Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Crepidula fornicata
(American slipper limpet)



Crepidula fornicata (American slipper limpet)


  • Last modified
  • 19 November 2018
  • Datasheet Type(s)
  • Invasive Species
  • Host Animal
  • Preferred Scientific Name
  • Crepidula fornicata
  • Preferred Common Name
  • American slipper limpet
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Mollusca
  •       Class: Gastropoda
  •         Subclass: Caenogastropoda
  • Summary of Invasiveness
  • At the end of the nineteenth century, C. fornicata was accidentally introduced in Europe where it found favourable conditions to settle and develop: free surfaces of sandy-coarse sediment, optimal water temperatu...

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The invasive habit of the slipper limpet, showing an area completely colonised by a community.
TitleInvasive habit
CaptionThe invasive habit of the slipper limpet, showing an area completely colonised by a community.
CopyrightXavier Caisey/Ifremer
The invasive habit of the slipper limpet, showing an area completely colonised by a community.
Invasive habitThe invasive habit of the slipper limpet, showing an area completely colonised by a community.Xavier Caisey/Ifremer
Single shell of a slipper limpet, showing right side of an adult.
TitleSingle shell
CaptionSingle shell of a slipper limpet, showing right side of an adult.
CopyrightPatrick Briand/Ifremer
Single shell of a slipper limpet, showing right side of an adult.
Single shellSingle shell of a slipper limpet, showing right side of an adult.Patrick Briand/Ifremer
Ventral view of a shell stack, showing the calcareous septum of the lower shell, a characteristic of this family.
TitleShell stack
CaptionVentral view of a shell stack, showing the calcareous septum of the lower shell, a characteristic of this family.
CopyrightPatrick Briand/Ifremer
Ventral view of a shell stack, showing the calcareous septum of the lower shell, a characteristic of this family.
Shell stackVentral view of a shell stack, showing the calcareous septum of the lower shell, a characteristic of this family.Patrick Briand/Ifremer


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Preferred Scientific Name

  • Crepidula fornicata Linnaeus, 1758

Preferred Common Name

  • American slipper limpet

Other Scientific Names

  • Patella fornicata

International Common Names

  • English: boat-shells; bungalows; slipper-limpet; thumbnails

Local Common Names

  • : common Atlantic slippershell
  • Denmark: toffelsnegl
  • France: crépidule
  • Germany: Pantoffelsnecke
  • Netherlands: muiltje
  • Sweden: toffelsnegl
  • UK/England and Wales: oyster pest

Summary of Invasiveness

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At the end of the nineteenth century, C. fornicata was accidentally introduced in Europe where it found favourable conditions to settle and develop: free surfaces of sandy-coarse sediment, optimal water temperature range, copious suspended organic matter as food and no specific predators; all this contributed to a rapid growth and reproductive success.

Oyster farming is the main cause of introduction and dispersal. Dredging and trawling of the oyster-growing areas has contributed to the spatial spread of  C. fornicata. It is now demonstrated that these fishing practices have, for decades, played a main role in the spread.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Mollusca
  •             Class: Gastropoda
  •                 Subclass: Caenogastropoda
  •                     Order: Littorinimorpha
  •                         Unknown: Calyptraeoidea
  •                             Family: Calyptraeidae
  •                                 Genus: Crepidula
  •                                     Species: Crepidula fornicata

Notes on Taxonomy and Nomenclature

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The name of the genus Crepidula means a slipper in Latin. The species epithet fornicata was given by the naturalist Linnaeus, due to the arched form of the colony (fornix = arch in Latin). The taxonomy adopted in the last ERMS classification places Crepidula in the family Calyptraeidae, which was given by Lamarck in 1799; the previous family name Crepidulidae (Flemming, 1822) is also found. The higher classification of the Gastropoda of Bouchet and Rocroi (2005) places Crepidula in clade Littorinimorpha of the Caenogastropoda. The genus Crepidula contains about thirty species distributed across the continents; some classification problems can arise when different Crepidula species are present in the same area.


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C. fornicata is a marine gastropod with a brown shell. Individuals reach about 6 cm long. The septum divides the interior of the shell into two parts: the external one where the foot and head can move and the internal one where the visceral mass is protected. Growth is rather rapid and a size of 2 cm is reached in 2 years. The plasticity of this species is important and shell can be deformed.

