Ecology & Distribution:
Calanoids form an order of the Copepoda; most calanoids are free-living and marine, though some groups are restricted to freshwater. The majority are planktonic, but some live on, or close to, the sea bottom. They are found in all oceans, from the surface to over 5000 m in depth. Many are known to perform diurnal migration, descending to deep water at day and rising to the surface at night. They are the dominant group in the marine zooplankton. Their feeding habits vary with species and with developmental stages of the same species. They may be herbivorous, mixed-mode feeders, predators, or scavengers. Calanoids form a very important link in the food chain of the aquatic environment. They feed on phytoplankton and microzooplankton, and at times attack animals which are much larger than themselves, such as chaetognaths and larval fish. Most calanoids store foods in a fat body or in a midgut oil sac, which often gives the body a red or blue color. They are preyed upon by larger zooplankton and are known to be the major food of larval fish, small pelagic fishes such as herring, and of some whales and seals.