Calanus pacificus

The female is about {{convert|3.1|mm|in}} in length, and typically ranges from {{convert|2.2|to|5.3|mm|in}} in length. The male has an average length of about {{convert|2.9|mm|in}}, and ranges in length from about {{convert|2.4|to|4.4|mm|in}}. The male has enlarged aesthetes (found on the antennules), which are likely used for chemoreception.

This copepod is found in the Pacific, from Alaska to Central America in coastal North America, and from Russia to southeast Asia in Asia.{{cite web|author1=Razouls C.|author2=de Bovée F.|author3=Kouwenberg J.|author4=Desreumaux N.|url=https://copepodes.obs-banyuls.fr/en/fichesp.php?sp=508|title=Diversity and Geographic Distribution of Marine Planktonic Copepods|year=2018|access-date=5 July 2018|publisher=Sorbonne Université, CNRS}}

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.{{cite journal|last1=Griffiths|first1=Arthur M.|last2=Frost|first2=Bruce W.|title=Chemical communication in the marine planktonic copepods Calanus pacificus and Pseudocalanus sp.|journal=Crustaceana|volume=30|issue=1|year=1976|pages=1–8|issn=0011-216X|doi=10.1163/156854076X00323|s2cid=85287105 |url=https://pdfs.semanticscholar.org/fb6a/316934f2aabf8a16534f0d71763ef2cf9308.pdf|archive-url=https://web.archive.org/web/20200227204511/https://pdfs.semanticscholar.org/fb6a/316934f2aabf8a16534f0d71763ef2cf9308.pdf|url-status=dead|archive-date=2020-02-27}} 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.{{cite journal|last1=Runge|first1=Jeffrey A.|title=Relationship of egg production of Calanus pacificus to seasonal changes in phytoplankton availability in Puget Sound, Washington|journal=Limnology and Oceanography|volume=30|issue=2|year=1985|pages=382–396|issn=0024-3590|doi=10.4319/lo.1985.30.2.0382|doi-access=free}} In addition, it has three generations per year,{{cite journal|last1=Sainmont|first1=Julie|last2=Andersen|first2=Ken H.|last3=Varpe|first3=Øystein|last4=Visser|first4=André W.|title=Capital versus income breeding in a seasonal environment|journal=The American Naturalist|volume=184|issue=4|year=2014|pages=466–476|issn=0003-0147|doi=10.1086/677926|pmid=25226182}} 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.{{cite journal|last1=Huntley|first1=M.|last2=Brooks|first2=E. R.|title=Effects of age and food availability on diel vertical migration of Calanus pacificus|journal=Marine Biology|volume=71|issue=1|year=1982|pages=23–31|issn=0025-3162|doi=10.1007/BF00396989}} The depth of migration is influenced by predation; when there are more predators, the intensity of diel vertical migration increases.{{cite journal|last1=Bollens|first1=Stephen M.|last2=Frost|first2=Bruce W.|title=Zooplanktivorous fish and variable diel vertical migration in the marine planktonic copepod Calanus pacificus|journal=Limnology and Oceanography|volume=34|issue=6|year=1989|pages=1072–1083|issn=0024-3590|doi=10.4319/lo.1989.34.6.1072|s2cid=84472360 |doi-access=free}}

C. pacificus is a particle feeder,{{cite journal|last1=Huntley|first1=M. E.|last2=Barthel|first2=K.-G.|last3=Star|first3=J. L.|title=Particle rejection by Calanus pacificus: discrimination between similarly sized particles|journal=Marine Biology|volume=74|issue=2|year=1983|pages=151–160|issn=0025-3162|doi=10.1007/BF00413918}} feeding on plankton, copepod nauplii, and marine snow.{{cite journal|last1=Dilling|first1=L.|author-link1=Lisa Dilling|last2=Wilson|first2=J.|last3=Steinberg|first3=D.|last4=Alldredge|first4=A.|title=Feeding by the euphausiid Euphausia pacifica and the copepod Calanus pacificus on marine snow|journal=Marine Ecology Progress Series|volume=170|year=1998|pages=189–201|issn=0171-8630|doi=10.3354/meps170189|url=https://www.int-res.com/articles/meps/170/m170p189.pdf|doi-access=free}} It generally feeds on the food of greatest abundance{{cite journal|last1=Landry|first1=M. R.|title=Switching between herbivory and carnivory by the planktonic marine copepod Calanus pacificus|journal=Marine Biology|volume=65|issue=1|year=1981|pages=77–82|issn=0025-3162|doi=10.1007/BF00397070}} 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,{{cite journal|last1=Sykes|first1=P. F.|last2=Huntley|first2=M. E.|title=Acute physiological reactions of Calanus pacificus to selected dinoflagellates: direct observations|journal=Marine Biology|volume=94|issue=1|year=1987|pages=19–24|issn=0025-3162|doi=10.1007/BF00392895}} 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.{{cite journal|last1=Huntley|first1=M. E.|last2=Sykes|first2=P.|last3=Rohan|first3=S.|last4=Marin|first4=V.|title=Chemically-mediated rejection of dinoflagellate prey by the copepods Calanus pacificus and Paracalanus parvus: mechanism, occurrence and significance|journal=Marine Ecology Progress Series|year=1986|volume=28|pages=105–120|doi=10.3354/meps028105|doi-access=free}} C. pacificus can take advantage of marine snow as food, with aggregations of various compositions being responsible for between about {{convert|.3|and|1.5|μg}} dry weight of fecal pellets copepod⁻¹ hr⁻¹ (per copepod per hour), at a maximum feeding rate. Assuming a 70% assimilation efficiency, this species can ingest from {{convert|.3|to|1.8|μg}} marine snow copepod⁻¹ hr⁻¹. Another important food source, diatoms, are able to be ingested at a rate of about {{convert|1.1|μg}} copepod⁻¹ hr⁻¹.

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Category:Calanoida

Category:Crustaceans described in 1948