The first particularity of this species is that the individuals gather under attractive substances and form colonies, called ‘chains’. Individuals settle on top of each other, forming clusters. Only one juvenile remains at the top of the stack, the others move to form a new colony. The population extends in three dimensions.

In a standard colony there are 5 or 6 individuals, but in dense populations, this creates amazing numbers of stacks with complex colonies where the juveniles attach anywhere and support a new chain.

Newel and Kofoed (1977) described the morphology of the feeding system and measured the feeding rates in C. fornicata. This ubiquistous species ingests a wide variety of organic and inorganic food, at a rate of about 1 litre h-1 g-1, and also ingests some of its own larvae (Pechenik et al., 2004). The pelagic larva is also able to filter a wide range of particles (Blanchard et al., 2008). The radula can also capture some deposited matter. This feeding mode helps it find sufficient food to develop large populations, contrary to other grazing patellids (Hoagland, 1977).

Being fixed, the animals have developed a particular reproduction. The species is protandric. Juveniles are males and individuals become rapidly hermaphrodites from the second year, and then are females during the rest of their life (10 years). Between males and females of the same stack, fecundation is direct and sperm can be stored in a receptacle. Females of 2 cm long can be ovigerous. The brood is protected, eggs are laid grouped in bags (about 50 eggs bag-1) and are first stored near the head and later fixed on the lower shell. After about a month, each female releases 10-20,000 free larvae. They are veliger, barrel-shaped with a central ring of filaments to move in the plankton. Their size (min. 400 µm) and their strength make them suitable for experimental use (Pechenik and Lima, 1984; Pechenik et al., 2002b, 2004). The pelagic phase is about 3-weeks long (depending of the temperature) then larvae metamorphose and fall to the bottom where they look for suitable supports. All kinds of hard material can be used but they prefer a congener shell.

Being ubiquitous, eurythermic and euryhaline, this species can be observed in all kinds of environments: rocky, gravel or sandy bottoms, as well as in muddy areas where are measured the highest densities in Europe. These characteristics have helped it to spread so successfully.


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C. fornicata is native to the Atlantic coast of the USA and fossils are found along the Massachussetts coasts (Zeigler et al., 1965). It is found together with three congeneric species: Crepidula plana, Crepidula convexa and Crepidula aculeata. Walne (1956) described its geographical area as ranging from Escuminac point (47°N) on the Canadian coastline, to the Caribbean islands. It seems that in its native area, C. fornicata is weakly spreading, due to unfavourable hydrological conditions (low winter temperatures, strong currents) and a great number of predators (Hoagland, 1977).

C. fornicata was imported into Europe along with American oysters (Crassostrea virginica) dredged from oyster beds of Atlantic estuaries. Hoagland (1985) wrote that the European populations came from Long Island Sound. Large quantities of oysters were introduced in England and with them also C. fornicata, both juveniles and adults.

The geographical distribution of C. fornicata now stretches over 24 degrees of latitude, reaching all European seasides and the English Channel which currently appears to be the most colonized area (Blanchard, 1997). It is currently limited to the northern hemisphere. In the western USA, it was imported with oysters in Puget Sound during the 1930s, and is now common along the Washington state coastline (Hoagland, 1974, 1977). In 1968, spreading populations were noted in the bays of Tokyo and Sagami in Japan (Habe and Maze, 1970).

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


JapanPresentIntroduced Invasive Habe and Maze, 1970In 1968 populations were noted in the bays of Tokyo and Sagami. Also found in Toyama Bay (S Kosuge, Institute of Malacology, Tokyo, personal communication, 1995)
-HonshuPresentIntroduced Invasive Habe and Maze, 1970The western coast is colonized
-ShikokuPresentIntroduced Invasive Habe and Maze, 1970All the coasts of the island are now colonized

