Invasion History

First Non-native North American Tidal Record: 1983
First Non-native West Coast Tidal Record: 2018
First Non-native East/Gulf Coast Tidal Record: 1983

General Invasion History:

Ascidiella aspersa was described from the Adriatic Sea in 1776. Its native range extends from southern Norway and Denmark, through the English Channel and Irish Sea to the Mediterranean (Kott 1998). Ascidiella aspersa has been widely introduced around the world, including the northwest Atlantic from Connecticut to Maine, the southwest Atlantic (Argentina), the southeast Atlantic (South Africa), the Indian Ocean (India), and the southwest Pacific (Australia, New Zealand).

North American Invasion History:

Invasion History on the West Coast:

In 2019, Ascidiella aspersa was collected from fouling plates in San Pedro Bay (ruiz et al. unpublished data, Nydam et al. 2022).  In subsequent surveys, it was found to have a wider distribution in southern California from Ventrua Harbor to San Diego Bay (Nydam et al. 2022).

Invasion History on the East Coast:

In 1983, Ascidiella aspersa was collected in the Cape Cod Canal (Richard Whittaker, personal communication to James T. Carlton) and in 1985, in Long Island Sound, probably near Avery Point, Connecticut. It now ranges from Long Island Sound to Mahone Bay, Nova Scotia (Whitlach and Osman 2000; MIT Sea Grant 2006; Moore et al. 2014). We have no records of this species between Long Island Sound and Chesapeake Bay, but we know of no recent studies of fouling organisms in this region. In the summer of 2002, tunics of A. aspersa were found on fouling plates in Chesapeake Bay, at Gloucester Point, in the York River (Ruiz et al., unpublished data), but live animals were not seen. Further sampling is needed to determine whether this tunicate is established in Chesapeake Bay. In 2012, the range of A. aspersa was extended north to Lunenburg Harbor, Nova Scotia, where extensive populations occurred in the inner harbor (Moore et al. 2014).

Invasion History Elsewhere in the World:

Ascidiella aspersa is abundant in parts of southern Australia, where it was probably introduced before 1899 (Kott 1985; Kott 1998; Keough and Ross 1999). In New Zealand, it was first collected in the early 1900s (Cranfield et al. 1998). It was recorded in India in 1976 from Madras on the Bay of Bengal (Nagabhushanam and Krishnamoorthy 1991). In 2010, A. aspersa was discovered in ports on the west, south, and east coasts of South Korea (Pyo et al. 2012). In 2012, it was found on the west coast of Hokkiado in northern Japan (Lutaenko et al. 2013). On the southern coast of South Africa, it occurs from Saldanha Bay to Port Elizabeth, but its date of introduction is unknown (Monniot et al. 2001). Across the Atlantic, in Argentina, it was first collected in several locations in 1962, and is now established in several harbors covering more than 5 degrees of latitude, from Chubut to Puerto Deseado (U.S. Museum of Natural History 2006; Tatián et al. 2010). 


Ascidiella aspersa is a solitary tunicate. It is oval-shaped, wider near the base and narrower at the top where the two siphons protrude, the oral siphon extends off the top and the atrial siphon extends off the side about a third of the way down the body. It grows up to 130 mm long and is usually attached on the posterior left side. The siphons are short and conical (cone-shaped) and ridged with 8-10 branchial lobes and six atrial lobes. Papillae are scattered over the body surface, especially on the right side and near the apertures. The test (outer covering) is firm but thin, rough and gristly, gray, black or brownish in color, and often with attached debris (Kott 1985, MarLin 2006).



Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Phlebobranchia
Family:   Ascidiidae
Genus:   Ascidiella
Species:   aspersa


Ascidia aculeata (Alder, 1863)
Ascidia affinis (Hancock, 1870)
Ascidia albida (Alder and Hancock, 1848)
Ascidia cristata (Risso, 1826)
Ascidia expansa (Kiare, 1893)
Ascidia minuta (Kiare, 1893)
Ascidia normanni (Alder and Hancock, 1870)
Ascidia opalina (MacGillivray, 1843)
Ascidia patula (Müeller, 1776)
Ascidia pedunculata (Hoffman, 1829)
Ascidia pellucida (Alder and Hancock, 1848)
Ascidia scabra (Müeller, 1776)
Ascidia sordida (Alder and Hancock, 1848)
Ascidia truncata (Herdman, 1881)
Ascidia aspersa (Müeller, 1776)
Phallusia aspersa (Trausted, 1883)
Ascidiella cristata (Roule, 1884)
Ascidia elliptica (Alder and Hancock, 1848)
Ascidia pustulosa (Alder, 1863)
Ascidia triangularis (Herdman, 1881)

Potentially Misidentified Species



Life History- A solitary tunicate is ovoid, elongate or vase-like in shape, with two openings or siphons. Most solitary tunicates attach to substrates by their side or base, but some attach with a conspicuous stalk. They are sessile filter feeders with two siphons, an oral and an atrial siphon. Water is pumped in through the oral siphon, where phytoplankton and detritus is filtered by the gills, and passed on mucus strings to the stomach and intestines. Waste is then expelled in the outgoing atrial water.

Solitary ascidians are hermaphroditic, meaning that both eggs and sperm are released to the atrial chamber. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but many species have a partial block to self-fertilization. Depending on species, eggs may be externally or internally fertilized. In external fertilizers, eggs and sperm are released through the atrial siphon into the surrounding water column were fertilization takes place. The eggs of A. ascidiacea are unusual, because they float in seawater of 30-35 PSU (Berrill 1928, cited by Mackenzie 2011). In internal fertilizers, eggs are brooded and fertilized within the atrial chamber and then released into the water column upon hatching. Fertilized eggs hatch into a tadpole larva with a muscular tail, notochord, eyespots, and a set of adhesive papillae. The lecithotrophic (non-feeding, yolk-dependent) larva swims briefly before settlement. Swimming periods are usually less than a day and some larvae settle immediately after release, but the larval period can be longer at lower temperatures. Once settled, the tail is absorbed, the gill basket expands, and the tunicate begins to feed by filtering (Barnes 1983). The life cycle is annual, with animals becoming senescent within 18 months after settlement (Millar 1954, cited by Makenzie 2011).




fish, crabs

Trophic Status:

Suspension Feeder



General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatVessel HullNone
General HabitatUnstructured BottomNone
General HabitatGrass BedNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Maximum Temperature (ºC)26Animals from Madras, India- Nagabhushanam and Krishnamoorthy 1992
Minimum Salinity (‰)18Typical Black Sea salinity, Field, Norway (Dybern 1969(
Maximum Salinity (‰)36Animals from Madras, India- Nagabhushanam and Krishnamoorthy 1992
Minimum Duration1Animals from Germany, Egg + Larva- Niermann-Kerkenberg and Hofman 1989
Maximum Duration1.5Animals from Madras, India- Egg + Larva- Nagabhushanam and Krishnamoorthy 1992
Minimum Length (mm)60Kott 1985; Nagabhushanam and Krishnamoorthy 1991
Maximum Length (mm)130MarLin 2006
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Economic Impacts

Ascidiella aspersa can foul aquaculture gear (Carman et al. 2010).

Ecological Impacts

Ascidiella aspersa can compete with native species for space and may impact the recruitment success of other species (Osman and Whitlach 2000).

