Botrylloides violaceus

Invasion History

First Non-native North American Tidal Record: 1966
First Non-native West Coast Tidal Record: 1966
First Non-native East/Gulf Coast Tidal Record: 1978

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General Invasion History:

Botrylloides violaceus was first described in Japan in 1927. It is native to the Northwest Pacific from northern Japan to southern Korea and northern China (Nishikawa 1991; Rho and Lee 1991; Rho and Park 1998; Rho et al. 2000).  Botrylloides violaceus is now widely introduced, being found in the Northeast Pacific, Northwest Atlantic, and parts of the Northeast Atlantic.

North American Invasion History:

Invasion History on the West Coast:

Botrylloides violaceus was first collected on the West coast in 1966 in Santa Barbara Harbor (Lambert, personal communication) and in San Francisco Bay in 1973 (Cohen and Carlton 1995). Subsequently, it was found in Bahia San Quintin, Mexico (Rodriguez and Ibarra-Obando 2008), Ensenada, Mexico (2000, Lambert and Lambert 2003), San Diego Bay, California (1994, Lambert, personal communication), Coos Bay, Oregon (1978, Carlton, unpublished data), Willapa Bay, Washington (1980, Cohen and Carlton 1995), Puget Sound, Washington (1998, Cohen et al. 1998), Prince William Sound, Alaska (1999, Lambert and Sanamyan 2001) and Kachemak Bay, Alaska (1999, Ruiz et al. 2006).

Invasion History on the East Coast:

On the East Coast, the history of the invasion of Botrylloides violaceus was complicated by confusions with B. diegensis. Botrylloides diegensis, possibly native to the northeast Pacific, was introduced to Eel Pond, adjacent to Woods Hole Harbor MA, by a scientist, who wanted a supply of experimental animals around 1972. He reported successful overwintering and reproduction of these animals (Carlton 1989). Consequently, later occurrences of Botrylloides sp. in the NW Atlantic were attributed to this species (Berman et al. 1992). Subsequent examination of Botrylloides sp. along the Northeast Coast of North America indicates that all the specimens found were actually B. violaceus (Gretchen Lambert, personal communication 2000), but the fate of the transplanted B. diegensis in the Eel Pond is unknown. Since B. violaceus is presumed to have been a recent (late 1970s) and local invader to the West Coast, it is unlikely that this species was introduced to Eel Pond instead of the reported B. diegensis. A separate invasion, around 1980 is more likely for B. violaceus.

Owing to the confusion with B. diegensis, the date of first introduction and pattern of early spread in the Northwest Atlantic is obscure. Whitlach et al. (1995) found B. violaceus in 1980 in Long Island Sound and by 1981-1982, B. violaceus had spread to Great Bay, New Hampshire, and to the Damariscotta River, Maine (1982, on oyster-culture nets, Dijkstra et al. 2007). By the mid 1990s it had reached Penobscot Bay (Whitlach and Osman 2001). In 2004, B. violaceus was found fouling aquaculture facilities in Savage Harbour, Prince Edward Island, Canada (Locke et al. 2007).

We are unsure of its range in estuaries south of Long Island Sound. However, in 2002, Gretchen Lambert confirmed our preliminary identifications of B. violaceus from lower Chesapeake Bay, collected in 2000 and 2001. Specimens were found on settling plates on both the Eastern (Kiptopeke/VA/Chesapeake Bay) and Western shores (Norfolk/VA/Little Creek (Hampton Roads); Poquoson/VA/Hampton Roads; Belle Isle Marina/VA/Rappahannock River; Amoco Refinery, Yorktown/VA/York River) (Ruiz et al., unpublished data). In July 2013, we found B. violaceus in the Indian River Inlet, Delaware, and the Chincoteague Inlet, Virginia, on the Atlantic coast of the DelMarVa peninsula (Paul Fofonoff, and Kristen Larson, personal observations). We are unsure of its invasion south of the Chesapeake Bay. Whether it is established here is unknown.

Invasion History Elsewhere in the World:

In the Northeast Atlantic, B. violaceus was first collected in 1993, in the Lagoon of Venice, in the Mediterranean Sea (Zaniolo et al. 1998). It has also been found in the Western Scheldt estuary, in the Netherlands, in 2000 (Gretchen Lambert, personal communication 2001) and in British waters in 2005 (MarLin 2006). In 2009, it was collected in three locations in Spain, Nazaré and Bueu on the Atlantic Ocean and Santander on the/Bay of Biscay (El Nagar et al. 2010).

Botrylloides violaceus has also been reported from the coast of Queensland, Australia (Kott 1985; Kott 1998), however, these reports may refer to another species (Gretchen Lambert, pers. comm.).

