Early krill life stages show a small-scale diel vertical migration

The divers discovered huge swarms of krill larvae and juvenile krill closely associated with the ice. Foto: Ulrich Freier, Alfred-Wegener-InstitutPolarTime members from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) together with international colleagues could analyse the distribution and behaviour of larval and juvenile krill beneath wintery Antarctic sea ice for the first time. Importantly, the expedition scientists discovered huge swarms of krill larvae and juvenile krill closely associated with the ice. In places the density reached ten thousand animals per square metre. “The distribution is very patchy. They seem to prefer the caves and terraces of the over-rafted areas, which are sheltered regions where the larvae can feed,” says chief scientist Dr. Bettina Meyer. During the day the scientists filmed the krill larvae directly feeding on the ice, but the picture was different at night, when the krill seemed to abandon the ice surface and descend in the upper 20 metres into the water column, perhaps to hide from predators, which come up to the surface at night. “The first time ever we were able to observe this daily migration of young krill stages. It happened at precisely the same time each evening”, explains Dr. Mathias Teschke from the Alfred Wegener Institute. “Their disperse distribution in the water column might prevent them from predation”, presumes chronobiologist Teschke. “This suggests that krill larvae may have an internal clock,” says Teschke, who will analyse the DNA of frozen krill larvae at the AWI to investigate this possibility. Read the full press release here.