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

Johanna N. J. Weston,Alan J. Jamieson

doi:10.3389/fmars.2022.824640

Johanna N. J. Weston, Alan J. Jamieson

Open Access

https://doi.org/10.3389/fmars.2022.824640

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Abstract

The hadal zone (depths &gt; 6,000 m) comprises isolated features that host high degrees of endemism, with species inhabiting only a single feature or a group of adjacent features. The amphipod, Hirondellea dubia is an abundant scavenger at the hadal depths of the Kermadec, Tonga, and New Hebrides trenches in the Southwest Pacific Ocean, particularly at depths &gt; 9,500 m. However, several records have hinted that H. dubia may not be restricted to the Southwest Pacific nor be exclusively hadal. Here, we present new records of H. dubia recovered by baited landers deployed to five hadal trenches during three expeditions and assess the geographic and vertical distribution of this species. To rule out the possibility of cryptic diversity, morphological taxonomy was paired with two mitochondrial markers (16S and COI) to test for species boundaries among the new and published molecular data using four delineation approaches (ABGD, CD-HIT, GMYC, and bPTP). We found H. dubia to be a single species and not restricted to the Southwest Pacific or hadal depths. This species’ geographic range extends from the Southwest Pacific to the Mariana Trench (Northwest Pacific), the Clarion-Clipperton Zone (Central Pacific), the South Sandwich Trench (Southern), and the Puerto Rico Trench (North Atlantic). This amphipod’s vertical range spans over half of the ocean’s total depth, between 4,700 and 10,817 m. This study presents an extraordinary geographic range extension to a species long considered endemic to a cluster of three Southwest Pacific trenches and shows a pan-oceanic distribution across extremely isolated hadal features.

Highlights

The deepest oceanic zone, the hadal zone, comprises subduction trenches, fracture zones/trench faults, and troughs that extend from depths of 6,000 to ∼11,000 m (Jamieson et al, 2010)
Given the widespread phenomenon of cryptic diversity in the deep sea, we aimed to rule out the possibility that cryptic species that are morphologically indistinguishable from H. dubia exist outside the Southwest Pacific Ocean
Hirondellea dubia was recovered during 14 baited lander deployments to the Mariana Trench (5,641–8,942 m), four to the San Cristobal Trench (6,515–8,407 m), two to the Santa Cruz Trench (7,431–8,428 m), seven to the Tonga Trench (6,793– 10,817 m), and four to the Puerto Rico Trench (6,954–8,378 m) (Table 1 and Figures 1, 2), which adds to the 45 historical records from the Kermadec, Tonga, New Hebrides, Mariana, and South Sandwich trenches and the Clarion-Clipperton Zone (Supplementary Material 1)

Summary

Introduction

The deepest oceanic zone, the hadal zone, comprises subduction trenches, fracture zones/trench faults, and troughs that extend from depths of 6,000 to ∼11,000 m (Jamieson et al, 2010). These hadal features are often separated by thousands of kilometers and defined by high hydrostatic pressure, near-freezing temperatures, food scarcity, and geologic instability (Jamieson et al, 2010; Stewart and Jamieson, 2018). As isolated habitats with strong environmental selection pressures, hadal features are thought to host a high number of endemic species, whereby a species inhabits a single trench or a group of adjacent trenches 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)

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