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| NAS - Nonindigenous Aquatic Species |
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Common Name: diatom
Synonyms and Other Names: Melosira subtilis
Taxonomy: available through 
Identification: This small and delicate diatom species generally forms cylindrical chains of a couple to over 30 cells. Valves may exhibit convex shape in the center. Irregular, rectangular areolae are typically arranged radially in uneven rows. There may be weakly silicified radial striae. Variously shaped spines generally occur around the valve rims. Cells typically contain two disc-like chromatophores (Kuzmin et al. 1970; Vinogradskaya and Bereza 1974; Stoermer et al. 1975; Main 1977).
Size: Diameter can range from around 3–15 µm (Kuzmin et al. 1970; Main 1977)
Native Range: S. subtilis is a Eurasian species known from various regions (Mills et al. 1993). Exact native range within this territory is unclear. See Remarks for some more details.
Nonindigenous Occurrences: S. subtilis was recorded for the first time in Lake Michigan in 1946. It occurred in Lake Ontario in 1972. It has also been recorded from Lake Erie and Lake Huron (Stoermer et al. 1975; Mills et al. 1993).
Ecology: S. subtilis most typically occurs at maximum abundance in disturbed littoral regions, river mouths, and harbors of the Great Lakes in eutrophic and frequently chloride-contaminated, slightly brackish habitats. It is known to respond positively to phosphorus enrichment, or if phosphorus and nitrogen are not limiting, to the addition of trace minerals. Maximum abundance in the Great Lakes probably occurs at temperatures around 18–19ºC and never below 9ºC, generally in early summer. Abundance in Lake Michigan was very high in the 1960s (Stoermer and Yang 1970; Stoermer et al. 1975; Stoermer and Ladewski 1976; Tarapchak and Stoermer 1976; Stoermer et al. 1978; Millie and Lowe 1983; Mills et al. 1993).
In various regions of Eurasia S. subtilis has been recorded at maximum abundance in spring, summer, and/or fall. It is often recorded in habitats with neutral to alkaline pH, increased ion content, and high phosphorus concentrations. In the Dnieper S. subtilis has reached maximum abundance at 19–25ºC (Kuzmin et al. 1970; Kuzmin and Okhapkin 1979; Vinogradskaya and Bereza 1974; Martin and Naef 1977; Guzkowska and Gasse 1990a,b).
Means of Introduction: S. subtilis was very likely introduced in ballast water to the Great Lakes basin (Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction: Unknown.
Remarks:
Within Eurasia S. subtilis occurs in many regions of the Volga and Dnieper river basins in the former USSR. It is unclear if it is endemic to these areas or not. It may have been present before the 1960s and 1970s when it was first recorded, but was assigned to a different taxon by previous investigators. This species is known from other areas of Eurasia such as Sweden, the North Sea, and Dutch rivers (Kuzmin et al. 1970; Vinogradskaya and Bereza 1974; Kuzmin and Okhapkin 1979).
S. subtilis is synonymous with Melosira subtilis.
References
Guzkowska, M. A. J. and F. Gasse. 1990. The seasonal response of diatom communities to variable water quality in some English urban lakes. Freshwater Biology 23:251-264.
Kuzmin, G. V. and A. G. Okhapkin. 1979. Saprobic characteristics of the Volga Reservoirs through algological studies. Pp. 171-175 in Mordukhai-Boltovskoi, P. D. (ed.). The River Volga and its Life. Monographiae Biologicae, vol. 33. 473 pp.
Kuzmin, G. V., I. V. Makarova, and L. N. Voloshko. 1970. Occurrence in the Volga of the little-known diatom Stephanodiscus subtilis. Hydrobiological Journal 6(3):79-81.
Main, S. P. 1977. Benthic diatom distribution in the Cedar River Basin, Iowa, USA. Proceedings of the Iowa Academy of Science 84(1):23-29.
Martin, P. and J. Naef. 1977. Plankton from Lake Geneva, characteristics of the year 1976. Compte Rendu des Seances de la Societe de Physique et d’Histoire Naturelle de Geneve 12(2-3):96-102.
Millie, D. F. and R. L. Lowe. 1983. Studies on Lake Erie’s littoral algae: host specificity and temporal periodicity of epiphytic diatoms. Hydrobiologia 99:7-18.
Mills, E. L., J. H. Leach, J. T. Carlton, and C. L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.
Stoermer, E. F. and J. J. Yang. 1970. Distribution and abundance of dominant plankton diatoms in Lake Michigan. Great Lakes Research Division, Publication No. 16, The University of Michigan, Ann Arbor, Michigan. 64 pp.
Stoermer, E. F. and T. B. Ladewski. 1976. Apparent optimal temperatures for the occurrence of some common phytoplankton species in southern Lake Michigan. Great Lakes Research Division Publication 18, The University of Michigan, Ann Arbor, Michigan. 49 pp.
Stoermer, E. F., B. G. Ladewski, and C. L. Schelske. 1978. Population responses of Lake Michigan phytoplankton to nitrogen and phosphorus enrichment. Hydrobiologia 57(3):249-265.
Stoermer, E. F., M. M. Bowman, and J. C. Kingston. 1975. Phytoplankton composition and abundance in Lake Ontario during IFYGL. National Environmental Research Center, Office of Research and Development, US Environmental Protection Agency, Corvallis, Oregon. 373 pp.
Tarapchak, S. J. and E. F. Stoermer. 1976. Environmental status of the Lake Michigan region. Volume 4. Phytoplankton of Lake Michigan. Consultants to Division of Environmental Impact Studies, U. S. Energy Research and Development Administration. 211 pp.
Vinogradskaya, T. A. and V. D. Bereza. 1974. The development of Stephanodiscus subtilis in the Dnieper and the Dnieper reservoirs. Hydrobiological Journal 10(2):53-54.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 8/2/2007 Citation for this information:
Rebekah M. Kipp. 2009. Stephanodiscus subtilis. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1698> Revision Date: 8/2/2007
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