Thousands of amphipods can reduce fish carcasses to bones, but these carrion experts are unexpectedly scarce in the area of the recently collapsed Larsen B ice shelf, where the Polarstern Expedition is currently conducting research

Baited traps consistently used to provide good numbers of amphipods throughout the expedition, whether designed to catch them or targeting fish. “Traps are secured on a metal frame, equipped with a weight and buoys designed to cope with the high pressure at the sea floor, and then dropped to the bottom. After 48 hours, the vessel returns, triggering the traps' release from the weights via an acoustic signal sent from a transmitter. Within 15 to 30 minutes, depending on the water depth, the traps float to the surface and are recovered,” explains Henri Robert.

Cédric and Henri, the two crustacean experts from the Royal Belgian Institute for Natural Sciences, Belgium were quite successful with catches between South Shetland and Joinville Islands. Their samples, obtained from various depths, typically provided several thousands of specimens belonging to a dozen species in total, usually accompanied by a fair number of scavenging isopods. The amphipods included a catch of about 100 specimens of Eurythenes gryllus, a huge size (at least huge for its group) cosmopolite deep-sea species, with a length of 10 cm and a bright orange colour (see photograph), side by side with a handful of another giant, a crimson and long-legged Eusirus, presumed to be still undescribed.

But using similar methods in the ice-free Larsen B area yielded another result: In agreement with the general scarcity of amphipods in this region, regardless of their diet, scavenger amphipods proved to be very scarce in two of the three stations, and reduced almost exclusively to two species. “The first one is a fast swimming and well-known circum-Antarctic species, already trapped by other researchers under the Ross Ice Shelf. It was numerous in all catches, and represented the majority of specimens caught in the two shallow stations. But another one, the most abundant in the deepest (800 m) sample, seems again to be new to science…” adds Cédric d’Udekem.

Photograph: Cédric d’Udekem
Text: Gauthier Chapelle & Cédric d’Udekem