Styela clava
(Asian tunicate)

Pictures

Picture	Title	Caption	Copyright
Title Habit Caption Styela clava (Asian tunicate); in natural habitat. Saint-Quay-Portrieux, Côtes-d'Armor, Brittany, France. September 2010. Copyright ©Matthieu Sontag (mirgolth)/via wikipedia - CC BY 3.0	Habit	Styela clava (Asian tunicate); in natural habitat. Saint-Quay-Portrieux, Côtes-d'Armor, Brittany, France. September 2010.	©Matthieu Sontag (mirgolth)/via wikipedia - CC BY 3.0

Identity

Preferred Scientific Name

• Styela clava Herdman 1881

Preferred Common Name

• Asian tunicate

Other Scientific Names

• Bostryorchis clava Redikorzev, 1916
• Styela barnharti Ritter and Forsyth, 1917
• Styela clava Herdman, 1881
• Styela clava clava Nishikawa, 1991
• Styela mammiculata Carlisle 1954

International Common Names

• English: club tunicate; leathery sea squirt; rough sea squirt

Summary of Invasiveness

S. clava, the clubbed tunicate, is a fouling organism native to the Pacific Coast of Asia. Because of its hardy nature and ability to withstand salinity and temperature fluctuations, S. clava has established a widespread non-native distribution, and its global spread is facilitated by human-assisted dispersal. S. clava is fast-growing, a prolific breeder and an efficient suspension feeder; it can reach extremely high densities and out-compete native organisms for food in the water column. S. clava also predates on the larvae of native species causing population declines. It fouls aquaculture and fishing equipment and is difficult and time-consuming to remove; hull fouling increases drag on vessels.

Taxonomic Tree

• Domain: Eukaryota
•     Kingdom: Metazoa
•         Phylum: Chordata
•             Subphylum: Tunicata
•                 Class: Ascidiacea
•                     Suborder: Stolidobranchia
•                         Family: Styelidae
•                             Genus: Styela
•                                 Species: Styela clava

Notes on Taxonomy and Nomenclature

Styela clava, the clubbed tunicate, is an ascidian (the term ascidian can be used interchangeably with the term 'sea squirt'). In other words, it belongs to the Class Ascidiacea, Subphylum Tunicata (hence, it is also a tunicate).

Description

S. clava is a large, club-shaped solitary ascidian with a tough leathery tunic with conspicuous bumps, growing up to 160mm long. It consists of an elongated, cylindrical body on top of a stalk of variable length. It can be brownish-white, yellowish-brown, reddish-brown, or yellowish-grey. There are two short siphons towards the top of the organism pointing upward, each with a 4-lobed opening. The body has conspicuous tubercles and rounded swellings on the upper portion and rounded longitudinal ridges on the lower half. The stalk surface is creased. Internally, the gut is a simple U-shaped loop (Fuller, 2005; and NIMPIS, 2002).

Distribution

Native range: S. clava was once restricted to the Pacific shores of Asia and Russia (Goldstien et al., 2010).

Known non-native range: Australasia-Pacific, Europe, and North America (NZPA, 2005, Davis and Davis, 2005, and Fuller, 2005). S. clava was first recorded outside its native range in 1932, when it was found on the Californian coast (Clarke and Therriault, 2007). See Davis et al. (2007) for information about the distribution and spread of S. clava in European waters.

S. clava has low natural dispersal ability; its global spread and abundance is thought to rely upon human-aided dispersal and a high tolerance to changing environmental conditions (Goldstien et al., 2010).

Distribution Table

The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Habitat

S. clava is present on coasts in low wave-energy environments and sheltered embayments in the upper sublittoral zone typically from 15-25m depth. As a fouling species, it is common on rocks and pylons and can reach densities of 500-1500 individuals per square metre. It is a hardy species, capable of withstanding salinity changes and temperature fluctuations. It can attach itself to concrete and cement, wood, vessel hulls and reefs. S. clava has also frequently been found on permanently submerged floating surfaces, such as buoys and pontoons. It has also been documented attaching itself to other organisms (Crassostrea gigas, Mytilus edulis, and Sargassum muticum). It can reach high densities on artificial substrates. (Clarke and Therriault, 2007; Davis and Davis, 2005; and NIMPIS, 2002).

