They are very important sources of food because of their large numbers and high nutritional value. in marine environments they are the predominant source of food for organisms like jellyfish, basking sharks, and whales (Davis 1955).
Byron (1982) supported this in his investigation in which he concluded that much of the variation of pigmentation is due to environmental conditions along with metabolic stimulation. However, many of the variations can be explained just by observing the difference in water temperatures. He stated that copepods had the darkest pigmentation in colder water.