Acartia is a genus of marine calanoid copepods. They are epipelagic, estuarine, zooplanktonic found throughout the oceans of the world, primarily in temperate regions.
Classification
This genus contains the majority of species in the family Acartiidae:
Acartia adriatica Steuer, 1910 Acartia amboinensis Carl, 1907 Acartia arbruta Smith et al., 2021 Acartia australis Farran, 1936 Acartia bacorehuisensis Zamora-Sánchez & Gómez-Aguirre, 1986 Acartia bermudensis Esterly, 1911 Acartia bifilosa (Giesbrecht, 1881) Acartia bilobata Abraham, 1970 Acartia bispinosa Carl, 1907 Acartia bowmani Abraham, 1976 Acartia cagayanensis Sakaguchi & Ueda, 2020 Acartia californiensis Trinast, 1976 Acartia centrura Giesbrecht, 1889 Acartia chilkaensis Sewell, 1919 Acartia clausi Giesbrecht, 1889 Acartia danae Giesbrecht, 1889 Acartia denticornis Brady, 1883 Acartia discaudata (Giesbrecht, 1882) Acartia dweepi Haridas & Madhupratap, 1978 Acartia edentata Srinui, Ohtsuka & Metillo in Srinui, Ohtsuka, Metillo & Nishibori, 2019 Acartia ensifera Brady, 1899 Acartia enzoi Crisafi, 1974 Acartia erythraea Giesbrecht, 1889 Acartia fancetti McKinnon, Kimmerer & Benzie, 1992 Acartia floridana Davis, 1948 Acartia forcipata I. C. Thompson & A. Scott in Thompson, Scott & Herdman, 1898 Acartia forticrusa Soh, Moon, Park, Bun & Venmathi Maran, 2013 Acartia fossae Gurney, 1927 Acartia hongi Soh & Suh, 2000 Acartia hudsonica Pinhey, 1926 Acartia italica Steuer, 1910 Acartia japonica Mori, 1940 Acartia jilletti Bradford, 1976 Acartia laxa Dana, 1852 Acartia lefevreae Bradford, 1976 Acartia levequei Grice, 1964 Acartia lilljeborgii Giesbrecht, 1889 Acartia limpida Dana, 1849 Acartia longiremis (Lilljeborg, 1853) Acartia longisetosa Brady, 1914 Acartia macropus Cleve, 1900 Acartia margalefi Alcaraz, 1976 Acartia mediterranea Pesta, 1909 Acartia mollicula Pavlova & Shmeleva, 2010 Acartia mossi (Norman, 1878) Acartia nadiensis Lee, S, Soh & W. Lee, 2019 Acartia nana Brady, 1914 Acartia negligens Dana, 1849 Acartia ohtsukai Ueda & Bucklin, 2006 Acartia omorii Bradford, 1976 Acartia pacifica Steuer, 1915 Acartia pietschmani Pesta, 1912 Acartia plumosa T. Scott, 1894 Acartia ponteloides (Kritchagin, 1873) Acartia ransoni Vaissière, 1954 Acartia remivagantis Oliveira, 1946 Acartia sarojus Madhupratap & Haridas, 1994 Acartia seshaiyai Subbaraju, 1968 Acartia simplex G. O. Sars, 1905 Acartia sinjiensis Mori, 1940 Acartia southwelli Sewell, 1914 Acartia spinata Esterly, 1911 Acartia spinicauda Giesbrecht, 1889 Acartia steueri Smirnov, 1936 Acartia teclae Bradford, 1976 Acartia tonsa Dana, 1849 Acartia tranteri Bradford, 1976 Acartia tropica Ueda & Hiromi, 1987 Acartia tsuensis ItoTak, 1956 Acartia tumida Willey, 1920
Reproductive and life cycle
Female Acartia release eggs freely in the water. Nauplii hatch and undergo six distinct life stages to become copepodites and then undergo another six life stages to become fully mature copepods.
Some species of Acartia are known to exhibit a diapause, a resting period when the species is dormant, as a part of their life cycle. These species produce "resting eggs" when environmental conditions are unfavorable for the development and growth of nauplii. Individual females can switch between producing resting eggs and subitaneous eggs (eggs that hatch immediately) as environmental conditions change. Resting eggs accumulate in the sediment and hatch when conditions are optimal. Production of resting eggs is driven by water temperature variations. Some species (A. hudsonica) produce resting eggs when water temperatures rise above a certain threshold, while others (A. tonsa, A. califoriensis) have been observed to produce resting eggs when water temperatures fall below a certain threshold. Hatching and development of the species occur when the water cools (A. hudonica) or warms (A. tonsa, A. califoriensis). Additionally, A. califoriensis is known to be adapted to anomalous water temperature variations. Hatching is only followed by a period of steady water temperatures in the favorable range. This ensures that a generation of the species is not killed off by a momentary warming followed again by colder temperatures.
Diet
Acartia primarily feed on phytoplankton and are also known to consume rotifers, ciliates, and their own eggs and nauplii.
Acartia feeding patterns are asymptotic relative to the abundance of food. When food is widely abundant Acartia approach a maximum food intake. When there is less food available, feeding adjusts to rates that correlate with food availability.
Behaviour
In a study of A. tonsa in the Narragansett Bay the species was found to exhibit a diel feeding pattern, that is, a night feeding pattern. The diel feeding cycle was tested under a variety of light conditions and was found to be endogenous, not related to light availability, but persistent regardless of whether the copepods were subjected to light or dark. This feeding pattern is only known to be disrupted at extremely low food levels, implying that either "food limitation has over-ridden other factors governing diel feeding rhythms and induced continuous feeding, or that a synchronized population-wide feeding rhythm has given way to intermittent, asynchronous feeding among individuals."
Acartia are also known to exhibit a diel vertical migration pattern, swimming to depths during the day and rising to surface waters at night. The diel vertical migration of A. tonsa was seen to be effected by light exposure: when exposed to continuous light the copepods did not migrate to the surface.
Both diel patterns are thought to be primarily adaptive behavior to avoid visual predators. The mechanism of the diel vertical migration of Acartia has been explored further to solve the question of whether the copepods react to chemical signals indicating the presence of predators, physical stimuli resulting from the movement of predator fish in the water, or visual cues based on the changing light modified by a much larger predator. In a study of A. hudsonica, the chemical response was ruled out. Additionally, other studies of Acartia (A. longiremis, A. grani and A. discandata) were found to have less chemoreceptors and more mechanoreceptive sensory hairs than other marine copepods, suggesting that diel feeding and migration patterns in Arcatia are primarily driven by physical and visual cues.
References