Molgula manhattensis

Invasion History

First Non-native North American Tidal Record: 1949
First Non-native West Coast Tidal Record: 1949
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Molgula manhattensis is native to the East and Gulf coasts of the United States. It was described from Manhattan Island, NY by De Kay in 1843 (De Kay 1843), but it was collected earlier by Gould (in 1841, near Boston), and earlier still by Couthouy (1838) in Massachusetts (Van Name 1912). In the northwest Atlantic, M. manhattensis occurs from Maine to Texas (Van Name 1921; Van Name 1945; Gosner 1978; McDougall 1943; US Museum of Natural History 2009). It was reported from several locations on the East Coast, from Boston to North Carolina in the 19th century (Gould 1841; DeKay 1843; Perkins 1871; Gould 1870; Verrill and Smith 1873). By the early 20th century, it was known over its present range on the Atlantic coast of North America (Van Name 1921). Some authors considered it synonymous with Ascidia tubifera and Molgula socialis, which gives it a wide European range, from Portugal to the White Sea (Van Name 1945; Carlton 2001 personal communication), while others consider it a distinct introduced species, confined to scattered European ports (Monniot 1969). Currently, M. tubifera is considered synonymous with M. manhattensis, while M. socialis has been found to be genetically distinct and presumably native to the northeast Atlantic (Haydar et al. 2011, Shenkar et al. 2011).

Recent genetic analysis supports M. manhattensis' native status in the northwest Atlantic, and introduced status in Japan, San Francisco Bay, and the Black Sea (Haydar et al. 2011). The genetic diversity of European populations was much lower than that of the northwest Atlantic M. manhattensis, but the presence of some unique genotypes led Haydar et al. (2010) to consider this species cryptogenic in Europe. However, this could be explained by under-sampling of American populations, or by the extinction of American source populations (James T. Carlton; April Blakeslee, personal communications). The data presented by Haydar et al. (2010) appear to us to be consistent with introduced status in Europe. In European waters, treating it separately from M. socialis, M. manhattensis ranges from Bergen, Norway to Galicia (northern Spain), and a few locations in the Mediterranean Sea, such as the Venice Lagoon (Monniot 1969; Dybern 1969; Vazquez and Urgorri 1992). 

Molgula manhattensis has been introduced to the Pacific coast of North America, from Newport Beach, California (Lambert and Lambert 1998) to British Columbia (Cohen and Carlton 1995; Cohen et al. 1998; Lambert 2003). It is also introduced to Japan (Asakura 1992), Australia (Hewitt et al. 1999), and Argentina (Orensanz et al. 2002). It is tolerant of a wide range of temperatures, salinity, and pollution levels (Van Name 1945).

North American Invasion History:

Invasion History on the West Coast:

Molgula manhattensis was first discovered in Tomales Bay, California in 1949 (Hedgepeth 1952, cited by Carlton 1979) and in San Francisco Bay in the 1950s (Hopkins 1968, cited by Cohen and Carlton 1995), where it is now abundant and widespread (Carlton 1979; Cohen and Carlton 1995; Cohen et al. 2005). Possible vectors include ship hull fouling or Eastern Oyster (Crassostrea virginica) aquaculture (Carlton 1979).

South of San Francisco Bay, M. manhattensis was collected in Long Beach Harbor and Newport Bay in 1984 (Lambert and Lambert 1998). Newport Bay marks the current southern limit for this tunicate on the West Coast (Lambert and Lambert 1998; Lambert and Lambert 2003; Ruiz et al. unpublished data). It has been found in most of the bays and harbors between San Francisco Bay and Los Angeles, including Elkhorn Slough (in 1998, Wasson et al. 2001), Morro Bay (in 2005, Needles 2007), Santa Barbara (in 2001, Fairey et al. 2002), Ventura (in 1994, Lambert and Lambert 1998), Channel Islands Harbor (in 2001, Fairey et al. 2002), and Marina del Rey (in 1995, Lambert and Lambert 1998).

