Acartia tonsa

written by Mika Laird

Order: Calanoida
Family: Acartiidae
Genus: Acartia
Species: Acartia tonsa

Acartia tonsa are calenoid copepods most commonly found in coastal regions such as estuaries and brackish waters. They are found in cold and warm waters world wide containing various levels of salinity. They are in higher concentrations during the spring and summer in the North Atlantic ocean and lay their eggs during the winter. In warm waters of estuaries they are found year round. A.tonsa are mostly found at depths of 0 to 5 meters and temperatures of 17 – 25 C. Sometimes they are found incredibly deep at 600 meters. 

Microscopic view of copepod in it's natural habitat.

Microscopic representational drawing of A.tonsa in it’s natural habitat: estuary mud with crabs and clams.

A.tonsa are easily identified by the length of their antennae in relation to the body, number of antennae, and the joint in their body between the fifth and sixth sections. Sizes range from 0.5 mm to 1.5mm. 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. 


Their bodies are translucent but contain some red coloring in various sections and have dark bits where their organs are located. They have multiple small legs used for feeding and locomotion. Males and females have slight differences in anatomy which helps to differentiate between them such as the placement and shape of the urosome. A.tonsa are considered “broad cast spawners” meaning they release their eggs into the environment instead of carry them like other copepod species.

stipple drawing of A.tonsa

A.tonsa life cycle begins with round fertilized eggs which sink, develop and hatch into nauplii within 48 hours of being laid. There are 6 stages for nauplii on their way to adulthood. A.tonsa stays in deeper waters to keep away from fish predators during most of the day but later move into shallow water at night. 

They feed on diatoms and other phytoplankton, by producing a feeding current in circular motion to pull in food with appendages. Then they use their maxillae to filter organisms from water. For mobile prey, such a ciliates, A.tonsa will stay motionless and sink in the water until prey is close by. They sense them with the receptors on their antennae then jump to catch the prey. 




A study completed by the Danish Institute for fisheries research  about prey switching behavior showed the feeding patterns of  A.tonsa partly depended on the availability of prey. One theory is that A.tonsa will change their feeding mode to the one that is most energy efficient depending on conditions and prey type.

A.tonsa will also change their choice of prey to suit whichever organism is most available. This study showed that ciliates were much easier for A.tonsa to capture using suspension feeding. They found that cilliates to be more desirable for the A.tonsa which meant they ate less diatoms than usual even though there was an abundance of diatoms available. They also thought that micro plankton populations are able to peak at the same time as phytoplankton due to the A.tonsa not eating as many of them because of their preference for ciliates. 

stipple drawing of cilliate tintinnid: petalotricha ampulla

Stipple drawing of cilliate tintinnid: Petalotricha ampulla


A different group of researchers conducted a similar study on feeding behavior and prey detection that showed a mixture of organisms introduced to A.tonsa for feeding. Researchers combined a ratio of ciliates to microflagellates. They found that the ciliates were much more difficult to capture. A.tonsa only ate a small amount of the group introduced to them each time. Based on the swim patterns of the cilliates and the ability to detect them, this caused the A.tonsa to switch to microflagellates. The researchers hypothesize that A.tonsa has the ability to switch between suspension feeding and raptorial feeding makes them much better at surviving in the ocean.



A.tonsa contributes to the environment by being the food source for many larger organisms in the food chain. They are responsible for helping cycle nutrients and energy. They are also important regulators of the marine nitrogen cycle, excreting both inorganic and organic nitrogen. Copepods are also used as a host for some ciliate protozoa. The parasites attach to the copepods before they move on to their next host, fresh water shrimp. A.tonsa help control the harmful growth of the red tide blooms due to their feeding on the algae, however this could also remove the food sources for other organisms such as mollusks. 

Drawing of a diatom: Detonula pumila.

Stipple drawing of a diatom: Detonula pumila

Humans grow A.tonsa in aquaculture tanks to provide food for fish hatcheries and are use to control the population of the dinoflagellate, Pfiesteria pisclcida, who has been killing coastal fish on the east coast in the United States. Humans also impact A.tonsa by the waste we deposit into the ocean. For example, the pastic microbeads which are produced for face and body wash,  break down small enough for A.tonsa to ingest while suspension feeing. They don’t seem capable of telling the difference between the nanoplastic and their regularly ingested organisms. Some states have banned the usage of microbeads in personal care products but others have not. Plastic has been a problem for a long time concerning the ocean pollution. Even though this is a small amount of plastic, the organisms affected, A.tonsa, other copepods and other microscopic organisms, are major contributors to the food web so negative impacts at this level will eventually affect higher trophic level. 

While copepods are large contributors to many aspects of the food web, they have a large influence on humans also. I think that these organisms could symbolize human’s desires to focus on small aspects of everyday things or how small things can make how we function as a society. Sometimes, small details are worth the effort to change or in the case of copepods, the environment and our own health, protection is required in the form of recycling. We are doing a service to all creatures, not just copepods, when we doing things for the environment that we can control.


Gonzalez, G. 2013. “Acartia tonsa”, Animal Diversity Web. Web. Accessed November 2015.

Kiørboe, Thomas, Saiz, Enric, Viitasalo, Markku (1996). Prey Switching Behaviour in the planktonic copepod Acartia tonsa. Marine Ecology. Vol. 143: 65-75.

“Acartia tonsa.” Animal Diversity Web. Web. 25 May 2016.

Per R. Jonson, Peter Tiselius. (1990). Feeing Behaviour, prey detection and capture efficiency of the copepod Acartia tonsa feeding on plaktonic ciliates. Marine Ecology. Vol. 60: 34-44.

Kiørboe, Thomas, Saiz, Enric, Viitasalo, Markku (1990). Diel feedind behavior in the marine copepod Acartia tonsa in relation to food availability. Marine Ecology. Vol. 68: 23-45.




Adventures In The Estuary

This is a stop motion animation, using 2D and 3D animation labs. Sand, pipe cleaners, sequins, beads, yarn, mini mannequin, foam and other random materials were used in the making. Adventures In The Estuary tells the tale of happens to them when they eat microbeads found in personal care products, which flow into the ocean from our bath tubs. The music for this was recorded during an audio class with a group of students and a jam band. Later, I created the final edit for this animation which was edit differently than the original song.