Ulva (Enteromorpha) prolifera O.F. Müller, 1778

Common Name: Green alga, grass kelp, sea lettuce

Synonyms and Other Names:

Enteromorpha compressa var. prolifera, Enteromorpha compressa var. trichodes, Enteromorpha polyclados, Enteromopha prolifera, Enteromorpha salina, Enteromorpha salina var. polyclados, Ulva compressa var. prolifera, Ulva enteromorpha f. prolifera

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Identification: This green, filamentous, branched, monosiphonous, and benthic macroalga has hollow thalli with longitudinal rows of quadrangular to polygonal cells. Cells contain starch grains, large parietal chloroplasts, and vacuoles that reach up to 40% of cell volume (Blomster et al. 1998, Hadi et al. 1989, Hayden et al. 2003, Holt 1980b, Young et al. 1984). Fronds of U. prolifera are known to reach 18 cm–1 m long. Cells are around 8–18 μm long (Hadi et al. 1989, Ohno et al. 1999, Ohno and Takahasi 1988, Young et al. 1984).

Size: fronds to 1m

Native Range: Unclear. Ulva prolifera is typically a marine species, known in North America from the coasts, inland salt springs, and western salt lakes (Catling and McKay 1980, Mills et al. 1993). It is present in various waters, generally brackish or salty, in Asia, Europe, and Central America (Doroftei et al. 2001, Gazale and Morucci 1990, 1991, Grintal 1974, Hadi et al. 1989, Han et al. 2002, Holt 1980a, Huh et al. 2004, Kukk 1978, Markham and Munda 1977, McClanahan et al. 2005, Pacheco-Ruiz and Zertuche-Gonzalez 1996, Palomo et al. 2004, Partaly 1978, Polderman 1975, Riouall 1976, Saifullah and Nizamuddin 1977 Schories et al. 1997, Storelli et al. 2001, Wennberg 1992, Yagci 2006, Yamaguchi et al. 2006).

Map Key
This map only depicts Great Lakes introductions.

Great Lakes Nonindigenous Occurrences: Ulva prolifera was first recorded in 1979 near the Windsor Salt Factory in Ontario, within the Lake St. Clair drainage (Catling and McKay 1980, 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 Ulva (Enteromorpha) prolifera are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
MI197919791Lake St. Clair

Table last updated 7/21/2024

† Populations may not be currently present.

Ecology: This edible crop species comprises different strains that are known to survive, grow, and reproduce in very low salinity (0.1–1‰), brackish, salty, or briny waters. Ulva prolifera has been recorded from a wide range of water temperatures, but many strains prefer temperatures around 15–25°C and reach an upper critical limit at 30–34°C. Ulva prolifera grows well in eutrophic conditions, in which it can become a dominant benthic species. It can sometimes be limited by phosphorus (Dan et al. 2002, Koeman and Van Den Hoek 1982, McClanahan et al. 2005, Murase et al. 2005, O’Brien and Wheeler 1987, Ohno et al. 1999, Ohno and Miyanoue 1980, Ohno and Takahasi 1988, Palomo et al. 2004, Soe-Htun et al. 1986, Yagci 2006).

Ulva prolifera exhibits different reproductive strategies. Some plants are sexual and produce biflagellate anisogametes and quadriflagellate meiospores, while others are asexual and can either produce biflagellate or quadriflagellate negatively phototactic zooids. Plants of different sexuality may not be morphologically distinct, and some populations comprise plants of mixed life histories. Zygotes can remain dormant for a year or more in female filaments of sexual plants. Different populations of U. prolifera frequently exhibit high genetic diversity because plants can reproduce sexually, are highly fecund, are perennials (allowing for the accumulation of diverse traits), and undergo a colonization process involving highly diverse propagules on which various selective forces act (Hirakoka et al. 2003, Huh et al. 2004).

Ulva prolifera is known to host gammarid amphipod species in a brackish lake in Japan (Yamaguchi et al. 2006). In European coastal waters, it is preferred over its congener U. intestinalis as a surface for benthic diatom colonization because it is monosiphonous and not broad or flattened (Holt 1980b).

