Copepods

Calanoids are of major importance to the commercial fishing industry. Like other copepods, this species filters minute animal algae from the water and eats it in large clumps. In turn, these copepods are eaten in large numbers by fish, such as herring and salmon. Calanoids thrive close to the surface of large expanses of water, both seas and lakes. Anatomically, they are easy to recognize. The fused head and thorax of an individual calanoid is oval and clearly separated from its abdomen. The multisegmented first antennae are long, about the same length as its body. The abdomen is much slimmer than its thorax.

Like other animal plankton, calanoids allow themselves to float with the current, although they can use their first antennae to swim upward in the water. Unlike most other genera of copepods, calanoids move from the surface to the depths of the water each day. At dawn, they sink to several hundred feet in the water; at dusk they rise to the surface again. There are several theories explaining this activity. The most likely reason is that they are escaping the dangerous ultraviolet rays of the sun. Another theory is that they are avoiding predators. In any case, this activity facilitates their fairly even distribution in the sea, since currents at various depths often run in different directions.