Thalassiosira pseudonana
(Hustedt) Hasle and Heimdal, (1957) 1970
Common Name:
A centric diatom
Synonyms and Other Names:
Cyclotella nana
Identification:
This diatom can occur singly or in chains up to 6 cells long. It typically exhibits a ring of fultoportulae around the edge of the valve face, costae that may run from the middle of the valve face to its edges, and one labiate process. The central region of the valve face is often bounded by an irregular siliceous ring and may or may not exhibit central fultoportulae. The valve face is often striated radially and hexagonal to polygonal areolae are often apparent in the central region (Belcher and Swale 1977, 1986, Harris et al. 1995, Hasle 1976, Lange et al. 1983, Lowe and Busch 1975, Muylaert and Sabbe 1996, Sabater and Klee 1990). Thalassiosira pseudonana can range in diameter from 2.5–15 µm (Belcher and Swale 1977, 1986, Harris et al. 1995, Hasle 1976, Lange et al. 1983, Lowe and Busch 1975, Muylaert and Sabbe 1996, Price et al. 1987).
Size:
2.5 to 15 microns
Native Range:
Unclear. Thalassiosira pseudonana is considered widespread. It is known from freshwater habitats in Europe and the former USSR, brackish and coastal waters of Europe, coastal waters of Japan, coastal waters of Australia, coastal waters of India, the Argentine Sea, the Baltic Sea, coastal waters on both sides of North America, and a few inland habitats in North America (Ake-Castillo et al. 1999, Belcher and Swale 1977, 1986, Blinn et al. 1981, Genkal and Prokina 1981, Harris et al. 1995, Hasle 1978, Kiss 1984, 1996, Lange et al. 1983, Lowe and Busch 1975, Mills et al. 1993, Muylaert and Sabbe 1996, Raman and Prakash 1989).
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This map only depicts Great Lakes introductions.
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Great Lakes Nonindigenous Occurrences:
Thalassiosira pseudonana was recorded for the first time in the Lake Erie drainage in an Ohio artesian well in 1973. It was later recorded from Lake Erie, Lake Ontario, Lake Michigan, and the Sandusky River, which flows into Lake Erie (Lowe and Kline 1976, Mills et al. 1993).
Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Thalassiosira pseudonana are found here.
Table last updated 12/18/2025
† Populations may not be currently present.
* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).
Ecology:
Thalassiosira pseudonana is a cosmopolitan species typically found in freshwater and coastal brackish habitats. It is usually a phytoplankton species but has also been recorded in the periphyton. It is eurythermal, experiencing good growth from 10–30°C, with an optimum around 21°C. Growth rates typically increase with increasing temperature, which confers T. pseudonana a competitive advantage at higher temperatures. Maximum abundance has been recorded in different regions of the world in late spring, summer, and late fall (Ferguson et al. 1976, Goldman and Ryther 1976, Harris et al. 1995, Hegseth and Saksaug 1983, Lowe and Busch 1975, Lowe and Kline 1976). The distribution and growth of T. pseudonana is primarily regulated by water temperature and day length (Brand et al. 1981, Ferguson et al. 1976, Hegseth and Skashaug 1983). Growth can be limited by changes in concentrations of vitamin B-12, silicon, selenium, zinc, nitrogen, phosphorus, or other vitamins (Guillard et al. 1973, Maestrini et al. 1997, Miao and Wang 2006, Price et al. 1987, Swift and Taylor 1974, Sunda and Huntsman 1992, 2005).
