Diel vertical migration

Diel vertical migration means that some creatures in the ocean like to swim up and down in the water during the day and night.

During the day, they are at the bottom of the ocean where it's dark and they go to sleep. But at night, they like to swim up to the top of the ocean where there is light from the moon and stars.

They do this because they are looking for food. During the day, there are some small animals that live at the bottom of the ocean that they like to eat. But at night, these small animals swim up to the top of the ocean to eat small plants that grow there.

So, our creatures swim up to the top of the ocean too, to eat these small animals. Then, when they are full and the sun starts to rise, they swim back down to the bottom to sleep again.

Some creatures that do this are krill, copepods, and some small fish. It's important for them to do this so they can find enough food to survive in the ocean.