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| NAS - Nonindigenous Aquatic Species |
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Common Name: diatom
Synonyms and Other Names: C. muelleri var. subsalsum; C. hohnii
Taxonomy: available through 
Identification: This small, somewhat silicified diatom species exhibits around 8 costae per µm on the valve, valve mantle, and girdle bands, arranged in a radiating pattern. At the valve and mantle joints there are centric tubular setae. There is no central labiate process on the valves. Valves are round to oval in shape and cells are cylindrical in side view. Cells occur singly or occasionally in groups of 2–3 forming short filaments. Spores are silicified. Living cells contain one chromatophore (Wujek and Graebner 1980; Johansen and Rushforth 1985). C. muelleri var. subsalsum valves range in length from 3–20 µm. Resting spores are around 4–12 µm in length. The range for specimens recorded from the Great Lakes is 3–10.5 µm and there have been no recorded spores (Wujek and Graebner 1980; Johansen and Rushforth 1985).
Size: to 20 microns
Native Range:
Widespread. Originally reported from Europe and subsequently from Russia and North
America. According to Rushforth and Johansen (1986) the taxonomy of this
group is somewhat questionable. C. muelleri is the only species reported
from Eurasia, but they found other species in North America.
C. muelleri var. subsalsum probably originated in a marine or brackish water environment.
Nonindigenous Occurrences: C. muelleri var. subsalsum was recorded for the first time in Saginaw Bay, Lake Huron, and tributaries flowing into this bay in 1978 (Wujek and Graebner 1980; Mills et al. 1993).
Other than the Great Lakes, it has been recorded from the Salton Sea,
California; the Pecos River, New Mexico; Great Salt Lake, Utah; the
Napier Dam, South Africa; and various locations in Kansas (Johansen and
Rushforth 1985; Mills et al. 1993; Reifel et al. 2007).
Ecology:
The genus Chaetoceros is generally a marine taxon. It is likely that C. muelleri var. subsalsum is an introduced species and not native to the Great Lakes, even though it was first described there. Other nonindigenous species in the genus Chaetoceros have been recorded in ballast water samples from vessels entering the Great Lakes (Mills et al. 1993).
The only Chaetoceros spp. known from North America are C. elmorei and C. muelleri. C. muelleri var. subsalsum is a mesohalobe variant of C. muelleri, originally described from the Great Lakes as a new species, C. hohnii. Extensive studies on material from North America and South Africa indicate that C. muelleri var. subsalsum is distinct from C. muelleri (Wujek and Graebner 1980; Johansen and Rushforth 1985).
In the Tittabbawassee River, which is part of the Lake Huron drainage, water chemistry at the time C. muelleri var. subsalsum was recorded fell within a preference range expected for a species of brackish or marine origin. Conductivity ranged from 570-2690 µmhos/cm and ion concentrations (such as chloride, potassium, sodium, magnesium, and calcium) were higher than those normally expected in freshwater. The pH at the time was 7.8–8.0 and the water temperature was 17–18ºC. Abundance of C. muelleri var. subsalsum ranged up to 188 cells per ml, which is less than 1% of the phytoplankton present at the time (Wujek and Graebner 1980). In the Pecos River, New Mexico, C. muelleri var. subsalsum has been recorded to reach a maximum abundance at conductivities of 1100-5200 µmhos/cm and temperatures around 25ºC (Johansen and Rushforth 1985).
C. muelleri var. subsalsum is capable of producing spores. It is unknown what triggers spore production in freshwater populations, as some populations produce none while others produce many. Salinity may be a factor. No spores have been recorded in populations from the Great Lakes (Wujek and Graebner 1980; Johansen and Rushforth 1985).
Means of Introduction: C. muelleri var. subsalsum was very likely introduced via ballast water to the Great Lakes (Mills et al. 1993).
Status: Reported. There have been no records since the first publication by Wujek and Graebner (1980).
Impact of Introduction: Unknown.
Remarks: C. muelleri var. subsalsum is synonymous with C. hohnii (Johansen and Rushforth 1985). Stoermer and Kreis (1978) recorded Chaetoceros spp. in the Great Lakes but gave no further details as to species, location, or description.
References
Johansen, J. R. and S. R. Rushforth. 1985. A contribution to the taxonomy of Chaetoceros muelleri Lemmermann (Bacillariophyceae) and related taxa. Phycologia 24(4):437-447.
Lange, C. B. and M. A. Tiffany. 2002. The diatom flora of the Salton Sea, California. Hydrobiologia 473:179-201.
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.
Reifel, K. M., B. K. Swan, E. Olivo, J. M. Watts, C. C. Trees, and S. H. Hurlbert. 2007. Influence of river inflows on plankton distribution around the southern perimeter of the Salton Sea, California. Hydrobiologia 576:167-183.
Stoermer, E. F. and R. G. Kreis, Jr. 1978. Preliminary checklist of diatoms (Bacillariophyta) from the Laurentian Great Lakes. Journal of Great Lakes Research 4:149-169.
Wujek, D. E. and M. Graebner. 1980. Note. A new freshwater species of Chaetoceros from the Great Lakes region. Journal of Great Lakes Research 6(3):260-262.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 6/21/2007 Citation for this information:
Rebekah M. Kipp. 2009. Chaetoceros muelleri subsalsum. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1674> Revision Date: 6/21/2007
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