North America

CanadaPresentWalne, 1956From Escuminac Point to the frontier of Antartic coast
-British ColumbiaLocalisedIntroduced Invasive Wonham and Carlson, 2005
-New BrunswickPresentNative Not invasive Walne, 1956Escuminac Point 47 degrees North
-Nova ScotiaPresentNativeDickinson et al., 1999
-Prince Edward IslandPresentNative Not invasive Provancher, 2008Canadian fauna, 2008 Bibliobazar ed.
-QuebecPresentNative Not invasive Provancher, 2008Candian fauna, 2008, Bibliobazar ed.
MexicoLocalisedIntroduced Not invasive Walne, 1956
USAPresentPresent based on regional distribution.
-ConnecticutPresentNative Not invasive Hoagland, 1985
-DelawarePresentNative Not invasive Karlson and Shenk, 1983; Gaffney and McGee, 1992Cap Henlopen
-FloridaLocalisedNative Not invasive Frazier et al., 1985Fixed on turtles
-MainePresentNative Not invasive Hoagland, 1985
-MassachusettsPresentNative Not invasive Johnson, 1972; Hoagland, 1974; Hoagland, 1977; Hoagland, 1979In Ipswich Bay and Cape Ann near Boston, in Buzzard Bay, in Vineyard Sound (Hoagland), in Woods Hole (Johnson)
-New JerseyPresentNative Not invasive Bottom and Ropes, 1988In Cap May
-New YorkPresentHoagland, 1985Long Island Sound
-North CarolinaPresentNative Not invasive Hoagland, 1985
-Rhode IslandPresentNative Not invasive Hoagland, 1979; Pechenik and Lima, 1984At Tiverton, on mussels (Hoagland) and Bissell Cowe (Pechenik)
-South CarolinaPresentNative Not invasive Hoagland, 1985
-TexasPresentWalne, 1956; Tunnell and Chaney, 1970On Texas just along coast
-VirginiaPresentNative Not invasive McGee and Targett, 1989Atlas of Potomac river and of Chesapeake Bay
-WashingtonPresentIntroduced Invasive Hoagland, 1974; Hoagland, 1977In the western USA it was imported with oysters in Puget Sound during the 1930s and is now common along the Washington state coastline

South America

UruguayPresent, few occurrencesIntroduced Not invasive Walne, 1956"some specimens were found on the Urugayan seaside"


BelgiumWidespreadIntroduced Invasive Adam and Leloup, 1934; Polk, 1976In Ostende Bay
DenmarkPresentIntroducedSparck, 1949; Hessland, 1951In the Limfjord
FinlandPresentIntroducedLeppäkoski and Olenin, 2000Present in the list of alien species in the Baltic Sea
FranceWidespreadIntroduced Invasive Marteil, 1965; Blanchard, 1995; Montaudouin and Sauriau, 1999; Martin et al., 2006; Blanchard, 2009From Belgium border to Arcachon Bay in Atlantic side and in Mediterranean lagoons
GermanyWidespreadIntroduced Invasive Werner, 1949; Hessland, 1951; Thieltges et al., 2003; Thieltges et al., 2004Wadden Sea, Sylt Islands
GreecePresentIntroduced Not invasive Galil and Zenetos, 2002Individuals have been observed in Savonikos Bay, near the Peiraias Port, because of hull founling
IrelandLast reported1982Introduced1902 Not invasive Arnold, 1960; Minchin and McGrath, 1995First recorded in 1902, no record since 1982
ItalyLocalisedIntroduced Not invasive Natale ADi, 1982On the northeastern coast of Sicily
MaltaLocalisedIntroduced Not invasive Cachia, 1981Introduced with hull fouling, from Portugal
NetherlandsWidespreadIntroduced Invasive Adam and Leloup, 1934; Nienhuis, 1992; Wolff, 2005First live specimen found in 1926, today common in the Sheldt estuary, Zeeland, Calandkanaal, Beerkanaal and near Rotterdam basins (Wolff)
NorwayPresent, few occurrencesIntroduced Invasive Bergan, 1969; Bergstad, 1974; Hoisaeter, 1986; Sjotun, 1997Several observed in Skagerrak. The extreme observation to the North is Kvitsoy, on the western coast
SpainWidespreadIntroduced Invasive Rolan, 1983; Rolan et al., 1985In galician bays, under the oyster cultures
SwedenPresentIntroducedForsman, 1951; Hessland, 1951Bohusland coast
UKWidespreadIntroduced Invasive Spencer, 1974; Utting and Spencer, 1992Southern coasts of England and Wales
-Channel IslandsWidespreadIntroduced Invasive Blanchard, 1995; Blanchard, 2009Jersey and Guernsey

History of Introduction and Spread

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The introduction of C. fornicata in Europe was well documented at the beginning of the twentieth century, first by British naturalists and then by scientists in other countries. It was observed that the main vector of introduction was the oyster, first Crassostrea virginica (from USA to Europe), then the European native oyster Ostrea edulis (from England to other European countries), and also the Japanese oyster Crassostrea gigas which was imported all over the world from USA and Japan to European shores (Blanchard, 1997).

