Hollow green weed, Conferva paradoxa, Enteromorpha clathrata var. hopkirkii, Enteromorpha intestinalis var. tubulosa, Enteromorpha erecta, Enteromorpha flexuosa subsp. paradoxa, Enteromorpha hopkirkii, Enteromorpha paradoxa, Enteromorpha paradoxa var. typica, Enteromorpha plumose, Enteromorpha prolifera var. tubulosa , Enteromorpha tubulosa, Scytosiphon erectus, Ulva paradoxa 

Ulva flexuosa subsp. flexuosa is yellow-green with tubular fronds, cylindrical stalks, and a blade expanding above the stalk which ends in a rounded tip. It is attached to the substrate by a small, round basal disc (Sahoo et al. 2003). Ulva flexuosa subsp. flexuosa has sparse branching, one to two pyrenoids (for carbon dioxide fixation), and quadrangular or rectangular cells arranged in approximately regular rows (Mares et al. 2011).

Ulva flexuosa subsp. paradoxa has an intensely branched stalk with rectangular cells arranged in long rows. These rows are somewhat unordered in the central parts of broader thalli, thinning to a single row of cells at the ends of branchlets (Mares et al. 2011).

Ulva flexuosa is considered a cosmopolitan species that has a worldwide distribution (Lougheed and Stevenson 2004).

In Muskegon Lake, the two subspecies co-occur in littoral zone macrophyte beds, although U. flexuosa subsp. paradoxa has been recorded to comprise 61% of the macroalgae present by biovolume, while U. flexuosa subsp. flexuosa only comprised 31%. In White Lake, Ulva sp. has been known to comprise 5% of the macroalgae present, and in Mona Lake, 20% (Lougheed and Stevenson 2004).

Ulva flexuosa is known from diverse habitats around the world and has been recorded in salinities ranging from 0.5–34‰. It has been recorded in tidal pools, on mudflats, in sea dikes, in polyhaline man-made waters, in oligohaline ponds, in drainage ditches, on rocks, and in warm calm waters below low tide (Kapraun 1970, Koeman and van den Hoek 1984, Hadi et al. 1989, Sahoo et al. 2003).

To reproduce, dioecious gametophytes produce male and female gametes that have two flagellae, while sporophytes produce zoospores with four flagellae (Koeman and van den Hoek 1984). Zoospores can be stored in the dark for over 50 days and still germinate with a 35% survival rate, suggesting that transport in ballast water is possible (Beach et al. 1995, Kolwalkar et al. 2007). Swarmers may be released with increasing exposure at night and greater desiccation, whereas vegetative growth may typically occur with shorter exposure times (Mairh et al. 1985).

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental	Socioeconomic	Beneficial

The Great Lakes range of U. flexuosa is currently limited to Muskegon, Mona and White Lake. However, as it is able to form blooms in Muskegon Lake—which has a lower conductivity than Lake Erie—there is potential for it to thrive in other locations in the Great Lakes (Lougheed and Stevenson 2004).

Ulva flexuosa has a moderate environmental impact in the Great Lakes.
Realized:
The first recorded bloom of U. flexuosa in the Great Lakes occurred in Muskegon Lake, where it dominated the macrophyte community. Ulva flexuosa supports a relatively low density and diversity of epiphytes compared to native macrophytes (Lougheed and Stevenson 2004). Moreover, U. flexuosa has formed dense, free floating mats in Muskegon Lake during bloom conditions.

Potential:
Blooms of U. flexuosa in Europe have been associated with the extirpation of species of red algae and epiphytes (Schories et al. 1997). If U. flexuosa was to replace Oedogonium and Cladophora, which support many diatoms, food webs depending on such epiphytes could be negatively affected (Lougheed and Stevenson 2004).

When U. flexuosa blooms in nutrient rich marine coastal areas, a decline in biodiversity of native algae has been observed, as well as cascading food web effects that negatively impact macroinvertebrates, shorebirds, and fish (Lougheed and Stevenson 2004). Mats of U. flexuosa have also impacted abiotic conditions, as the dense algal cover alters redox conditions and chemical interactions between the sediment and water column (Lougheed and Stevenson 2004). It is hypothesized that shading of macrophytes could become problematic in Great Lakes if blooms were sustained for long periods of time (Lougheed and Stevenson 2004).

Ulva flexuosa has a moderate socio-economic impact in the Great Lakes.
Realized:
Ulva flexuosa is known to foul a variety of permanent man-made structures and boats. This can lead to expensive repairs of fouled boat motors. There are even reports of it growing on boats treated with antifouling paint (Kolwalker et al. 2007, Lougheed and Stevenson 2004).

Mats of U. flexuosa washed up on the shores of Muskegon Lake during the bloom of 2003 discouraged beach use by tourists (Lougheed and Stevenson 2004). In addition to the cost to boat users, these blooms also decreased the value of lakeshore property and discouraged tourism (Lougheed and Stevenson 2004).

Ulva flexuosa has a moderate beneficial impact in the Great Lakes.
Potential:
Ulva flexuosa is used as a bioindicator for metal contamination, including lead and iron (Ho 1987, Tabudravu et al. 2002). Ulva flexuosa was also found to be an economically efficient species for bioabsorption in industrial settings. It could be used as an eco-friendly alternative for wastewater treatment in dye manufacturing, tannery, textile, and cosmetic industries (Sivasamy et al. 2012).

Regulations (pertaining to the Great Lakes region).
There are no known regulations for this species.

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

Control
Biological
There are no known biological control methods for this species .

Physical
There are no known physical control methods for this species.

Chemical

The presence of U. flexuosa is associated with high nutrient availability and high levels of salinity (Lougheed and Stevenson 2004, Shories et al. 1997). The reduction of pollution and nutrient run-off could decrease the viable habitat for U. flexuosa.

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