Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Ulva pertusa



Ulva pertusa


  • Last modified
  • 25 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Ulva pertusa
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Plantae
  •     Phylum: Chlorophyta
  •       Class: Chlorophyceae
  •         Order: Ulvales
  • Summary of Invasiveness
  • U. pertusa is a macroscopic green seaweed widely distributed in the Indo-Pacific Ocean. It has delicate but tough glossy bright to dark green blades up to 20 cm long. The blade is rounded when young but becomes l...

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A very large free-floating specimen. Combarro, Pontevedra, Spain. 16th May 2009.
TitleFree-floating specimen
CaptionA very large free-floating specimen. Combarro, Pontevedra, Spain. 16th May 2009.
CopyrightJavier Cremades Ugarte
A very large free-floating specimen. Combarro, Pontevedra, Spain. 16th May 2009.
Free-floating specimenA very large free-floating specimen. Combarro, Pontevedra, Spain. 16th May 2009.Javier Cremades Ugarte
Habit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
CaptionHabit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
CopyrightJavier Cremades Ugarte
Habit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
HabitHabit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.Javier Cremades Ugarte
Habit. Camariñas, A Coruña, Spain. 27th March 2009.
CaptionHabit. Camariñas, A Coruña, Spain. 27th March 2009.
CopyrightJavier Cremades Ugarte
Habit. Camariñas, A Coruña, Spain. 27th March 2009.
HabitHabit. Camariñas, A Coruña, Spain. 27th March 2009.Javier Cremades Ugarte
Habit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
CaptionHabit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
CopyrightJavier Cremades Ugarte
Habit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.
HabitHabit on herbarium sheet. Ensenada de Lourido, A Coruña, Spain. 21st May 2009.Javier Cremades Ugarte
Habit on rocky shores, on mussels below the Fucus belt. Combarro, Pontevedra, Spain. 16th May 2009.
TitleHabit on rocky shores
CaptionHabit on rocky shores, on mussels below the Fucus belt. Combarro, Pontevedra, Spain. 16th May 2009.
CopyrightJavier Cremades Ugarte
Habit on rocky shores, on mussels below the Fucus belt. Combarro, Pontevedra, Spain. 16th May 2009.
Habit on rocky shoresHabit on rocky shores, on mussels below the Fucus belt. Combarro, Pontevedra, Spain. 16th May 2009.Javier Cremades Ugarte
Base of blade with characteristic concentric wrinkles around the holdfast.
TitleBase of blade
CaptionBase of blade with characteristic concentric wrinkles around the holdfast.
CopyrightJavier Cremades Ugarte
Base of blade with characteristic concentric wrinkles around the holdfast.
Base of bladeBase of blade with characteristic concentric wrinkles around the holdfast.Javier Cremades Ugarte
Surface view of cells, mostly with two pyrenoids
CaptionSurface view of cells, mostly with two pyrenoids
CopyrightJavier Cremades Ugarte
Surface view of cells, mostly with two pyrenoids
CellsSurface view of cells, mostly with two pyrenoidsJavier Cremades Ugarte
Free-floating specimen on muddy bottom. Combarro, Pontevedra, Spain. 16th May 2009.
TitleFree-floating specimen
CaptionFree-floating specimen on muddy bottom. Combarro, Pontevedra, Spain. 16th May 2009.
CopyrightJavier Cremades Ugarte
Free-floating specimen on muddy bottom. Combarro, Pontevedra, Spain. 16th May 2009.
Free-floating specimen Free-floating specimen on muddy bottom. Combarro, Pontevedra, Spain. 16th May 2009.Javier Cremades Ugarte
Transverse section of blade in lower zone showing two layers of oblong cells with rounded corners.
TitleTransverse section of blade
CaptionTransverse section of blade in lower zone showing two layers of oblong cells with rounded corners.
CopyrightJavier Cremades Ugarte
Transverse section of blade in lower zone showing two layers of oblong cells with rounded corners.
Transverse section of bladeTransverse section of blade in lower zone showing two layers of oblong cells with rounded corners.Javier Cremades Ugarte
Tranverse section of blade in fertile zone showing the cells full of spores.
TitleTranverse section of blade
CaptionTranverse section of blade in fertile zone showing the cells full of spores.
CopyrightJavier Cremades Ugarte
Tranverse section of blade in fertile zone showing the cells full of spores.
Tranverse section of bladeTranverse section of blade in fertile zone showing the cells full of spores.Javier Cremades Ugarte


