Trace Elemental Analysis of the Exoskeleton, Leg Muscle, and Gut of Three Hadal Amphipods.

Hadal trenches are the deepest areas worldwide. Amphipods are considered a key factor in hadal ecosystems because of their important impacts on the hadal environment. Amphipods have benthic habits, and therefore, serve as good metal biomonitors. However, little is known about the hadal amphipod metal accumulations. In the present study, Alicella gigantea, Hirondellea gigas, and Scopelocheirus schellenbergi were sampled from the New Britain Trench (8824m, 7.02S 149.16E), Mariana Trench (10,839m, 11.38N 142.42E), and Marceau Trench (6690m, 1.42N 148.74E) in the West Pacific Ocean, respectively. The elemental concentrations of the three hadal amphipods were subsequently investigated. Nine trace elements (V, Cr, Mn, Co, Ni, Se, Mo, Ag, and Cd) of three tissues (exoskeleton, leg muscle, and gut) of the hadal amphipods were detected by using inductively coupled plasma mass spectrometry (ICP-MS) method. The concentrations of Cr, Cd, and Mn were comparably higher among those nine examined elements. The greatest accumulations of the elements Cr, Ag, and V in the exoskeleton and leg muscle were observed in H. gigas, and elements Mn, Co, and Se showed the highest accumulations in the gut in H. gigas among the three hadal amphipods. In addition, comparisons of the leg muscle trace element accumulation between the hadal amphipods and non-abyssal and shallow water decapoda and amphipoda species showed that the hadal amphipods possessed comparably higher concentrations of the trace elements Cd, Co, Mo, Ag, and V. This finding suggested a bottom-up effect of food availability and indicated the effects of human activities within the hadal environments. This study reveals the trace element bio-accumulation of three hadal amphipods, and suggests that deep-sea amphipods are potential indicator species for trace element bioavailability in the deep-sea environment.