Invasion History

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

General Invasion History:

Ascidia sp. A was discovered in 1983 in San Diego and San Francisco Bay. Since its discovery it has become established in other areas in Califonia including Alamitos Bay, King Harbor and Marina Del Ray (Santa Monica Bay) and Port Hueneme (Lambert and Lambert 1998; Lambert and Lambert 2003). In 2012, Ascidia sp. A was absent in samples taken from bays and harbors along the California coast and 'It may no longer be present' (Gretchen Lambert 2012, personal communication). Further sampling will be needed to confirm whether Ascidia sp. A is extinct in West Coast waters.

North American Invasion History:

Invasion History on the West Coast:

Ascidia sp. A is an unidentified solitary tunicate that appears to be an invader of the California coast. It was first collected in San Diego Bay and San Francisco Bay in 1983 and subsequently established there and in Alamitos Bay, King Harbor and Marina Del Ray (Santa Monica Bay) and Port Hueneme (Cohen and Carlton 1995; Lambert and Lambert 1998; Lambert and Lambert 2003). In 2012, Ascidia sp. A was absent in samples taken from bays and harbors along the California coast and 'It may no longer be present' (Gretchen Lambert 2012, personal communication).


Ascidia sp. A does not match any previously described species. It is long and flat with a thin and translucent tunic; the oral siphon is long and the atrial siphon is shorter and emerges from the posterior half of body. The branchial sac is without folds. The eggs are yellow (Lambert and Lambert 1998). This is not the Ascidia sp. A of Hawaiian harbors (Carlton and Eldredge, 2009, Gretchen Lambert, personal communication).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Phlebobranchia
Family:   Ascidiidae
Genus:   Ascidia
Species:   sp. A


Potentially Misidentified Species

Ascidia ceratodes

Ascidia zara



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. 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).



Trophic Status:

Suspension Feeder



General HabitatMarinas & DocksNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Maximum Length (mm)60(Lambert and Lambert 1998)
Broad Temperature RangeNoneWarm temeprate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Ascidia sp. A. was common to abundant in fouling communities along the California coast from San Diego to San Francisco Bay (Lambert and Lambert 1998; Lambert and Lambert 2003). However, specific impacts were not reported. In sampling done in 2011, at many locations on the California coast, this species was absent (Gretchen Lambert 2012, personal communication). Its establishment and impacts are unknown on the West Coast.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1983 Def Unk
NEP-V Northern California to Mid Channel Islands 1993 Def Unk
P020 San Diego Bay 1983 Def Unk
P030 Mission Bay 1994 Def Unk
P090 San Francisco Bay 1993 Def Unk
P050 San Pedro Bay 1995 Def Unk
P060 Santa Monica Bay 1994 Def Unk
P062 _CDA_P062 (Calleguas) 1995 Def Unk
P064 _CDA_P064 (Ventura) 1995 Def Unk
P065 _CDA_P065 (Santa Barbara Channel) 1995 Def Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Cohen, Andrew N. and 10 authors (2005) <missing title>, San Francisco Estuary Institute, Oakland CA. Pp. <missing location>

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Fay, R. C.; Vallee, J. A. (1979) A survey of the littoral and sublittoral ascidians of southern California, including the Channel Islands., Bulletin of the Southern California Academy of Sciences 78(2): 122-135

Lambert, C. C.; Lambert, G. (1998) Non-indigenous ascidians in southern California harbors and marinas., Marine Biology 130: 675-688

Lambert, Charles C; Lambert, Gretchen (2003) Persistence and differential distribution of nonindigenous ascidians in harbors of the Southern California Bight., Marine Ecology Progress Series 259: 145-161