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Preferred Scientific Name

  • Ulva pertusa Kjellman, 1897

International Common Names

  • English: sea lettuce

Local Common Names

  • Japan: ana-awosa
  • Netherlands: zeesla

Summary of Invasiveness

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U. pertusa is a macroscopic green seaweed widely distributed in the Indo-Pacific Ocean. It has delicate but tough glossy bright to dark green blades up to 20 cm long. The blade is rounded when young but becomes lobed and more or less basally perforated when old. U. pertusa is found growing in the lower littoral and upper subtidal zones of a wide variety of habitats: on rocks, in pools, on other marine organisms, or even on man-made substrates. It is an opportunistic species recently introduced in Europe (Atlantic and Mediterranean Sea) and, reputedly, in Pacific North America (Baja California, Mexico). Its introduction is probably attributable mainly to the shellfish translocations.  

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Plantae
  •         Phylum: Chlorophyta
  •             Class: Chlorophyceae
  •                 Order: Ulvales
  •                     Family: Ulvaceae
  •                         Genus: Ulva
  •                             Species: Ulva pertusa

Notes on Taxonomy and Nomenclature

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Ulva pertusa was originally described from Japan (Kjellman, 1897) and is very similar to the northern species Ulva fenestrata Postels & Ruprecht (1840) described from the Kamchatka Peninsula. The latter species has a more delicate and regularly perforated blade (Nagai, 1940); further investigations are required to confirm these separate taxonomic identities. Ulva spathulata Papenfuss (1960), described from South Australia could also be a taxonomic synonym (see Heesch et al., 2007). A sterile mutant of U. pertusa was described by Migita (1985) in Omura Bay (Japan).


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Thallus forms a distromatic blade, 5–20 (-40) cm long, irregularly orbicular, lobed, thick and tough when small, but oval and more delicate towards the margins when large. Blade bright to dark green, glossy, without marginal teeth, and generally with perforations of variable size and irregular shape. Perforations are present in young individuals, but become larger and more abundant with age and towards the base, where they may be confluent and eventually divide the blade longitudinally and contribute to the spathulate appearance of some thalli. Basal part of the blade cuneate and thick (up to 500 µm), without central cavity and with characteristic concentric wrinkles around the holdfast. The thickness of the blade declines gradually from the base upwards, from 125–200 µm in the rhizoidal zone, through 100–150 µm in the upper basal zone, and 60–80 µm in the medial zone, to only 40–60 µm in the apical and marginal zones. In surface view, cells lack regular ordering or are regularly ordered only in small groups; isodiametric to elongate, with rounded corners, rarely slightly polygonal and between 10–25 x 8-20 µm. Internally, they contain a parietal chloroplast with (1-) 2 (-3) pyrenoids. In transverse section, the cells of the lower zones are markedly larger and clearly oblong, 30–45 x 10-20 µm, often two times higher than broad and with apex rounded, never acuminate. Towards the base, these cells become intermingled with rhizoidal cells, with similar morphology but darker and with prolongations towards the centre of the blade. In the medial zones, cells are larger, 25–30 x 15–20 µm, and somewhat more oblong; while in the apical and marginal zones of the blade they have rounded, squarish or somewhat oblong outline, measuring 20–25 x 15–20 µm, and very narrow intercellular spaces. Fertile individuals show very evident sporangial or gametangial sori appearing as a thick marginal band clearly delimited by its olive green or yellowish color and contains up to 16 tetraflagellate zoospores or 32 biflagelate gametes (Kjellman, 1897; Yabu and Tokida, 1960; Kamiya et al., 1993; Verlaque,et al., 2002; Baamonde et al., 2007; Heesch et al., 2007; Aguilar-Rosas et al., 2008). This species was originally described from Japan (Hakodate, Enoshima and Yokohama).