Means of Introduction: Unknown, although U. prolifera was very likely introduced from the Atlantic coast of North America to the Great Lakes basin.

Status: The last record was from 1979 and it is unknown what the current status of the population is.

Great Lakes Impacts:  

There is little or no evidence to support that Ulva prolifera has significant environmental impacts in the Great Lakes.
While blooms of U. prolifera have had significant negative environmental and socio-economic impacts in Asia (Xu et al. 2012), these impacts have not been realized in the Great Lakes. Moreover, the persistence of a population in the Great Lakes region is still uncertain.

Negative effects have not been realized in the Great Lakes because of the small and uncertain nature of the U. prolifera population (Mills et al. 1993).

However, in recent years, large blooms (over 1 million tons) of U. prolifera on the coastline of Asia have lead to declines in seagrass beds due to shading, disruption of feeding by wading birds, and an overall loss of algal biodiversity (Xu et al. 2012). In those “green tides,” Ulva prolifera released allelochemicals that inhibited growth and photosynthesis in native competitors (Xu et al. 2012). The massive blooms covered large extents of the sea bottom (13,000-30,000 km2) and decoupled biogeochemical cycles between the sediments and the water column. These chemical changes exposed native flora and fauna to oxygen deficiency and anoxia (Xu et al. 2012).

Ulva prolifera mats that formed on intertidal sandflats in Scotland were also found to significantly decrease the macrofaunal diversity. These negative impacts were particularly on species that use planktonic larval recruitment (Bloam et al. 2000). In intertidal flats of the Wadden Sea, dense mats of U. prolifera and other Ulva spp. have been associated with fewer occurrences of brown and red algae (Schories et al. 1997).

Domestically, U. prolifera, among other species, has been responsible for green tides in waters off the coast of Washington (Waaland and Hayden 1998).

There is little or no evidence to support that Ulva prolifera has significant socio-economic impacts in the Great Lakes.
China has been experiencing an increase in U. prolifera-dominated green tides since 2007, with a notable event just prior to the 2008 Beijing Olympics. There were significant impacts on the tourism industry as well as on aquaculture. The cost for emergency mitigation action in China during the 2008 bloom was estimated to cost around 200 million Euro. According to Nai-hao et al. (2011) green tides are responsible for aquaculture losses of approximately 86 million Euro annually.

In Spanish waters, U. prolifera is one of the species responsible for fouling intertidal oyster culture systems, although this problem can be partly controlled by snail grazing (Cigarria et al. 1998).

There is little or no evidence to support that Ulva prolifera has significant beneficial effects in the Great Lakes.
Zhuang et al. (2012) proposed the use of U. prolifera as green feedstock, biofuel substitute, and chemical production. Ulva prolifera is edible and is considered an economically viable food option in Japan and China (Dan et al. 2002).


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.

There are no known biological control methods for this species.

Ulva prolifera can be physically harvested from the water and beaches. However, depending on the size of the bloom this may not be an economically viable option (Nai-hoa et al. 2011).

Ulva prolifera blooms occur in eutrophic marine waters. As a result, the reduction of pollution and nutrient run-off could decrease the viable habitat for U. prolifera.

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

Remarks: Ulva was described by Linneaus to consist of green seaweeds with distromatic blades. Link, later removed some species from Ulva and moved species that had a distinct tubular form to Enteromorpha. After conducting a phylogenetic DNA analysis, Hayden et al. (2003) found that the separation of the two genera was artificial and that species in Enteromorpha should be returned to the original Ulva classification. While ITIS lists U. flexuosa under the genus Enteromorpha, Enteromorpha species are now recognized as belonging to the genus Ulva.

References (click for full reference list)

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

Contributing Agencies:

Revision Date: 5/18/2021

Citation for this information:
Kipp, R.M., M. McCarthy, and A. Fusaro, 2024, Ulva (Enteromorpha) prolifera O.F. Müller, 1778: 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=2714, Revision Date: 5/18/2021, Access Date: 7/21/2024

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.