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| NAS - Nonindigenous Aquatic Species |
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Common Name: brown alga
Taxonomy: available through 
Identification: This alga comprises brown filamentous half-discs exhibiting heterotrichous growth. Many of the filaments are frequently tangled and some are modified as rhizoids. The erect filaments are greatly reduced in comparison to those of S. fluviatilis. Filaments may exhibit some branching and are uni- or biseriate. In both the erect and prostrate regions of this alga there are relatively long hairs that grow basally out of an enclosed meristem (Schloesser and Blum 1980). This species is ≤2 mm in diameter and erect filaments are greatly reduced in comparison to S. fluviatilis, which has also been introduced to the Lake Michigan drainage. See Schloesser and Blum (1980) for more detailed cell dimensions.
Size: <2mm diameter
Native Range:
Unknown. S. lacustris was first described from the Great Lakes drainage, where it is considered an exotic species (Mills et al. 1993).
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Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences: S. lacustris first occurred in Lake Michigan in 1975 (Schloesser and Blum 1980; Mills et al. 1993).
Ecology:
It is quite rare for a brown alga to grow in a freshwater system. In the Great Lakes drainage no sexual reproduction occurs in S. lacustris, which indicates that this species could have evolved in a marine environment instead of a freshwater habitat. In Lake Michigan, S. lacustris was recorded from the sublittoral zone on the western shore at 9–10 m depth and was observed growing epilithically on igneous rocks and gravel (Schloesser and Blum 1980; Mills et al. 1993).
Cells of this species contain physodes, which are vesicles filled with compounds that may be unpalatable to grazers. S. lacustris in the Great Lakes reproduces asexually, probably via propagules that break off as tri-branched nodules, as well as unilocular zoidocysts that form at the ends of branched basal filaments (Schloesser and Blum 1980).
Means of Introduction: S. lacustris was very likely introduced in ships’ ballast water or via aquarium release to the Great Lakes basin (Mills et al. 1993).
Status: Established where recorded.
Impact of Introduction: Unknown.
Remarks:
References
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.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 7/31/2007 Citation for this information:
Rebekah M. Kipp. 2009. Sphacelaria lacustris. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=1676> Revision Date: 7/31/2007
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