The star ascidian is a colonial sea-squirt (2). The individual members of the colony (known as zooids) are embedded in a jelly-like coating called a 'test' in groups of 3-12 around a common opening; this arrangement gives rise to the star-like patterns referred to by the common name (3). Sea-squirts earn their common name because they expel a jet of water when disturbed (3). They are also known as 'tunicates' due to the tunic-like test of many species. The colour of colonies is variable, but includes blue, brown and yellow; furthermore the colour of the zooids often contrasts with that of the test (3). Sea-squirts belong to the same phylum as humans, the 'chordates'. The free-swimming larval stage is a 'tadpole larva', which possesses a stiff chord known as a 'notochord' as well as a nerve chord, which pass along the flexible tail; the possession of both a notochord and a nerve chord at some point in the lifecycle of an animal is a crucial defining characteristic shared by all chordates (3).

As the name says, the star ascidian is star-shaped. Each point of the star is an animal and the center of the star is their joint waste hole. Star ascidians are the most common colony-forming sea squirts present in the Netherlands. They look like sturdy, smooth, cartilaginous crust, covered with star-shaped figures. In the delta region, there are more species of colony-forming sea squirts. They were carried here in the 1970s-1990s by ships and when mussel and oyster fishermen transported shellfish.

All sea-squirts filter suspended particles from the water. They maintain a current that passes through their body by beating tiny hair-like structures known as 'cilia'; the water enters through an opening called the 'inhalant siphon', and passes through the pharynx, where plankton and detritus become trapped in mucus and are passed to the stomach. The water then passes out through a second opening called the 'exhalent siphon'. In the star ascidian, the exhalent siphons of all the members of the colony open into a shared chamber, known as the cloaca, water then passes out of a shared exhalent siphon at the centre of the colony (3). In the star ascidian, the zooids are hermaphroditic (3); after fertilisation, eggs are retained until the tadpole larvae have formed (2). The larvae are then released through the exhalent siphon, and live in the water column for about 36 hours, before settling and forming new colonies (2). Asexual reproduction can also take place through budding (3). Colonies may live for up to one and a half years (3). Star ascidians are predated upon by cowries (members of the genus Trivia), which are gastropod molluscs; cowries also lay their eggs into holes made in the star-ascidian test (3).

The star tunicate, Botryllus schlosseri is a colonial tunicate not native to the U.S., but now occurs on both North American coasts. Colonies grow in flat sheets or lobes on hard substrata and are composed of many (hundreds to thousands) clonal, asexually produced zooids arranged in approximately star- or flower-shaped clusters called systems. Each system is comprised of approximately 20 oval- to tear-shaped zooids.Color is variable but all zooids within a colony are the same color. Zooids are often orange, yellow, black, red, gray-green, or white and are embedded in a firm fleshy matrix (the test) that is often purple or brown to colorless. Each zooid possesses its own incurrent siphon while all zooids within a colony share a single, large common excurrent siphon (NIMPIS 2002, Cohen 2005).

 Flat or fleshy colonies with zooids 2-4 mm across arranged in conspicuous star shaped systems, each with a central cloacal opening. Colonies vary greatly in colour including green, violet, brown and yellow.

This species is a compound, colonial ascidian, with small, bean-shaped zooids embedded in a common matrix or tunic. The colony grows to form encrusting patches that typically reach 3-4 mm in thickness and 2-10 cm in diameter. Individual zooids lie horizontally relative to the substrate, and are organized into radial, star-shaped clusters or "systems", with each system measuring 0.5-1 cm in diameter. Each zooid grows up to 5 mm in length. Zooids are characterized by a pharynx with 9-10 rows of stigmata, and a hood that covers the opening of the atrial siphon. Color varies among colonies, but often includes a combination (=bi-colored) of yellow, orange, red, brown, grey, or black.

A colonial ascidian forming compact sheets. Zooids are elliptical and are arranged in star-systems around common cloacal openings, with typically 6-12 zooids in a system. This species comes in a vast range of colours and colour patterns. There is often a single dark spot at the centre of each zooid. 4mm thick x 70mm wide sheets. This species can be distinguished from Botrylloides leachi by the arrangement of its zooids into star-like systems around common exhalant openings rather than long, meandering systems. The other species which might be confused are the polyclinids Aplidium nordmanni and Sidnyum elegans.

