Drifting animals, copepods, krill, jellyfish, larval fish, grazing, phytoplankton, marine food webs, diel vertical migration, plankton nets, biomass monitoring, fisheries, climate indicators, marine snow, and ecosystem change
Zooplankton
Zooplankton are drifting animals and animal-like organisms that feed in aquatic food webs and transfer energy from phytoplankton to fish and larger predators.
What zooplankton are
Zooplankton are animals and animal-like organisms that drift with water currents. Some are microscopic; others, such as jellyfish, are visible without a microscope. They are not one species or one group, but a lifestyle shared by many organisms.
Who counts as zooplankton
Copepods, krill, larval crabs, fish eggs, fish larvae, tiny snails, arrow worms, jellyfish, and many single-celled predators can all be zooplankton. Some spend their whole lives drifting. Others are plankton only as eggs or larvae before becoming swimmers or bottom-dwellers.
What they eat
Many zooplankton graze on phytoplankton. Others eat bacteria, marine snow, smaller zooplankton, or mixed particles. Feeding styles vary widely: some filter water, some grasp prey, and some pulse through the water like tiny predators in slow motion.
A bridge in food webs
Zooplankton turn tiny cells into food that larger animals can use. Young fish, forage fish, whales, seabirds, and many invertebrates depend on them directly or indirectly. When zooplankton size or timing changes, fish survival can change too.
Vertical migration
One of the largest daily migrations on Earth is mostly invisible: zooplankton moving upward at night and downward during the day. The movement helps them feed near the surface while reducing the risk of being seen by predators in daylight.
Carbon transport
Zooplankton affect the carbon cycle by grazing, respiring, producing fecal pellets, and moving carbon-rich material downward. Their waste and dead bodies can become marine snow, and migrating zooplankton carry carbon into deeper water.
Monitoring ecosystems
Scientists sample zooplankton with nets, imaging systems, acoustics, microscopes, DNA tools, and long-term surveys. Because zooplankton respond to temperature, ice, currents, and food supply, they can act as early indicators of ecosystem change.
Why it matters
Zooplankton are small enough to fit in a teaspoon of seawater and important enough to influence fisheries. They are the living middle of many aquatic food webs, linking blooms, marine snow, fish recruitment, whales, and climate-driven shifts in the ocean.