Acartia tonsa

Geographic Range

These calenoid copepods were originally observed in the Indo-Pacific region. This species is now regarded as cosmopolitan and is found in the Atlantic, Indian and Pacific Oceans, the Sea of Azov, the Baltic, Black, Capsian, Mediterranean, and North Seas, and also the Gulf of Mexico and other marine environments, as well as estuaries. Its wide geographical range may be the result of transportation in the ballast water of ships. (Knott, 2010; Kouwenberg, 2012; Mauchline, 1998)


These copepods are free-swimming, planktonic crustaceans that can tolerate a wide range of temperatures (-1 to 32ºC) and salinities (1 ppt to 38 ppt), and can survive sudden changes in these conditions. They are most commonly found in depths from 0-50 meters and temperatures of 17-25ºC, though they have been found as deep as 600 meters. They are commonly found in coastal waters, including brackish estuaries, and often inhabit environmental niches that avoid overlap with closely related species. For example, it is the dominant species of copepod in the lagoons of the North Adriatic Sea, while Acartia clausi is the dominant copepod species in adjacent coastal waters. ("Encyclopedia of Life", 2013; Danilo Calliari, et al., 2008; Sei, et al., 2006)

  • Range depth
    1 to 60 m
    3.28 to 196.85 ft

Physical Description

These copepods are small crustaceans ranging from 0.5 mm to 1.5 mm in length. They have translucent, bilaterally symmetrical bodies, and can be differentiated from closely related species by their long first antennae (at least half the length of their bodies) and biramous (branched) second antennae, as well as the presence of a joint between their fifth and sixth body segments. Their bodies lack a protective carapace and have three segments: prosome (head and sensory organs), metasome (housing their legs and swimmerets), and urosome (where their sexual organs are located). These copepods use a pair of maxillipeds to chew food. Females are typically slightly larger than males and their antennae are longer and straighter; males' antennae are curved at the tips and are used for grasping the female during reproduction. Males and females can also be differentiated based on the morphology of their urosomes and swimmerets (pleopods). Male urosomes have five somites (four in females), and female swimmerets are modified for egg brooding and tend to be thicker and more filamentous than those of males. (Hubareva, et al., 2008; Marcus and Wilcox, 2007; Mauchline, 1998; Thor, 2003)

  • Sexual Dimorphism
  • female larger
  • sexes shaped differently
  • Range length
    0.5 to 1.5 mm
    0.02 to 0.06 in
  • Average basal metabolic rate
    0.00057 cm3.O2/g/hr


Life cycle and development for this copepod is typical of most copepods. Fertilized eggs, which are spherical, approximately 70-80 µm in diameter, and covered in short spines, slowly sink. Eggs develop and hatch into nauplii within approximately 48 hours (at 25°C, an average water temperature for this species). If water temperatures are too cold, eggs will usually sink to the bottom and enter diapause, hatching when water temperatures rise above 10°C. Nauplii have a maxillopodan eye, which is a simple, median eye with several photoreceptors. These copepods go through six nauplius stages before becoming copepodites, losing their maxillopodan eyes. Copepodites then metamorphose through six additional stages, finally becoming sexually mature adults. Development from newly fertilized egg to adult takes less than 3 days, on average. ("Acartia tonsa Dana, 1849 – a planktonic copepod", 2013; Marcus and Wilcox, 2007; Mauchline, 1998; Saiz, et al., 1993; Teixeira, et al., 2010)


Limiting factors of this species' breeding season can include the amount of light, temperature, salinity, and oxygen concentration. In northern parts of its range, breeding tends to occur during the late summer and early fall, and in southern areas there is often a breeding peak in the early spring; if conditions are optimal, this species may breed year-round. Multiple generations are produced per breeding season. These copepods are polygynandrous, and rely on hydromechanical signals to find mates rather than pheromones. A male and female encounter each other spontaneously and, when a female comes within range, a male detects her movements, and responds in kind. The pair perform a series of synchronized "hops" until the male is close enough to catch the female, followed by mating. ("Acartia tonsa Dana, 1849 – a planktonic copepod", 2013; Bagøien and Kiørboe, 2005; Holste and Peck, 2005; Mauchline, 1998; Saiz, et al., 1993; Sei, et al., 2006)