Atlantic, Azores, Azores Exclusive Economic Zone, British Isles, Canada, Cobscook Bay, European waters (ERMS scope), Greek Exclusive Economic Zone, Gulf of Maine, Gulf of Mexico, Irish Exclusive economic Zone, Kerkennah Islands, Mediterranean Sea, New Zealand Exclusive Economic Zone, North Coast of Norway, North East Atlantic, North West Atlantic, Oostende, Sas van Goes, South Africa (country), Swedish Exclusive Economic Zone, United Kingdom, United Kingdom Exclusive Economic Zone, Wimereux, Zeeland

semi-cosmopolitan

Bay of Fundy to North Carolina

United States

Origin: Exotic

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Botryllus schlosseri was introduced from Europe and is now found on both coasts of North America as well as Australia and the Asian Pacific (NIMPIS 2002).On the Atlantic coast of North America, it is occurs from Maine (occasionally north to the Bay of Fundy) south to Florida and the Gulf of Mexico (Cohen 2005). Occurrence down the Atlantic seaboard may be disjunct, possibly due to discontinuity of hard substrates, but collection records indicate its presence in New Jersey and the North Carolina (NIMPIS 2002, Hiscock 2007, Salem Sound Coastwatch undated). Mook (1993) identified Botryllus schlosseri as established and seasonally abundant in the India River Lagoon (Carlton and Ruckelshaus 1997).

Botryllus schlosseri has been introduced to the Northeast Pacific, with confirmed records ranging from Alaska to Baja California, Mexico. In addition, this species has been reported from several other locations around the world, including parts of northeast United States and Canada, southeast Asia, Australia, and New Zealand. Its native geographical range includes Great Britain, northern Europe, and the Mediterranean.

Very common and widespread around the coasts of Britain. It also occurs around Ireland and in mainland Europe from the Faeroe Islands and Norway, reaching as far south as the Mediterranean. It is also known from the western Atlantic along parts of the coast of North America, where it is thought to have been introduced on the hulls of ships (2).

Widespread and common all round the British Isles.

Individual Botryllus schlosseri zooids are usually 2.5-5 mm in length, system clusters around 5-10 mm in diameter and colonies are typically 10 cm or less across (Cohen 2005).Chadwick-Furman and Weissman (1995) reported that colonies in the field populations they studied had lifespans ranging from an average of 82-247 days and that colony life expectancy was seasonally dependent. This is in sharp contrast to colonies that have been maintained in the laboratory for more than 7 years (Rinkevich and Shapira 1998).B. schlosseri colonies grew exponentially as juveniles attaining colony sizes of up to 1400 zooids within 69 days (Chadwick-Furman and Weissman 1995).

Colonial Botryllus schlosseri is similar in appearance to other colonial tunicates such as those belonging to the genus Botrylloides. The systems (zooid clusters) of Botrylloides species tend to be elongate in shape, often arranged in meandering double rows, but only occasionally exhibiting the star pattern typical of B. schlosseri (Cohen 2005).

In the Northeast Pacific, Botryllus schlosseri is most similar to B. tuberatus Ritter and Forsyth, 1917 and two other non-native botryllid species found in the region, Botrylloides perspicuus (Herdman, 1886) and Botrylloides violaceus Oka, 1927.

Known from rocky shores.

circalittoral of the Gulf and estuary

Depth range based on 942 specimens in 1 taxon.
Water temperature and chemistry ranges based on 107 samples.

Environmental ranges
  Depth range (m): 0 - 52
  Temperature range (°C): 7.624 - 24.735
  Nitrate (umol/L): 0.311 - 8.618
  Salinity (PPS): 34.243 - 37.969
  Oxygen (ml/l): 4.519 - 6.351
  Phosphate (umol/l): 0.081 - 0.598
  Silicate (umol/l): 1.016 - 4.820

Graphical representation

Depth range (m): 0 - 52

Temperature range (°C): 7.624 - 24.735

Nitrate (umol/L): 0.311 - 8.618

Salinity (PPS): 34.243 - 37.969

Oxygen (ml/l): 4.519 - 6.351

Phosphate (umol/l): 0.081 - 0.598

Silicate (umol/l): 1.016 - 4.820
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

 Grows on a variety of stable substrata including algae and artificial substrata. Thrives in sheltered areas including docks. Although mainly found on the lower shore and in shallow depths, Berrill (1950) notes that it has been found at depths of several hundred metres.

Typically occurs on the lower shore and in shallow depths, but has been recorded at depths of several hundred meters (2). It seems to fare particularly well in sheltered sites, such as docks, and grows on a wide range of stable substrates including rock, algae and artificial surfaces (2).

