According to Encyclopedia.com, zooplankton are the prey of the majority of ocean creatures, from the smallest fishes to the largest whales. Zooplankton are considered the second step of the oceanic food web, which starts with phytoplankton.
Zooplankton is often used as food for fresh and saltwater aquarium fish and invertebrates. It is mainly made of cultured daphnia. It is preferred by many fish owners because its high moisture content accurately replicates the diets of fish in the wild, as opposed to dry food, which does not. Zooplankton contains a significant amount of astaxanthin, which enhances the color of fish.
Because zooplankton are open ocean-dwelling creatures, their offspring are moved by ocean currents, ensuring their survival through distribution and high genetic diversity. Consistent distribution means that only a small percentage of zooplankton are affected by natural occurrences such as storms and extreme temperatures.
Zooplankton are not able to obtain necessary nutrition through ocean nutrients or sunlight. Instead, they consume other organisms, mainly phytoplankton. They are carnivorous, omnivorous and detrivorous, meaning that they are able to eat other organisms, plant matter and decay from dead marine organisms or algae. Zooplankton rise to the ocean surface during the day, and descend at night.