Habitat List

Biology and Ecology

Nutrition
S. clava is a suspension feeder that consumes matter such as phytoplankton, zooplankton, oyster larvae and other suspended organic materials (NIMPIS, 2002). S. clava has a high filtration rate (Clarke and Therriault, 2007).

Reproduction
S. clava is hermaphroditic but male and female gonads mature at different times, hence they are not self-fertile. The gonads are closely applied to the visceral surface of the body wall. It reproduces sexually, is oviparous and larval development is usually of one day duration. Spawning in S. clava is temperature dependant and it is believed to only be able to spawn in waters above 15°C. Fertilisation is external and eggs and larvae are planktonic for between one to three days (24-28 hours at 20°C is given by Clarke and Therriault, 2007), after which they settle and metamorphose into the sessile adult. The short planktonic phase leads to short larval dispersal distances – human-aided dispersal contributes towards the wide distribution of S. clava. Reproduction occurs throughout all but the coldest periods. S. clava can live 2-3 years and reaches maturity at around 10 months (JNCC, 1997; NIMPIS, 2002; and Parker et al. 1999).

Associations

S. clava may be contributing to the establishment of the macroalga Undaria pinnatifida by facilitating settlement in San Antonio Bay, northern Patagonia, Argentina (Pereyra et al., 2015).

Means of Movement and Dispersal

Introduction pathways to new locations
Aquaculture:S. clava can be transported on fouled aquaculture and fishing equipment. Another method of dispersal includes being transferred on oysters (JNCC, 1997).
Ship/boat hull fouling: Possible methods of dispersal include transport on ships' hulls (JNCC, 1997). As well as commercial fishery and shipping vessels, recreational boats are also a potential vector. S. clava may be transported overland via towed vessels (Darbyson et al., 2009).
Military: S. clava was possibly transported on the hulls of warships following the end of the Korean War in 1951 (JNCC, 1997).
 

Pathway Causes

Pathway Vectors

Impact Summary

Impact

When S. clava populations explode they often out-compete many native species for food. S. clava can reach densities of 500-1500 individuals per square metre. These extreme densities can have negative impacts on native and aquaculture species through competition for space and food, as well as predation of larvae from the water column. S. clava invasiveness is enhanced through its hardy nature; it is capable of withstanding salinity changes and temperature fluctuations (JNCC, 1997; NIMPIS, 2002).

It can also occur as a fouling organism on vessels, aquaculture and fishing equipment and other artificial structures. Dense fouling occurs on fishing equipment, moorings, ropes, etc. It can be time consuming to remove and can result in tangling of fishing gear. Hull fouling increases drag on vessels, requires an increase in the frequency of hull cleaning, and increases fuel costs. In Japan it has been known to impact upon human health causing an asthmatic condition in oyster shuckers when hammering open Styela fouled oysters in poorly ventilated areas (NIMPIS, 2002).

The tremendous density and abundance of S. clava in Prince Edward Island is considered a serious threat to the long-term economic viability of the shellfish industry there. Locke et al. (2007) discuss why Prince Edward Island has proved so invisible for ascidians; they suggest that the aquaculture and agriculture industry may be one factor (for example, by producing high and fluctuating estuarine nutrient levels). The green crab (Carcinus maenas) may also facilitate S. clava invasion (see Locke et al., 2007). 
 

Risk and Impact Factors

• Negatively impacts aquaculture/fisheries
• Threat to/ loss of native species

• Competition - monopolizing resources
• Fouling
• Predation

Uses

Styela clava is eaten as seafood in Korea (Fuller, 2005).