A very common ascidian, occurring on the lower shore, on seaweeds and kelp stipes in shallow water, and on exposed rock surfaces. Commonest in places with considerable wave or current exposure.

Botryllus schlosseri is a suspension feeder whose diet includes suspended phytoplankton, zooplankton and suspended organic matter (Millar 1971, NIMPIS 2002).

Animal / predator
adult of Erato voluta is predator of Botryllus schlosseri

Animal / rests in
egg capsule of Trivia monacha rests inside nibbled hole common test of Botryllus schlosseri

Various invertebrate species such as flatworms, crustaceans, and gastropods have been reported to feed on Botryllus schlosseri colonies (Cohen 2005).Invasion History: The European native range of Botryllus schlosseri is believed to encompass the Mediterranean, and may also include the Adriatic and Black seas, Great Britain and France, Norway, and the Faroe Islands (Cohen 2005, Salem Sound Coastwatch undated).Ruiz et al. (2000) indicate that the first records of B. schlosseri on the east coast of North America date to 1841 in Massachusetts, while the earliest reported occurrence in the Gulf of Mexico appears to be 1921. On the U.S. west coast, the earliest reports of B. schlosseri include reports from San Francisco Bay dating to the mid 1940s, San Diego Bay and Mission Bay dating to the early 1960s, and from a Puget Sound oyster farm in the late 1960s or early 1970s. Broader distribution up and down the Pacific coast of North America from British Columbia to Mexico was only documented starting in the mid-1990s (Lambert and Lambert 1998, Cohen 2005).The species has been broadly introduced elsewhere as well, and can now be found in Australia (since 1905), Tasmania and New Zealand (since 1928), Japan, and Hong Kong. Ship hull fouling is probably the most common introduction vector for B. schlosseri, but accidental introduction in shipments of live oysters or other wild-harvested or cultured organisms has probably also played a role in expanding the range of this organism (Cohen 2005). Potential to Compete With Natives: B. schlosseri competes with other attached benthic filter feeders for space and possibly food as well. Fast-growing B. schlosseri colonies may overgrow neighboring organisms and alter community dynamics (NIMPIS 2002, Cohen 2005). Harms and Anger (1983) report barnacles and mussels as among the most important space competitors with B. schlosseri.Schmidt and Warner (1986) examined spatial competition among B. schlosseri and three other encrusting colonial ascidian species and reported no significant overgrowth among competing species. Possible Economic Consequences of Invasion: An abundant harbor fouling organism, Botryllus schlosseri is a nuisance species that fouls boat hulls, marine equipment, aquaculture gear, and other submerged structures. It can also overgrow and compete for space with cultured oysters and mussels (NIMPIS 2002, Cohen 2005).

Carlton and Ruckelshaus (1997) indicate that Botryllus schlosseri is seasonally common in Florida fouling communities, as is the co-occurring non-native ascidian Styela plicata and the cryptogenic (native range uncertain) B. niger (= Botrylloides nigrum).

Reproduction in B. schlosseri, a sessile hermaphrodite, includes a sexual and an asexual component.Sexual reproduction involves the release of male gametes into the water followed by uptake in the incurrent siphons of nearby colonies and interanal fertilization of eggs (Phillippi et al. 2004). Asexual reproduction involves a synchronized budding process that occurs on an approximately weekly basis to increase the size of the clonal colony until it becomes large enough to reproduce sexually. Closely genetically related colonies may fuse with one another when they come into contact, resulting in larger "chimera" (made up of genetically distinct individuals) colonies that may reach sexual maturity more rapidly than smaller unfused colonies. Sexual maturity in field populations in Monterey, CA was attained in 49 days, corresponding to 7 asexual replication cycles (Chadwick-Furman and Weissman 1995, Salem Sound Coastwatch undated).Reproductive seasonality appears quite variable across the broad distribution range of the species.

Internal gestation and development to a free-swimming "tadpole" larval stage is followed by release to the water column and a short (up to 24-36 hours) planktonic duration that is probably capable of only local (1-10 km) dispersal (Berrill 1950, 1975, Hiscock 2007).

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 28 barcode sequences available from BOLD and GenBank.  Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.  See the BOLD taxonomy browser for more complete information about this specimen and other sequences.


Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 28
Specimens with Barcodes: 31
Species With Barcodes: 1

Genomic DNA is available from 4 specimens with morphological vouchers housed at British Antarctic Survey

United States

Rounded National Status Rank: NNA - Not Applicable

Rounded Global Status Rank: GNR - Not Yet Ranked

Common and widespread (3).

Not currently threatened.

No conservation action has been targeted at this species.