Copepods eat and are eaten. Tiny copepods (the smallest look like specks of dust) live most everywhere in the ocean in numbers too vast to count. They're a key link in ocean food webs. They eat diatoms and other phytoplankton—and are eaten in turn by larger drifters, larval fishes and filter feeders. Copepods may be the most abundant single species of animal on Earth.
Cope is greek meaning an “oar” or “paddle;” pod is Greek for “foot.” Copepods have antennae and appendages that are used like paddles for movement. Some species swim in a jerky fashion, while others move more smoothly.
The open ocean is the world's "plankton pasture," home to the tiny drifting plants and animals that power enormous food webs. Copepods are the single most important group of animal plankton. Small fish feed on them and are in turn eaten by bigger fish, sea birds, seals and whales. We, too, depend on fish nourished by ocean plankton.
A single copepod may eat from 11,000 to 373,000 diatoms in 24 hours!