Uses List

Human food and beverage

• Food

Similarities to Other Species/Conditions

Small specimens of S. clava up to 30 mm length may have no stalk and could possibly be confused with other Styela species. The test (protective covering, also called the tunic) of S. clava is leathery and the gut loop is simple and vertical, whereas the test of S. plicata is whitish, almost naked, tough but not leathery and the gut loop is deeply curved (Kott 1985; NIMPIS, 2002).

Prevention and Control

Prevention: Monitoring water samples for species of invasive ascidians can help ensure early detection and response. However current methods (use of recruitment plates and dissection microscopes) are costly and time-consuming and it is difficult to distinguish different species from observing egg and larval stage under a dissecting microscope. Use of polymerase chain reaction (PCR) based detection is being investigated and could provide easier and earlier identification of S. clava (including of egg and larval stages) (Stewart-Clark et al. 2009). Control of potential vectors (e.g. fishery and shipping vessels and fouled aquaculture equipment) can also help prevent spread. (See Locke et al. 2009 for vector control efforts in Prince Edward Island; see MAF Biosecurity New Zealand, 2008 for suggestions on S. clava vector management in New Zealand).

Exposure, temperature and salinity: NIMPIS (2002) states that, "In some power plants, raw water systems, reservoirs, locked marinas and impoundments, water levels can be lowered (drawn-down) to expose fouling infestations to the air. Subsequent freezing or desiccation due to ambient temperatures may kill a large proportion of the exposed population." The authors go on to state that this method has been successful in controlling S. clava. Various combinations of salinity, temperature and exposure to air have proved successful in killing S. clava fouled on oysters without harming the oysters (NIMPIS, 2002).

The dipping of dredged oysters, and associated species, in saturated or strong salt solutions is extremely effective in killing ascidians without harming the oysters. Brine dipping of oysters fouled with Sargassum muticum, Codium fragile ssp. tomentosoides and S. clava was found to be an effective control. Brine dipping infested oysters is considered the cheapest, safest and most effective method of control of fouling species, however, this requires collection of all the fouled oysters to place them in a bath as it is not possible to implement in the open environment (NIMPIS, 2002).

Chemical control: Hydrated lime (calcium hydroxide) and acetic acid are natural chemicals that can be used to remove fouling tunicates. Spraying or immersion treatments with a saturated solution of hydrated lime or 5% acetic acid are effective at removing fouling tunicates, but are also biocidal to a variety of non-target organisms. There is also some concern about alteration of estuarine pH if the chemicals were to be heavily used (Locke et al., 2009). The synthetic chemical medetomidine can reduce S. clava larval mobility and settlement and may have potential as a management tool to control S. clava fouling. (Willis et al., 2011).

Physical control: High pressure water blasting has been used as a removal strategy for other tunicates but has been of limited use for S. clava because of its tough tunic (Clarke and Therriault, 2007).

Alternative approaches: There is interest in marketing S. clava as a food item – they are already eaten as a delicacy in Korea. Marketing S. clava (removed from aquaculture operations) for the Korean community in North America could offset some of its damaging economic effects on the aquaculture industry (Karney and Rhee, 2009).

Darbyson et al. (2009) discussed the use of anti-fouling paints.

When the problem of invasive ascidians including S. clava emerged in Prince Edward Island, various management approaches were adopted. This included ballast water control, and more recently, use of chemical control to remove S. clava from mussel socks. Quarantine has also been imposed (see the case study by Locke et al. 2009; see also information provided by Fisheries and Oceans Canada on invasive tunicate control).

The New Zealand government have also implemented a management strategy after S. clava was first discovered in 2005. (see New Zealand Government report on Styela clava ; also see full report: MAF Biosecurity New Zealand, 2008)

In Australia, a two year study was undertaken to rank the impact and invasion potential of existing and potential introduced marine species found within Australian waters. S. clava was identified as a 'medium priority species' having a reasonably high impact (see Hayes et al., 2005).

