Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Amphibalanus improvisus
(bay barnacle)



Amphibalanus improvisus (bay barnacle)


  • Last modified
  • 13 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Threatened Species
  • Natural Enemy
  • Preferred Scientific Name
  • Amphibalanus improvisus
  • Preferred Common Name
  • bay barnacle
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Crustacea
  •         Class: Maxillopoda
  • Summary of Invasiveness
  • A. improvisus is a small sessile crustacean, typical for the shallow fringe of sea (less than 10 m deep), occurring in marine and brackish environments. A. improvisus has been dispersed by shipment out...

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Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava bay, preserved in alcohol
TitleAmphibalanus improvisus: View from above, showing scale
CaptionAmphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava bay, preserved in alcohol
Copyright©Ekaterina Shalaeva
Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava bay, preserved in alcohol
Amphibalanus improvisus: View from above, showing scaleAmphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava bay, preserved in alcohol©Ekaterina Shalaeva
Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
TitleAmphibalanus improvisus: Lateral view, showing scale
CaptionAmphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
Copyright©Ekaterina Shalaeva
Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
Amphibalanus improvisus: Lateral view, showing scaleAmphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol©Ekaterina Shalaeva
Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
TitleClose-up of Amphibalanus improvisus.
CaptionAmphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
Copyright©Ekaterina Shalaeva
Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol
Close-up of Amphibalanus improvisus.Amphibalanus improvisus on a Mytilus galloprovincialis shell. Collected in 2001, Black Sea, Balaklava Bay, preserved in alcohol©Ekaterina Shalaeva


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Preferred Scientific Name

  • Amphibalanus improvisus (Darwin, 1854)

Preferred Common Name

  • bay barnacle

Other Scientific Names

  • Balanus improvisus Darwin, 1854

International Common Names

  • English: bay barnacle
  • French: petite balane ivoire

Local Common Names

  • Denmark: brakvandsrur
  • Estonia: tavaline toruvak
  • Finland: merirokko
  • Germany: Brackwasser-Seepocke; Ostsee Seepocke
  • Latvia: juras zile
  • Lithuania: juros gile
  • Netherlands: brakwaterpok
  • Norway: brakkvannsrur
  • Poland: pskla baltycka
  • Sweden: brackvattenlevande havstulpan; slat havstulpan

Summary of Invasiveness

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A. improvisus is a small sessile crustacean, typical for the shallow fringe of sea (less than 10 m deep), occurring in marine and brackish environments. A. improvisus has been dispersed by shipment outside its natural distribution area, which is considered to be the western Atlantic. It was first recorded as invasive in Europe and California in the middle of the nineteenth century, with further distribution records to the Pacific and Australasia (Carlton et al., 2011). Its success worldwide has been attributed to the fact that it is euryhaline and eurythermal, able to self-fertilize, establish and mature rapidly, has a high reproductive capacity and long settlement period, and utilizes a wide range of food. The species damages man-made constructions and ships, causing substantial economic expense, and threatens biological diversity, competing with local species for food as well as space. A. improvisus is included in alert lists in the Baltic and Pacific (Australia). The potential of becoming established from warm temperate to tropical and polar regions has been indicated.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Crustacea
  •                 Class: Maxillopoda
  •                     Subclass: Thecostraca
  •                         Superorder: Thoracica
  •                             Order: Sessilia
  •                                 Family: Balanidae
  •                                     Genus: Amphibalanus
  •                                         Species: Amphibalanus improvisus

Notes on Taxonomy and Nomenclature

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A recent revision of balanomorph barnacles (Pitombo, 2004) has transferred Balanus improvisus to the genus Amphibalanus. The name change is now widely accepted, but some literature sources and internet databases have used the genus name Balanus.

Nomenclatural history and variations are given in detail in Henry and McLaughlin (1975). The variation “assimilis”, described by Darwin in 1854, lives on the open coast in South America and is regarded by some authors as a distinct, tropically distributed species of the “amphitrite group” (Southward, 2008).

In some Germanic languages the species common name  means “brackish water barnacle”, reflecting the ability of the barnacle to live in water with lower salinity, such as estuaries. The English common name “Bay barnacle” indicates the ability of the species to live in inlets and enclosed bodies of water.


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Full details of morphology and anatomy of adults can be found in Darwin (1854); Pilsbry (1916); Broch (1924); Tarasov and Zevina (1957, in Russian); Henry and McLaughlin (1975); and Southward (2008). For details of larval morphology see Jones and Crisp (1954); Korn (1991); Elfimov (1995); and Murina and Grintsov (1995).

A. improvisus has a low, cone-shaped or semi-globe shape. It may be cylinder-shaped in crowded populations, but according to Southward (2008) it does not react to crowding by production of very tall specimens.

The calcareous shell is made up of white to greyish plates. Walls never ribbed or folded longitudinally. Uneroded calcareous shells have a smooth surface and may be covered by a thin yellowish epidermis, which is often more resilient on the radii. The radii are narrow and oblique and do not completely cover the alae that is nearly horizontal. The carina is lower than the rostrum. The operculum situated off centre, so that terga are close to the carina. The operculum is rounded at the rostral end. In water the opening is narrow and diamond shaped with partly- erect tergoscutal flaps. In juveniles' opening (Southward, 2008) a white ground is crossed by five black bands of speckles, whereas adults display the same dark bands, but the ground colour is white speckled with purple.

The variant “assimilis” has longitudal white hyaline lines (Darwin, 1854).

Base of the shell calcareous, flat and thin. Canals inside run radially to the place (approximately centre of the basal plate) where cyprid antennas were attached (Tarasov and Zevina, 1957; Leppäkoski, 1999) forming a star-like pattern.

A. improvisus normally grows to around 10 mm in diameter, the largest specimens reaching 23 mm (Tarasov and Zevina, 1957).

The shells can remain in place long after the animal that constructed and inhabited it is dead.


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Southward (2008) noted that some of the records in the tropics may relate to the variety “assimilis”, which is a distinct, tropically distributed species of the “amphitrite” group. Unlike A. improvisus, it lives on the open coast and is not an estuarine species. 

West Atlantic 

A. improvisus is considered to be native on the east coast of North America. In its native range it is distributed from the Gulf of St. Lawrence in Quebec Province, Canada (Brunel et al., 1998) southward to Florida (Pollock, 1998).

Further south, the species is found in the Gulf of Mexico and Caribbean region (Henry and McLaughlin, 1975), and on the Brazilian Coast (in estuarine areas in northeast Brazil; Farrapeira, 2010). In the Southwest Atlantic A. improvisus was found in Uruguay and Argentina by Darwin (1854).

Orensanz et al. (2002) reviewed the species from Uruguay and Argentina as cryptogenic. It was also listed as cryptogenic in Brazil by Neves and da Rocha (2008)

East Pacific

A. improvisus is generally considered as non-native in the East Pacific. On the west coast of America its range is from British Columbia down to central California (Carlton, 1979) with occasional records of sporadic occurrence in southern California as far south as San Diego Bay. Presently it is found in California, Oregon and the state of Washington (Wonham and Carlton, 2005).

Data on distribution on the west coast of Mexico, western Colombia, Peru and Ecuador is based on old collection records (Darwin, 1854; Henry and McLaughlin, 1975) and needs to be reviewed (Carlton et al., 2011). 

North East Atlantic 

Darwin (1854) mentions A. improvisus from a few places in England and one locality in Scotland. At the present time its distribution in the UK remains restricted to estuaries (Furman, 1990; Southward, 2008) including the Thames, Severn, Daugleddau, Conwy, Ribble, Forth, Dart and Tamar. A. improvisus is known from Ireland in Lough Foyle (O'Riordan, 1967) and Dundalk, Dublin and Cork Harbours (Crisp and Southward, unpublished survey). Furman and Yule (1991) noted that populations in the UK estuaries are fluctuating; e.g. in the Thames A. improvisus was present in 1854, absent in 1954, and recolonized by 1982.

In continental Europe, A. improvisus is known from estuarine and brackish waters in the Baltic and North Sea. In the Baltic Weidema (2000) states the northernmost limit of distribution as the Northern Quark, 63°N and the easternmost point at about 25°E in the Gulf of Finland. In Norway the species is found in several localities between Oslo fjord and Stavanger, but not north of this (Sneli, 1972). Along the southern coastline of the North Sea, it is common in brackish waters of the Netherlands (Gittenberger et al., 2010). 

