As well as being established as providing a food source for krill, there is also evidence that some species of krill are behaviourally adapted to utilize the sea ice as a shelter from threats. This can manifest in two forms, the first being where krill larvae will inhabit the ice substrate until they undergone metamorphosis and become recruited into swarms as free-swimming zooplanktonic organisms, the second being where adult individuals will retreat into crevices in the ice after detecting a threat.
There is significant evidence for the latter, at least. For example, O’Brien (1988) found from observations of populations of Antarctic Krill (Euphausia superba) under sea ice that individuals would seek out crevices in the ice above after perceiving a threat, showing a clear behavioral adaption to utilize the sea ice as a shelter. Taki et al (2005) also found that Euphausia superba appeared in higher densities at shallower depths in the Scotia Sea during the Summer and Autumn months. While feeding on increased abundances of algae was likely a factor, the use of the ice as a shelter from predators for spawning was also hypothesized.
As for sea ice’s value as a nursery for krill larvae, Meyer et al (2009) found that whilst the larvae of krill are perfectly capable of existing unassociated with sea ice, samples of krill larvae collected from beneath the ice were in a better condition than those that were not, suggesting that sea ice’ value as a shelter for larvae is also connected to it’s value as a food source.
This evidence shows that whilst sea ice is primarily a food source to krill, it also serves as a valuable shelter from predators as well as a safe area for krill larvae to inhabit until they are recruited into swarms.