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U. pertusa is a widespread native of the Indo-Pacific, from the Sakhalin-Kuril Islands in the North to New Zealand in the South. As an exotic it is found on both the Atlantic and Mediterranean coasts of Europe (The Netherlands, France and Spain) and on the Pacific shores of North America (Mexico). However, since species-level identification in the cosmopolitan genus Ulva is notably difficult because of a lack of morphological and anatomical diagnostic characters (Bliding, 1968; Hoeksema and van den Hoek, 1983; Koeman, 1985), the actual range of this “cryptic” organism could even be wider than currently assumed.
The records of the septentrional Ulva fenestrata from the Indian Ocean (India, Sri Lanka, Pakistan, Singapore and Somalia) might in fact be U. pertusa (see Jaasund, 1977). In southern Australia, U. pertusa has probably been misidentified as U. rigida (Heesch et al., 2007).

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Sea Areas

Atlantic, NortheastPresentIntroducedCoat et al., 1998; Baamonde et al., 2007; Stegenga et al., 2007
Indian Ocean, EasternPresentNativeDurairatnam, 1961; Heesch et al., 2007
Indian Ocean, WesternPresentJaasund, 1976; Oyieke and Ruwa, 1987; Jagtap, 1993; Ormond and Banaimoon, 1994
Mediterranean and Black SeaPresentIntroduced1984Verlaque, 2001; Verlaque et al., 2002Mediterranean Sea (Thau Lagoon)
Pacific, Eastern CentralPresentHayden and Waaland, 2004; Aguilar-Rosas et al., 2008
Pacific, NorthwestPresentNativeKjellman, 1897; Okamura, 1921; Takamatsu, 1939; Nagai, 1940; Tokida, 1954; Iwamoto, 1960; Dong and Tseng, 1984; Lee and Kang, 1986; Noda, 1987; Chihara, 1990; Tokuda et al., 1994; Yoshida, 1998; Kunii and Minamoto, 2000; Han et al., 2003; Shimada et al., 2003
Pacific, SouthwestPresentNativeHeesch et al., 2009
Pacific, Western CentralPresentNativeWeber Bosse Avan, 1913; Teo and Wee, 1983; Silva et al., 1987; Coppejans and Prud'homme, 1992


ChinaWidespreadNativeDong and Tseng, 1984
IndonesiaPresentPresent based on regional distribution.
-MoluccasPresentNativeWeber Bosse Avan, 1913
-Nusa TenggaraPresentNativeWeber Bosse Avan, 1913; Coppejans and Prud'homme, 1992
-SulawesiPresentNativeWeber Bosse Avan, 1913
JapanWidespreadNativeOkamura, 1921; Noda, 1987; Chihara, 1990; Tokuda et al., 1994; Yoshida, 1998
-HokkaidoPresentNativeKjellman, 1897; Nagai, 1940; Iwamoto, 1960; Shimada et al., 2003
-HonshuPresentNativeKjellman, 1897; Takamatsu, 1939; Kunii and Minamoto, 2000; Shimada et al., 2003; Hiraoka et al., 2004
-KyushuPresentNativeShimada et al., 2003Green tides
-ShikokuPresentNativeShimada et al., 2003
Korea, Republic ofWidespreadNativeLee and Kang, 1986; Han et al., 2003
MalaysiaPresentNativePhang and Wee, 1991
PhilippinesWidespreadNativeSilva et al., 1987
SingaporePresentNativeTeo and Wee, 1983
Sri LankaPresentNativeDurairatnam, 1961As Ulva fenestrata Postels & Ruprecht (see Jaasund, 1977)
TaiwanPresentNativeOkamura, 1921
YemenPresentOrmond and Banaimoon, 1994


KenyaPresentOyieke and Ruwa, 1987
MauritiusPresentJagtap, 1993
TanzaniaPresentJaasund, 1976

North America

MexicoPresent1978Aguilar-Rosas et al., 2008Baja California. Although Aguiar-Rosas et al. (2007) consider U. pertusa as an alien it might be a native species
USAPresentPresent based on regional distribution.
-CaliforniaPresent1999Hayden and Waaland, 2004


FrancePresentIntroducedCoat et al., 1998; Verlaque, 2001; Verlaque et al., 2002
NetherlandsPresentIntroduced1995Stegenga et al., 2007
Russian FederationPresentPresent based on regional distribution.
-Eastern SiberiaPresentNativeTokida, 1954Sakhalin Island
-Russian Far EastPresentNativeOkamura, 1921; Nagai, 1940
SpainWidespreadIntroduced1990Baamonde et al., 2007Widespread in the northwest Iberian Peninsula


