Zooplankton are small aquatic animals that drift with the currents of water. Many zooplankton are microscopic, but some, like krill and copepods, can be seen with the naked eye. Zooplankton play an important role in the food web of aquatic ecosystems, serving as both a food source for larger animals and as primary consumers of phytoplankton (microscopic plants).
Though they are often thought of as simple organisms, zooplankton are actually quite diverse, made up of many different groups of animals including protozoans (single-celled), rotifers (multi-celled), crustaceans (including shrimp, krill, and crabs), mollusks (such as squid and octopus), and even fish larvae. This diversity is reflective of their importance in aquatic ecosystems; zooplankton occupy nearly every niche in the water column from surface to seafloor.
Most zooplankton are herbivorous, feeding on phytoplankton or other organic matter. Some groups, however, are carnivorous and prey on other zooplankton or small organisms such as nematodes. These predators play an important role in controlling population numbers and keeping nutrient cycling efficient. Without them, populations of their prey would explode unchecked and could lead to serious imbalances in ecosystem health.
While they may seem insignificant due to their size, zooplankton have a profound impact on the oceans and freshwater systems they inhabit. They serve as a vital link in the food chain connecting primary producers (phytoplankton) to top predators (large fish, marine mammals). Through their grazing pressure on phytoplankton blooms, zooplaknton help regulate primary productivity which ultimately drives the ocean’s carbon cycle—a key player in global climate change mitigation efforts. Additionally, many commercially important fish species spend at least part of their life cycle as planktonic larvae before settling into adult habitats; without healthy populations of zooplaknton these species would not be able to replenish themselves sustainably