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| NAS - Nonindigenous Aquatic Species |
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Common Name: Diatom
Taxonomy: available through 
Identification: This cylindrical diatom displays flat or somewhat concave valves that form chains via long threads connecting them together. There may be 2–5 marginal labiate processes between the valve face and the mantle, 4–6 central pore-like fultoportulae on the valve face, and generally 2 rings of strutted processes on the mantle. Areolae are loculate, often hexagon-shaped, and arranged in radial rows. Silicification may vary from population to population (Hasle 1978; Hasle and Syvertsen 1990; Edlund et al. 2000).The diameter of T. baltica in Lake Ontario is around 16–27 µm but may be as great as 120 µm in other regions. Diameter could be inversely related to salt content in water (Hasle 1978; Edlund et al. 2000).
Size: diameter <120 microns, smaller in Great Lakes
Native Range:
Exact native range is unclear. The type locality is the Baltic Sea and a large number of records exist from this sea, polar seas, inland Eurasian seas, and many parts of coastal Europe. T. baltica has also been recorded off the coasts of Japan and the western United States (Hasle 1978; Hasle and Syvertsen 1990; Edlund et al. 2000).
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences: T. baltica was first recorded in sediment cores from Lake Ontario around 1988 (Edlund et al. 2000). It has since been recorded in Lake Erie and Lake Superior as well (EPA 2008).
Ecology: T. baltica is a euryhaline species that grows rapidly and often occurs in areas experiencing anthropogenic impacts. It may form resting cells that could survive dark, anoxic conditions. It can very likely tolerate ballast water exchange as it has survived conditions with conductivity as low as 300 µmho/cm in Lake Ontario and salinity as high as 44‰ in other regions of the world. Growth rates reach a maximum at salinities around 4–8‰ but growth at 80% or more of the maximum rate has still been recorded at salinities varying from 0.5–20‰. Below a salinity of 2‰ growth may vary depending on the exact ionic composition of water in which populations occur.
In the Baltic and Arctic Seas T. baltica occurs most abundantly in areas influenced by large Canadian and Siberian rivers or other regions of relatively low salinity. It typically does not occur in regions of relatively high salinity such as the Oslofjord. T. baltica can be consumed by species such as copepods and its skeleton may be passed completely intact into fecal pellets. In fecal pellets of such invertebrates T. baltica settles out of the water column much faster than when it is not consumed (Schrader 1971; Paasche 1975; Hasle and Syvertsen 1990).
Means of Introduction: T. baltica was very likely introduced in ballast water to the Great Lakes basin (Edlund et al. 2000).
Status: Established where recorded.
Impact of Introduction:
A) Realized: Unknown.
B) Potential: Edlund et al. (2000) indicate that Julius et al. (1998) recorded the local extirpation of Stephanodiscus niagarae from its type locality in Lake Ontario around the time of introduction of T. baltica. The local extirpation of the native species could have occurred as a result of the introduction of T. baltica and/or increasing unsuitability of abiotic conditions in the lake.
Remarks: T. baltica may be synonymous with T. subsalina from the Baltic Sea. The two may or may not be one species that varies morphologically with changing salinity (Hasle 1978).
References
Edlund, M. B., C. M. Taylor, C. L. Schelske, and E. F. Stoermer. 2000. Thalassiosira baltica (Grunow) Ostenfeld (Bacillarophyta), a new exotic species in the Great Lakes. Canadian Journal of Fisheries and Aquatic Sciences 57:610-615.
EPA Monitoring Data. 2008. EPA Great Lakes National Program Office.
Hasle, G. R. 1978. Some fresh water and brackish water species of the diatom genus Thalassiosira. Phycologia 17(3):263-292.
Hasle, G. R. and E. E. Syvertsen. 1990. Arctic diatoms in the Oslofjord, Norway, and the Baltic Sea. A biogeographic and paleogeographic problem. Pp. 285-300 In H. Simola (ed.). Proceedings of the tenth international diatom symposium: Joensuu, Finland, Aug. 28-Sept. 2, 1988. Koeltz Scientific Books.
Julius, M. L., E. F. Stoermer, C. M. Taylor, and C. L. Schelske. 1998. Local extirpation of Stephanodiscus niagarae Ehrenb. (Bacillariophyta) in the recent limnological record of Lake Ontario. Journal of Phycology 34:766-771.
Paasche, E. 1975. The influence of salinity on the growth of some plankton diatoms from brackish water. Norwegian Journal of Botany 22(3):209-215.
Schrader, H. J. 1971. Fecal pellets role in sedimentation of pelagic diatoms. Science 174(4004):55-57.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 5/8/2009 Citation for this information:
Rebekah M. Kipp. 2009. Thalassiosira baltica. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2717> Revision Date: 5/8/2009
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