These copepods are dioecious and both sexes may be reproductively active throughout the year; breeding season depends largely on environmental factors such as water temperature. Females produce eggs for 3-4 weeks at a time and can release a brood of 20-53 eggs every 5-6 days. During mating, males clasp females with their claw-like antennae and deposit spermatophores onto their urosomes, where the eggs are fertilized. After fertilization, eggs are released. Males may mate consecutively with multiple females. ("Acartia tonsa Dana, 1849 – a planktonic copepod", 2013; Drillet, et al., 2008; Holste and Peck, 2005; Marcus and Wilcox, 2007; Mauchline, 1998)

  • Breeding interval
    During breeding season, females produce egg clutches every 5-6 days.
  • Breeding season
    This species may breed year round under optimal conditions; most typically, they breed during warmer months.
  • Range number of offspring
    20 to 50
  • Average gestation period
    48 hours
  • Average age at sexual or reproductive maturity (female)
    3 days
  • Average age at sexual or reproductive maturity (male)
    3 days

These copepods exhibit no parental care to their young once fertilized eggs have been released. ("Acartia tonsa Dana, 1849 – a planktonic copepod", 2013; Drillet, et al., 2008; Holste and Peck, 2005; Mauchline, 1998)


Females survive longer than males, 70-80 days versus 15 days. Longevity is influenced by food availability, predation, salinity, and temperature. (Danilo Calliari, et al., 2008; Holste and Peck, 2005; Marcus and Wilcox, 2007; Mauchline, 1998; Miller and Roman, 2008; Richmond, et al., 2006; Sei, et al., 2006)

  • Range lifespan
    Status: wild
    14 to 80 days
  • Typical lifespan
    Status: wild
    14 to 80 days


Individuals spend most of the day in deeper waters in order to avoid predators, rising into shallower waters at night. The presence of predatory fish can disrupt their movement patterns. These copepods are social with conspecifics but avoid members of other species. They spend most of their time feeding and behaviors associated with feeding are affected by water turbulence and prey type. When approaching prey or potential mates, these copepods "jump" by thrusting their antennules and swimming legs in the direction they intend to move. (Mauchline, 1998; Saiz, 1994)

Home Range

These isopods swim freely in the water column and do not establish territories.

Communication and Perception

This species uses a set of sensory antennae to detect the surrounding environment. These antennae detect abnormal vibrational patterns, food particulates, chemicals, and nearby mates. In their naupliar larval stages, antennae are used for swimming, becoming modified for sensory purposes in adulthood. These copepods have simple eyes that are unable to form complete images, but are highly photosensitive. (Jakobsen, et al., 2005; Mauchline, 1998)

Food Habits

This species is omnivorous. Individuals feed on nauplii of other copepods (such as Canuella perplexa), dinoflagellates, cilliates (such as Strombidium sulcatum), protozoans, phytoplankton, bacterioplankton, algae, and diatoms (such as Thalassiosira weissflog). They feed in two different ways, depending on what type of prey is available in the greatest numbers. To feed on immotile prey (plankton, diatoms, etc), they produce a feeding current using their feeding appendages and thoracopods to draw in food. They then filter the cells by using their second maxillae to squeeze water out. To feed on motile prey (ciliates, etc), these copepods sink in the water without moving their feeding appendages and sense prey using mechanoreceptors on their antennae, then reorienting themselves and "jumping" to catch their prey when they are 0.1-0.7 mm away. Each method is specialized for its prey type; mechanoreceptors will not help to sense immotile prey and motile prey can escape feeding currents. (Jakobsen, et al., 2005; Kiørboe, et al., 1996; Mauchline, 1998; Roman, et al., 2006; Saiz and Kiørboe, 1995; Saiz, 1994; Stoecker and Eglof, 1987; Tackx and Polk, 1982; Turner and Tester, 1989)

  • Other Foods
  • microbes


These copepods are a food source for many species including birds, corals, crustaceans, fishes, jellyfishes, poplychaete worms, seahorses and whales. ("Encyclopedia of Life", 2013; Buskey, et al., 1986; Kimor, 1979; Marcus and Wilcox, 2007; Mauchline, 1998)

This species exhibits a startle behavior to light and water vibrations, consisting of a short burst of swimming speed when an individual is stimulated. This photophobic behavior may be an adaptation to avoid predators such as cnidarian medusae and ctenophores, which cast shadows from above during the day. (Buskey, et al., 1986; Mauchline, 1998; Suchman and Sullivan, 1998)