Regional Impacts

NA-ET3Cape Cod to Cape HatterasEcological ImpactCompetition
In Long Island Sound, 'Ascidiella's primary effect was the reduction of available substrate on which other species could recruit successfully' (Osman and Whitlach 2000).
NA-ET3Cape Cod to Cape HatterasEconomic ImpactFisheries
Ascidiella aspersa was found fouling aquaculture gear at eight sites, and cultured Bay Scallops (Argopecten irradians) at two sites, of 26 aquaculture sites surveyed on Marthas Vineyard (Carman et al. 2010).
N195_CDA_N195 (Cape Cod)Economic ImpactFisheries
Ascidiella aspersa was found fouling aquaculture gear at eight sites, and cultured Bay Scallops (Argopecten irradians) at two sites, of 26 aquaculture sites surveyed on Marthas Vineyard (Carman et al. 2010).
M040Long Island SoundEcological ImpactCompetition
Long Island Sound, 'Ascidiella's primary effect was the reduction of available substrate on which other species could recruit successfully' (Osman and Whitlach 2000).
NWP-4bNoneEconomic ImpactFisheries
Ascidiella aspersa has damaged the the culture of the Japanese Weathervane Scallop (Mizuhopecten yessoensis) in hanging cages in Funka Bay, Hokkaido (Kanamori et al. 2017)
MAMassachusettsEconomic ImpactFisheries
Ascidiella aspersa was found fouling aquaculture gear at eight sites, and cultured Bay Scallops (Argopecten irradians) at two sites, of 26 aquaculture sites surveyed on Marthas Vineyard (Carman et al. 2010).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEA-II None 0 Native Estab
NEA-III None 0 Native Estab
AR-V None 0 Native Estab
MED-II None 0 Native Estab
WA-I None 1995 Def Estab
CIO-II None 1976 Def Estab
AUS-IV None 1962 Def Estab
AUS-V None 1952 Def Estab
AUS-VII None 1952 Def Estab
AUS-VIII None 1899 Def Estab
AUS-IX None 1952 Def Estab
NZ-IV None 1946 Def Estab
NZ-VI None 1946 Def Estab
NA-ET3 Cape Cod to Cape Hatteras 1983 Def Estab
MED-VII None 0 Native Estab
SA-I None 1962 Def Estab
NEA-V None 0 Native Estab
MED-IX None 0 Native Estab
MED-VIII None 0 Native Estab
MED-VI None 0 Native Estab
MED-V None 0 Native Estab
MED-IV None 0 Native Estab
MED-III None 0 Native Estab
MED-I None 0 Native Estab
NEA-IV None 0 Native Estab
NA-ET2 Bay of Fundy to Cape Cod 2000 Def Estab
WA-IV None 2001 Def Estab
WA-V None 2001 Def Estab
M040 Long Island Sound 1985 Def Estab
M010 Buzzards Bay 1983 Def Estab
M020 Narragansett Bay 1997 Def Estab
M130 Chesapeake Bay 2002 Def Unk
N180 Cape Cod Bay 2000 Def Estab
N170 Massachusetts Bay 2000 Def Estab
N100 Casco Bay 2003 Def Estab
B-I None 0 Native Estab
N130 Great Bay 2006 Def Estab
N195 _CDA_N195 (Cape Cod) 2007 Def Estab
N140 Hampton Harbor 2007 Def Estab
RS-3 None 2003 Def Estab
M023 _CDA_M023 (Narragansett) 2009 Def Estab
NWP-4a None 2010 Def Estab
NWP-3a None 2010 Def Estab
NWP-4b None 2012 Def Estab
NA-ET1 Gulf of St. Lawrence to Bay of Fundy 2012 Def Estab
AR-IV None 2018 Def Estab
NEP-VI Pt. Conception to Southern Baja California 2018 Def Estab
P050 San Pedro Bay 2018 Def Estab
P064 _CDA_P064 (Ventura) 2021 Def Estab
