Invasion History

First Non-native North American Tidal Record: 1986
First Non-native West Coast Tidal Record: 1986
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Microcosmus squamiger is native to the coast of Australia, where it is widespread. Available records include most of the Australian states (Kott 1985; Australian Faunal Directory 2009), but we are unaware of records from the Northern Territories. It also occurs in several locations including the Indo-Pacific region, from Vizhinjam, India, the Arabian Sea (Abdul and Sivakumar 2007), the Red Sea (Michaelsen 1918, cited by Kott 1985), Ibo Island, Mozambique, (Monniot 2002), and New Zealand (1st record in 2003, Inglis et al. 2005). This species appears to have been frequently transported in ship fouling and may be introduced in New Zealand and is definitely introduced in South Africa, where it is known from the harbor of Port Elizabeth, in the Indian Ocean (Rius et al. 2008; Griffiths et al. 2009). Other recent invasions have occurred on the coasts of California and Mexico (Lambert and Lambert 1998; Lambert and Lambert 2003; Rius et al. 2008; Rodriguez and Ibarra-Obando 2008), the western Mediterranean (Mastrototaro and Dappiano 2005; Turon et al. 2007), the Atlantic coast of Spain, Madeira, and the Canary Islands (Turon et al. 2007).

North American Invasion History:

Invasion History on the West Coast:

Microcosmus squamiger was first collected in Alamitos Bay, Long Beach, California in 1986 (Lambert and Lambert 1998). By 1994 its range extended from San Diego Bay to Santa Barbara Harbor (Lambert and Lambert 1998; Lambert and Lambert 2003). In 2000 it was collected in Ensenada, Mexico, (Lambert and Lambert 2003) and in 2002 it was observed fouling cultured oysters in Bahia San Quintin, Baja California (Rodriguez and Ibarra-Obando 2008). In 2015-2016, M. squamiger was found growing on several fouling plates at the Oakland Yacht Club in San Francisco Bay (Tracy et al. 2017). We consider this population to be established.

Invasion History in Hawaii:

Microcosmus squamiger is not established in Hawaii, but has been found in fouling on ships travelling from California to Honolulu, Pearl Harbor, and Barber's Point harbors (Godwin 2003).

Invasion History Elsewhere in the World:

Microcosmus squamiger was first collected in the Mediterranean Sea in 1971 at Savona, Italy in the western basin near the French border, but was initially misidentified by Monniot as M. exasperatus (Monniot 1981, Mastrototaro and Dappiano 2005). In 1963 it was collected in the Tyrrhenian Sea at Bizerte, Tunisia (Mastrototaro and Dappiano 2005), and the central basin, at Taranto, Italy by 1977 (Mastrototaro and Dappiano 2005). This seems to be its present eastward limit - it has not been recorded in the Adriatic or the eastern basin where M. exasperatus has been found (Turon et al. 2007). To the west, M. squamiger occurs along the Mediterranean coast of Spain from Barcelona to Alicante (in 1988) and Algeciras Bay near Gibraltar (in 1996) (Turon et al. 2007). In 1994 it was collected at Cape Trafalgar on the Atlantic Ocean and has subsequently been collected at several sites in the Gulf of Cadiz, at Cascais, Portugal and on the Bay of Biscay at Santander and in the Ria San Vicente (Turon et al. 2007). It has also been collected at Madeira and Tenerife, Canary Islands off the coast of northwest Africa (Turon et al. 2007).


Description

Microcosmus squamiger is a solitary tunicate, but usually occurs in dense clumps or aggregates. Each tunicate can grow up to 50 mm in diameter. The surface of the tunic rises into ridges and swellings with adhesive projections. The tunic is purple, leathery, tough, and sometimes hard and brittle. The apertures are usually located on short, wart-like siphons about a third of the body length and are directed away from each other. But sometimes the oral siphon is terminal with a long straight siphon, while the atrial siphon is short and about half-way along the body (Kott 1985).

This species is frequently confused with the very similar species Microcosmus exasperatus (Mastrototaro and Dappiano 2005; Turon et al. 2007). One of the few characteristics used to distinguish between the two species is the shape of the internal siphonal spines. The spines of M. squamiger are very short, about 15-25 µm long, and shaped like fingernails with serrated rims, while M. exasperatus has longer pointed spines, about 40-50 µm long, which are posteriorly hooked (Kott, 1985; Mastrototaro and Dappiano 2005).


Taxonomy

Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Stolidobranchia
Family:   Pyuridae
Genus:   Microcosmus
Species:   squamiger

Synonyms

Microcosmus claudicans squamiger (Hartmeyer and Michaelsen, 1928)
Microcosmus exasperatus australis (Michaelsen, 1908)

Potentially Misidentified Species

Microcosmus exasperatus
Many confused records in the Mediterranean- most reports of M. exasperatus are actually M. squamiger (Turon et al. 2007).

Ecology

General:

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 the 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).

Food:

Phytoplankton; Detritus

Trophic Status:

Suspension Feeder

SusFed

Habitats

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


Tolerances and Life History Parameters

Maximum Duration1Swimming time of larva (Turon et al. 2010)
Maximum Length (mm)50Kott 1985
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Economic Impacts

Oyster culture racks, ropes, and shells (of Crassostrea gigas, Pacific Oyster) in Bahia San Quintin, Baja California, Mexico were badly fouled by tunicates beginning in 2002. Microcosmus squamiger was a major organism in this fouling (Rodriquez and Ibarra-Obando 2008).

