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| NAS - Nonindigenous Aquatic Species |
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Common Name: brown alga
Taxonomy: available through 
Identification: This alga has a flat holdfast and appears woolly and yellow to brown in subaerial conditions but is darker brown to black and more loosely tangled when growing submersed. Filaments are typically 2 or 4 seriate, may be branched, and are monosiphonous or polysiphonous. Some are modified to form rhizoids. The alga often grows prostrate on its substrate but may also send out erect branches that in turn can grow laterally. In the Lake Michigan basin, there are uniseriate hairs apparent growing at the base of intercalary meristematic cells. However, these hairs were not mentioned in the original description from western China (Jao 1943; Thompson 1975).In its type locality S. fluviatilis does not grow to more than 1 mm high in subaerial habitat but when growing submersed it can grow up to 11 mm high (Jao 1943).Compare to S. lacustris, which also occurs in the Lake Michigan basin, and can probably only reach up to around 1 mm high (Schloesser and Blum 1980).
Size: to 11mm
Native Range:
Unclear, but S. fluviatilis was originally recorded from western China (Jao 1943; Mills et al. 1993).
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences: S. fluviatilis first occurred in 1975 in Gull Lake, Michigan, which is part of the Lake Michigan watershed (Mills et al. 1993).
Ecology:
It is very rare for a brown alga to grow in a freshwater environment, and Sphacelaria is typically a marine genus. In fact, this genus is likely the only one in the order Sphacelariales with species known to survive freshwater conditions (Jao 1943; Timpano 1978; Mills et al. 1993). In Gull Lake, Michigan, S. fluviatilis was found on the undersides of pebbles at a depth of around 60–75 cm. In this water body, no sexual reproduction occurs, which indicates that this species could have evolved in a marine system. Vegetative reproduction occurs by free-floating propagules (Thompson 1975; Mills et al. 1993).
In China in the type locality, S. fluviatilis grows on the sides of sandstone rocks in shady damp habitats in places that are underwater from around April to October and above water in other months. In freshwater culture in the lab using river water from the type locality, S. fluviatilis does not display any of the reproductive structures that marine algae from this family typically do, such as propagules, sporangia, and gametangia. However, it is suspected that reproduction via vegetative propagules occurs in the type locality (Jao 1943). Finally, the ultrastructure (i.e. organelle organization) of this species does not vary in a way that explains why it is able to persist in freshwater environments (Timpano 1980).
Means of Introduction: S. fluviatilis was very likely introduced via aquarium release or another form of accidental release to the Great Lakes basin (Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction: Unknown.
Remarks:
References
Jao, C. C. 1943. Studies on the freshwater algae of China. XI. Sphacelaria fluviatilis, a new freshwater brown alga. Sinensia 14:151-154.
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.
Schloesser, R. E. and J. L. Blum. 1980. Sphacelaria lacustris sp. nov., a freshwater brown alga from Lake Michigan. Journal of Phycology 16:201-207.
Timpano, P. 1978. Preliminary studies of Sphacelaria fluviatilis a fresh water phaeophyte. Transactions of the Kansas Academy of Science 81(2):96.
Timpano, P. 1980. The ultrastructure of the fresh water phaeophyte Sphacelaria fluviatilis. Journal of Phycology 16(suppl.):44.
Thompson, R. H. 1975. The fresh water brown alga Sphacelaria fluviatilis new record. Journal of Phycology 11(suppl.):5.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 7/30/2007 Citation for this information:
Rebekah M. Kipp. 2009. Sphacelaria fluviatilis. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1686> Revision Date: 7/30/2007
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