P040 Newport Bay 2021 Def Estab
P020 San Diego Bay 2021 Def Estab
P040 Newport Bay 2019 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
4420 Berger and Whitlach 1997 1985 1985-01-01 Avery Point, Groton Def 41.3154 -72.0634
4421 Whitlach and Osman 2000 1997 1997-01-01 Jamestown Def 41.4971 -71.3673
4422 MIT Sea Grant 2003 2000 2000-08-11 Fall River Def 41.7062 -71.1620
4423 MIT Sea Grant 2003 2000 2000-08-15 Colt State Park, Bristol Def 41.6698 -71.3009
4424 MIT Sea Grant 2003 2000 2000-08-15 Roger Williams University dock Def 41.6484 -71.2609
4425 MIT Sea Grant 2003 2000 2000-08-17 Potters Cove, Prudence Island Def 41.6423 -71.3414
4426 MIT Sea Grant 2003 2000 2000-08-16 North Kingstown Def 41.6237 -71.4126
4427 MIT Sea Grant 2003 2000 2000-08-17 Prudence Island T-Wharf, Bay Islands Park Def 41.5882 -71.3245
4428 MIT Sea Grant 2003 2000 2000-08-15 Wickford Marina, Wickford Def 41.5754 -71.4423
4429 MIT Sea Grant 2003 2000 2000-08-06 Newport Shipyard, Newport Def 41.4901 -71.3217
4430 MIT Sea Grant 2003 2000 2000-08-06 Coasters Harbor, Newport Def 41.5107 -71.3270
4431 MIT Sea Grant 2003 2000 2000-08-10 Woods Hole Def 41.5254 -70.6725
4433 MIT Sea Grant 2003 2000 2000-08-10 Sandwich Marina Def 41.7704 -70.5036
4434 MIT Sea Grant 2003 2000 2000-08-07 Deer Island, Boston Def 42.3518 -70.9606
4435 MIT Sea Grant 2003 2000 2000-08-07 Rowes Wharf, Boston Def 42.3570 -71.0409
4436 MIT Sea Grant 2003 2000 2000-08-08 Hawthorne Cove Marina, Salem Def 42.5220 -70.8823
4437 MIT Sea Grant 2003 2000 2000-08-08 Tucks Point Marina, Beverly Def 42.5676 -70.7787
4438 MIT Sea Grant 2003 2000 2000-08-08 Gloucester State Pier Def 42.6158 -70.6625
4439 MIT Sea Grant 2003 2003 2003-08-04 ort Harbor Marine, South Portland Def 43.6414 -70.2414
4440 MIT Sea Grant 2003 2003 2003-08-04 Portland Yacht Services Def 43.6651 -70.2401
6041 Carman et al. 2009 2007 2007-06-01 Martha's Vineyard Def 41.4579 -70.5866
6823 MIT Sea Grant 2011 2009 2009-09-16 Mystic Marine Fuel, Mystic Def 41.3334 -71.9759
6824 MIT Sea Grant 2011 2009 2009-07-16 Point Judith Marina, Matunuck Def 41.3788 -71.5169
7344 Kott 1998 None 9999-01-01 Provence Native 43.0000 6.0000
7345 Mueller 1776, cited by Kott 1985 None 9999-01-01 Adriatic Sea Native 43.0000 14.0000
7346 Mueller 1776, cited by Kott 1998 None 9999-01-01 Oslofjord Native 59.3500 10.5833
7347 Hoffman 1829, cited by Kott 1998 None 9999-01-01 Helgoland Native 54.1825 7.8853
7348 Macgillivray 1843, cited by Kott 1998 None 9999-01-01 Aberdeen Native 57.1526 2.1100
7349 Alder and Hancock 1848, cited by Kott 1998 None 9999-01-01 Cullercoats Native 55.0333 -1.4333
7350 Kott 1998 None 9999-01-01 Lamlash Bay Native 55.5373 5.1235
7351 Alder 1849, cited by Kott 1998 None 9999-01-01 Bantry Bay Native 51.6500 -9.7167
7352 Alder 1863, cited by Kott 1998 None 9999-01-01 Fowey Harbour Native 50.3343 4.6329
7353 Hancock 1870, cited by Kott 1998 None 9999-01-01 Roach River Native 51.5833 0.8000
7354 Kiaer, 1893, cited by Kott 1998 None 9999-01-01 Aure Native 63.2686 8.6078