AustraliaPresentPresent based on regional distribution.
-South AustraliaPresentNativeHeesch et al., 2007Misidentified as U. rigida and U. spathulata
New ZealandWidespreadNativeHeesch et al., 2009One of the most frequent species of Ulva in both Islands

History of Introduction and Spread

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The first reliable record of U. pertusa outside of its native area was in 1984 from Mediterranean Sea (Thau Lagoon, France), where it could have been introduced as early as 1971-1977 along with massive official importations of Japanese oysters from the Pacific (Verlaque, 2001; Verlaque et al., 2002). Later, this species was also reported from the European Atlantic coasts. The oldest individual from these coasts was recollected in 1990 at A Coruña Bay (Galicia, Spain) (Baamonde et al., 2007) followed by other specimens collected in 1994 from French Brittany (Coat et al., 1998, misidentified as Ulva rotundata; see also Shimada et al., 2003 and Hayden and Waaland, 2004); it also occurs in The Netherlands at least since 1995 (Verlaque et al., 2002; Stegenga et al., 2007). The well-known high potential to disperse of Ulva species, the difficulty in species-level identification in the field, and the current patchy distribution are all factors that suggest that the actual range of U. pertusa along European Atlantic shores may even be considerably wider and more continuous (Baamonde et al., 2007). However, U. pertusa was not found in a recent morphological and molecular investigation of distromatic Ulva species from Ireland and southern Britain (Loughnane et al., 2008).

More recently, the species has been reported from the Eastern North Pacific in the USA (1999, California) (Hayden and Waaland, 2004) and for Mexico, where it has been labelled an exotic introduction (1978, Baja California) (Aguilar-Rosas et al., 2008). Yet, the native range of U. pertusa along the Pacific Ocean has been considerably widened as more research evidence accumulates (see Heesch et al., 2007) and it cannot be discounted that it may even reach to North America coasts.
The expansion of U. pertusa into new areas is expected to continue in the near future given its great reproductive potential and its broad tolerance to wide changes in temperature, salinity and light intensity (Okuda, 1975; Kakinuma et al., 2001; 2004; Han et al., 2003; Kim et al., 2004).

Risk of Introduction

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U. pertusa is an opportunistic, highly competitive seaweed with high rates of nutrient assimilation and propagule production. Moreover, it tolerates a wide range of environmental conditions. For these reasons, this species has a high potential for further spread to new territories. As a common component of marine fouling, it can be easily introduced, accidentally by this pathway, mainly through marine traffic or careless shellfish translocations for aquaculture purposes.



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This species is mainly found growing in the intertidal zone on a wide variety of habitats: on rocks, in pools, or from the lower littoral to the upper subtidal zone as epiphytes on other seaweeds or seagrasses, epizootics on barnacles and shells, or on a great variety of artificial floating or fixed man-made substrates. It also frequents in coastal lagoons. Although it can live in places ranging from sheltered to moderately exposed to wave action, it is a common and dominant species especially under sheltered conditions such as where protected by breakwaters. In Asia (Japan, Korea, Philippines, Indonesia) it is considered one of the most common species growing in the intertidal and subtidal zones (up to 27 m depth; Weber van Bosse, 1913) on rocky localities. As a member of the Ulvales, U. pertusa is an opportunistic species that becomes dominant in habitats well-lit and rich in nutrients. Wave action often frees them; as free-floating, they continue to grow and they are able to form green tides (Shimada et al., 2003; Hiraoka et al., 2004).