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Description

Botrylloides violaceus is a colonial tunicate that can vary in color, ranging from purple, light lavender, red, yellow, orange and brown. In all cases the colony is entirely one color. Botrylloides violaceus colonies are encrusting, usually 2 – 3 mm in thickness (Saito et al. 1981) and can be large, up to 200 mm x 20 mm.  The tunic is soft, easily torn and the zooids are easily freed from the tunic (Lambert 2003). Zooids are arranged in ladder-like chains, with several common cloacal openings. Between chains of zooids the tunic surface is sometimes elevated. Zooids have 10-11 rows of stigmata and 9-12 stomach folds. Ova (reproductive cells) are located dorsal-posterior to testis, consisting of up to 16 follicles. The larvae of B. violaceus are incubated in the tunic. They are nourished by the tunic vascular system and continue to grow even after the adult zooid dies. The larvae are particularly large (up to 3 mm in length) with 24-32 lateral ampullae (Saito et al. 1981; Nishikawa 1991; Lambert 2003). Fully developed larvae are released from the incubatory pouch via the common cloacal openings (Saito et al. 1981).

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Taxonomy

Ecology

General:

Life History- A colonial (or compound) tunicate consists of many zooids, bearing most or all of the organs of a solitary tunicate, but modified to varying degrees for colonial life. Colonial tunicates of the genera Botrylloides have small zooids, usually not organized in systems, and fully embedded in a mass of tunic material. Each zooid has an oral siphon and an atrial canal, opening to a shared cloacal chamber. Water is pumped into the oral siphon, through finely meshed ciliated gills on the pharynx, where phytoplankton and detritus is filtered, and passed on mucus strings to the stomach and intestines. Excess waste is expelled in the outgoing atrial water (Van Name 1945; Barnes 1983).

Colonial tunicates reproduce both asexually, by budding, and sexually, from fertilized eggs developing into larvae. Buds can form from the body wall of the zooid. Colonies vary in size and can range from small clusters of zooids to huge spreading masses. The zooids are hermaphroditic, with eggs and sperm being produced by a single individual. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but many species have a partial block to self-fertilization. Eggs are internally fertilized and embryos are incubated in a brood pouch. Once they are mature, 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 can 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 (Van Name 1945; Barnes 1983).

In all part of its native and introduced range, B. violaceus is more frequently reported from anthropogenic stuctures than from natural surfaces, (Simkanin et al. 2012). Dock floats are especially favored habitats, probably because their motion provides rapid water exchange, and a fresh supply of food-laden water (Glasby 2001). Other colonized man-made structures include pilings, piers, aquaculture structures, and boat hulls (Carman et al. 2010; Davidson et al. 2010; Simkanin et al. 2012). Natural habitats include rocky reefs, bivalve colonies, seaweeds, and eelgrass (White and Orr 2011; Simkanin et al. 2012; Wong and Vercaemer 2012; Carman et al. 2016). Predation may limit or slow the spread of B. violaceus to natural habitats (Simkanin et al. 2013). In habitats in Cape Cod and Massachusetts Bays, settlement was much higher on floating docks, than in eelgrass or rocky habitats (Wagstaff 2017). In experiments with controlled injections of larvae, increased propagule pressure resulted in increased recruitment, as did unoccupied vs occupied space, and plates on floating docks versus those on natural rocks (Simkanin et al. 2017).

Food:

Phytoplankton, detritus

Consumers:

fish, snails, crabs, urchins, starfish

Competitors:

Colonial tunicates, bryozoans

Trophic Status:

Suspension Feeder

SusFed

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Habitats

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

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	-0.6	Field, based on coldest site in geographical range, Boston MA (Zerebecki and Sorte 2011)
Maximum Temperature (ºC)	27.4	Experimental, 24 h 50% survival, using animals acclimated at 17 C from Lynn Harbor MA (Sorte et al. 2013). For Bodega Bay CA animals, acclimated at 12 C, the median lethal temperature was 25. 3 C (Zerebecki and Sorte 2011)
Minimum Salinity (‰)	16	Experimental data, Dijkstra and Harris 2007; Epelbaum et al. 2009
Maximum Salinity (‰)	38	highest tested, Epelbaum et al. 2009
Minimum Reproductive Salinity	16	Some colonies metamorphosed at salinities at 16-35 PSU, but showed reduced growth, and their colonies had fewer zooids than those at higher salinities (Lambert et al. 2016).
Minimum Duration	0.2	Larval period (Saito et al. 1981)
Maximum Duration	0.4	Larval period (Saito et al. 1981)
Broad Temperature Range	None	Cold temperate-Warm Temperate
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

Economic Impacts

Shipping and Industry: The colonial ascidian Botrylloides violaceus is becoming an abundant component of ship and dock fouling communities in the Northeast and Northwest Atlantic, and the Northeast Pacific (Berman et al. 1992; Cohen and Carlton 1995; Lambert et al. 1998; Ruiz et al. 2000; Lambert and Lambert 2003; Dijkstra et al. 2007). It has been found in aquaculture operations in the Gulf of St. Lawrence, Canada but no negative impacts have been reported yet (Ramsay et al. 2008). Due to its abundance, wide distribution, and frequent dominance, this ascidian is likely to have substantial impacts on shipping, aquaculture, and fisheries.

