Some of the most abundant animals in the world—and the most numerous zooplankton in the sea—are the various species of copepods. Most are herbivorous, like cattle, though some are carnivorous mini-tigers, even eating other copepods. Either way, in their quest to track down their daily meals, copepods live a more complicated life than do cattle.
The main copepod across the temperate northern hemisphere is Calanus finmarchicus. Growing up to almost ¼ inch (6 mm) long, an adult copepod weighs about 1/12,000 ounce (0.002 g). Thus it would take 12,000 copepods piled onto a scale to measure one ounce (28 g).
This northern copepod is strictly herbivorous. According to biologist Steve Katona at College of the Atlantic, one copepod could devour all the single-cell phytoplankton in half a cup of water in just one day. The copepod feeds by moving its appendages back and forth like fans to create water currents. When a candidate green phytoplankton cell moves within range, appendages called second maxillae open like arms to ensnare the cell and move it up to the animal’s gaping mouth. It is far more work than bending down to eat grass or hay.