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| NAS - Nonindigenous Aquatic Species |
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Common Name: diatom
Synonyms and Other Names: Microsiphona potamos
Taxonomy: available through 
Identification: This relatively small centric diatom forms chains of 1–10 cells, connected by tubular marginal processes that are cleft at the end and that may vary in length depending on salinity. It exhibits a flattened to slightly rounded valve face and a high mantle. Silicified, granulated, and knobby ribs occur in radial arrangements on the valves and mantle. There are typically 5–8 processes per valve and 5–8 rows of areolae between them (Hasle and Evensen 1976; Kiss et al. 1994).The valve diameter of S. potamos is around 2.6–6.5 μm (Hasle and Evensen 1976; Belcher and Swale 1978; Genkal and Kuzmin 1980; Kiss et al .1994).
Size: diameter <7 microns
Native Range:
Unclear. S. potamos is widespread but it is uncertain to which region(s) it should be considered native. See Remarks section for more details.
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences: S. potamos first occurred in Lake Erie in 1963 at Toledo, Ohio. It has also been recorded from other parts of Lake Erie and its drainage, Lake Ontario, Lake Huron and Lake Superior (Lowe and Kline 1976; Nicholls et al. 1983; Mills et al. 1993; EPA 2008).
Ecology: S. potamos is generally considered a warm stenothermic and photophilic species with a broad salinity tolerance, typically found in freshwater rivers, freshwater lakes, tidal estuaries, and coastal waters. It is particularly abundant in eutrophic waters and may co-occur with species of blue-green algae (Hasle and Evensen 1976; Marshall and Alden 1990; Ueno 1992; Mills et al. 1993; Kiss et al. 1994; Bothar and Kiss 1995; Marshall et al. 2006).
At the Grand River mouth on Lake Erie, the occurrence of S. potamos has been associated with relatively elevated concentrations of phosphorus, nitrogen, and chloride (Nicholls et al. 1983). S. potamos may reach maxima in abundance in spring, summer, and/or fall (Lowe and Kline 1976; Nicholls et al. 1983; Sabater and Munoz 1990; Kiss et al. 1994; Marsgall et al. 2006).
Means of Introduction: S. potamos was very likely introduced in ballast water via ships entering the Great Lakes from North American river drainages outside the basin or from European ports (Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction: Unknown.
Remarks: S. potamos was first described from the Jensensee in Germany under the name S. subsalsus but then redescribed as S. potamos from the Little Miami River at Cincinnati (Kiss et al. 1994). It is now known from North American rivers on both sides of the continent, and parts of Europe including France, England, Germany, Austria, Hungary, the Ukraine, Russia, and Spain (Belcher and Swale 1978; Sabater and Munoz 1990; Mills et al. 1993; Kiss et al. 1994). S. potamos is also now known from Japanese coastal waters (Ueno 1992) and from the La Trobe River in Australia (Chessman 1985). Some authors have recorded this species as Microsiphona potamos. Hasle and Evensen (1976) showed that it is actually very similar to other species of Skeletonema, and thus suggested the new name.
References
Belcher, J. H. and E. M. F. Swale. 1978. Skeletonema potamos and Cyclotella atomus Bacillariophyceae in the plankton of rivers in England and France. British Phycological Journal 13(2):177-182.
Bothar, A. and K. T. Kiss. 1995. Changes in phytoplankton and zooplankton in the Danube near God, Hungary (1669 km of river) between 1991-1994. Opuscula Zoologica (Budapest) 27-28:137-146.
Chessman, B. C. 1985. Phytoplankton of the La Trobe River, Victoria. Australian Journal of Marine and Freshwater Research 36:115-122.
EPA Monitoring Data. 2008. EPA Great Lakes National Program Office.
Genkal, S. I. and G. V. Kuzmin. 1980. Taxonomy and biology of little known fresh water Skeletonema spp. Bacillariophyta. Gidrobiologicheskii Zhurnal 16(4):25-30.
Hasle, G. R. and D. L. Evensen. 1976. Brackish water and freshwater species of the diatom genus Skeletonema. II. Skeletonema potamos comb. nov. Journal of Phycology 12:73-82.
Kiss, K. T., E. Acs, and A. Kovacs. 1994. Ecological observations on Skeletonema potamos (Weber) Hasle in the River Danube, near Budapest (1991-92, daily investigations). Hydrobiologia 289(1-3):163-170.
Lowe, R. L. and P. A. Kline. 1976. Planktonic centric diatoms from the Sandusky River, Ohio, USA. Pp. 143-152 in D. B. Baker, W. B. Jackson, and B. L. Prater (eds.) International Reference Group on Great Lakes Pollution from Land Use Activities. Sandusky River Basin Symposium, Tiffin, Ohio, USA, May 2-3, 1975. US Government Printing Office: Washington, D.C. 475 pp.
Marshall, H. G., R. V. Lacouture, C. Buchanan, and J. M. Johnson. 2006. Phytoplankton assemblages associated with water quality and salinity regions in Chesapeake Bay, USA. Estuarine, Coastal and Shelf Science 69(1-2):10-18.
Marshall, H. G. and R. W. Alden. 1990. A comparison of phytoplankton assemblages and environmental relationships in three estuarine rivers of the lower Chesapeake Bay. Estuaries 13(3):287-300.
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.
Nicholls, K. H., R. Taylor, and Y. Hamdy. 1983. The influence of the Grand River on phytoplankton near the northeastern shore of Lake Erie, USA/Canada during 1979. Archiv fuer Hydrobiologie 98(2):146-172.
Sabater, S. and I. Munoz. 1990. Successional dynamics of the phytoplankton in the lower part of the River Ebro, Spain. Journal of Plankton Research 12(3):573-592.
Ueno, S. 1992. Studies on the life cycle and the distribution of marine planktonic diatoms Skeletonema costatum (Grev.) Cleve and Skeletonema tropicum Cleve in Japanese coastal waters. Journal of Shimonoseki University of Fisheries 40(1):23-58.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 5/25/2007 Citation for this information:
Rebekah M. Kipp. 2009. Skeletonema potamos. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1689> Revision Date: 5/25/2007
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