Cephalopods Occupy the Ecological Niche of Epipelagic Fish in the Antarctic Polar Frontal Zone

Recent data from research cruises and explorator fishing in the Antarctic Polar Frontal Zone (APFZ) of the Scotia Sea, together with data from dietary studies of Antarctic vertebrate predators, have revealed a large, previously overlooked trophic system in the Southern Ocean (Fig. 1). The upper trophic levels of this open-ocean epipelagic community are exceptional in that they contain no fish species. Fishes are replaced by cephalopods, including the ommastrephid squid, Martialia hyadesi. This squid preys on mesopelagic m.yctophids (lanternfish), which feed largely on copepods. We identify here a geographically distinct, Antarctic, open-ocean food chain which is of importance to air breathing predator species but where Antarctic krill, Euphausia superba, is absent. This system is probably prevalent in areas of higher primary productivity, especially the Scotia Sea and near the peri-Antarctic islands. Squid stocks in the APFZ may have potential for commercial exploitation, but they, and the predators they support, are likely to be sensitive to overfishing. Squid have a short, semelparous lifecycle, so overfishing in a single year can cause a stock to collapse.