Zooplankton are small animals that drift in the water column. Many zooplankton species exhibit diel vertical migration (DVM), which is a daily movement from deep water to the surface at night and back to deep water during the day. This migration is thought to be regulated by the zooplankton's circadian clock, which is an internal clock that regulates daily rhythms in behavior, physiology, and metabolism.

DVM is thought to be a way for zooplankton to avoid predation and to find food. During the day, zooplankton are more vulnerable to predation by fish and other predators that live in the surface waters. By moving to deeper water during the day, zooplankton can reduce their risk of being eaten. Many zooplankton also feed on phytoplankton, which are microscopic plants that live in the surface waters. By moving to the surface at night, zooplankton can access a greater abundance of food. In conclusion, The genetic clocks in zooplankton species regulate vertical migration.