Biochemical tracers in spiny icefish (Chaenodraco wilsoni) as indicators of variability in the diet of Antarctic krill (Euphausia superba) in a highly dynamic environment

Abstract

Spiny icefish (Chaenodraco wilsoni), a common high-Antarctic ichthyofauna icefish, exhibits variable feeding habits in regions around the Southern Ocean. In the Bransfield Strait (BS), C. wilsoni has received considerable attention as it preys predominantly on krill. Antarctic krill (Euphausia superba), the keystone species in the Southern Ocean, has a versatile feeding strategy, particularly in a highly dynamic environment. The central basin of the BS is a highly dynamic environment, providing an ideal place to explore the application of biochemical tracers in a specialist predator to reveal the diet of its prey. In this study, fatty acid and stable isotopic data demonstrated that the trophic niche of C. wilsoni expanded from late austral summer to early fall, which was primarily reflected in variability in the food availability of krill, i.e., herbivorous features were weakened, benthic-feeding features were strengthened, and omnivorous features showed no significant difference. A highly dynamic hydrography, coupled with an unusual diatom bloom in the BS during 2016, may have resulted in krill's prolonged filtering on diatoms in the water column, which was further reflected in the difference in biochemical tracers of C. wilsoni from late austral summer to early fall. The study demonstrated that biochemical tracers can be used to reflect the variability in the diet of prey, particularly in a highly dynamic environment.