Zooplankton, the microscopic invertebrates consisting of small animals and the immature stages of larger animals, move up and down the water column in a type of migration called diel vertical migration.
Whether they reside in the ocean or in freshwater habitats, these plankton travel to safer depths in the morning and rise closer to the water’s surface as the sun sets.
The purpose of this unusual daily routine? Zooplankton’s favorite snacks live up there. Unfortunately, this is also the most dangerous place for zooplankton—the closer they are to sunlight, the more visible they are to predators.
In order to eat without being eaten, they must wait until dark to make the upward trek. It’s a delicate dance between searching for prey on the ocean’s surface and avoiding becoming someone’s next meal.