The consumption of the native oyster (Ostrea edulis) became fashionable in London in the middle of the nineteenth century, to the point where stocks rapidly decreased. To face the growing demand, some fishmongers decided to import American oysters (Crassostrea virginica). Fresh oysters were delivered in barrels and to stored in bays (such as Liverpool Bay and the Thames estuary) before being sold. This trade went on until the 1920s (Cole, 1952; Utting and Spencer, 1992; Minchin et al., 1995). These American oysters originated from areas (probably Long Island Sound, following Hoagland (1985)) where C. fornicata was also present. The imported oysters carried limpets fixed on their shells and although many of the introduced limpet populations died some of them survived and developed in their new environment.

The first live animals were found in the south of Liverpool Bay by naturalists (McMillan, 1938). “Crepidula fornicata has been found amongst the shells of Ostrea virginica (Gmelin) of which, vast numbers were planted (apparently in vain) on the shore near Beaumaris” said Darbishire in 1886. Some years later, others were then observed on the eastern coast of England and in the Thames estuary (Crouch, 1893; Cole, 1915). A population progressively developed in the rivers Blackwater and Crouch, which became the centre of future spread in England. The larval pelagic phase of the species was also one of the causes of spread and can partly explain species observations along the southern coasts of the North Sea, coming from the Thames estuary and spreading northwards towards Belgium, The Netherlands, Germany and Denmark.

A second step in introduction was observed during the Second World War with the landing in Normandy, on D-Day, of thousands of vessels and floating landing stages. These vessels were stored for several months or even years in the Thames estuary and harbours along the Channel, especially in the Severn which was highly colonized by C. fornicata. Immediately after the war, limpet populations were observed at the landing places (Arromanches) and the harbours of Cherbourg and Brest where allied boats had been waiting to discharge their cargos at the end of the war. These boats had come from the USA (Boston or Baltimore) or northern Europe.

The last introduction of C. fornicata took place during the development of the Japanese oyster (Crassostrea gigas) industry, during the 1970s. The Portuguese oyster (Ostrea angulata) had recently been introduced for aquaculture but had been attacked by a virus at the end of the 1960s. To meet the general decrease in stocks, the introduction of a new species (already tested by several oyster farmers) was decided upon. Tons of oyster spats and adult populations of C. gigas were rapidly introduced from the USA and Japan, and along with them many parasites and alien species. The worldwide introduction of the Japanese oyster is known to be one of the great ecological disasters (Zibrowius, 1991). It is generally now accepted and proven by molecular analyses that O. angulata is a synonym of C. gigas.

Once it was introduced into each oyster pond, population centers developed progressively and C. fornicata became a problem not only in the European oysterbeds, but also outside of them. Dredging and trawling along the oyster beds dispersed the populations in throughout the area. It was demonstrated that in the dredged areas, C. fornicata became much more developed that in areas were this activity was prohibited or limited (Blanchard, 1997). Forty years after this massive introduction, fishery practices have dispersed C. fornicata to many of the bays and estuaries in Europe. Estimations of stocks often give thousands of fresh tons per km-2.


