stylistic:tone, linguistic:paraphrasing
Vertical migration

Krill typically follow a diurnal vertical migration. It has been assumed that they spend the day at greater depths and rise during the night toward the surface. The deeper they go, the more they reduce their activity, apparently to reduce encounters with predators and to conserve energy. Swimming activity in krill varies with stomach fullness. Sated animals that had been feeding at the surface swim less actively and therefore sink below the mixed layer. As they sink they produce feces which employs a role in the Antarctic carbon cycle. Krill with empty stomachs swim more actively and thus head towards the surface.

Vertical migration may be a 2–3 times daily occurrence. Some species (e.g., Euphausia superba, E. pacifica, E. hanseni, Pseudeuphausia latifrons, and Thysanoessa spinifera) form surface swarms during the day for feeding and reproductive purposes even though such behaviour is dangerous because it makes them extremely vulnerable to predators.

Experimental studies using Artemia salina as a model suggest that the vertical migrations of krill several hundreds of metres, in groups tens of metres deep, could collectively create enough downward jets of water to have a significant effect on ocean mixing.

Dense swarms can elicit a feeding frenzy among fish, birds and mammal predators, especially near the surface. When disturbed, a swarm scatters, and some individuals have even been observed to moult instantly, leaving the exuvia behind as a decoy.

Krill normally swim at a pace of 5–10 cm/s (2–3 body lengths per second), using their swimmerets for propulsion. Their larger migrations are subject to ocean currents. When in danger, they show an escape reaction called lobstering —flicking their caudal structures, the telson and the uropods, they move backwards through the water relatively quickly, achieving speeds in the range of 10 to 27 body lengths per second, which for large krill such as E. superba means around 0.8 m/s (3 ft/s). Their swimming performance has led many researchers to classify adult krill as micro-nektonic life-forms, i.e., small animals capable of individual motion against (weak) currents. Larval forms of krill are generally considered zooplankton.