Black Sea and Mediterranean 

A. improvisus is found in the Caspian, Black and Aral Sea from many littoral locations and is considered as a non-native, well established species there, being very widespread.

There are few records from the Mediterranean, and it is unknown whether A. improvisus is established here (Kocak et al., 1999; Zenetos et al., 2005). A. improvisus is known from off-shore platforms in the Adriatic Sea (Relini et al., 1976; 1998). Koukouras and Matsa (1998) didn't find it in the Aegean Sea, but included the species in the checklist of Cirripedia for all parts of the Mediterranean sea. 

African Coast

Early findings of A. improvisus from African coasts (Broch, 1927; Gruvel, 1912; Nilsson-Cantell, 1938) need to be reviewed. Henry and McLaughlin (1975) suggested that specimens found by Stubbings (1967) from West Coast of Africa are A. improvisus  rather than Balanus amphitrite as the author had described. Bishop (1951) recorded A. improvisus from three localities in West Africa. Some authors such as Jones et al. (2000) included the west coast of Africa to the Cape of Good Hope in current habitat of the species, but recent reports from South Africa don't list the species (Griffiths et al., 2009; 2011). 

Western Pacific 

In Western Pacific the species is considered established in the Russian part of the Sea of Japan.

A. improvisus is a fouling agent in Japanese ports, from where there are detailed records. There are records from Malaysia and the East China Sea, but data on distribution and spread in the region are still limited. Several occurrences have been noted from Australian ports, but the claims were not confirmed (Wiltshire et al., 2010). In New Zealand this species seems to be established.

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, Eastern CentralBroch, 1927; Bishop, 1951; Henry and McLaughlin, 1975Status need to be reviewed
Atlantic, NortheastWidespread2011Introduced Invasive Kotta et al., 2006a; Darwin, 1854; Hoek, 1876; Broch, 1924; Gislen, 1950; Barnes and Barnes, 1962; Bassindale, 1964; Polk, 1976; Hayward et al., 1990; Sandrock et al., 1991; Jansson, 1994; Brattegard et al., 1997; Olszewska, 1999; Reise et al., 1999; Goulletquer et al., 2002; Leppakoski et al., 2002; Müller, 2004; Gollasch and Nehring, 2006; Reise et al., 2006; DAISIE, 2009; Dziubinska and Szaniawska, 2010; Jazdewski and Grabowski, 2011; Noel, 2011
Atlantic, NorthwestWidespread2011Native Invasive Bousfield, 1954; Branscomb, 1976; Brunel et al., 1998; Pollock, 1998; Carlton et al., 2011
Atlantic, SoutheastGruvel, 1912Status need to be reviewed
Atlantic, SouthwestPresentIntroduced Invasive Darwin, 1854; Henry and McLaughlin, 1975; Calado and Sousa, 2003; Farrapeira, 2009; Farrapeira, 2010
Atlantic, Western CentralPresent Invasive Darwin, 1854; Henry and McLaughlin, 1975; Southward and Newman, 1977; Espinosa Garduno, 1980; Spivey, 1981; Kaplan, 1988
Indian Ocean, WesternNilsson-Cantell, 1938Status need to be reviewed
Mediterranean and Black SeaPresent2011Introduced Invasive Buchinsky, 1885; Neu, 1935; Derzhavin, 1956; Sayenkova, 1956; Tarasov and Zevina, 1957; Henry and McLaughlin, 1975; Brayko, 1982; Brayko, 1985; Zevina and Poltarukha, 1999; Aladin et al., 2002; Gomoiu et al., 2002; Grigorovich et al., 2003; Zenetos, 2005; DAISIE, 2009
Pacific, Eastern CentralPresent2011Introduced Invasive Carlton, 1979; Carlton et al., 2011First recorded in San Francisco Bay in 1853
Pacific, NorthwestPresentIntroduced Invasive Tarasov and Zevina, 1957; Kawahara, 1963; Utinomi, 1966; Utinomi, 1968; Utinomi, 1970; Huang, 1994; Iwasaki and Kinoshita, 2004; Otani, 2004; Iwasaki, 2006; Liu, 2008; Seo and Lee, 2009; Doi et al., 2011
Pacific, SoutheastPresentIntroducedDarwin, 1854; Carlton et al., 2011
Pacific, SouthwestPresent2011Introduced Invasive Foster and Willan, 1979; Cranfield et al., 1998; Ahyong and Wilkens, 2011
Pacific, Western CentralPresentIntroduced Invasive Bishop, 1951; Jones et al., 2000; Ahyong and Wilkens, 2011


AzerbaijanWidespreadIntroduced1955 Invasive Tarasov and Zevina, 1957Usual form in the fouling and on the littoral
ChinaPresentIntroduced Invasive Ren and Liu, 1978; Huang, 1994; Liu and Xiangui, 2007; Liu, 2008
-BeijingLocalisedIntroduced Invasive Huang et al., 1994On oil platforms, Bohai Sea
-HebeiLocalisedIntroduced Invasive Ren and Liu, 1978; Huang et al., 1994Shanhaiguan; On oil platforms, Bohai Sea
-LiaoningLocalisedIntroduced Invasive Ren and Liu, 1978; Huang et al., 1994Lushun, Dalian; On oil platforms, Bohai Sea
-ShandongLocalisedIntroduced Invasive Ren and Liu, 1978; Huang et al., 1994On oil platforms, Bohai Sea
-TianjinLocalisedIntroduced Invasive Ren and Liu, 1978; Huang et al., 1994Tanggu
IndonesiaPresentPresent based on regional distribution.
-SumatraPresentIntroducedJones et al., 2000Strait of Malacca
IranPresentIntroduced Invasive Nasrolahi et al., 2006; Nasrolahi, 2007
JapanWidespread2011Introduced1952 Invasive Kawahara, 1963; Utinomi, 1966; Utinomi, 1968; Utinomi, 1970; Iwasaki and Kinoshita, 2004; Otani, 2004; Iwasaki, 2006; Doi et al., 2011First record in Honshu
Korea, Republic ofPresentIntroduced1970 Invasive Kim, 1992Near Pusan
MalaysiaPresentPresent based on regional distribution.
-Peninsular MalaysiaPresentIntroducedJones et al., 2000Strait of Malacca
SingaporePresentIntroducedJones et al., 2000
TurkeyPresentIntroduced Invasive Neu, 1935; Gonlugur-Demirci, 2006In Golden Horn Bay, near Istanbul
TurkmenistanWidespreadIntroduced Invasive Mamkina, 1981Also found on river crustaceans
VietnamPresentIntroduced Invasive Zevina et al., 1992; Zvyagintsev, 2000On ships, port Danag


CongoUnconfirmed recordGruvel, 1912Unreliable record
EgyptLocalisedHenry and McLaughlin, 19751 specimen from lake Maryut
GambiaUnconfirmed recordStubbings, 1967Needs to be checked
MoroccoUnconfirmed recordBroch, 1927One dead specimen, unreliable record
NigeriaUnconfirmed recordStubbings, 1967Needs to be checked

North America

CanadaPresentPresent based on regional distribution.
-British ColumbiaPresentIntroduced1853 Invasive Carlton, 1979
-New BrunswickWidespreadNative Invasive Bousfield, 1954; Brunel et al., 1998
-Nova ScotiaPresentDarwin, 1854; Bousfield, 1954; Brunel et al., 1998
-QuebecWidespreadNative Invasive Bousfield, 1954; Brunel et al., 1998
MexicoPresentNative Invasive Henry and McLaughlin, 1975; Espinosa Garduno, 1980
USAPresentPresent based on regional distribution.
-AlabamaPresentNative Invasive Kaplan, 1988
-CaliforniaPresentIntroduced Invasive Carlton, 1979; Newman, 1979First recorded in San Francisco Bay in 1853
-DelawarePresentHenry and McLaughlin, 1975
-FloridaPresentNative Invasive Moore and Frue, 1959; Henry and McLaughlin, 1975
-HawaiiPresentNative Invasive Kaplan, 1988
-LouisianaPresentNative Invasive Henry and McLaughlin, 1975; Kaplan, 1988
-MarylandPresentNative Invasive Henry and McLaughlin, 1975; Branscomb, 1976
-MassachusettsPresentNative Invasive Henry and McLaughlin, 1975
-MississippiPresentNative Invasive Kaplan, 1988
-North CarolinaPresentNative Invasive McDougall, 1943; Henry and McLaughlin, 1975
-OregonPresentIntroduced Invasive Carlton, 1979; Newman, 1979
-South CarolinaPresentNative Invasive Zullo, 1966From gastropod shell
-TexasPresentNative Invasive Henry and McLaughlin, 1975; Kaplan, 1988; Davidson et al., 2008
-VirginiaPresentIntroduced Invasive Branscomb, 1976
-WashingtonPresentIntroduced Invasive Carlton, 1979