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
Belgium England and Wales 1911 Hitchhiker (pathway cause) Yes Polk (1962)
England and Wales USA 1872 Hitchhiker (pathway cause) Yes Cole (1952); McMillan (1938) The introduction of the slipper limpet in England is linked to oyster importation of Crassostrea virginica from the USA from the end of 19th century to the 1920s set on shores before being sold
Europe USA 1970s Hitchhiker (pathway cause) Yes Zibrowius (1991) The introduction in Europe of Crassostrea gigas is known to be one of the main vector alien marine species
Europe Japan 1970s Hitchhiker (pathway cause) Yes Zibrowius (1991) The introduction in Europe of Crossostrea gigas is known to be one of the main vector of alien marine species
France 1930s 1970s Hitchhiker (pathway cause) Yes Blanchard (1995) From England and Japan, in the 1930s with imports of farmed Ostrea edulis, during World War II and allied shipping operations in Normandy, and in the 1970s with import of Crassostrea gigas
Netherlands England and Wales 1922 Hitchhiker (pathway cause) Yes Adam and Leloup (1934) The transport of native oyster (Ostrea edulis)

Risk of Introduction

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The risk of introductions in new areas is very likely, because no real control can be set on such a marine species which is capabale of larval transport. Moreover, naval traffic is increasing so that feasability of accidental transport is real on hulls or in tank waters; fishery pressure by dredging is also increasing along the coasts. Global warming may also favour the spread of this species from temperate areas to further northwards. Coasts of the northern countries, such as in the Baltic sea or Ireland, could be colonized in the future.


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Few publications focus on the natural habitat of C. fornicata (McGee and Target, 1989; Shenk, 1986). The habitat of the C. fornicata is varied but is preferred as: a depth between 0 and 15 metres, a bay or estuary protected from direct flow and water agitation, a flat sandy and gravelly ground with shells (empty or not), and a lack of specific predators. Several publications have noted that this typical habitat is similar to that of most oyster species (Hoagland, 1977).

Habitat List

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Coastal areas Principal habitat Harmful (pest or invasive)
Coastal areas Principal habitat Natural
Mud flats Secondary/tolerated habitat
Intertidal zone Secondary/tolerated habitat
Estuaries Principal habitat
Lagoons Secondary/tolerated habitat
Inshore marine Secondary/tolerated habitat
Benthic zone Principal habitat Natural

Biology and Ecology

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Dupont et al. (2003) conclude from molecular genetic data that the French populations of C. fornicata established after 1940, and derive from several genetically diverse source populations, either in Europe or in North America.

Reproductive Biology

The protandric status of the species and the fact that individuals are fixed in the same colony, are a reproduction warranty (Dupont et al., 2006). Each female lays between 10 and 20,000 eggs at each time and can have 3 or 4 laying periods in a year (Richard et al., 2006). The eggs are protected in bags during 3 weeks until they become strong larvae which are delivered in the plankton where they stay and grow for 1 month, depending on the water temperature and the available food (Pechenik and Lima, 1984; Pechenik et al., 2002). They grow from 400 to 1000 µm during this period, then they metamorphose and fall on the bottom to look for a suitable grounds (especially shells, but also gravel or anything rather flat and smooth). 

Physiology and Phenology

This species is ubiquistous which allows it to develop in all kinds of environmental conditions, even brackish waters. The flow is created by the cilia movement in the mantle cavity, so that the water enters on a side, then through the gills, where particles are trapped, and goes out on the opposite side (Newell and Kofoed, 1977). When the turbidity level rises or when the water quality is no longer suitable, the filtering rate decreases, although the species is able to survive in poor conditions.


This suspension-feeding species eats phytoplanckton during both the pelagic larval phase and as an adult. During the adult phase, C. fornicata filters at about the same rate as other filter feeding molluscs (Newell and Kofoed, 1977), but the quality of the particles (size and composition) can be extremely varied (detritic particulate matter, pure phytoplankton, dissolved matter). Also a large range of size in phytoplankton seems to be eaten by the larva. Blanchard et al. (2008) have compared the growth conditions of oyster and C. fornicata larvae under several food conditions and the latter is obviously less selective in cell size.


Pechenik et al. (2002a) found that C. fornicata was not a host for trematodes.


