Molgula ficus is a solitary tunicate native to Australia and the Indo-West Pacific region including the Gulf of Thailand, Singapore and Hong Kong. In the East Pacific, it was discovered in surveys in Southern California between 1994 and 1997, but may have been introduced earlier. Molgula ficus was originally misidentified as the native California species Molgula verrucifera, but is much larger, and is not a brooder. Since its discovery in Southern California it has been found from San Diego Bay, north to Channel Islands Harbor, adjacent to Port Hueneme. One additional collection was made in San Francisco Bay near Alameda in 2005, but M. ficus does not appear to be established here. It was probably introduced through ship fouling. There are no reported impacts in California, but in Chile where it was introduced in 1997, it has caused problems for scallop aquaculture by fouling ropes and other equipment.
Image Credit: Brianna Tracy, University of San Diego
|Bioregion||Region Name||Year||Invasion Status||Population Status|
|NEP-VI||Pt. Conception to Southern Baja California||1994||Def||Estab|
|P090||San Francisco Bay||2005||Def||Estab|
|NEP-V||Northern California to Mid Channel Islands||2005||Def||Estab|
|P020||San Diego Bay||1994||Def||Estab|
|P023||_CDA_P023 (San Louis Rey-Escondido)||1996||Def||Estab|
|P050||San Pedro Bay||1995||Def||Estab|
|P060||Santa Monica Bay||0||Def||Estab|
|P027||_CDA_P027 (Aliso-San Onofre)||0||Def||Unk|
Molgula ficus is a round solitary tunicate with both siphons on the upper surface directed away from one another. The oral siphon has six wedge-shaped lobes, while the atrial siphon has four. The siphons are usually separated by a thickened median ridge of tunic. In larger specimens, the ridge between siphons is often lost and the siphons are larger and more divergent with external longitudinal furrows between the lobes around the apertures. The siphons are fringed with two rows of small pointed papillae. In smaller specimens, the tunic is white, thin, and papery with some external irregular processes and usually with sand and mud adhering to it. In larger specimens the tunic is firmer, almost leathery and often clean of debris. This species often occurs in aggregations (Kott 1985). The size ranges from 20-40 mm in California and occasionally up to 89 mm in Australia (Kott 1985; Lambert 2007).
Molgula ficus is native to the Indo-West Pacific region. It was described from Shark Bay, Western Australia in 1859 and has been collected from sites around the continent. It has also been collected in Thailand, Singapore, and Hong Kong (Kott 1985; Kott 2005). It was discovered in Southern California in 1994 and in Chile in 1997, having been introduced through ship fouling.
Molgula ficus was discovered in Southern California in 1994, but was originally confused with the native species Molgula verrucifera. Molgula ficus was originally misidentified by P. Kott as the native California species M. verrucifera, but is much larger, and is not a brooder (see Lambert 2007). When Gretchen Lambert compared large numbers of M. verrucifera collected from sites along the coast and in harbors between 1994 and 1997, she realized that the larger harbor form was a distinct species and identified it as M. ficus. Since then it has been found from San Diego Bay north to Channel Islands Harbor, adjacent to Port Hueneme (Lambert 2007). One collection of M. ficus was made in San Francisco Bay in Ballena Bay, Alameda in 2005. In 2015-2016, two additional specimens were collected at Oyster Point and Coyote Point marinas, in San Francisco Bay (Tracy et al. 2017) - and we now consider this an established population. Ship fouling is a likely vector for the transport of M. ficus to California and Chile.
Molgula ficus was collected in Antofagasta Bay, Chile in 1997 (Clarke and Castilla 2000). It is now common on ropes used for scallop culture and in the intertidal beds of Pyura praeputialis, another Australian tunicate (Clarke and Castilla 2000; Lambert 2007).
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).
|General Habitat||Marinas & Docks|
|General Habitat||Vessel Hull|
|Salinity Range||Polyhaline||18-30 PSU|
|Salinity Range||Euhaline||30-40 PSU|
|Minimum Length (mm)||20||California, Lambert 2007|
|Maximum Length (mm)||40||California, Lambert 2007, occasionally up to 80 mm in Australia (Kott 1985)|
|Broad Temperature Range||Warm temperate-Tropical|
|Broad Salinity Range||Polyhaline-Euhaline|
|Molgula ficus is common on ropes used for scallop culture (Clarke and Castilla 2000).|