Molgula manhattensis

Invasion History

First Non-native Panama (Pacific) Tidal Record: 1973

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Panama Invasion History:

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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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