Ecological Impacts

Competition: Microcosmus squamiger now greatly outnumbers Styela canopus in San Diego Bay. It forms single-species patches at some locations suggestive of competition (Lambert and Lambert 2003), for example it forms dense monospecific crusts, and can outcompete native species in shallow water communities. Microcosmus squamiger is considered a potential threat to Mediterranean littoral communities, but further monitoring is needed to assess its impacts (Turon et al. 2007).

Regional Impacts

NEP-VIPt. Conception to Southern Baja CaliforniaEconomic ImpactFisheries
Oyster culture racks, ropes, and shells (of Crassostrea gigas, Pacific Oyster) in Bahia San Quintin, Baja California, Mexico were badly fouled by tunicates, beginning in 2002. Microcosmus squamiger was a major organism in this fouling (Rodriquez and Ibarra-Obando 2008).
NEP-VIPt. Conception to Southern Baja CaliforniaEcological ImpactCompetition
Microcosmus squamiger now greatly outnumbers Styela canopus, an earlier invader, in San Diego Bay. It forms single-species patches at some locations, suggestive of competition (Lambert and Lambert 2003).
P020San Diego BayEcological ImpactCompetition
Microcosmus squamiger now greatly outnumbers an earlier invader, Styela canopus in San Diego Bay. It forms single-species patches at some locations, suggestive of competition (Lambert and Lambert 2003).
MED-IINoneEcological ImpactCompetition
'The ability of M. squamiger to form dense, monospecific crusts that outcompete native species in shallow water communities (authors' personal observation) indicates that it is a potential threat to Mediterranean littoral communities and deserves further monitoring' (Turon et al. 2007).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1986 Def Estab
AUS-II None 0 Native Estab
AUS-IV None 0 Native Estab
AUS-V None 0 Native Estab
AUS-VII None 0 Native Estab
AUS-IX None 0 Native Estab
AUS-X None 0 Native Estab
AUS-XII None 1928 Native Estab
AUS-III None 0 Native Estab
AUS-VIII None 0 Native Estab
RS-1 None 0 Crypto Estab
RS-2 None 0 Crypto Estab
RS-3 None 0 Crypto Estab
MED-I None 1996 Def Estab
AUS-XIII None 0 Native Estab
MED-II None 1971 Def Estab
WA-V None 1950 Def Estab
MED-III None 1963 Def Estab
P020 San Diego Bay 1994 Def Estab
P050 San Pedro Bay 1986 Def Estab
P030 Mission Bay 1994 Def Estab
P023 _CDA_P023 (San Louis Rey-Escondido) 1994 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 1994 Def Estab
P040 Newport Bay 1994 Def Estab
P060 Santa Monica Bay 1994 Def Estab
P062 _CDA_P062 (Calleguas) 1994 Def Estab
P064 _CDA_P064 (Ventura) 1996 Def Estab
P058 _CDA_P058 (San Pedro Channel Islands) 1992 Def Estab
MED-IV None 1977 Def Estab
EA-III None 1995 Crypto Estab
NZ-IV None 2004 Crypto Estab
SP-XXI None 2003 Def Unk
P065 _CDA_P065 (Santa Barbara Channel) 2001 Def Estab
NEA-V None 1994 Def Estab
WA-I None 1992 Def Estab
CIO-I None 0 Crypto Estab
CIO-II None 2004 Crypto Estab
NEA-VI None 2009 Def Estab
NEP-V Northern California to Mid Channel Islands 2015 Def Estab
P090 San Francisco Bay 2016 Def Estab
MED-VI None 2015 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
767427 Ruiz et al., 2015 2013 2013-07-19 SeaWorld Marina, Mission Bay, CA, California, USA Def 32.7676 -117.2314
767463 Ruiz et al., 2015 2013 2013-07-29 Mission Bay Yacht Club, Mission Bay, CA, California, USA Def 32.7778 -117.2485
767482 Ruiz et al., 2015 2013 2013-08-04 Bahia Resort Marina, Mission Bay, CA, California, USA Def 32.7731 -117.2478
767496 Ruiz et al., 2015 2013 2013-07-31 Campland on the Bay, Mission Bay, CA, California, USA Def 32.7936 -117.2234
767697 Ruiz et al., 2015 2013 2013-07-24 NAB ACU-1 Docks, San Diego Bay, CA, California, USA Def 32.6786 -117.1615
767749 Ruiz et al., 2015 2013 2013-07-18 NAB Fiddlers Cove, San Diego Bay, CA, California, USA Def 32.6524 -117.1486
767766 Ruiz et al., 2015 2013 2013-07-26 Pier 32 Marina, San Diego Bay, CA, California, USA Def 32.6516 -117.1077
767775 Ruiz et al., 2015 2013 2013-07-20 Chula Vista Marina, San Diego Bay, CA, California, USA Def 32.6252 -117.1036
767789 Ruiz et al., 2015 2013 2013-07-28 Marriott Marquis and Marina, San Diego Bay, CA, California, USA Def 32.7059 -117.1655

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