to change gradually from abyssal to hadal depths, which contrasts with the ecotone shift characteristic of subduction trenches. A large population of Bathycallisoma schellenbergi (Birstein & Vinogradov, 1958), a quintessential hadal amphipod, was present at the flat bottom of the WZFZ. Further, an mtDNA phylogeny resolved a degree of phylogeographic structure between the B. schellenbergi WZFZ population and four previously sampled Pacific Ocean subduction trench populations, indicating these features are not interconnected through ongoing gene flow. Combined, these data indicate that some amphipods have far broader distributions than previously understood, with some species present in both hadal subduction trenches and non-subduction fracture zones and basins interspersed across the abyssal plains. This initial exploration highlights that whilst non-subduction features are an overlooked minor fraction of the total hadal area, they are essential to our understanding of the ecological and evolutionary dynamics across the hadal zone.

Biogeography, diversity and environmental relationships of shelf and deep-sea benthic Amphipoda around Iceland

“…With a saddle depth averaging 600 m in the Strait of Denmark and 480 m between Iceland and the Faroe Islands and a maximum depth of c. 840 m, the depth increases towards the abyssal basins on each side of the ridge exceeding 3,000 m. Depth, or rather ecological and environmental variables that change with depth, such as hydrostatic pressure, temperature, food availability, or competition, have been demonstrated to have a large impact on species distributions ( Rex & Etter, 2010 ; Brown & Thatje, 2011 ; Tittensor et al, 2011 ). In contrast, there are several examples of amphipod species, mostly within the more motile scavenger and predator guilds, with large depth distributions and thus at least the intrinsic capability to overcome topographical barriers ( Lacey et al, 2018 ; Lörz, Jażdżewska & Brandt, 2018 ; Weston et al, 2021 ).…”

Pandora’s Box in the Deep Sea –Intraspecific Diversity Patterns and Distribution of Two Congeneric Scavenging Amphipods

“…400 bp) sequences were analyzed (Table 4). It derives from the higher concentration of variable sites (4.5%) in the shorter fragment of 16S amplified by former authors studying P. tenuipes (Ritchie et al, 2015;Weston et al, 2021).…”

“…In the present study, the datasets of two mitochondrial (cytochrome c oxidase subunit I [COI] and 16S rRNA) as well as one nuclear (28S rRNA) marker were analyzed. The material was obtained from published articles available by March 2021 (Ritchie et al, 2015;Jażdżewska and Mamos, 2019;Iguchi et al, 2020;Mohrbeck et al, 2021;Weston et al, 2021) supplemented by newly produced sequences. Figure 1 summarizes all datasets that have been used in this study, and information on new material collection, DNA extraction, amplification and sequencing is presented below.…”

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

“…Eurythenes magellanicus is known from the Milne-Edwards Trench (Eustace et al 2016), and this study expands its range southward into the Atacama Trench. Further, this is the first account of E. maldoror in the Peru-Chile Trench, expanding its distribution to the eastern South Pacific Ocean (Havermans 2016;Weston et al 2021). Surprisingly, Eurythenes sp.…”

“…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 2020aWeston et al , 2021. They have been the focus of ecological and physiological studies, including metabolism (Premke and Graeve 2009), feeding strategies (Hargrave 1985;Premke et al 2006;Blankenship and Levin 2007), population demographics (Ingram and Hessler 1987;Christiansen et al 1990;Thurston et al 2002;Blankenship et al 2006), and biomonitoring (Reid et al 2018).…”