''Calanus pacificus'' is a species of copepod found in the Pacific Ocean. The female has an average length of about , and the male has a value of about .

Description

The female is about in length, and typically ranges from in length. The male has an average length of about , and ranges in length from about . The male has enlarged aesthetes (found on the

antennule Antennae ( antenna), sometimes referred to as "feelers", are paired appendages used for sensing in arthropods. Antennae are connected to the first one or two segments of the arthropod head. They vary widely in form but are always made of one o ...

s), which are likely used for

chemoreception A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...

Distribution

This copepod is found in the Pacific, from Alaska to Central America in coastal North America, and from Russia to southeast Asia in Asia.

Ecology

Life cycle and reproduction

When the male senses a potential mate (likely through pheromones), it swims irregularly, alternating zig-zags with looping and figure eights. This is likely to find the potential mate or as a precopulatory behaviour. ''C. pacificus'' This copepod typically lays a clutch of 24 to 54 eggs. The egg production rate increases with an increase in food, indicating that ''C. pacificus'' is an income breeder, relying on food stores gained concurrently with reproduction to breed. In addition, it has three generations per year, with generations being about 10 to 25 days. This copepod does not migrate until it is a nauplius stage III, when it moves closer to the surface. This behaviour continues until it is a nauplius stage V. Then, until maturity, the depth during the day gets progressively deeper. The depth of migration is influenced by predation; when there are more predators, the intensity of diel vertical migration increases.

Feeding

''C. pacificus'' is a particle feeder, feeding on plankton, copepod nauplii, and

marine snow In the deep ocean, marine snow (also known as "ocean dandruff") is a continuous shower of mostly organic detritus falling from the upper layers of the water column. It is a significant means of exporting energy from the light-rich photic zone to ...

. It generally feeds on the food of greatest abundance and size. However, it also rejects low quality food, likely through chemical means, in addition to rejecting inert particles. Examples of low quality food include '' Ptychodiscus brevis'', which produces neurotoxins, and '' Protoceratium reticulatum'', which causes regurgitation or an elevated heart rate. Additionally, the presence of the latter decreases the intake of a preferred food, '' Gyrodiniurn resplendens''. This allows ''P. reticulatum'' to decrease the concentration of ''C. pacificus'' when the former is in bloom. ''C. pacificus'' can take advantage of marine snow as food, with aggregations of various compositions being responsible for between about dry weight of fecal pellets copepod⁻¹ hr⁻¹ (per copepod per hour), at a maximum feeding rate. Assuming a 70%

assimilation Assimilation may refer to: Culture *Cultural assimilation, the process whereby a minority group gradually adapts to the customs and attitudes of the prevailing culture and customs **Language shift, also known as language assimilation, the progre ...

efficiency, this species can ingest from marine snow copepod⁻¹ hr⁻¹. Another important food source, diatoms, are able to be ingested at a rate of about copepod⁻¹ hr⁻¹.

References

{{Taxonbar, from=Q6551233 Calanoida Crustaceans described in 1948