Central America and Caribbean

Costa RicaPresent Invasive Henry and McLaughlin, 1975
HondurasPresentHenry and McLaughlin, 1975
JamaicaPresentDarwin, 1854On a vessel from Trinidad
Puerto RicoPresentHenry and McLaughlin, 1975
Trinidad and TobagoPresent Invasive Darwin, 1854; Henry and McLaughlin, 1975; Bacon, 1976

South America

ArgentinaPresentDarwin, 1854
BrazilWidespread Invasive Henry and McLaughlin, 1975; Farrapeira, 2009; Farrapeira, 2010In estuaries
-AlagoasPresent Invasive Calado and Sousa, 2003; Farrapeira, 2010
-BahiaPresent Invasive Castro, 1997; Farrapeira, 2010
-CearaPresent Invasive Farrapeira, 2010
-MaranhaoPresent Invasive Farrapeira, 2010
-ParaibaPresent Invasive Coelho et al., 1970; Young, 1994; Farrapeira, 2010
-PernambucoPresent Invasive Rosa and Farrapeira-Assunção, 1998; Farrapeira, 2009; Farrapeira, 2010
-Rio Grande do NortePresent Invasive Farrapeira, 2010
-SergipePresent Invasive Young, 1994
ColombiaDarwin, 1854Report based on specimens from British Museum
EcuadorPresentDarwin, 1854; Henry and McLaughlin, 1975Guayaquil; Report based on specimens from British Museum
PeruPresentDarwin, 1854; Henry and McLaughlin, 19751926 collections
UruguayPresentDarwin, 1854


BelgiumWidespread2011Introduced Invasive Polk, 1976; Kerckhof and Cattrijsse, 2001; Vandendriessche et al., 2003; Müller, 2004
DenmarkWidespreadIntroduced Invasive Kruger, 1927; Barnes and Barnes, 1962; Jensen and Knudsen, 2005
EstoniaWidespread20111850 Invasive Järvekülg, 1979; Leppakoski, 2002; Põllumäe et al., 2006; Simm and Põllumäe, 2006
FinlandWidespreadIntroduced Invasive Leppäkoski and Olenin, 2000; Weidema, 2000
FrancePresent1872 Invasive Gruet et al., 1976; Goulletquer et al., 2002; Müller, 2004
GermanyWidespread1858 Invasive Barnes and Barnes, 1962; Nehring and Leuchs, 1999; Gollasch and Nehring, 2006; Nehring, 2006
GreecePresent Invasive Koukouras and Matsa, 1998; Koukouras, 2010
IrelandLocalisedIntroduced1950 Invasive O'Riordan, 1967; Minchin and Eno, 2002; Minchin, 2007; Guiry and Guiry, 2011
ItalyPresent, few occurrencesIntroduced Invasive Relini et al., 1976; Relini et al., 1998; Galil, 2011In Adriatic Sea
LatviaWidespreadIntroduced Invasive Järvekülg, 1979; Leppäkoski and Olenin, 2000; Weidema, 2000
LithuaniaWidespreadIntroduced Invasive Järvekülg, 1979; Leppäkoski, 1999; Barien, 2002; Zaiko et al., 2007
NetherlandsWidespreadIntroduced1827 Invasive Waardenburg, 1827; Hoek, 1876; Bishop, 1947; Wolff, 2005; Gittenberger et al., 2010
NorwayLocalisedIntroduced1900 Invasive Broch, 1924; Sneli, 1972; Brattegard et al., 1997; Reise et al., 1999; Hopkins, 2002
PolandWidespreadIntroduced Invasive Olszewska, 1999; Olszewska, 2000; Jazdewski and Grabowski, 2011
Russian FederationPresentPresent based on regional distribution.
-Central RussiaPresentIntroduced Invasive Panov et al., 1999; Panov et al., 2002; Orlova et al., 2006
-Northern RussiaPresentIntroduced Invasive Panov et al., 2002; Orlova et al., 2006
-Russian Far EastWidespreadIntroduced Invasive Tarasov and Zevina, 1957; Korn, 1991; Zvyagintsev, 2000; Ovsyannikova, 2008
-Southern RussiaWidespread2011Introduced Invasive Derzhavin, 1956; Sayenkova, 1956; Tarasov and Zevina, 1957; Turpaeva and Simkina, 1963; Birshtain et al., 1968; Brayko, 1982; Brayko, 1985; Zevina and Poltarukha, 1999; Aladin et al., 2002; Gomoiu et al., 2002; Grigorovich et al., 2003; DAISIE, 2009
SpainWidespreadIntroduced Invasive Reise et al., 1999; Southward, 2008; Macho et al., 2010; Noel, 2011
SwedenPresentIntroduced Invasive Gislen, 1950; Barnes and Barnes, 1962; Jansson, 1994; Leppäkoski and Olenin, 2000; Gren et al., 2009
UKLocalised2011 Invasive Darwin, 1854; Bassindale, 1964; Rainbow, 1984; Minchin and Eno, 2002; Southward, 2008; Muxagata and Williams, 2011Estuaries, harbours
UkraineWidespreadIntroduced Invasive Alexandrov et al., 2007


AustraliaPresent, few occurrences2010Introduced Invasive Jones et al., 2000; Ahyong and Wilkens, 2011
-Western AustraliaPresent, few occurrences2010Introduced1940 Invasive Bishop, 1951
New ZealandPresent2011Introduced1975 Invasive Foster and Willan, 1979; Cranfield et al., 1998; Ahyong and Wilkens, 2011

History of Introduction and Spread

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Most sources suggest (Newman and Ross, 1976; Zullo and Miller, 1986) that A. improvisus originates on the North Atlantic coast of America. Paleontological records support this theory (Carlton and Zullo, 1969). The species is known in fossil records from Florida (Newman, 1979), whereas examination of late Cenozoic barnacle faunas from numerous Pacific Coast localities has failed to uncover A. improvisus. Newman (1954) also noted the absence of this species in Indian mound material at Brooks Island, San Francisco Bay, although Balanus glandula was common on mollusc shells now frequented by A. improvisus. Some fossil records may indicate (Tavora et al., 2005) that South America is the source area, but they need to be reviewed (Carlton et al., 2011).

In the Americas, according to a recent review on barnacle invasions (Carlton et al., 2011), A. improvisus and A. amphitrite constituted the majority of invasion events in the first 100 years after 1853. In 1853 A. improvisus was first found in San Francisco Bay (Carlton and Zullo, 1969), where it is supposed to have arrived on ship hulls during the Gold Rush. The ships were often abandoned, providing a good opportunity for colonisation by fouling organisms from the Atlantic. A. improvisus spread along the coast from California (Carlton, 1979) and reached British Columbia in 1955 (Rivera et al., 2011).

A. improvisus may have been introduced to South American coasts on Spanish ships as early as the sixteenth century. The suggestion is supported by Darwin's (1854) report on A. improvisus specimens from the British Museum which may be dated from the earlier 1800s. A. improvisus is now widespread and established in harbours on the east coast of South America (Nehring, 2006; Carlton, 2009; Farrapeira, 2009, 2010). In contrast, Southward and Newman (1977) suggested that A. improvisus colonised the Caribbean only in the twentieth century, possibly through the Panama canal (Davidson et al., 2008).

There is a debate around the origin of A. improvisus in Europe. Some authors (Davadie, 1963; Gislen, 1950; Nilsson-Cantel, 1978; Zullo and Miller, 1986; Leppakoski,1999; Reise et al., 1999; Nehrin and Leuchs, 1999) consider it to be a non-indigenous species and noted the lack of verified fossils in the Eastern Atlantic and Mediterranean. They suppose that A.improvisus reached Europe with trading vessels from America and started colonisation of the Baltic in the middle of the nineteenth century, spreading through human activities. Now it is regarded as a pest and is given as one of the 100 worst alien species in Europe (DAISIE, 2009).