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C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
59 35

Air Temperature

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Parameter Lower limit Upper limit
Mean minimum temperature of coldest month (ºC) 5

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Depth (m b.s.l.) 0-10 Optimum Found up to 100 m in the Atlantic and intertidal areas
Dissolved oxygen (mg/l) 8-10 Optimum 5-10 tolerated; it can support low oxygen concentration and live in anaerobiose some hours
Salinity (part per thousand) 30 Optimum 20-40 tolerated; adult fecundity is not affected by low salinity (10 ppt)
Turbidity (JTU turbidity) Optimum 0-10 g/l tolerated temporarily; the filtration rate is reduced at a minimum above 0.6 g/l. The quantity of pseudofaeces rises with suspension matter concentration, up to high levels
Velocity (cm/h) Optimum 5 cm/s
Water temperature (ºC temperature) 15-20 Optimum 5-30 tolerated; the formation of egg capsules is triggered by temperatures of 10 and larvae appear above 10. High sensibility to cold temperatures

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Asterias rubens Predator Adult not specific
Cliona celata Predator Adult/Fry not specific
Dicentrarchus labrax Predator Adult not specific
Limanda limanda Predator Adult not specific
Ocenebra erinacea Predator Adult/Fry not specific
Pagurus pollicaris Predator Fry not specific

Notes on Natural Enemies

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In the USA, the large whelk Busicon carita is known predator of shellfish. The decapode Pagurus pollicaris eats the juveniles (Shenck, 1986), the sponge Cliona celata and the gastropod Ocenebra erinacea pierce the shells (Orton, 1924) as does the driller Urosalpinx cinerea (Pratt, 1974). The flatfish Pleuronectes limanda [Limanda limanda] (Orton, 1924) and the bass Dicentrarchus labrax (Kelley, 1987) eat and scratch large quantities of adult animals. The starfish, Asterias rubens eat individuals (Orton, 1924). Several carnivorous crabs are observed when limpets are scratched and meat exposed, after dredging for example.

No use of natural enemies is carried out in the field to control C. fornicata. The highest densities of C. fornicata are in oyster ponds where it is dangerous for shellfisheries to introduce enemies which are not species specific.

Means of Movement and Dispersal

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Natural Dispersal

The species is generally fixed, so adults are dispersed on the sea bottom individually or as stacks with current during the periods of high wave energy. Crepidula fixed on wood or floating vessels can be carried far from their native areas, as it is mentioned for the first observation in Belgium (Polk, 1962) or Greece (Galil and Zenetos, 2002).

Accidental Dispersal

Oyster-farming practices with exchanges of spat or adult batches is the main cause of the C. fornicata introduction in European oyster beds. In addition, fishery practices of throwing overboard all the non-valuable species, especially with C. fornicata, for several decades, is the main cause of dispersal around the shellfish areas (Hamon et al., 2002).

Impact Summary

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Economic/livelihood Negative
Environment (generally) Negative


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When the population is dense, the ground cover can reach densities of up to 10,000 individuals/m-2 as in the bays of Brittany (Blanchard, 2009), and severe and irreversible impacts can occur on the sediment, on the biodiversity or on the concentration of suspensed matter. Only dense populations have a real impact.

Economic Impact

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The activities which have fallen victim to C. fornicata such as dredging or trawling, and shellfish-farming especially oysterfarming, are those which, for less than a hundred years, contributed, accidentally or not, to its spread. Dense limpet populations disturb fishery or oyster farming activities to such an extent that in some bays (Sheldt estuaries in Zeeland, Thames estuary and Fal River (Fitzgerald, 2007) in Great Britain, the Norman gulf or the Atlantic Marennes pond in France, cleaning operations are necessary. Regularly, oyster grounds must be cleaned before sowing new seed or when the C. fornicata populations create a too large negative effect. When limpets are fixed on oysters, oyster farmers must pick off limpets before selling the products, which creates an extra economic burden (Blanchard, 1997).

Expensive treatment methods have been developed, often without success. Public spending is constantly increasing. Yet applying the regulations or laws at the earliest observations would suffice to halt this spread. We are now observing in dense areas, the consequences of insufficient surveillance and precautions during the importation period.

Environmental Impact

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Trophic competition

C. fornicata is a suspension feeder filtering about 1 litre h-1g-1. For a dense population of several thousands of individuals, the diversion of tons of phytoplankton and organic matter can have an impact on the available concentration and a trophic competition can occur with the other suspension-feeders. It seems that in most areas, no mortality is observed in other species due to lack of food. Only during some periods of the year, when the food level is low, signs of slower growth can be observed in the other species (de Montaudouin and Sauriau, 1999; Decottignies et al., 2007a, b). Competition can also occur for larvae, because the limpet larvae have a high feeding rate, but Blanchard et al. (2008) observe that oyster and limpet larvae generally eat different kinds of food.

