Bait-attending amphipods of the Tonga Trench and depth-stratified population structure in the scavenging amphipod Hirondellea dubia Dahl, 1959

Abstract

BackgroundThe hadal zone encompasses the deepest parts of the world’s ocean trenches from depths of ∼6,000–11,000 m. The communities observed at these depths are dominated by scavenging amphipods that rapidly intercept and consume carrion as it falls to the deepest parts of the trenches. New samples collected in the Tonga Trench provide an opportunity to compare the amphipod assemblages and the population structure of a dominant species, Hirondellea dubia Dahl, 1959, between trenches and with earlier data presented for the Tonga Trench, and other trenches in the South Pacific.MethodsOver 3,600 individual scavenging amphipods across 10 species were collected in seven baited traps at two sites; in the Horizon Deep site, the deepest part of the Tonga Trench (10,800 m) and a site directly up-slope at the trench edge (6,250 m). The composition of the bait-attending amphipods is described and a morphometric analysis of H. dubia examines the bathymetric distribution of the different life stages encountered.ResultsThe amphipod assemblage was more diverse than previously reported, seven species were recorded for the first time from the Tonga Trench. The species diversity was highest at the shallower depth, with H. dubia the only species captured at the deepest site. At the same time, the abundance of amphipods collected at 10,800 m was around sevenfold higher than at the shallower site. H. dubia showed clear ontogenetic vertical structuring, with juveniles dominant at the shallow site and adults dominant at the deep site. The amphipods of the deeper site were always larger at comparable life stage.DiscussionThe numbers of species encountered in the Tonga Trench is less than reported from the New Hebrides and Kermadec trenches, and six species encountered are shared across trenches. These findings support the previous suggestion that the fauna of the New Hebrides, Tonga and Kermadec Trenches may represent a single biogeographic province. The ontogenetic shift in H. dubia between the two Tonga Trench sites supports the hypothesis of interspecific competition at the shallower bathymetric range of the species, and the presence of competitive physiological advantages that allow the adults at the trench axis to exploit the more labile organic material that reaches the bottom of the trench.

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

“…nov. is not novel to Eurythenes or the Peru-Chile Trench (Eustace et al 2016). Similar instances have been documented in other abundant hadal scavenging amphipods, including Bathycallisoma schellenbergi (Birstein and Vinogradov, 1958) from the Kermadec and New Hebrides trenches (Lacey et al 2018), Hirondellea dubia Dahl, 1959 from the Tonga and Kermadec trenches (Blankenship et al 2006;Lacey et al 2018;Wilson et al 2018), and Hirondellea gigas (Birstein & Vinogradov, 1955) from the Izu-Bonin Trench (Eustace et al 2013). This demographic trend was consistent with the SO209 expedition, indicating that the ontogenetic vertical stratification pattern is constrained by depth in the Peru-Chile Trench and not confounded by latitude.…”

Scientific and technological progress in the microbial exploration of the hadal zone

“…Amongst the most abundant animals living in hadal habitats are amphipods of the superfamily Lysianassoidea. The discovery of this animal can be traced to a study in 1959 in which the scavenging amphipod Hirondellea dubia was described (Dahl 1959;Wilson et al 2018). Amphipods that inhabit the hadal zone play key roles in other deep-ocean ecosystems and the endemism of these species renders them good models for the study of feeding behaviors, evolutionary processes and the restricted distribution of animals in hadal trenches.…”

The Multi-Ocean Distribution of the Hadal Amphipod, Hirondellea dubiaDahl, 1959 (Crustacea, Amphipoda)

“…Historical records for H. dubia are compiled in Supplementary Material 1 (Dahl, 1959;Jamieson et al, 2011Jamieson et al, , 2021bRitchie et al, 2015;Lacey et al, 2016;Leduc and Wilson, 2016;Wilson et al, 2018;Bribiesca-Contreras et al, 2021). Absence records were inferred, with an absence defined as an instance when a published species list for a hadal feature included Lysianassoidea species but not H. dubia (Dahl, 1959;Hessler et al, 1978;Belyaev, 1989;France, 1993;Jamieson, 2015;Lacey et al, 2016;Jażdżewska and Mamos, 2019;Weston et al, 2021b).…”

“…Hirondellea dubia Dahl, 1959, the fifth hadal hirondellid, is a dominant scavenger at the Kermadec, Tonga, and New Hebrides trenches in the Southwest Pacific Ocean. At depths greater than 8,000 m, H. dubia is abundant with single traps having recovered more than 12,000 individuals (Blankenship et al, 2006;Lacey et al, 2016;Wilson et al, 2018).…”

“…Hirondellea dubia is considered restricted to hadal depths (Jamieson et al, 2011;Wilson et al, 2018). However, several records hint that H. dubia may not be entirely hadal, nor be endemic to the Southwest Pacific Ocean.…”