Sphacelaria fluviatilis Jao, 1943

Common Name: A brown alga

Synonyms and Other Names:

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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, oppositely branched, and are monosiphonous or polysiphonous (Wehr and Sheath 2003). 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, uniseriate hairs are apparent 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). This is in contrast with 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: Up to 11mm

Native Range: Unclear, but Sphacelaria fluviatilis was originally recorded from western China (Jao 1943, Mills et al. 1993).

Map Key
This map only depicts Great Lakes introductions.

Great Lakes Nonindigenous Occurrences: Sphacelaria fluviatilis first occurred in 1975 in Gull Lake, Michigan, which is part of the Lake Michigan watershed (Mills et al. 1993).

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Sphacelaria fluviatilis are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†

Table last updated 12/10/2023

† Populations may not be currently present.

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 suggests 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 through the rest of the year. In freshwater lab culture 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 (e.g., 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: Sphacelaria 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.

Great Lakes Impacts:

There is little or no evidence to support that Sphacelaria fluviatilis has significant environmental impacts in the Great Lakes.

The population of S. fluviatilis in Gull Lake, Michigan is small and unlikely to provide a significant food for any lake herbivores (Wehr and Sheath 2003). Furthermore, it is not known to reproduce sexually and therefore is not expected to affect the genetic composition of native algal populations (Wujek et al. 2006).

There is little or no evidence to support that Sphacelaria fluviatilis has significant socio-economic impacts in the Great Lakes.

There is little or no evidence to support that Sphacelaria fluviatilis has significant beneficial effects in the Great Lakes.


Regulation (pertaining to the Great Lakes region)
There are no known methods of regulation for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

There are no known biological control methods for this species.

There are no known physical control methods for this species.

There are no known chemical control methods for this species.

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: There is a limited amount of research that has been conducted on the population of S. fluviatilis in Gull Lake (Michigan). It was identified over 40 years ago, and while a population is still present, it does not seem to be expanding because it only undergoes vegetative reproduction.

References (click for full reference list)

Other Resources:
Author: Kipp, R.M., M. McCarthy, and A. Fusaro

Contributing Agencies:

Revision Date: 9/12/2019

Citation for this information:
Kipp, R.M., M. McCarthy, and A. Fusaro, 2023, Sphacelaria fluviatilis Jao, 1943: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?Species_ID=1686&Potential=N&Type=0&HUCNumber=DGreatLakes, Revision Date: 9/12/2019, Access Date: 12/10/2023

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.