North of San Francisco and Tomales Bays, it was found in Coos Bay, Oregon (in 1974, Carlton 1989; Wonham and Carlton 2005), Humboldt Bay, California (in 1996, Boyd et al. 2002), Willapa Bay, Washington (in 2000; Cohen et al. 2001), Puget Sound, Washington (in 1998; Cohen et al. 1998), Vancouver Island, British Columbia (in 1998, Lambert 2003) and Prince Rupert, British Columbia (in 2009, Murray et al. 2011). In 2010, it was discovered heavily fouling a barge in Yaquina Bay, Oregon, its first record in that estuary (Estabrook et al. 2010). Its current northern limit is Prince Rupert, British Columbia (Murray et al. 2011).

Invasion History Elsewhere in the World:

One specimen of Molgula manhattensis was collected in 1973 in Panama Bay, on the Pacific side of the Panama Canal (USNM 19556, US Museum of Natural History 2007) but we know of no other records from the Canal area. In the Northwest Pacific, it was first recorded in Japan in Hiroshima Harbor in 1972 and in Tokyo Bay in 1975 (Asakura 1991; Nishikawa 1991). It now ranges from Golden Horn Bay, Sea of Japan, near Vladivostok, Russia (in 1999, Zvyagintsev et al. 2003) to Guangdong (Canton), China (Huang 2001). In the Southwest Pacific, M. manhattensis was first recorded in Australia in Port Phillip Bay, Victoria, in 1967 (Kott 1985, Keough and Ross 1999). By 1976, it had become established in Moreton Bay, in Queensland, Australia (Kott 1985). In the Southwest Atlantic, it is established in Mar del Plata, Argentina (in 1945, Orensanz et al. 2002).

In European waters, M. manhattensis ranges from Bergen, Norway to Galicia, Spain and a few locations in the Mediterranean Sea, such as the Venice Lagoon (Monniot 1969; Dybern 1969; Vazquez and Urgorri 1992). It has also been identified by molecular analysis from Germany (Sylt, Wadden Sea), the Netherlands (Grevelingen and Delfzijl), Belgium (Oostende) and France (Le Havre) (Haydar et al. 2011).

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Description

Molgula manhattensis is a solitary ascidian species with a globular-like body with some lateral compression. Large specimens of M. manhattensis can measure 20-50 mm in length and height. The tunic is firm, tough and moderately thick. Some areas on the tunic may develop into small hair-like projections called papillae which frequently catch and accumulate particles or organisms to its tunic and siphons. Molgula manhattensis is typically greenish-olive or yellowish-green. The divergent siphons are fairly close together at the anterior end. The oral siphon is shorter and stouter with six lobes around the opening. The atrial siphon has four lobes around the somewhat square opening and the length of the siphon can be up to half the body length. Molgula manhattensis usually attaches a small area of its ventral surface to a substrate, although when found in dense clusters, attachment areas become variable (Van Name 1945, Lambert 2003; Gretchen Lambert, personal communication 2012).

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Taxonomy

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

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Habitats

General Habitat	Grass Bed	None
General Habitat	Coarse Woody Debris	None
General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Vessel Hull	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None

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Tolerances and Life History Parameters

Minimum Salinity (‰)	10	Field data- Cory 1967; Wass 1972
Maximum Salinity (‰)	35	Field data; Probably tolerates higher salinities
Minimum Duration	0	Larval period, Graves 1933
Maximum Duration	0	Larval period, Graves 1933
Maximum Length (mm)	25	Antero-posterior, large specimens, rarely reach 35 mm (Van Name 1945)
Minimum Height (mm)	25	Dorso-ventral. large specimens, rarely reach 35 mm (Van Name 1945)
Broad Temperature Range	None	Cold-temperate-Warm-Temperate
Broad Salinity Range	None	Mesohaline-Euhaline

General Impacts

Economic Impacts

Fisheries: Molgula manhattensis is regarded as a serious fouler of oyster cultch (empty shells, placed to encourage spat settlement) and living oysters (Andrews 1953; Andrews 1973).

Shipping and Industry: Molgula manhattensis is an important ship-fouling organism (Lippson and Lippson 1984; Millar 1971; Visscher 1927).