However, there are records of fossil specimens of the species from the Tertiary in Hungary (Kolosvary, 1942), and the Pliocene in Spain (Kerckhof, 2002; Menesini and Casella,1988). Kerckhof and Cattrijsse (2001) found A. improvisus in archaeological material from Antwerp, Belgium, dating back from the seventeenth century, but it was absent from a ninth century site in Belgium (Kerckhof, 2002). Hoek (1876) pointed out that the species was recorded from Holland as early as 1827, although the species might not been properly recognised, as it was difficult at the time to distinguish between A. improvisus, Balanus crenatus and Semibalanus balanoides. Strasse (1999) suggested that A. improvisus may have a history similar to that of the bivalve mollusc Mia arenaria, becoming extinct in Northeast Atlantic waters during the last glaciation and then being re-introduced by human activities as the earliest transatlantic voyages took place between the thirteenth and seventeenth centuries.

In the UK, there is debate as to whether A. improvisus is native. It is not included in the non-native species list by Eno et al. (1997), but Southward (2008) considered the species as an emigrant from America. In Ireland it is only estimated to have arrived before 1950 (Minchin and Eno, 2002; Minchin, 2007).

In the southern Baltic the first record of A. improvisus dates back to 1844 (Gislen, 1950). It was recorded on the German North Sea coast in 1858 on buoys in the Elbe estuary (Gollasch and Nehring, 2006), and in Finland in 1868 near Turku (Leppakoski and Olenin, 2000). The first record from the Atlantic coast of France is from 1872 (Goulletquer et al., 2002). The first Danish record seems to be from 1880 in Copenhagen (Kruger, 1927; Jensen and Knudsen, 2005). In 1895 the first Swedish record from the west coast (Gislen, 1950) took place. The earliest record from Norway seems to be from 1900, when A. improvisus was found in Oslofjord, and until 1969 it was only found in this fjord.

A. improvisus was found on the Swedish Baltic coast in 1919 (Gislen, 1950). Its distribution was given as up to 64°N by Leppakoski and Olenin (2000), but some authors indicate that it may have spread further north in recent years (Brattegard and Holthe, 1997Rivera et al., 2011).

A. improvisus has invaded the Black and Caspian Seas. The first record from the Black Sea dates back to 1844 (Gomoiu et al., 2002), but the species may inhabited the basin much earlier: Derzhavin (1956) indicates than it could have been transported on ships from ancient Greece and Phoenicia. The start of invasion and spread in the Caspian Sea is well-recorded (Tarasov and Zevina, 1957). It arrived in the Caspian Sea in 1955 (Sayenkova, 1956; Grigorovich et al., 2003), presumably through the Volga-Don Canal from the Asov and the Black Sea. In summer 1956 the species could be found everywhere in the basin (Tarasov and Zevina, 1957) and now it is a dominant fouling organism (Aladin, et al., 2002).

There are few recent records from the Mediterranean, and it is unknown whether A. improvisus is established here (Zenetos et al., 2005). The first record may be from 1972 (Streftaris et al., 2005) or 1976 from off-shore platforms in the Adriatic Sea (Relini et al., 1976). In a recent review by Galil (2011) the species is not mentioned in the list of alien crustaceans of the Mediterranean Sea.

In the Russian part of the Sea of Japan A. improvisus is now considered established (Zvyagintsev, 2003; Ovsyannikova, 2008). The first record as an exotic species was in 1969 when it was found on man-made installations (Zevina and Gorin, 1971) in the Peter the Great Bay. However, the species might have inhabited the waters well before detailed scientific research was started here in the 1960s.

In the second half of the twentieth century A. improvisus colonised the Western Pacific, probably through human introduction. In Japan it was first recorded in 1952 (Utinomi, 1968, 1970), and it has been spreading slowly across Japan since that time (Iwasaki, 2004, 2007). After the Second World War it was described from Vietnam by Zevina et al. (1992) and Zvyagintsev (2000), where it may have arrived on Russian military ships.

The species is recorded from several locations in North and Central Western Pacific (Jones et al., 2000), but little is known about the pattern of its spread and invasiveness in the region.

In the Southwest Pacific the species was first reported in Western Australia by Bishop in 1951, who suggested that A. improvisus had become established in one of the Australian ports during the 1940s. However, later Allen (1953) could not substantiate this claim when investigating fouling of submerged surfaces on the eastern Australian coast. In a review, Jones (1992) didn't include this species as present in Australian waters, but Australia appeared as a location in a later review (Jones et al., 2000). Recently the species has been reported from ships' hulls in Australian ports, but there are no records of its having become established (Wiltshire et al., 2010; Ahyong and Wilkens, 2011) in these waters.

In New Zealand, A. improvisus was initially observed on an oil platform which had been transported from Japan to New Zealand (Foster and Willan, 1979) in 1975, and the species is now reported as established.


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
California Atlantic, Northeast Before 1853 Hitchhiker (pathway cause) Yes Darwin (1854)
Colombia Atlantic, Northwest Before 1854 Hitchhiker (pathway cause)Darwin (1854)
Ecuador Atlantic, Northwest After 1840
France Atlantic, Northwest After 1872 Hitchhiker (pathway cause) Yes First found between Charente and Capbreton, SE Biscay
France Japan 1976 Yes Gruet et al. (1976) On Crassostrea gigas
Germany After 1840 Hitchhiker (pathway cause) Yes Hentschel (1923)
Japan After 1945 Hitchhiker (pathway cause) Yes Utinomi (1966); Utinomi (1970)
New Zealand Japan 1975 Hitchhiker (pathway cause) Yes Foster and Willan (1979) On semisubmersible oil platforms and drill vessels from Osaka
Texas California   Hitchhiker (pathway cause)Davidson et al. (2008) On derelict vessels towed between oceans through the Panama Canal
Vietnam Russian Federation 1950 Hitchhiker (pathway cause)Zvyagintsev (2000) On Russian shipping lines on routes from Bering Sea

Risk of Introduction

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Rivera et al (2011) modelled the potential for high-latitude marine invasions of A. improvisus along western North America. According the author's calculations, there is a potential of habitat extension from the modern frontier in British Columbia (Port Alberni) to the Prince William Sound and Aleutian Islands reaching 61-61.5º N. If global warming is considered, the north habitat border may shift as far as 68.5- 69.0º in America, creating a possibility of invasion of the species on much of the southeast coast of Alaska. In Europe (Norway) the northern border may shift to 65.5 or in case of potential effect of global warming to 71-71.5º N.

Findings of the species in Australian ports indicates a possibility of a wider invasion in the region.

Rivera et al. (2007) noted that uniform warming of 2°C may nudge northward some of the northern hemisphere limits of A. improvisus but would decrease its tropical coverage and lead to a global decrease in suitable habitat.


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Habitat type and substrate use is similar in native and invaded habitat. A. improvisus occurs in a very wide range of habitats with brackish water conditions, from bays and estuaries to shallow marine habitats with preferably stony and stony-sandy bottoms (Jarvekiulg, 1979). Vertical distribution can vary, generally reflecting the difference in tidal range at each location, usually 0-80 cm.

The species is known for its ability to tolerate high levels of pollution, such as thick oil film in the Caspian Sea (Tarasov and Zevina, 1957). It can tolerate intermittent exposure to fresh water (Darwin, 1854) and often goes further up estuaries than other native species (Southward, 2008).

The species can often be found on ship hulls, sluices and oil platforms. On ships it tolerates places with strong water flow (Tarasov and Zevina, 1957).

Within the habitat range the species tends to colonize all available substratum suitable for a cyprid larva settlement. Many authors noted an ability of A. improvisus to live on a wide range of hosts.

In northern Europe the species can be found attached to algae (such as bladder wrack, Fucus vesiculosus) (Birshtain et al. 1968; Hayward and Ryland 1995; Weidema, 2000; Southward, 2008). In Brazil it attaches directly to mangrove roots from the lower region to shallow sublittoral places (Farrapeira, 2010).

A. improvisus is often found attached to bivalve shells and dead molluscs. On sandy beaches of the northwestern Black Sea it colonised almost all bivalve shells at 2-10 m depth (Vinogradov, 1956). In the Baltic it has been found on Mytilus edulis (Laihonen and Furman, 1986) and Mya arenaria (Olszewska, 2000). In the southern Baltic A. improvisus is the only representative of the Cirripedia which grows on the mussel Mytilus trossulus, which is the dominant element of the bottom fauna in this area. The sporadic occurrence of this barnacle on another Baltic bivalve species, the cockle Cerastoderma glaucum, has also been noted (Olszewska, 1999).