Bibliography

C.L. Clarke and T.W. Therriault, 2007. Biological Synopsis of the Invasive Tunicate Styela clava (Herdman 1881). Canadian Manuscript Report of Fisheries and Aquatic Sciences 2807.

References from GISD

Berman, J., L. Harris, W. Lambert, M. Buttrick, and M. Dufresne. 1992. Recent Invasions of the Gulf of Maine: Three Contrasting Ecological Histories. Conservation Biology Volume 6, No. 3, September 1992.

Boyd, M. J., T. J. Miulligan, and F. J. Shaughnessy. 2002. Non-Indigenous marine species of Humboldt Bay, California. A Report to the California Department of Fish and Game: February 28, 2002.

Centre for Environment, Fisheries & Aquaculture Science (CEFAS)., 2008. Decision support tools-Identifying potentially invasive non-native marine and freshwater species: fish, invertebrates, amphibians. http://www.cefas.co.uk/projects/risks-and-impacts-of-non-native-species/decision-support-tools.aspx

Davidson, J., T. Landry, and G. Johnson. UNDATED. Pathophysiology and Ecology of Styela clava. RESEARCH - Research Summary, Environmental Integrity Theme. http://www.aquanet.ca/English/research/ei15_04.php

Davis, M. H., and M. E. Davis. 2005. Styela clava (Tunicata: Ascidiacea) - a new addition to the fauna of the Portuguese coast. J. Mar. Biol. Ass. U.K. (2005), 85, 403-404.

Dyrynda, P.E.J. 2001. Distributions and ecological impacts of non-native species within natural estuarine channels (Poole Harbour, UK). In Abstracts: Second International Conference on Marine Bioinvasions, March 9-11, 2001. New Orleans, LA http://massbay.mit.edu/publications/marinebioinvasions/mbi2_abstracts.pdf

Fuller, P. 2005. Styela clava. USGS-NAS (Nonindigenous Aquatic Species Database, Gainesville, FL.). http://nas.er.usgs.gov/queries/FactSheet.asp?SpeciesID=1292

Hewitt, C. L., M. L. Campbell, R. E. Thresher, R. B. Martin, S. Boyd, B. F. Cohen, D. R. Currie, M. F. Gomon, M. J. Keough, J. A. Lewis, M. M. Lockett, N. Mays, M. A. McArthur, T. D. O'Hara, G. C. B. Poore, D. J.Ross, M. J. Storey, J. E. Watson, and R. S. Wilson. 1998. Introduced and cryptogenic species in Port Phillip Bay, Victoria, Australia. Marine Biology International Journal on Life in Oceans and Coastal Waters.

JNCC (Joint Nature Conservation Committee). 1997. Non-native marine species in British waters: a review and directory. Editors: N. Clare Eno, Robin A. Clark & William G. Sanderson. http://www.jncc.gov.uk/page-1722

Lambert C. C., and G. Lambert. 1998. Non-indigenous ascidians in southern California harbors and marinas. Marine Biology (1998) 130: 675±688 .

Minchin, D., and S. Gollasch. 2003. Fouling and Ships' Hulls: how Changing Circumstances andSpawning Events may Result in the Spread of Exotic Species. Biofouling, 2003 Vol 19 (Supplement), pp 111-122.

National Introduced Marine Pest Information System (NIMPIS), 2002. Styela clava species summary. National Introduced Marine Pest Information System (Eds: Hewitt C.L., Martin R.B., Sliwa C., McEnnulty, F.R., Murphy, N.E., Jones T. & Cooper, S.). Web publication. http://www.marine.csiro.au/crimp/nimpis/spsummary.asp?txa=6836

NZPA. 2005. Sea squirt alert at Picton. The New Zealand Herald.

