Vertical distribution and population structure of the necrophagous amphipod Eurythenes gryllus in the West European Basin

Abstract

During 3 cruises to the West European Basin benthopelagic nekton was captured by use of an acoustically released vertical array of 8 to 10 baited traps. The traps were exposed from 5 to 1000 m above the bottom. Nearly all of the 1692 amphipods trapped in total during 18 deployments were identified as the lysianassid amphipod Eurythenes gryllus Lichtenstein. Most individuals were recovered from traps deployed 15 m above the sea floor. Above 30 m, catch rates decreased significantly. However, the vertical distribution differed by age and sex: indeterminate juveniles and adult females were only trapped up to 50 m above the bottom Catch rates of juvenile males and females decreased with increasing distance from the bottom, whereas adult males showed a bimodal distribution with maxima at 15 and at 300 m above the sea floor. Males were prevalent in all but 2 deployments. The characteristic vertical distribution and the population structure at the depths sampled imply an ontogenetic vertical migration of E. gryllus females release their brood near the bottom. The youngest stages stay within a few meters above the sea floor, whereas older stages, especially adult males, migrate into higher water layers.

Aggregations of Arctic deep-sea scavengers at large food falls: temporal distribution, consumption rates and population structure

“…An equal sex ratio confirms the expectations of a continuously breeding population. This sex ratio coincides with that found in the North Atlantic Ocean (Charmasson & Calmet 1987, Christiansen et al 1990, but is markedly different from that found in the north-eastern Pacific (Baldwin & Smith 1987), in the central North Pacific (Ingram & Hessler 1987) and in the south-eastern Pacific at a depth of 7800 m (Thurston et al 2002), where females dominate. In our collections only Stn V showed preponderance of females.…”

“…The ontogenetic migration postulated for Eurythenes gryllus (Christiansen et al 1990) may be complex. With increasing size, immature E. gryllus move up into the water column, adopting an abysso-pelagic rather than a benthic lifestyle (Ingram & Hessler 1983, Smith & Baldwin 1984, Charmasson & Calmet 1987, Christiansen et al 1990).…”

“…Comparing the bait-attending fauna of different areas within the North Atlantic, Mediterranean Sea and Pacific, the scavenger communities have been found to differ in terms of species composition and the numbers of individuals attracted (Priede et al 1990, Christiansen 1996, Priede & Merrett 1998, Janssen et al 2000, Legezynska et al 2000. In the deep sea, scavenging communities are dominated mostly by lysianassoid amphipods and large fish, both highly efficient necrophages (Christiansen et al 1990, Priede et al 1991. One of the most important scavenging amphipods attracted to food falls in the deep sea is the cosmopolitan lysianassoid Eurythenes gryllus (Lichtenstein, 1822), which seems to play an important role in biological processes in deep water (Charmasson & Calmet 1990).…”

Extreme food webs: Foraging strategies and diets of scavenging amphipods from the ocean’s deepest 5 kilometers

“…3) as evidence that juveniles rely on detrivory to a greater degree than adults. Similar ontogenetic shifts from mainly detrivory to carnivory have been noted in other lysianassoid species based on gut content analyses (Christiansen and Diel-Christiansen 1993), including Hirondellea gigas from the Philippine Trench (Hessler et al 1978). Adults have the capacity to withstand long periods between meals because of their lipids stockpiled from previous nutritious meals, but recently hatched individuals may not have this metabolic advantage (Ingram and Hessler 1987).…”

“…First, the deep sea is notoriously difficult to observe. Second, the majority of deep-sea scavenging amphipods are collected with baited traps (e.g., Shulenberger and Hessler 1974;Christiansen et al 1990;De Broyer et al 2004); amphipods with access to bait in traps almost always satiate themselves with it. Collection methods designed to prohibit deep-sea amphipods from consuming bait do exist, but they often collect amphipods with empty guts or guts containing amorphous material (Smith and Baldwin 1984;Sainte-Marie 1992).…”