In September 1999 the species was found on shells of the soft-shell clam Mya arenaria on the beach near Brzezno (Gulf of Gdansk). The presence of A. improvisus on M. arenaria could be further evidence of the tendency of barnacles to colonise all available habitats, even if they are not always optimal (Olszewska, 2000).

In the Caspian Sea it uses an endemic bivalve Didacna sp. (Riedel et al., 2006). In Brazil it attaches directly to living oysters and mussels, as well as on stones and empty shells on the muddy sediment (Farrapeira, 2010). In the Sea of Japan it settles on the native bivalve Corbicula japonica, which may live in freshwater, and on the oyster Crassostrea gigas, but also on seagrass and macroalgae (Ovsyannikova, 2008).

Apart from mollusc shells, A. improvisus has been reported growing on other hosts, such as the carapace of fresh-water beetles and crayfishes in northern Iran (Southward, 2008). In Florida it has been found on a brackish water turtle, the diamond-backed terrapin (Ross and Jackson, 1972). In South America Farraepeira (2009; 2010) has reported it on numerous organisms.

Habitat List

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Estuaries Principal habitat Harmful (pest or invasive)
Estuaries Principal habitat Natural
Lagoons Principal habitat Harmful (pest or invasive)
Lagoons Principal habitat Natural
Coastal areas Principal habitat Harmful (pest or invasive)
Coastal areas Principal habitat Natural
Coastal dunes Principal habitat Harmful (pest or invasive)
Coastal dunes Principal habitat Natural
Intertidal zone Principal habitat Harmful (pest or invasive)
Intertidal zone Principal habitat Natural
Mangroves Principal habitat Harmful (pest or invasive)
Mangroves Principal habitat Natural
Inshore marine Principal habitat Harmful (pest or invasive)
Inshore marine Principal habitat Natural
Pelagic zone (offshore) Principal habitat Natural
Host Principal habitat Harmful (pest or invasive)
Host Principal habitat Natural
Vector Principal habitat Harmful (pest or invasive)
Vector Principal habitat Natural

Biology and Ecology

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In British populations of A. improvisus, Furman et al. (1989) noted high levels of polymorphism and heterozygosity in most estuarine populations except for a small isolated Conwy population, where self-fertilisation and inbreeding is possible. Factors determining the genetic differentiation in British populations are water currents and water traffic, but not salinity.

Analyses of isozyme patterns by Furman (1990) revealed a high degree of genetic similarity amongst populations in the British Isles and the Baltic, the West coast of Sweden, and North America. The results indicate that populations of A. improvisus cluster by geographical and salinity patterns. Less heterozygote deficiency was observed in the Baltic, showing higher stability and outcrossing here. Johannesson and Andre (2006) analysed genetic data from 29 species inhabiting the low saline Baltic Sea and found that essentially only A. improvisus seemed to be panmictic over the Baltic Sea–North Sea salinity gradient due to high dispersive capacity.

Gamfeldt et al. (2005) hypothesised that increasing genetic diversity within species enhances ecosystem processes such as success of larval settlement of A. improvisus. Possible mechanisms that explain this pattern may be facilitation of gregarious response through the presence of founder genotypes, ensuring genetic complementarity to increase future reproductive potential. The study of settlement pattern of the species indicates that changing intraspecific genetic diversity could have community-scale consequences for larval recruitment and space occupancy.

Barien (2002) assessed cytogenetic damage in A. improvisus (aneugenic effects) inhabiting the Baltic Sea at Butinge oil terminal, showing the high genotoxicity level in the zone of sewage effluent from Palanga town and Mazeikiai oil refinery. Extensive cytogenetic injuries in gonadal cells of A .improvisus indicated the potential long-term hazards of pollutants to ecological health and integrity of this aquatic species. 

Reproductive Biology

Although hermaphroditism is universal in sessile barnacles, only a few species are known to be facultative self-fertilisers. Furman and Yule (1990) tested the ability of A. improvisus to self-fertilise. Individuals were observed to carry well-developed ovaries and well-developed testes at the same time. Fertilisation took place and the eggs developed to larvae in both isolated and communal individuals. Self-fertilisation appears to take place somewhat later than cross-fertilisation. These laboratory results on self-fertilisation are supported by field observations, in which isolated individuals were found with fertilised egg masses. A. improvisus can thus be added to the list of facultatively self-fertilising cirripedes. The ability to self-fertilise is especially advantageous for individuals of a species such as A. improvisus, which often has sparse and isolated populations (Weidema, 2000).

Prior to copulation the barnacle acting as male briefly stops pumping water and beating the cirri, and the extremely long penis is extended into the mantle cavity of the recipient barnacle (Crisp and Southward, 1961). Eggs form in the mantle cavity. Egg size is about 180 µm, and contrary to other species, there is little geographic variation in this size (Barnes and Barnes, 1965). A. improvisus may produce 1000 to 10,000 eggs per season (Costlow and Bookhout, 1957) and gives several generations in a year. Embryos are brooded in an ovisac inside the mantle cavity. Development to hatching takes about 21 days at 18°C (Furman and Yule, 1990). 

Physiology and Phenology

Larvae hatch as nauplii, and a new brood can be released every 5-6 days (Gamfeldt et al., 2005). There are six nauplius stages of which the first may be non-feeding, the others feeding in plankton, and a non-feeding cypris stage (Barnes and Barnes, 1965). Nauplius larvae show strongly positive phototaxis, which decreases in the last nauplius stage (Lang et al., 1979). Both eggs and nauplii of A. improvisus are smaller than those of most other barnacle species (Barnes and Barnes, 1965; Ross et al., 2003). Development through the six nauplius stages takes about one week in the laboratory (O'Connor and Richardson, 1996; Dahlstrom et al., 2000), but this depends on temperature.

The last naupliar stage moults into the cyprid larvae, which settle on hard substrate and transform into barnacles. Cyprid larvae are most prone to settling when they are 3-4 days old (Sjogren et al., 2008). Settlement increases in the presence of extract from adult conspecifics, and significantly more cyprids settled at 5 and 10 ppt than at other salinities between 2 and 35 ppt (Dineen and Hines, 1992). The same authors noted that surface effects were less obvious as age of cyprids increased.

Settlement may also be influenced by light (larvae are positively phototrophic), quality of the substratum and flow velocity (Smyth, 1946). De Wolf (1973) noted that number of cyprids increases soon after low water and decreases during the period of high water. Intensity of the flow also influences the settlement: cyprids can attach when velocity of the flow is 0.25 m/sec, but not more than 0. 56 m/sec. The ability of the cyprids to prefer rough surfaces over smooth ones to settle in depressions is well known (Shalaeva, 1997; Rainbow, 1984). Dahlstrom et al. (2004) noted that surface wettability may act as a determinant in the settlement of A. improvisus that prefer hydrophobic surfaces in the laboratory conditions.

Chemical hormonal substances may influence the settlement of A. improvisus larvae. Thus, Dahlstrom et al. (2000) observed that settlement of cyprid larvae may be affected by surface active adrenoceptor compounds. Zega et al. (2007) found that, neurotransmitters such as dopamine and serotonin can regulate the settlement process of cyprid larva of A. improvisus. Dopamine significantly stimulated settlement of 2- and 4-day-old cyprids, while serotonin exerted an inhibitory effect, regardless of cyprid age.

Time of naupliar release and cyprid settlement vary. Bousfield (1955) states that diapason from 10-30°C is acceptable for larvae development. McDougall (1943) described a reproductive peak in North Carolina in winter (water temperature 5.5-11°C) with a maximum in January, when temperature was about 7°C. In the UK, nauplii are released from May to late September and settlement is recorded from May to September (Jones and Crisp, 1954).

In the Asov Sea (Vorobjev, 1949) larva release was noted in the first half of summer. In the Black Sea (Shalaeva and Lisitskaya, 2004) in 2000-2001 naupliar stages started to appear in plankton when water temperature was 10°C, reaching maximum numbers (150 - 250/m3) in May (water temperature 16°C) and August-September (water temperature 20°C). In these periods, larvae of A. improvisus constituted nearly half of all meroplankton. Larvae disappeared from plankton when water temperature reached 25°C.