Ecological Impacts

Competition: Botrylloides violaceus frequently displaces other fouling organisms, including native and introduced tunicates, bryozoans, barnacles, and mussels through competition for space and food. Evidence of this was found during experiments with fouling plates in New England waters (Myers 1990; Osman and Whitlatch 1995; Stachowicz et al. 1999; Osman and Whitlatch 2000; Stachowicz et al. 2002a,b; Osman and Whitlatch 2004; Bullard et al. 2004; Agius 2007; Altman and Whitlatch 2007; Rajbanshi and Pederson 2007; Dijkstra and Harris 2009). B.violaceus, in conjunction with other introduced tunicates, is abundant in harbors of Long Island Sound but its abundance decreases sharply in outer coast locations where colonies are susceptible to predation by fishes and gastropods. In experiments, B. violaceus was found to be most successful in communities of low diversity (Stachowicz et al. 1999; Stachowicz et al. 2002a) and in years with high water temperatures in spring (Stachowicz et al. 2002b). On the West Coast, B. violaceus is a recent invader of San Diego Bay, CA. At two locations in California (Mission Bay, 1997; Los Angeles Harbor, 2000) it has formed extensive areas of 100% cover, indicating strong competitive ability (Lambert and Lambert 2003). B. violaceus was one of several invasive fouling species which showed increased growth (% coverage) at temperatures above the ambient temperature of 13.5C in Bodega Harbor, California, while the native species Distaplia occidentalis showed reduced survival (Sorte et al. 2010). Modelling and field observations indicate that increasing water temperatures in the Gulf of Maine will increase the season for asexual reproduction of B. violaceus, as well as the frequency of sexual reproduction (Dijkstra et al. 2017).

Botrylloides violaceus, Botryllus schlosseri, and a native sponge Halichrondria panicea were found to adversely affect native eelgrass Zostera marina in southeastern Nova Scotia by fouling the leaves of the grass, and reducing the availability of light. Fouling increased the mortality of the plants. The violet morph of B. violaceus had a more negative effect than the lighter-colored tunicates, which transmitted more light through their bodies (Wong and Vercaemer 2012). Negative effects on eelgrass are likely to be widespread.

Habitat Change: By 2003-2006, tunicates, including B. violaceus, replaced the mussel Mytilus edulis as the dominant species in fouling communities in Portsmouth Harbor, New Hampshire (Dijkstra and Harris 2009). A major functional habitat change occured because while mussels (e.g. M. edulis) provided a year-round structure for other organisms to settle upon, in what is known as secondary settlement, most tunicates do not provide this secondary settlement structure type. However, B. violaceus dies off seasonally which creates large areas of bare substrate for organisms to colonize (Dijkstra and Harris 2009). Based on experiments on fouling of eelgrass plants in Nova Scotia, the spread of Botrylloides violaceus and Botryllus schlosseri is likely to have an adverse impact on eelgrass beds, increasing mortality of the plants and decreasing their productivity (Wong and Vercaemer 2012).

Herbivory: Experiments by Byrne and Stachowicz (2009) indicate that B. violaceus has a lower filtration rate than the possibly native B. diegensis in Bodega Harbor, California. Similar results were obtained for other exotic/native species pairs. It is suggested that the cumulative effect of increased invasions in fouling filter-feeding communities may increase seasonal consistency of filtration, due to spreading out of recruitment times, rather than increased rates.

Food/Prey: Gastropods (Costoanachis avara, C. translirata), crabs, starfish, and fishes (Tautogolabrus adspersus, Tautoga onitis) may prey upon newly settled (less than one week old) B. violaceus in Long Island Sound, NY. This predation may restrict the tunicate's distribution, especially in open coast areas (Osman and Whitlatch 2004).