Habitat List

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Mud flats Secondary/tolerated habitat Natural
Mud flats Secondary/tolerated habitat Productive/non-natural
Intertidal zone Principal habitat Natural
Intertidal zone Principal habitat Productive/non-natural
Estuaries Secondary/tolerated habitat Natural
Estuaries Secondary/tolerated habitat Productive/non-natural
Lagoons Secondary/tolerated habitat Natural
Lagoons Secondary/tolerated habitat Productive/non-natural
Inshore marine Principal habitat Natural
Inshore marine Principal habitat Productive/non-natural
Benthic zone Principal habitat Natural
Benthic zone Principal habitat Productive/non-natural

Biology and Ecology

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In U. pertusa, the chromosome numbers are n=9 and 2n=18 (Yabu and Park, 1968). In GenBank ( there are many accessions with sequence information for the chloroplast-encoded RUBISCO large subunit gene (rbcL) and the nuclear-encoded internal transcribed spacers (ITS1, ITS2).
Bliding (1968) reportedly attempted fertilization of gametes of different species of Ulva but they did not lead to viable zygote formation, arguing against the possibility of interspecies gene exchange in this genus. If hybridization does occur, it would not appear to be either frequent or viable because Ulvales communities generally appear to remain multispecific. A sterile mutant of U. pertusa was found in Omura Bay (Japan) by Migita (1985).
Reproductive Biology
Ulva is a green algae genus with a biphasic life cycle that alternates isomorphic generations (Smith, 1947; Bold and Wynne, 1985; Hoek et al., 1995).The diploid sporophyte of U. pertusa produces tetraflagellate zoospores, whereas haploid male and female gametophytes release biflagellate gametes. Fertile specimens occur continually from February to October (Sawada, 1972; Okuda, 1975; Hiraoka et al., 1998). Gametes can develop directly to adult gametophytes by parthenogenesis (Yabu and Tokida, 1960). The sterile mutant of U. pertusa can be easily maintained under axenic laboratory conditions (Migita, 1985; Kakinuma et al., 2001).
This species shows a broad seasonal reproductive period from early spring to later autumn with a peak between spring and summer (Okamura, 1921; Sawada, 1972).
Physiology and Phenology
U. pertusa can be found year-round but it apparently shows a seasonal peak of abundance between spring and summer. In some areas, there are no observations for winter (Mediterranean Sea) (Verlaque et al., 2002). According to Floreto et al. (1993), its growth rate was highest at 15ºC, at a light intensity of between 48 and 64 µmol m-2 s-1,and a high salinity (35 psu). According to Ohno (1977), the fronds of this species can increase by about 775% after one week at 19-22.5°C. On the Izu Peninsula (Central Japan), its optimum temperature for photosynthesis is 25-30ºC (Yokohama, 1972). Choi and Kim (2005) showed that the range of photosynthetic pigment, nitrogen, and phosphorous content in tissues of U. pertusa is significantly higher in sandy than in rocky environments.
The pattern of the photosynthesis-temperature curve implies the existence of at least two enzyme systems: one heat-resistant, the other heat-susceptible (Mizusawa et al., 1978). In the laboratory, minimum photon irradiance for growth and reproduction was 5 and 10 µmol m-2 s-1 respectively; individuals growing in shaded habitats can be ready to sporulate rapidly upon an increase in irradiance (Han et al., 2003). U. pertusa survives upto 24 h frozen at -15ºC (Terumoto, 1960).
U. pertusa can live with other species of the same genus.
Environmental Requirements
The northern and southern latitudinal range limits of U. pertusa seem to be southern Sakhalin–Kuril Islands (Okhotsk and Japan Seas, 47th parallel north) and Stewart Island (New Zealand, 47th parallel south), respectively (Nagai, 1940; Tokida, 1954; Heesch et al., 2007).
The seasonal range of sea-surface temperatures tolerated by U. pertusa is very wide, from about 0ºC to 16-18ºC along the Okhostsk Sea coasts, and from 27-28ºC to about 30-31ºC at Singapore (Tokida, 1954; Teo and Wee, 1983). Also, the salinity tolerated by this species range from 17-18 psu in coastal lagoons and estuarine areas to 35 psu at open sea places (Iwamoto, 1960; Floreto et al., 1994). The main environmental factor limiting its growth is considered to be mostly water temperature and nutrient supply (Matsukawa and Umebayashi, 1987; 1988).

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Salinity (part per thousand) 35 Optimum 17-35 tolerated
Water temperature (ºC temperature) 15 Optimum 0-31 tolerated. Survives after 24 h freezing at -15 (Terumoto, 1960)

Notes on Natural Enemies

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A high number of species prey upon Ulva species, e.g. gastropod molluscs, crustaceans (hapacticoid copepods, amphipods), echinoderms (sea urchins) and fish. Myrionema strangulans is a microscopic brown algae widespread in temperate seas very common and abundant as epiphyte on Ulva blades. Other than predation and epiphytism, there are no other known natural enemies that could pose a risk to Ulva populations.