In the Sea of Japan (Korn, 1991) the larvae of A. improvisus are found in plankton from June with 2-3 abundance peaks from August to October. At a depth of 1 m the number of the larvae reaches 800/m3 considerably exceeding that of other species and indicating a successful acclimatisation of the barnacle in the new region.

Nasrolahi et al. (2006) studied effects of salinity on larval stage survival. With increasing salinity, larval size decreases and development time to cyprid larva increased (8- 25ppt takes 7 days, above 36ppt – 9 days). Larval survival was highest at 12ppt (60%), against 14% at 36 ppt.

Morphology of larvae stages, metamorphosis and early juvenile development has been described and illustrated in great detail (Doochin, 1951; Korn, 1991; Glenner and Hoeg, 1993; Shalaeva, 1996; 2003). Murina and Grinsov (1995) gave an illustrated description and a key to 6 naupliar stages of A. improvisus from the Black Sea.

A. improvisus gives 2- 3 generations in a season. In the Miami area (Moore and Frue, 1959) the species has three settlement and three survival peaks. Similarly, along the Swedish west coast the species may have three generations in one summer season (Stephenson, 1938). Growth of the shell is very fast; in 2 weeks a newly metamorphosed individual may have a diameter of 4 mm and 20 mm (Tarasov and Zevina, 1957). At Tvarminne in Finland they grew from 3 to a maximum of 16 mm in 10 weeks (Laihonen and Furman, 1986). A. improvisus moults every 2-4 days at 20°C (Costlow, Bookhout, 1953). The shell plates grow continuously as the body gets bigger (Costlow, 1956). Moulting can be induced and inhibited by the same hormones as in decapod crustaceans (Davis and Costlow, 1974).

Generally, the species has a longevity of one year, but occasionally individuals can live for just over two years. 

Population Size and Density

A. improvisus reaches maximum size in 2-3 weeks (Elfimov et al., 1995). Tarasov and Zevina (1957) observed that on natural substrata biomass does not exceed 1.5 kg/m2 and density 10,000-11,000/m2. On ships, the biomass can reach 5-8 kg/m2 and on stationary constructions up to 15,000 kg/m2 with density 50,000/m2 (Brayko, 1982). Tarasov and Zevina (1957) showed that density changes depending on depth. Thus, on metallic constructions in the Caspian Sea, at 0-0.5 m depth the density was 55,000-57,000/m2, whereas it was just 24,000-28,000/m2 at 1-5 m depth.

Other factors affecting size and density of subtidal A. improvisus populations were investigated in Chesapeake Bay, USA (Branscomb, 1976). Populations were affected by both biotic and physical factors. The flatworm Stylochus ellipticus, the predominant predator on barnacles, and the bryozoan, Victorella pavida, the major spatial competitor, were major factors in summer. In winter a combination of high winds (25 knots) and low air temperature (-9°C) were the major eliminating factors.

Population size and density can affect reproductive ability of the species. Thus, according to Brayko (1982) in populations with high density A. improvisus matures faster, giving ten generations a month compared with seven generations in low-density populations. However, in crowded conditions each adult gives less eggs. 


Adult A. improvisus is a filter/suspension feeder which feeds on microplankton and deitritus (Olenin, 2006). Additionally, in the splash zone mineral pieces constitute up to 60% of gastric content (Kuznetsov, 1978). According to Resnichenko et al. (1976), level of consumption of A. improvisus is 1.5 higher than other crustaceans, giving rapid growth and reproduction.

The barnacle creates a feeding current by pumping movements of the opercular plates and regular beating of the “cirri”, modified thoracic legs, and filters edible particles with the setae on these cirri. The current speed and the strength of the beating of the cirri can be adjusted to the concentration and size of food particles (Crisp and Southward, 1961; Rainbow, 1984). In laboratory experiments they feed on phytoplankton, but had slower body growth than in the field (Costlow and Bookhout, 1953, 1957).

In field experiments, consumption of Enteromorpha intestinalis promoted the growth and settlement success of A. improvisus (Kotta et al., 2006b). In laboratory experiments examining larval survival and growth under different algal feeding regimes, development time was shortest (6 days) with a mixed diet of Chaetoceros calcitrans, Chlorella vulgaris and Scenedesmus quadricauda (Nasrolahi et al., 2007). Highest mortality occurred for monoalgal diets of S. quadricauda while the highest survival was achieved with a monoalgal diet of C. calcitrans

The following natural food sources have been recorded:


Natural Food Sources

Life stage

Artemia sp. (Furman and Yule 1990; Dahlstrom et al. 2000)


Chaetoceros calcitrans ( Nasrolahi et al. 2006)


Chlamydomonas sp (Costlow and Bookhout, 1953)


Chlorella vulgaris ( Nasrolahi et al. 2006)


Chlamydomonas sp (Costlow and Bookhout, 1953)


Enteromorpha intestinalis ( Kotta et al. 2006)


Isochrysis galbana (Lang et al.,1979; Dahlstrom et al., 2000)

Adult, larva

Nitzschia closterium (Costlow and Bookhout, 1953)


Rhodomonas baltica (Furman and Yule 1990)


Scenedesmus quadricauda (Nasrolahi et al. 2006)


Skeletonema costatum (Furman and Yule, 1990)


Tetraselmis suecia (Lang et al., 1979)



A. improvisus is often found together with other species of barnacles (Henry and McLaughlin, 1975). Relationships between the Cirripedia species may be competitive. Thus, Kerckhof (2002) notes that in Belgian waters, A.improvisus suffers from competition from other alien barnacles such as Balanus amphitrite, B. crenatus and Elminius sp. In British estuaries A. improvisus may be out-competed by Elminius modestus (Southward, 2008), the other immigrant in European waters.

A. improvisus often lives with different species of bivalve molluscs. When settling on molluscs they prefer the posterior end of the shell, near the in- and exhalent openings, so they can benefit from the feeding current of the mussel (Laihonen and Furman, 1986; Riedel et. al., 2006).

In fouling communities in the Western Baltic Sea (Durr and Wahl, 2004) A. improvisus is the only species which is able to coexist with Mytilus edulis. M. edulis was dominant over A. improvisus where both species were present. In the Caspian Sea, association with bryozoan Conopeum seurati and bivalve Didacna sp. was studied by Riedel et. al. (2006). Largest specimens of A. improvisus were attached near the shell gap where Didacna inhales water, benefitting from the water current. Competition for food sources between the species was noted.

Ability to coexist with particular species of encrusting bryozoan colonies and the sponge Tedania ignis was noted by Farrapeira (2010) in Brazil. Brascomb (1976) found that Victorella pavida was the major spatial competitor of A. improvisus in Chesapeake bay, USA (native range).

A. improvisus is well known as an incidental commensal on mobile benthic and nektonic crustacean hosts such as crabs, prawns and portunids. Farrapeira (2010) found the species using crustacean carapaces in estuarine muddy bottoms as an available hard substrate to live on.

Tarasov and Zevina (1957) noted that an ability of the species to live on beetles such as Hydrous piceus and Cybister laterimarginalis may assist invasion of A. improvisus into brackish lakes of the Caspian region. 

Environmental Requirements

A. improvisus is highly euryhaline, living in almost fresh water in some localities in the native area. Thus, Darwin (1854) found it in the estuary of La Plata River in almost freshwater conditions. The same ability was noted for introduced areas (Turpaeva and Simkina, 1963; Davenport, 1976; Jarvekiulg, 1979; Leppäkoski, 1999; Zaiko et al, 2007). In central California the species was found in the freshwater Delta Mendota irrigation canal (Zullo et al., 1972). Maximum salinity that A. improvisus can withstand is 30-60 ppt (Tarasov and Zevina, 1957) noted in the Asov Sea.

Turpaeva and Simkina (1963) conducted experiments on the tolerance of Black Sea A. improvisus to reduced salinities. Individuals taken from very saline water are capable of enduring an extremely great dilution of water. Observations on the growth, rate of oxygen consumption, and spawning of A. improvisus disclose that a salinity range from 18 ppt to 5 ppt is tolerated by the animals in all stages of development and that they are capable of reproduction. With reduction in salinity to 3 ppt and less, most of the barnacles die in a few months and none of them are capable of reproduction.