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Regional Impacts

NEP-VI	Pt. Conception to Southern Baja California		Ecological Impact	Competition
The colonial tunicate Botrylloides violaceus is a recent invader of San Diego Bay. At two locations, in Mission Bay, in 1997, and in Los Angeles Harbor in 2000, it formed extensive areas of 100% cover, indicating strong competitive ability (Lambert and Lambert 2003).
P030	Mission Bay		Ecological Impact	Competition
The colonial tunicate Botrylloides violaceus is a recent invader of San Diego Bay. At one location in Mission Bay, in 1997 (South Shore Boat Ramp) and one in Los Angeles Harbor in 2000, it formed extensive areas of 100% cover, indicating strong competittive ability (Lambert and Lambert 2003).
P050	San Pedro Bay		Ecological Impact	Competition
The colonial tunicate Botrylloides violaceus is a recent invader of San Diego Bay. At two locations, in Mission Bay, in 1997, and in Los Angeles Harbor (Watchorn Marina) in 2000, it formed extensive areas of 100% cover, indicating strong compeition (Lambert and Lambert 2003).
P130	Humboldt Bay		Ecological Impact	Competition
In fouling plate experiments in Humboldt Bay (Nelson 2009), found that colonial tunicates (Botryllus schlosseri and Botrylloides violaceus), growing in sheets, were able to quicly occupy space on fouling plates, but did not decrease recruitment or species richness.
NEP-IV	Puget Sound to Northern California		Ecological Impact	Competition
In fouling plate experiments in Humboldt Bay, (Nelson 2009) found that colonial tunicates (Botryllus schlosseri and Botrylloides violaceus), growing in sheets, were able to quicly occupy space on fouling plates, but did not decrease recruitment or species richness.
NEP-V	Northern California to Mid Channel Islands		Ecological Impact	Competition
Botrylloides violaceus was one of several invasive fouling species which showed increased growth (% coverage) at temperatures 3.5 and 4.5⁰C above the ambient temperature in Bodega Harbor (13.5⁰C), while tha native Distaplia occidentalis showed reduced survival (Sorte et al. 2010). Botrylloides violaceus was one of a group of 7 non-native species, most of which were rare or absent in 1970-1971 species, but were among the 8 most abundant species in 2006. Spawning periods and abundance of species in this group appeared to be favored by a 1⁰C increase in average temperatures at this site over a 30-year period (Sorte and Stachowicz 2011).
P112	_CDA_P112 (Bodega Bay)		Ecological Impact	Competition
Botrylloides violaceus was one of several invasive fouling species which showed increased growth (% coverage) at temperatures 3.5 and 4.5⁰C above the ambient temperature in Bodega Harbor (13.5⁰C), while the native Distaplia occidentalis showed reduced survival (Sorte et al. 2010). Botrylloides violaceus was one of a group of 7 non-native species, most of which were rare or absent in 1969-1971 surveys, but were among the 8 most abundant species in 2006. Spawning periods and abundance of species in this group appeared to be favored by a 1⁰C increase in average temperatures at this site over a 30-year period (Sorte and Stachowicz 2011).
NEP-IV	Puget Sound to Northern California		Ecological Impact	Food/Prey
In feeding trials, the native crabs Hemigrapsus oregonensis, the flatworm Eurylepta leoparda and the nudibranch Hermissenda crassicornis fed heavily on the native tuinicate Distaplia occidentalis but at much lower rates on the non-native Botryllus schlosseri and Botrylloides violaceus) (Kincaid and de Rivera 2020).
CA	California		Ecological Impact	Competition
Botrylloides violaceus was one of several invasive fouling species which showed increased growth (% coverage) at temperatures 3.5 and 4.5⁰C above the ambient temperature in Bodega Harbor (13.5⁰C), while tha native Distaplia occidentalis showed reduced survival (Sorte et al. 2010). Botrylloides violaceus was one of a group of 7 non-native species, most of which were rare or absent in 1970-1971 species, but were among the 8 most abundant species in 2006. Spawning periods and abundance of species in this group appeared to be favored by a 1⁰C increase in average temperatures at this site over a 30-year period (Sorte and Stachowicz 2011)., The colonial tunicate Botrylloides violaceus is a recent invader of San Diego Bay. At two locations, in Mission Bay, in 1997, and in Los Angeles Harbor (Watchorn Marina) in 2000, it formed extensive areas of 100% cover, indicating strong compeition (Lambert and Lambert 2003)., In fouling plate experiments in Humboldt Bay (Nelson 2009), found that colonial tunicates (Botryllus schlosseri and Botrylloides violaceus), growing in sheets, were able to quicly occupy space on fouling plates, but did not decrease recruitment or species richness., The colonial tunicate Botrylloides violaceus is a recent invader of San Diego Bay. At one location in Mission Bay, in 1997 (South Shore Boat Ramp) and one in Los Angeles Harbor in 2000, it formed extensive areas of 100% cover, indicating strong competittive ability (Lambert and Lambert 2003)., Botrylloides violaceus was one of several invasive fouling species which showed increased growth (% coverage) at temperatures 3.5 and 4.5⁰C above the ambient temperature in Bodega Harbor (13.5⁰C), while the native Distaplia occidentalis showed reduced survival (Sorte et al. 2010). Botrylloides violaceus was one of a group of 7 non-native species, most of which were rare or absent in 1969-1971 surveys, but were among the 8 most abundant species in 2006. Spawning periods and abundance of species in this group appeared to be favored by a 1⁰C increase in average temperatures at this site over a 30-year period (Sorte and Stachowicz 2011).

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