Living in open waters can be dangerous for zooplankton. Being at the base of the food web means they are popular food items for many sea creatures. To protect themselves from predators, zooplankton have developed unique defense mechanisms.
Even though these small animals are often considered “drifters,” many are actually adept swimmers. Zooplankton migrate to deep, dark waters during the day to avoid being seen by predators. They return to the surface only at night when it is safer to feed. This daily journey can be as much as 400 feet each way, which would be equivalent to a round trip of more than 200 miles for a human.
Some zooplankton have dramatic escape responses. Copepods are tiny, torpedo-shaped crustaceans with long antennae. They use these antennae to sense water movements, such as the “bow wave” created by a lunging fish. When they detect this threatening motion, copepods respond with rapid jumps. Each jump occurs within a few thousandths of a second and can move this small animal more than 500 times its body length away from the predator.
Zooplankton are some of the smallest animals in the sea, but they have to escape the hungry mouths of fish, and even giants like baleen whales. Having superhero-like defense behaviors helps zooplankton survive against predators much larger than themselves.