Barnacles need time to adapt to changed salinity, the period becoming longer with lower salinity concentrations. The adaptation is most clearly pronounced in growth rate: at lower salinities the growth rate decreases only for a limited time period; after which it surpasses the usual speed and the barnacles reach a larger size than those living in salinity conditions that are normal to them.

Foster (1970) found that A. improvisus can, with gradual acclimation, be induced to be active in a salinity of about 2% due to remarkable tolerance of dilution of the blood. The author observed closing of the opercular valves while the salinity decreases. Then the blood and mantle cavity fluid are maintained for some time at a level initially considerably hyperosmotic to the medium, but the blood is still only slightly hyperosmotic to the fluid remaining in the mantle cavity. The barnacle is able to adjust to small changes of environmental salinity by tissue acclimation, but evade too severe salinity changes by withdrawing into the protection of the shell. This is typical of osmoconformers lacking specific organs for effective regulation. There is no permanent control, and in time the blood concentration approximates to the external level. Foster suggests that distribution into regions of low salinity may be due to a wide tissue resistance and not to any ability to regulate. Fyhn (1976) also describes response to different salinities.

A. improvisus tolerates temperatures as low as -2°C and up to 35°C (Southward, 1957). The species shows optimum cirral activity at high temperature and a change in rate only below 10°C, allowing continued cirral activity in very low temperatures. In hot conditions, cirral activity only stops at 35°C, similar to the tropical species B. eburneus. The author suggests that the ability to withstand temperature ranges may be connected with the remarkable euryhalinity: the flexible mechanism of osmoregulation facilitates tolerance to a wider range of temperatures.

In the Miami area (Moore and Frue, 1959) survival of A. improvisus is increased by higher temperatures and decreased by crowding and high river discharge. In the Baltic the temperature range for A. improvisus is 1.8 – 22.7°C (Jarvekiulg, 1979), whereas optimum temperature for free swimming nauplius larvae is around 14°C (Leppäkoski, 1999).

A. improvisus has a wide tolerance for oxygen concentration in the water; and can be found in the polluted and eutrophical parts of the Baltic, Black, Caspian and other Seas (Poulsen, 1935; Leppakoski and Olenin, 2000; Ovsyannikova, 2008). Furthermore, it is tolerant of oxygen concentrations as low as 1 ml/l3. It can tolerate 0.3 – 0.4 mg/l concentration of NH4 (Jarvekiulg, 1979). Tolerant to eutrophication; preference for organically enriched sites in ports with good foraging conditions (Leppäkoski, 1999).


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Af - Tropical rainforest climate Preferred > 60mm precipitation per month
Am - Tropical monsoon climate Preferred Tropical monsoon climate ( < 60mm precipitation driest month but > (100 - [total annual precipitation(mm}/25]))
As - Tropical savanna climate with dry summer Preferred < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Preferred < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
BS - Steppe climate Preferred > 430mm and < 860mm annual precipitation
BW - Desert climate Preferred < 430mm annual precipitation
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
Ds - Continental climate with dry summer Preferred Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Ammonium [ionised] (mg/l) 0.4 Optimum Up to 0.3-0.4 tolerated
Salinity (part per thousand) 10 20 Optimum 1.65-60 tolerated
Water temperature (ºC temperature) 10 20 Optimum -2 to + 35°C tolerated

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Asterias rubens Predator Adult not specific
Boschmaella balani Parasite Adult to species Bocquet-Vedrine and Parent, 1972
Carcinus maenas Predator Adult not specific
Crangon crangon Predator Larval not specific Kuhl, 1968
Mytilus edulis Predator Larvae not specific Järvekülg, 1979
Stylochus ellipticus Predator Adult to species Branscomb, 1976
Stylochus tauricus Predator Adult to species Murina et al., 1995
Tridentiger bifasciatus Predator Adult not specific Matern and Brown, 2005

Notes on Natural Enemies

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Larvae can be consumed passively by bivalve molluscs and other suspension feeders. Thus, Jarvekiulg (1979) found that Mytilus edulis can filter balanid larvae. Other specific predators which feed on balanid larvae include Crangon crangon larvae and jellyfish (Tarasov and Zevina, 1957; Kuhl, 1968).

Benthofagous fish often feed on adult A. improvisus. Matern and Brown (2005) observed that in San Francisco Estuary, the shimofuri goby (Tridentiger bifasciatus) consumes cirri (the part of the body protruding from the shell) of A. improvisus, which is not utilised by other resident fish. In the Baltic region (Kiel Fjord, Baltic Sea) field experiments showed that the starfish Asterias rubes, which is the dominant local predator, and the crab Carcinus maenas, both prey upon the mussel Mytilus edilis and its associated epibionts, namely A. improvisus (Laudien and Wahl, 1999).

On the east coast of North America the flatworm Stylochus ellipticus is a dominant predator of A. improvisus (Branscomb, 1976). On the Crimea shore in the Black Sea the flatworm S. tauricus feeds on A. improvisus (Murina and Grintsov, 1995). The predation rate (the number of barnacles eaten by one polyclad in a month) ranges between five and ten.

Two parasitic crustaceans have been found on A. improvisus: the rhizocephalan crustacean Boschmaella balani (Bocquet-Vedrine and Parent, 1972) and the isopod crustacean Hemioniscus balani (Tarasov and Zevina, 1957).

Means of Movement and Dispersal

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A. improvisus has spread by a combination of remote and marginal dispersal. In Japan, the average speed of spread is estimated to be 13.9 km/year (Iwasaki and Kinoshita, 2004). In the Baltic Sea, where spread is assisted by the anti-clockwise current pattern, the approximate (minimum) rate of spread for A. improvisus from Königsberg (1844) to Turku (1868) was 30 km/year (Leppakoski and Olenin, 2000).

Remote dispersal is mostly human-mediated. Vectors of balanomorph barnacles are listed by Carlton et al. (2011) and include shipping (fouling on hulls and other parts of the ship, in ballast water), and movement of organisms for aquaculture. Grigorovich et al. (2003) indicates that over a 40-year period since 1952, vectors related to shipping shifted from those associated with hull fouling to those associated with ballast water discharge.

All types of spread have been facilitated by the fact that the barnacle can attach to a range of substrates, mobile or motionless. Introduction of the species to all areas is considered to be accidental.

Pathway Causes

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CauseNotesLong DistanceLocalReferences
AquacultureOn commercial bivalve shells Yes Yes Gruet et al., 1976
Habitat restoration and improvementOn oyster shells Yes Yes Carlton et al., 2011
HitchhikerOn vessels, worldwide Yes Yes Carlton et al., 2011
Interconnected waterwaysOn vessels Yes Yes Carlton et al., 2011
Military movementsOn vessels Yes Yes Carlton et al., 2011

Impact Summary

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

Economic Impact

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The major economic impact of A. improvisus is from fouling of ships and hydrotechnical constructions. Fouling of man-made constructions by barnacles can cause an increased corrosion rate leading to deterioration and/or prevention of normal functioning, causing significant economic loss.

Leppakoski and Olenin (2000) consider A. improvisus to be the only barnacle from which the fouling impacts may be economically significant in the Baltic. In Finland, for example, A. improvisus was causing problems in structures all along the coast as far north as Vaase in the northern part of the Bothnian Sea (Leppäkoski, 1999; Weidema, 2000).

Gren et al. (2009) counted the cost of damage of A. improvisus in the Baltic (Sweden) measured as control costs of fouling. It varied between 166-418 million SEK (Swedish krona) per year, of which fouling control of recreational boats accounts for approximately 74 percent. A. improvisus is considered the most problematic fouling organism in Swedish waters, and is probably responsible for most of these costs.

Fouling can cause technical problems and economic loss to installations such as power plants. Iwasaki (2006) indicates that barnacles block water cooling intakes in power stations.

Fouling of boat hulls by barnacles slows vessels' speed, increasing transit time and reducing manoeuvrability. A 1 mm thick coating of slime on a boat hull reduces speed up to 15% (Gordon and Mawatari, 1992).

The application of anti-fouling paints incurs significant economic cost plus negative effects on the marine environment (Tarasov and Zevina, 1957; Weidema, 2000). 


Fouling of cages and shells of mariculture mollusca such as blue mussels and oysters (Leppäkoski, 1999, 2002) reduces productivity of marine farming.

Fish production may be reduced by influencing the food web of commercial fish species, because the species is rarely consumed by fish (Gollasch and Leppäkoski, 1999). However, Tarasov and Zevina (1957) suggested that in the Caspian Sea A. improvisus may be consumed by some benthofagous fish such as Rutilus frisii.