Osman, R.W. & Whitlatch, R.B. 1999. Ecological interactions of invading ascidians within epifaunal communities of Southern New England. In Abstracts: First National Conference on Marine Bioinvasions, January 24 -27, 1999. Massachusetts Institute of Technology, Cambridge, MA http://massbay.mit.edu/publications/marinebioinvasions/mbi1_abstracts.pdf

Parker, L. E., S. Culloty, R. M. O'Riordan, B. Kelleher, S. Steele, and G. Van der Velde. 1999. Preliminary study on the gonad development of the exotic ascidian Styela clava in Cork Harbour, Ireland. Journal of Marine Biol Ass. U.K. 79:1141-1142.

Parry, G. D., and B. F. Cohen. 2001Exotic species established in Western Port, including an assessment of the status of the exotic species Corbula gibba, Alexandrium spp, Gymnodinium spp and Undaria pinnatifida. Marine and Freshwater Resources Institute: Report No. 45.

Pederson, J., R. Bullock, J. Carlton, J. Dijkstra, N. Dobroski, P. Dyrynda, R. Fisher, L. Harris, N. Hobbs, G. Lambert, E. Wasem, A. Mathieson, M. Miglietta, J. Smith, J. Smith, and M. Tyrrell. 2003. Rapid assessment survey of non-native and native marine species of floating dock communities. MARINE INVADERS IN THE NORTHEAST: Massachusetts Institute of Technology Sea Grant College Program, Cambridge, Massachusetts.

The Ocean Biogeographic Information System (OBIS) Dataset Extent Map, Distribution of Styela clava http://www.iobis.org/OBISWEB/ObisControllerServlet?category=all&names=data&tableName=0&searchName=styela+clava&x=20&y=13

Wasson, K., C. J. Zabin, L. Bedinger, M. C. Diaz, and J. S. Pearse. 2001. Biological invasions of estuaries without international shipping: the importance of intraregional transport. Biological Conservation 102 (2001) 143-153.

Whitlatch, R., R. Osman, A. Frese, R. Malatesta, P. Mitchell, and L. Sedgewick. 1995. The ecology of two introduced marine ascidians and their effects on epifaunal organisms in Long Island Sound. Pages 29-48 in Proceedings of the Northeast Conference on Non-Indiginous Aquatic Nuisance Species. Connecticut Sea Grant Publication Number CT-SG-95-04.

Whitlatch, R.B. and Osman, R.W. 1999. Geographical distributions and organism-habitat associations of shallow-water introduced marine fauna in New England. In Abstracts: First National Conference on Marine Bioinvasions, January 24 -27, 1999. Massachusetts Institute of Technology, Cambridge, MA http://massbay.mit.edu/publications/marinebioinvasions/mbi1_abstracts.pdf

References

Biosecurity New Zealand MAF, 2008. Assessment of population management options for Styela clava. Ministry of Agriculture and Forestry. http://www.biosecurity.govt.nz/files/pests/salt-freshwater/styela-clava-population-management.

Clarke CL; Therriault TW, 2007. Biological Synopsis of the Invasive Tunicate Styela clava (Herdman 1881). Canadian Manuscript Report of Fisheries and Aquatic Sciences 2807.

Darbyson EA; Hanson JM; Locke A; Willison JHM, 2009. Settlement and potential for transport of clubbed tunicate (Styela clava) on boat hulls. Aquatic Invasions [Proceedings of the 2nd International Invasive Sea Squirt Conference, Prince Edward Island, Canada, 2-4 October 2007.], 4(1):95-103. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Darbyson_etal2.pdf

Davis MH; Davis ME, 2008. First record of Styela clava (Tunicata, Ascidiacea) in the Mediterranean region. Aquatic Invasions, 3(2):125-132. http://www.aquaticinvasions.ru/2008/AI_2008_3_2_Davis_Davis.pdf

Davis MH; Lützen J; Davis ME, 2007. The spread of Styela clava Herdman, 1882 (Tunicata, Ascidiacea) in European waters. Aquatic Invasions, 2(4):378-390. http://www.aquaticinvasions.ru/2007/AI_2007_2_4_Davis_etal.pdf