7355 Kiaer, 1893, cited by Kott 1998 None 9999-01-01 Bergen Native 60.3894 5.3330
7356 US National Museum of Natural History 2012 None 9999-01-01 Spain Native 45.5000 -13.5300
7358 US National Museum of Natural History 2012 None 9999-01-01 Naples, Zoological Station Native 40.8450 14.2583
7359 Mastrototaro and Dappiano 2005 None 9999-01-01 Taranto, Mar Piccolo Native 40.4667 17.2333
7360 Monniot and Monniot 1994 None 9999-01-01 Cap Vert Native 14.7447 -17.5203
7361 Naranjo et al. 1996 None 9999-01-01 Algeceiras Native 36.1311 -5.3960
7362 Koukouros et al. 1996 None 9999-01-01 Aegean Sea Native 39.0000 23.0000
7363 Koukouros et al. 1996 None 9999-01-01 Black Sea Native 44.6133 33.5300
7364 Chebbi et al. 2010 None 9999-01-01 Bizerte Lagoon Native 37.2667 9.8667
7369 Dinçaslan et al. 2007 None 9999-01-01 Izmir Bay Native 38.4220 27.1290
7370 Koukouros et al. 1996 None 9999-01-01 Levantine Basin, Mediterranean S Native 34.0000 35.5000
7371 Gemarec and Monniot 1966 None 9999-01-01 south coast, Britann Native 47.6600 -3.5000
7372 El Nagar et al. 2010 2009 2009-01-01 Muros Native 42.7760 -9.0580
7373 OBIS, in Appeltans et al. 2012 None 9999-01-01 Morocco Native 32.5000 -8.0000
7374 Tatian et al. 2010 1962 1962-01-18 Punta Pardelas Def -42.6167 -64.2667
7375 U.S. National Museum of Natural History 2006 1978 1978-07-18 Nintas Point, Chubut Def -42.8833 -64.7000
7376 Tatian et al. 2010 1962 1962-02-12 Puerto Madryn Def -42.7667 -65.0500
7377 Tatian et al. 2010 2007 2007-05-22 Puerto Deseado Def -47.7500 -65.9167
7378 Monniot et al. 2001 2001 2001-01-01 Saldanha Bay Harbour Def -33.0347 18.0097
7379 Monniot et al. 2001 2001 2001-01-01 Cape Town Harbour Def -33.9253 18.4239
7380 Monniot et al. 2001 2001 2001-01-01 Port Elizabeth Def -33.9581 24.6000
7381 Emara and Belal 2004 2003 2003-01-01 Lake Timsah and Bitter Lakes, Suez Canal Def 30.3333 32.3833
7382 Nagabhushanam and Krishnamoorthy 1992 1976 1976-01-01 Chennai (Madras) Def 13.0839 80.2700
7383 Rajagopal et al. 1997 1990 1990-01-01 Kalpakkam Def 12.5576 80.1754
7384 Kott 1985 1985 1985-01-01 Swan River estuary Def -31.9472 115.9161
7385 Kott 1985 1985 1985-01-01 Bunbury Def -33.3400 115.6419
7386 Kott 1985; Huisman et al. 2008 1952 1952-01-01 Albany Def -35.0228 117.8814
7387 Kott 1985, Huisman et al. 2008 1985 1985-01-01 Esperance Def -33.8611 121.8814
7388 Wiltshire et al. 2010 2001 2010-01-01 Port Adelaide Def -34.8461 138.5031
7389 Wiltshire et al. 2010 1996 1996-01-01 Port Lincoln Def -34.7322 135.8586
7390 Kott 1985 1899 1989-01-01 Port Phillip Bay Def -38.1500 144.8667
7391 Kott 1985 1952 1952-01-01 Entrecasteaux Channel Def -43.2167 147.2833
7392 Kott 1985 1985 1985-01-01 Spring Bay, Tasman Sea Def -42.2600 147.9700
7393 Kott 1985 1946 1946-01-01 Otago Harbour Def -45.8167 170.6500
7394 Cranfield et al. 1998 1998 1998-01-01 Lyttleton Harbour Def -43.6167 172.7333
7395 Cranfield et al. 1998 1998 1998-01-01 Portobello Def -45.8398 170.6509
7396 Cranfield 1998 1998 1998-01-01 Halfmoon Bay Def -46.9000 168.1333


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