Environmental Impact

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The compounds of anti- fouling paints used on ships and hydrotechnical constructions are highly toxic to the marine environment as a whole (Weidema, 2000; Leppakoski, 2002).

A. improvisus tends to form dense layers on the surface of artificial structures and other substrata, inhibiting water flow, attracting associate fauna and producing organic debris (Leppäkoski, 1999; Weidema, 2000). The increase in biodeposition and mechanical trapping of organic material caused by A. improvisus may result in increasing eutrophication of semi-enclosed systems, providing an important source of material to the benthic environment, including the important detritus food chain (Kotta et al., 2006a, b; Weidema, 2000). This may potentially increase the energy flows from pelagic system to benthos and cause a shift from pelagic production to benthic production.

A. improvisus may be involved in competition for food and/or space with local or introduced species. For example, Jarvekiulg (1979) observed competition for attachment places and food between the filter feeders A. improvisus, Mytilus edulis (sea forms) and Dreissena polymorpha (zebra mussel, brackish water form) in the Pernu Bight. Salinity is the main factor on which the result of competition depends: increased salinity is favourable for the two sea forms and not for zebra mussels. Durr and Wahl (2004) also described A. improvisus as a strong competitor for space, but mentioned that it does not have a negative effect on community diversity in the Baltic. The same authors detected that while A. improvisus had no significant effect on recruitment of species, a negative synergistic effect of blue mussels and barnacles on species richness and diversity H-1 (Shannon Index) may be significant in the Western Baltic.

A. improvisus can affect biodiversity and community structure. Leppäkoski and Olenin (2000) noted that the barnacle was facilitating settlement of other organisms in the Baltic, changing community structure. In dense populations of A. improvisus, biodiversity of associated species such as hironmide larvae, ostracod and copepod crustaceans and juvenile bivalves increase compared to adjacent sites without the barnacle (Leppäkoski, 1999). Additionally, empty shells of the barnacle serve as new microhabitats for small annelids, crustaceans and chironomids.

The overall impact of A. improvisus on habitats and communities requires further investigation. After introduction of A. improvisus (along with more than 100 other species) in the Baltic sea during the last two centuries, no extinction of native species had been recorded in 2002 (Leppakoski et al., 2002). Reise et al (2006) state than they found “no evidence that they (non-native) species generally impair biodiversity”, but that the species expand ecosystem functioning adding new ecological traits, increasing functional redundancy and intensifying existing traits. Aladin et al. (2002) concluded that, despite some negative effects of certain non-native species, in general they contribute to rich biodiversity in the Caspian Sea.

Risk and Impact Factors

Top of page Invasiveness
  • Invasive in its native range
  • Proved invasive outside its native range
  • 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
  • Capable of securing and ingesting a wide range of food
  • Highly mobile locally
  • Benefits from human association (i.e. it is a human commensal)
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Altered trophic level
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Increases vulnerability to invasions
  • Infrastructure damage
  • Modification of hydrology
  • Modification of natural benthic communities
  • Modification of nutrient regime
  • Modification of successional patterns
  • Monoculture formation
  • Negatively impacts human health
  • Negatively impacts aquaculture/fisheries
  • Negatively impacts tourism
  • Reduced amenity values
  • Reduced native biodiversity
  • Transportation disruption
  • Negatively impacts animal/plant collections
Impact mechanisms
  • Competition
  • Filtration
  • Fouling
  • Interaction with other invasive species
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 

Tarasov and Zevina (1957) tentatively suggested that A. improvisus could be used as a food source for introduced benthofagous fish such as Rutilus frisii kutum in the Caspian Sea. 

Environmental services 

Due to ability to accumulate toxic substances, barnacles are suitable biomonitors to employ in programmes designed to assess changes in metal pollution in some regions (Silva et al., 2006). Thus, in the Gulf of Gdansk, Poland, A. improvisus accumulates trace metal concentrations (Cu, Zn, Fe, Cd, Pb, Mn, Ni) (Rainbow et al., 2000). Analysis of covariance has shown significant geographical and temporal differences in the local bioavailabilities of trace metals to barnacles, as reflected in the concentrations of accumulated trace metals. However, as the lifespan of the species is not longer than two years, it has limited value for long-term studies.

Uses List

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Animal feed, fodder, forage

  • Fishmeal

Detection and Inspection

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Paavola et al. (2005) noted the ability of A. improvisus to invade brackish waters, where native species richness seems to be low. Availability of empty niches, suitable environmental conditions and proper vectors may be the most effective predictors for the risk of invasion and therefore need to be included in the risk assessment procedure.

Gollasch (2002) reviewed effectiveness of risk assessment methods in nordic countries, Australia and the USA. The methods include decision support systems, creation of a “black list” for target species, and matching climate in native and non- native zones. Hewitt and Hayes (2002) detailed risk assessment methods for bioinvasions. Haugom et al. (2002) specified risk assessment in ballast water. Taylor et al. (2002) described methods of preventive treatment and control techniques for ballast water. Bishop and Hutchings (2011) evaluated the usefulness of port surveys focused on target pest identification for exotic species management.

Identification of the larval form of A. improvisus (for example in ballast water) requires a microscope and picture guides. Using sources such as Korn (1991), Murina and Grintsov (1995) or Ross et al. (2003) may be useful for identification. Adult forms may be identified using a magnifying glass and literature sources with pictures and photos (Darwin, 1854; Pilsbry, 1916; Broch, 1924; Tarasov and Zevina, 1957; Henry and McLaughlin ,1975; Southward, 2008). Some identification keys are given in Tarasov and Zevina (1957) and Southward (2008).

Similarities to Other Species/Conditions

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A. improvisus is similar in appearance to a group of quite closely related shallow water barnacles. Ways to distinguish in the field:

The shell of Balanus crenatus appears not notched on the top, calcareous base lacks the star-like pattern and its operculum is centred. The carina of Amphibalanus eburneus is not lower than the rostrum, the scuta are cross-striated, cuticle is more resilient on plates rather than on the radii. The main band in the middle of the tergoscutal flap of Amphibalanus amphitrite is above the micropylar opening. More morphological detail on differences in the Balanus amphitrite complex are given in Henry and McLaughlin (1975).

Prevention and Control

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Physical/mechanical control 

Mechanical methods may be simple and effective, and, perhaps, pose less risk for the environment than chemical control. The following methods are widely used to control A. improvisus and other barnacles:

Ballast waters: mid ocean exchange of ballast water is necessary to get rid of planktonic larvae.

Fishing and other equipment and infrastructure (nets, trays, etc); Onshore washing, manual cleaning (scrubbing and/or brushing); air drying; lowering below the photic zone during major spawning; oxygen deficiency.

Aquaculture stock: manual and mechanical cleaning; hot water, freshwater, or chemical solution treatment; lowering lines below the photic zone during major spawning.

Chemical control 

Use of anti fouling components in coating is a basic chemical method of prevention (Hellio, 2009; Banerjee et al., 2011) which is continually being developed and improved in terms of effectiveness and economic cost.

Some antifouling compounds such as tri-butyl-tin and copper are now considered as dangerous for marine environments. There has been some research carried out trying to identify natural substances that may specifically hinder settling of A. improvisus. Some of these studies have been successful and anti-barnacle compounds are patented. Toth and Lindeborg (2008) found that water-soluble compounds from the breadcrumb sponge Halichondria panicea deters attachment of the barnacle. Pinori et al. (2011) indicated that protection from A. improvisus is achieved by trace amounts of a macrocyclic lactone (ivermectin) included in rosin-based coatings.

Gaps in Knowledge/Research Needs

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The provisional cryptogenic status of A. improvisus requires a comprehensive taxonomical review of the species, which should include analysis of fossil remains and examination of museum collections. The reexamination may reveal earlier dates of invasions such regions as Baltic and South America and clarify the invasion history in the Mediterranean region.

Overall, study of the pattern of invasion and reinvasion of the species and changes in distribution (such as moving northwards or southward) can be a monitor of global change in the marine environment.


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Links to Websites

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DAISIE Delivering Alien Invasive Species Inventories for Europe
NIMPIS 2011 improvisus general information, National Introduced Marine Pest Information System,


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31/12/11 Original text by:

Ekaterina Shalaeva, Consultant, UK

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