Means of Movement and Dispersal

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Natural Dispersal (Non-Biotic)

U.pertusa, like most Ulva species, can live and grow in a free-floating form. Even as fragments Ulva specimens can survive for long periods of time in the water column after which they can regenerate and reproduce again (A Gittenberger, GiMaRIS, The Netherlands, personal communication, 2011).
Vector Transmission (Biotic)
It is highly probable that U. pertusa was introduced into Europe with oyster transfers from the Pacific (Verlaque, 2001; Verlaque et al., 2002; Baamonde et al., 2007).
Accidental Introduction
Potential accidental introductions of U. pertusa outside of its native area are probably related to the arrival of plants as part of fouling and/or to the presence of gametes and spores in ballast water (Carlton, 1985; Sidharthan et al., 2004; Hewitt et al., 2007). According to Aguilar-Rosas et al. (2008), the presence of this species in Baja California (Mexico) is probably related to commercial vessel traffic, cruise ships, yachts, and sailboats from southern California.
Intentional Introduction
There are no records of intentional introduction of U. pertusa outside its native area.

Impact Summary

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Economic/livelihood Positive
Environment (generally) Negative
Human health Positive

Economic Impact

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The economic impact of U. pertusa is more positive than negative as it is used for human and animal consumption (Chapman and Chapman, 1980; Trono, 1999; Alcantara and Noro, 2006) and it can also be employed as environmental biofilter due to its efficiency in removing nitrogenous compounds from seawater (Dongyan et al., 2004; Tarutani et al., 2004).

Environmental Impact

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Impact on Habitats

U. pertusa is a highly competitive seaweed with high rates of nutrient assimilation and propagule production (Yabu and Tokida, 1960; Dongyan et al., 2004), which tolerates a wide range of environmental conditions. As such it has a high potential for further spread to new territories. When nutrients are very abundant, whether because of natural causes or human activity (eutrophication), Ulva species (both laminar and tubular forms) are often the main components of ‘‘green tides’’ seen in areas with sandy, silty or muddy substrata (Fletcher, 1996; Sidharthan et al., 2004). Green tides form because these species are able to grow in suspension and can accumulate to high densities in calm areas. However, these blooms do not require the presence of any particular species of Ulva (Hiraoka et al., 2004; Baamonde et al., 2007).
Impact on Biodiversity
Allelopathic properties are not usually associated with “green tides” of ulvoid macroalgae (Valiela et al., 1997), although some bloom-forming macroalgae are chemically defended against herbivory (Paul et al., 2001). Further, extracts from U. pertusa and other macroalgae have been shown to have inhibitory effects on dinoflagellates (Jeong et al., 2000) and extracts from Ulva fenestrata, a very similar species, have allelopathic properties. These properties could alter competitive interactions by inhibiting germination or development of algae and invertebrates (Nelson et al., 2003).
There may be loss of genetic diversity as a result of competition or hybridization between alien and native species. In northwest Spain, although U. pertusa has present since the 1990s, a recent study of nearly 400 Ulva herbarium sheets found very few specimens of this species (Baamonde et al., 2007). If hybridization of Ulva pertusa with other present species does occur, it would not appear to be either frequent or viable (Bliding, 1968) since Ulvales communities generally appear to remain multispecific (Baamonde et al., 2007).
In view of these considerations, it seems unlikely that the introduction of U. pertusa will have significant negative environmental consequences other than an increase in local marine biodiversity (Baamonde et al., 2007).

Social Impact

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U. pertusa can be the main component of ‘‘green tides’’ (Sidharthan et al., 2004). However, despite the negative social effects of these blooms (impacts on tourism, shell fishing, etc.), they cannot reasonably be considered a negative social impact of this species in particular but has a negative consequence of eutrophication.

