As far down as it goes - Critter of the Week - Scopelocheirus schellenbergi

With the Kermadec Trench Expedition coming to a close (1), we thought we would stay on the theme of trenches for a little longer and present to you Scopelocheirus schellenbergi (we dare you to say that name three times in in quick succession). It is one of only a handful species of truly hadal amphipods that make depths of >6,000 m their home (it’s the equivalent of living on the peak of Mt Everest, which is ‘only’ 8,848 m high). Scopelocheirus schellenbergi have been recorded from deep-sea trenches and various regions around the globe (e.g. the north and south Pacific but also in the Puerto Rico Trench and the Orkney Trench in the south Atlantic). Both their shallowest (5,155 m) and deepest (10,437 m) record are from the Tonga Trench and it is still  mindboggling for most of us to imagine such active life down there.

These animals are voracious scavengers that can reduce a fish carcass in the matter of just a few hours (2, and make sure to watch this lime-lapse video). They eat just about anything that arrives from the waters above and it is thought that they thereby fill an important ecological function by recycling nutrients back into the environment.

You may be interested in some fascinating studies that look at vertical zonation patterns of amphipods in the trenches of the southwest Pacific region (3). The authors present the population structure of S. schellenbergi (and 3 other amphipods) from the Tonga Trench, and conclude that younger animals live in the shallower limits of their depth range while the older ones progressively migrate deeper. Another paper (4) concludes that there is not a single ubiquitous hadal food web and that species can display a range of foraging modes, therefore, making the most of the little food that is around.

References:
1) http://web.whoi.edu/hades/taking-stock/
2) http://web.whoi.edu/hades/amphipods-all-the-way-down/
3) Blankenship LE, Yayanos AA, Cadien DB, Levin LA. 2006. Vertical zonation patterns of scavenging amphipods from the Hadal zone of the Tonga and Kermadec Trenches. Deep-Sea Research Part I-Oceanographic Research Papers 53(1):48-61.
4) Blankenship & Levin (2007) Extreme food webs: Foraging strategies and diets of scavenging amphipods from the ocean’s deepest 5 kilometers http://www.www.aslo.net/lo/toc/vol_52/issue_4/1685.pdf

Left: still image from 8500 m in Kermadec Trench, bait fish being decimated by hadal amphipods, most likely Hirondellea dubia and Scopelocheirus schellenbergi, which both occur in high abundances at this depth. Right: Scopelocheirus schellenbergi collected from 8500 m. Credit: University of Aberdeen, HADEEP.