Invasion History

First Non-native North American Tidal Record: 2009
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2009

General Invasion History:

The native range of Clavelina lepadiformis extends from southern Norway and the Shetland Islands to the Atlantic coast of Spain and the Mediterranean Sea (Berrill 1950; de Caralt et al. 2002; MarLin 2006). It has been introduced to the Azores (Cardigos et al. 2006), to the east coast of South Africa (Monniot et al. 2001), and the US East Coast (Rheinhardt et al. 2010). These introductions are probably the result of ship fouling.

North American Invasion History:

Invasion History on the East Coast:

In October 2009, Clavelina lepadiformis was discovered in the Thames River, near New London, Connecticut, and in nearby Stonington Harbor. Colonies were found at only these two locations in a survey of 11 sites from Fishers Island Sound, which is part of Long Island Sound (Rheinhardt et al. 2010).

Invasion History Elsewhere in the World:

Clavelina lepadiformis was reported in Madeira and the Canary Islands, but its invasion status is unknown, so we consider it cryptogenic here (Wirtz 1998). Its status as an introduced species is more definite in the Azores, where it first appeared in 1971 on the island of Sao Miguel. It later dispersed to all of the Azores (Cardigos et al. 2006). On the Indian Ocean coast of South Africa, C. lepadiformis was discovered at Port Elizabeth and the Knysna Estuary (Monniot et al. 2001; Robinson et al. 2005). Between 2008 and 2011, it was collected on Chejudo Island, South Korea, in the East China Sea (Pyo and Shin 2011). 

In the Mediterranean, the status of Clavelina lepadiformis is complex. A native clade is present in rocky areas on the open coast of Catalonia, Spain, but in harbors, a genetically distinct form, with differing life history and population biology is present. These two clades could represent cryptic species, but have not been formally separated. The harbor form is identical to widespread European Atlantic clades and appears to represent a recent introduction by shipping. However, the date of introduction is not known (Tarjuelo et al. 2001; de Caralt et al. 2002; Turon et al. 2003).


Clavelina lepadiformis is a colonial tunicate made up of groups of transparent zooids joined at the base by short stolons (MarLin 2006). Fully developed zooids are 5-6 cm long and are clear with white, yellow or pink bands around the oral siphon and along the dorsal lamina, giving them a light-bulb appearance (Berrill 1950; Reinhardt et al. 2010). Eggs and larvae vary in color and are visible in the atrial cavity. In the Mediterranean the eggs and embryos are most often yellowish white but can be pink or red in other regions (Fish & Fish 1996; Xavier Turon, pers. comm.). Colonies can be large and may consist of a few or tens to hundreds of zooids. In some areas colonies regress in winter and re-grow in spring, although in the Mediterranean this may not be the case (MarLin 2006).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Aplousobranchia
Family:   Clavelinidae
Genus:   Clavelina
Species:   lepadiformis


Ascidia lepadiformis (Müller, 1776)
Clavelina pumillo (Milne-Edwards, 1841)
Clavelina rissoana (Milne-Edwards, 1841)
Clavelina savigniana (Milne-Edwards, 1841)

Potentially Misidentified Species



Colonial (or compound) tunicates consist of many zooids, bearing most or all of the organs of a solitary tunicate, but modified to varying degrees for colonial life. Zooids of the genera Clavelina are elongated, completely or partially embedded in the tunic, and are connected by basal stolons. Each zooid has an oral and atrial siphon, which open on the colony surface, and a body divided into two regions – a thorax and abdomen. The thorax contains the pharynx and below it, the abdomen contains the stomach, intestine, ovaries, testis, and heart. Water is pumped into the oral siphon, through finely meshed ciliated gills on the pharynx, where phytoplankton and detritus is filtered, and passed on mucus strings to the stomach and intestines. Excess waste is then expelled in the outgoing atrial water (Van Name 1945; Barnes 1983).

Colonial tunicates reproduce both asexually, by budding, and sexually, from fertilized eggs developing into larvae. Buds can form from the body wall of the zooid or from the stolons. Colonies vary in size, and can range from small clusters of zooids to huge spreading masses. The zooids are hermaphroditic, with eggs and sperm being relased to the atrial chamber. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but some species have a partial block to self-fertilization. Eggs are brooded in the atrial cavity, and hatch into a tadpole larva, with a muscular tail and a notochord, eyespots, and three adhesive papillae in a triangle formation. The lecithotrophic (non-feeding, yolk-dependent) larva is expelled on hatching, and swims briefly before settlement. Swimming periods are usually less than a day, and some larvae can settle immediately after release, but the larval period can be longer at lower temperatures. On settlement, the tail is absorbed, the gill basket expands, and the tunicate begins to feed by filtering (Van Name 1945; Barnes 1983).


Phytoplankton, detritus

Trophic Status:

Suspension Feeder



General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatVessel HullNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)14Field, Dybern 1969; Fish and Fish 1996
Maximum Salinity (‰)40MacKenzie 2011
Maximum Duration0.1Larval duration up to 3 hrs, Fish and Fish 1996
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

There are no known impacts of Clavelina lepadiformis in its introduced range.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEA-III None 0 Native Estab
NEA-II None 0 Native Estab
AR-V None 0 Native Estab
B-I None 0 Native Estab
B-II None 0 Native Estab
NEA-IV None 0 Native Estab
NEA-V None 0 Native Estab
MED-I None 0 Native Estab
MED-II None 0 Native Estab
B-III None 0 Native Estab
MED-III None 0 Native Estab
MED-VII None 0 Native Estab
MED-IV None 0 Native Estab
MED-VI None 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 2009 Def Estab
M040 Long Island Sound 2009 Def Estab
NEA-VI None 1971 Def Estab
WA-V None 2001 Def Estab
WA-I None 1995 Def Estab
NWP-3a None 2011 Def Estab
NWP-4a None 2010 Def Estab
WA-IV None 2009 Def Estab
NZ-IV None 2017 Def Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
6826 Reinhardt et al. 2010 2009 2009-11-11 New London Def 41.3512 -72.0946
6827 Reinhardt et al. 2010 2009 2009-10-16 Stonington Def 41.3345 -71.9105


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