Risk and Impact Factors

Top of page Invasiveness
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Pioneering in disturbed areas
  • Tolerant of shade
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Reproduces asexually
Impact outcomes
  • Modification of natural benthic communities
Impact mechanisms
  • Allelopathic
  • Competition - monopolizing resources
  • Competition - shading
  • Fouling
  • Rapid growth
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect as a commodity contaminant
  • Difficult to identify/detect in the field
  • Difficult/costly to control


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Economic Value

In Asia, this species has been used as natural food and in the production of processed single-cell detritus (SCD) feeds for gastropod culture (Uchida and Numaguchi, 1996; Uchida et al., 1997; Alcantara and Noro, 2006). U. pertusa is a rich source of C16 and C18 PUFAs, whose levels are enhanced by culturing the algae at low temperature, low light intensity and high salinity. This fatty acid profile suggests that it can be a promising food for marine animals (Floreto et al., 1993; Alcantara and Noro, 2006).
U. pertusa is also used for human nutrition in Asia (Trono, 1999) and it can be employed as a dietary supplement with hypocholesterolaemic properties (Yu et al., 2003a,b). Furthermore, it can be used as a treatment to reduce high fever temperatures in humans (Levring et al., 1969).
Environmental Services
In Asia, this species has several uses as a biofilter. Also, it can take up sea urea and alanine directly without bacterial decomposition to inorganic nitrogen (Liu and Dong, 2001; Dongyan et al., 2004). Its high rates of nutrient assimilation and its environmental plasticity render U. pertusa a good candidate for the development of integrated multi-trophic aquaculture techniques (IMTA) (Neori et al., 2004). 


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Apart the careful observations of morphological and cytological characters described previously, the best way to confirm the taxonomic identity of U. pertusa remain the analysis of rbcL and ITS sequence information.

Similarities to Other Species/Conditions

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Species-level identification in the cosmopolitan genus Ulva is typically difficult due to a combination of few diagnostic morphological and anatomical characters and high intraspecific variability (Bliding, 1968; Hoeksema and van den Hoek, 1983; Koeman, 1985). Also, many of these characters change with age and environmental conditions (Steffensen, 1976; Mshigeni and Kajumulo, 1979; Tanner, 1986). Therefore it is often recommended to use supplementary tools such as molecular techniques (Woolcott and King, 1993; Malta et al., 1999; Shimada et al., 2003). All these reasons suggest U. pertusa to be a cryptic alien that can go unnoticed countless times by misidentification as local species of the genera (Verlaque et al., 2002; Baamonde et al., 2007; Aguilar-Rosas et al., 2008). However, the precise combination of morphological, anatomical, and reproductive characters of U. pertusa, if are carefully considered and observed should allow a readily discrimination from other congeners found in the same area. Macroscopically, the most stable and distinctive feature is the presence of numerous perforations concentrated around the base of the blade, leaving narrow bands of tissue between them that act as wires that attach the blade to the holdfast. These perforations are very different from those found in other likewise perforated species because, in the latter, they usually are more homogeneous, small in size, and usually scattered all over the lamina. Also highly characteristic are the notorious concentric wrinkles at the base of the blade. The wide fertile margin of the blade is very evident in reproductive individuals and the larger number of spores / gametes per cell (16 / 32, respectively) contrast with the (4) 8 / 16 produced by other Ulva species (Yabu and Tokida, 1960). Microscopically, the blade of this species lacks marginal teeth and mostly has cells with two pyrenoids each.

Prevention and Control

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Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.


The Code of Practice of the International Council for the Exploration of the Sea (ICES, 1995) provides a practical set of rules to prevent harmful introductions through the import of oysters and other non-native organisms. It is mainly based on quarantine measures to be carried out in the exporting and importing countries.
SPS measures
The French imports of Japanese oysters in the 1970s were subjected to immersion in fresh water to kill predatory turbellarians. Gruet et al. (1976) clearly demonstrated that this method was inadequate to kill most of the other epifauna and epiflora. The British approach appears to be by far the best. By importing limited amounts of broodstock to produce larvae and subsequently destroying the broodstock, seed oysters without accompanying exotics can be obtained (Utting and Spencer, 1992).


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09/06/09 Original text by:

Javier Cremades Ugarte, Departamento de Biología, Animal, Biología Vegetal y Ecología, Facultad de Ciencias, Universidad de A Coruña, Campus de la Zapateira, Spain

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