Ecosystem Roles

This species is integral to the oceanic food chain. It feeds on algae and phytoplankton, and is a food source for fish and large mammals. These pelagic copepods can represent 55-95% of the copepod populations in some areas. They also play an important role in the mixing and cycling of nutrients and energy in marine ecosystems, forming a trophodynamic link connecting primary (phytoplankton) and tertiary (e.g., planktivorous fish) production, and are considered a keystone species. They are also important regulators of the marine nitrogen cycle, excreting both inorganic nitrogen (as ammonium) and organic nitrogen (urea). (Holste and Peck, 2005; Mauchline, 1998; Miller and Roman, 2008; Turner, et al., 1979)

These copepods can act as hosts for ciliate protazoa (Epistylus sp.). These parasites attach to the cuticle using their stalked-suckers, causing lesions in the cuticle that lead to subsequent bacterial infection, as well as infections by an epibiont, Zoothamnium intermedium. They serve as intermediate hosts for an ectoparasitic bopyrid isopod, Probopyrus pandalicola, whose definitive host is freshwater shrimp. Resarchers have also isolated a virus from this species, "Acartia tonsa copepod circo-like virus" (AtCopCV), which may significantly impact population sizes. (Beck, 1979; Dunlap, et al., 2013; Turner, et al., 1979; Utz, 2008)

Commensal/Parasitic Species
  • Epistylus sp. (Order Sessilida, Phylum Ciliophora)
  • Zoothamnium intermedium (Family Vorticellidae, Class Oligohymenophora)
  • Probopyrus pandalicola (Family Bopyridae, Order Isopoda)
  • Acartia tonsa copepod circo-like virus

Economic Importance for Humans: Positive

These copepods are food for many fish species that account for a tremendous portion of many countries' economies (food, tourism, etc). They are also grown in mass aquaculture tanks to provide food for commercial fish hatcheries. Additionally, they have been used as a control species for Pfiesteria piscicida, an estuarine dinoflagellate that has been responsible for many coastal fish kills. These copepods can also limit the growth of coastal harmful algal blooms, including red tides, which not only affect coastal ecosystems but can present a health threat to humans. (Mauchline, 1998; Roman, et al., 2006; Teixeira, et al., 2010)

  • Positive Impacts
  • research and education
  • controls pest population

Economic Importance for Humans: Negative

If these copepods overfeed on algae, they may adversely affect the feeding and growth of many species of marine fish and mollusks that seafood industries rely on. (Mauchline, 1998; Teixeira, et al., 2010)

Conservation Status

This species is not endangered under the IUCN Red List, CITES appendices, nor the United States Endangered Species Act list. It is a ubiquitous, cosmopolitan copepod that can be found inhabiting almost every ocean. ("IUCN Red List", 2012; Kouwenberg, 2012; Mauchline, 1998)


Gonzalo Gonzalez (author), University of Michigan-Ann Arbor, Alison Gould (editor), University of Michigan-Ann Arbor, Jeremy Wright (editor), University of Michigan-Ann Arbor.



lives on Antarctica, the southernmost continent which sits astride the southern pole.

Arctic Ocean

the body of water between Europe, Asia, and North America which occurs mostly north of the Arctic circle.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

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Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

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living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

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living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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living in the southern part of the New World. In other words, Central and South America.

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Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

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living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

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bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.


active at dawn and dusk


a period of time when growth or development is suspended in insects and other invertebrates, it can usually only be ended the appropriate environmental stimulus.


animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature


an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females


union of egg and spermatozoan


a method of feeding where small food particles are filtered from the surrounding water by various mechanisms. Used mainly by aquatic invertebrates, especially plankton, but also by baleen whales.


An animal that eats mainly plants or parts of plants.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body


referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).


A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


an animal that mainly eats all kinds of things, including plants and animals


found in the oriental region of the world. In other words, India and southeast Asia.

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reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


photosynthetic or plant constituent of plankton; mainly unicellular algae. (Compare to zooplankton.)


an animal that mainly eats plankton


the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


movements of a hard surface that are produced by animals as signals to others


uses sight to communicate

year-round breeding

breeding takes place throughout the year


animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)


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