Ecological Impacts

Competition: In Chesapeake Bay, where it is native, Molgula manhattensis is capable of rapidly settling on and overgrowing most other fouling community organisms (Andrews 1953; Calder and Brehmer 1967; Otsuka and Dauer 1982). It frequently attains 100% cover on settling plates (Otsuka and Dauer 1982; Ruiz et al. unpublished data). Where introduced, extremely dense populations have been noted in San Francisco Bay, clogging bottom trawls (Ganssle 1968, cited by Cohen and Carlton 1995). Communities of M. manhattensis and Pinuauy crocea occupied considerable space on fouling plates in the winter of 1980-1981, but were displaced by heavy settlement of mussels in spring (Okamura 1986). When another tunicate, Ciona intestinalis was removed in experimental trials, M. manhattensis covered up to 92% of fouling plates (Blum et al. 2007). Complete cover of M. manhattensis was observed at some sites and times in Newport and Alamitos Bays, California (Lambert and Lambert 2003), suggestive of competition.

Habitat Change: The rapid growth of Molgula manhattensis means that it can quickly cover fouled surfaces with multiple layers of tunicates ~10-20 mm deep. This is likely to inhibit settlement of many other organisms (Osman and Whitlatch 1995). Although, hydroids, Polydora spp., Corophium spp. (and related genera), and bryozoans do settle on its tunic (Otsuka and Dauer 1982), and the presence of M. manhattensis did not affect recruitment on adjacent bare surfaces (Osman and Whitlatch 1995).

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Regional Impacts

P090	San Francisco Bay		Ecological Impact	Competition
Extremely dense populations have been noted in San Francisco Bay, clogging bottom trawls (Ganssle 1968, cited by Cohen and Carlton 1995). Communities of Molgula manhattensis and Pinuauy crocea occupied considerable space on fouling plates in the winter of 1980/81, but were displaced by heavy settlement of mussels in Spring (Okamura 1986). When another tunicate, Ciona intestinalis was removed from experimental trials, M. manhattensis covered up to 92% of fouling plates (Blum et al. 2007).
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Extremely dense populations have been noted in San Francisco Bay, clogging bottom trawls (Ganssle 1968, cited by Cohen and Carlton 1995). Communities of Molgula manhattensis and Pinuauy crocea occupied considerable space on fouling plates in the winter of 1980/81, but were displaced by heavy settlement of mussels in Spring (Okamura 1986). When another tunicate, Ciona intestinalis was removed from experimental trials, M. manhattensis covered up to 92% of fouling plates (Blum et al. 2007).
NEP-VI	Pt. Conception to Southern Baja California		Ecological Impact	Competition
Complete cover of Molgula manhattensis was observed at some sites and times in Newport and Alamitos Bays (Lambert and Lambert 2003), suggestive of competition.
P040	Newport Bay		Ecological Impact	Competition
Complete cover of Molgula manhattensis was observed at some sites and times in Newport and Alamitos Bays (Lambert and Lambert 2003), suggestive of competition.
P050	San Pedro Bay		Ecological Impact	Competition
Complete cover of Molgula manhattensis was observed at some sites and times in Newport and Alamitos Bays (Lambert and Lambert 2003), suggestive of competition.
CA	California		Ecological Impact	Competition
Extremely dense populations have been noted in San Francisco Bay, clogging bottom trawls (Ganssle 1968, cited by Cohen and Carlton 1995). Communities of Molgula manhattensis and Pinuauy crocea occupied considerable space on fouling plates in the winter of 1980/81, but were displaced by heavy settlement of mussels in Spring (Okamura 1986). When another tunicate, Ciona intestinalis was removed from experimental trials, M. manhattensis covered up to 92% of fouling plates (Blum et al. 2007)., Complete cover of Molgula manhattensis was observed at some sites and times in Newport and Alamitos Bays (Lambert and Lambert 2003), suggestive of competition. Extremely dense populations have been noted in San Francisco Bay, clogging bottom trawls (Ganssle 1968, cited by Cohen and Carlton 1995). Communities of Molgula manhattensis and Pinuauy crocea occupied considerable space on fouling plates in the winter of 1980/81, but were displaced by heavy settlement of mussels in Spring (Okamura 1986). When another tunicate, Ciona intestinalis was removed from experimental trials, M. manhattensis covered up to 92% of fouling plates (Blum et al. 2007).

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