Goldstien SJ; Schiel DR; Gemmell NJ, 2010. Regional connectivity and coastal expansion: differentiating pre-border and post-border vectors for the invasive tunicate Styela clava. Molecular Ecology, 19(5):874-885. http://www.blackwell-synergy.com/loi/mec

ISSG, 2011. Global Invasive Species Database (GISD). Invasive Species Specialist Group of the IUCN Species Survival Commission. http://www.issg.org/database

Karney RC; Rhee WY, 2009. Market potential for Styela clava, a non-indigenous pest invading New England coastal waters. Aquatic Invasions [Proceedings of the 2nd International Invasive Sea Squirt Conference, Prince Edward Island, Canada, 2-4 October 2007.], 4(1):295-297. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Karney_Rhee.pdf

Krone R; Wanke C; Schröder A, 2007. A new record of Styela clava Herdman, 1882 (Urochordata, Ascidiacea) from the central German Bight. Aquatic Invasions, 2(4):442-444. http://www.aquaticinvasions.ru/2007/AI_2007_2_4_Krone_etal.pdf

Locke A; Doe KG; Fairchild WL; Jackman PM; Reese EJ, 2009. Preliminary evaluation of effects of invasive tunicate management with acetic acid and calcium hydroxide on non-target marine organisms in Prince Edward Island, Canada. Aquatic Invasions [Proceedings of the 2nd International Invasive Sea Squirt Conference, Prince Edward Island, Canada, 2-4 October 2007.], 4(1):221-236. http://www.aquaticinvasions.ru/2009/AI_2009_4_1_Locke_etal.pdf

Locke A; Hanson JM; Ellis KM; Thompson J; Rochette R, 2007. Invasion of the southern Gulf of St. Lawrence by the clubbed tunicate (Styela clava Herdman): potential mechanisms for invasions of Prince Edward Island estuaries. Journal of Experimental Marine Biology and Ecology [Proceedings of the 1st International Invasive Sea Squirt Conference, Woods Hole, Massachusetts, USA, April 21-22, 2005.], 342(1):69-77. http://www.sciencedirect.com/science/journal/00220981

Locke A; Hanson JM; MacNair NG; Smith AH, 2009. Rapid response to non-indigenous species. 2. Case studies of invasive tunicates in Prince Edward Island. Aquatic Invasions, Special issue "Proceedings of the 2nd International Invasive Sea Squirt Conference",.

Minchin D; Davis MH; Davis ME, 2006. Spread of the Asian tunicate Styela clava Herdman, 1882 to the east and south-west coasts of Ireland. Aquatic Invasions, 1(2):91-96. http://www.aquaticinvasions.ru/2006/AI_2006_1_2_Minchin.pdf

Pereyra PJ; Narvarte M; Tatián M; González R, 2015. The simultaneous introduction of the tunicate Styela clava (Herdman, 1881) and the macroalga Undaria pinnatifida (Harvey) Suringar, 1873, in northern Patagonia. BioInvasions Records, 4(3):179-184. http://www.reabic.net/journals/bir/2015/3/BIR_2015_Pereyra_etal.pdf

Willis KJ; Woods CMC, 2011. Managing invasive Styela clava populations: inhibiting larval recruitment with medetomidine. Aquatic Invasions [Proceedings of the 3rd International Invasive Sea Squirt Conference, Woods Hole, USA, 26-28 April 2010.], 6(4):511-514. http://www.aquaticinvasions.net/2011/AI_2011_6_4_Willis_Woods.pdf

World Register of Marine Species (WoRMS), 2012. Styela clava. http://www.marinespecies.org/aphia.php?p=taxdetails&id=103929.

Principal Source

Global Invasive Species Database

Contributors

Reviewed by: Expert review underway: Andrew N. Cohen San Francisco Estuary Institute Oakland California USA

Last Modified: Thursday, March 23, 2006

Distribution Maps