Spatial competition

C. fornicata stacks, when numerous in densely colonized areas, prevent other larvae and juveniles from settling and spatial competition occurs. Most species shift into other areas but many other of epifaunal species decrease in number or disappear because of available ground surfaces (Blanchard, 2009). For the flat fish Solea solea, Le Pape and al. (2004) demonstrated that the spatial competition which occurs between the fish and the C. fornicata favours the latter.

Impact on Habitats

Dense populations spread and completely cover the ground, so that the sediment disappears under the stacks and has no more exchange with the water. By trapping the suspended matter and producing lots of mucous pseudofaeces, a dense population transforms the primary sandy sediment into a muddy one with a high organic content, which becomes rapidly anoxic and unsuitable for other species. Empty shells are trapped in this mud and the sediment becomes more compact. The levels of bottom sediment rise by firstly, disturbing the normal flow, the limpet population stops the finer particles in the suspended matter which is trapped; secondly, the large biodeposited matters of such populations stay in place and are not scattered by streams. The bottom then accumulates several centimeters of mud each year where dead shells are included.

When the original ground is a nursery for commercial fishes, the complete occupation of the area means the disappearance of the fish which has economical consequences (Le Pape et al., 2004). In some bays where natural mud deposition is observed, presence of dense colonized limpet populations reinforces the ground modifications (Ehrhold et al., 1998). Above 50% coverage, return to the previous situation becomes no longer possible (Blanchard, 2009).

Impact on Biodiversity

With a growing limpet community the ground is progressively covered, the original endofauna disappears often completely when new epifauna increases on the stacks and in the interstices. A new limpet community appears with lot of suspension-feeders (bryozoans, ascidians, fixed annelids and cirripeds) and several little carnivorous species of crustaceans in the interstices. The biodiversity seems to have decreased, if we consider the large scale of a bay, but at a local scale, the number of species is rather the same (de Montaudouin and Sauriau, 1999).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
  • Capable of securing and ingesting a wide range of food
  • Benefits from human association (i.e. it is a human commensal)
  • Long lived
  • Fast growing
  • Has high reproductive potential
  • Gregarious
  • Has high genetic variability
Impact outcomes
  • Altered trophic level
  • Conflict
  • Damaged ecosystem services
  • Ecosystem change/ habitat alteration
  • Modification of natural benthic communities
  • Negatively impacts cultural/traditional practices
  • Negatively impacts aquaculture/fisheries
  • Reduced native biodiversity
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Fouling
  • Interaction with other invasive species
  • 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

Similarities to Other Species/Conditions

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Thirty species of Crepidula can be found over the world, but only some can be confused with C. fornicata, the others being of different size, colour, ornementations (lines, spots) or shape. Generally, phenoplasticity is common in the genus Crepidula, so care must be taken as C. fornicata can be present in different forms depending of the shape of the support, and can be extremely flat or completely rolled up around a stone.

Gaps in Knowledge/Research Needs

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New industrial uses of this product, either the meat or the shell, should be investigated. Up to now, the different uses found in the literature are not satisfactory: the shell is used generally as calcareous improvement and the meat is often used for poultry. The chemical or the pharmacological industries have to look into this product to find new openings.


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Links to Websites

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GISD/IASPMR: Invasive Alien Species Pathway Management Resource and DAISIE European Invasive Alien Species Gateway source for updated system data added to species habitat list.
Global Invasive Species Database GISD aims to increase awareness about invasive alien species and to facilitate effective prevention and management. It is managed by the Invasive Species Specialist Group (ISSG) of the Species Surviva
Global register of Introduced and Invasive species (GRIIS) source for updated system data added to species habitat list.
IFREMER (selective breeding) français de recherche pour l'exploitation de la mer (French Research Institute for Exploitation of the Sea)
Marine Life Information Network: Biology and Sensitivity Key Information
Non-native species in Great Britain


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France: French Institute for Marine Research, Technopole Brest, 29280 Plouzane,


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21/05/09 Original text by:

Michel Blanchard, laboratoire Benthos, département DYNECO, IFREMER, BP 70 - 29280 PLOUZANE, France

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