Although non-toxic itself, this species is often associated with relatively polluted regions, places where chemical oxygen demand is elevated and nutrient concentrations are very high, and waters experiencing red tides (de Almeida and Gil 2001, Gao et al. 2006, Mallin et al. 1995, Raman and Prakash 1989, Weckstrom and Juggins 2006). Thalassiosira pseudonana grows well at pH of 7–8.8, but its growth rates are reduced at higher pH because CO2 becomes limiting (Chen and Durbin 1994). It is capable of quickly adapting to changes in irradiance by adjusting cell volume (Thompson et al. 1991). Like many diatoms, T. pseudonana can use metals as a source of energy and have resistance to toxic metals (Wang et al. 2021, Chasapis et al. 2022). T. pseudonana has multiple adaptive mechanisms to shifting environmental conditions (including deficiencies in nitrogen, phosphorus, and iron as well as shifting salinity and light levels) which likely enhance its ability to acclimate and thrive in new environments (Ma et al. 2022, Strauss et al 2023). The species also is able to adapt rapidly to temperature fluctuations and rapid warming and to resist acidification, which may allow it to evolve rapidly under global warming scenarios (Schaum et al. 2018, Valenzuela et al 2018).
Thalassiosira pseudonana, like many diatom species, is capable of sexual reproduction. In general, the rate of reproduction increases with increasing temperature. It has a dormant stage that is most likely a physiological resting cell (Armbrust et al. 2001, Brand et al. 1981, McQuoid 2005). Purely asexual lines of T. pseudonana have been documented (Koester et al. 2018), these strains escape the fate of mitotic cell reduction likely due to the open girdle bands. McQuoid (2005) reported growth of T. pseudonana after 2 years in storage, indicating the presence of a dormant state that seems to be triggered by temperature and light cues.
Great Lakes Means of Introduction:
Thalassiosira pseudonana was very likely introduced in ballast water to the Great Lakes basin. It was first discovered in an artesian well but was probably originally introduced elsewhere in the basin at a location more easily accessible to ships carrying ballast water (Mills et al. 1993).
Great Lakes Status:
Overwintering and reproducing in warmer regions of the Great Lakes (Lakes Erie, Ontario and Michigan). Small members of the Thalassiosira genus are rarely identified to the species level, but populations likely persist in all reported locations.
Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...
There is little or no evidence to support that Thalassiosira pseudonana has significant environmental impacts in the Great Lakes.
Thalassiosira pseudonana has been found in the Great Lakes basin composing 31% of the periphyton community and 90% of the plankton community (Lowe and Busch 1975).
There is little or no evidence to support that Thalassiosira pseudonana has significant socio-economic impacts in the Great Lakes.
Thalassiosira pseudonana may have a moderate beneficial effect in the Great Lakes.
Thalassiosira pseudonana was found to be useful for mariculture because it has a high fatty-acid composition (Volkman et al. 1989). Thalassiosira pseudonana is also used as a model organism for silica biomineralization and because its entire gene sequence has been published. Biomineralizaton is a growing field that is using diatoms to accelerate silica formation and form macromolecular assemblies that might act as structure-directing templates (Sumper and Brunner 2008).
Management:
Regulations (pertaining to the Great Lakes region)
| Jurisdiction | Regulation | Law | Description | Date Effective |
| Illinois | Other | 515 ILCS 5/20-90 | This species is not on the Illinois Aquatic Life Approved Species List and if it is not otherwise native to Illinois it is illegal to be imported or possessed alive without a permit. | 7/9/2015 |
Note: Table last updated 7/5/2022. Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
There are no known control methods for this species.
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
Remarks:
In 1958, Guillard isolated three diatom clones from an estuarine habitat (3-H), slope water (7-15), and open ocean (13-1). These clones were considered for years to be different forms of T. pseudonana. However, it turns out that clone 7-15 is identical to T. guillardii from brackish water and clone 13-1 is another species. Only clone 3-H is still considered to be T. pseudonana (Hasle 1982). Thalassiosira pseudonana is the first eukaryotic marine phytoplankton whose genome has been fully sequenced (Armbrust et al. 2004; Arshad et al. 2021).
References
(click for full reference list)
Author:
Kipp, R.M., M. McCarthy, and A. Fusaro
Contributing Agencies:
Revision Date:
9/9/2025
Citation for this information:
Kipp, R.M., M. McCarthy, and A. Fusaro, 2025, Thalassiosira pseudonana (Hustedt) Hasle and Heimdal, (1957) 1970: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=1692, Revision Date: 9/9/2025, Access Date: 12/18/2025
This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.