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Life history traits and population dynamics of the invasive ascidian, Ascidiella aspersa, on cultured scallops in Funka Bay, Hokkaido, northern Japan

  • Makoto Kanamori (a1) (a2), Katsuhisa Baba (a3), Masafumi Natsuike (a4) and Seiji Goshima (a2)


The European sea squirt, Ascidiella aspersa was first found as an alien species in 2008 from Funka Bay, Hokkaido, northern Japan, causing serious damage to the scallop aquaculture industry. We investigated A. aspersa on cultured scallops and larval occurrence from July 2010 to June 2014 to clarify life history traits and population dynamics, and consider the relation between the life history of A. aspersa and the process of scallop aquaculture. Larvae of A. aspersa were found from June to December, and recruitment on cultured scallops occurred mainly between July and October. The ascidians grew well and their weights increased until February. We found that 60–80% of A. aspersa that had settled in summer had eggs or sperm in autumn, and 90–100% of A. aspersa matured early the following summer. Maturity size in September was 17–20 mm as male, 22–24 mm as female. Scallops in Funka Bay are hung in the spring and harvested from winter to the next spring. Ascidiella aspersa settle as larvae in early summer, and grow well until winter, resulting in overgrowth on scallops in the harvest season. The linking of the process of scallop aquaculture and the life history of A. aspersa explains why this invasive ascidian has caused serious damage to the aquaculture industry in the bay. In comparison to the earlier descriptions of the native population, A. aspersa in Funka Bay has longer reproductive and growth periods, earlier initiation of reproduction, and possibly smaller maturity size.


Corresponding author

Correspondence should be addressed to: M. Kanamori, Fisheries Research Department, Hakodate Fisheries Research Institute, Hokkaido Research Organization, 20-5, Benten, Hakodate, Hokkaido 040-0051, Japan email:


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Berrill, N.J. (1950) The tunicata with an account of the British species. London: Ray Society.
Blossey, B. and Nötzold, R. (1995) Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis. Journal of Ecology 83, 887889.
Bourque, D., Davidson, J., MacNair, N.G., Arsenault, G., LeBlanc, A.R., Landry, T. and Miron, G. (2007) Reproduction and early life history of an invasive ascidian Styela clava Herdman in Prince Edward Island, Canada. Journal of Experimental Marine Biology and Ecology 342, 7884.
Brewin, B.I. (1946) Ascidians in the vicinity of the Portobello Marine Biological Station, Otago Harbour. Transactions of the Royal Society of New Zealand 76, 87131.
Carlton, J.T. (2000) Quo Vadimus Eotica Oceanica? Marine bioinvasion ecology in the twenty-first century. In Pederson, J. (ed.) Marine bioinvasions: Proceedings of the First National Conference, January 24–27, 1999. Cambridge, MA: Massachusetts Institute of Technology, pp. 610.
Carman, M.R., Morris, J.A., Karney, R.C. and Grunden, D.W. (2010) An initial assessment of native and invasive tunicates in shellfish aquaculture of the North American east coast. Journal of Applied Ichthyology 26, 811.
Colautti, R.I., Ricciardi, A., Grigorovich, I.A. and Maclsaac, H.J. (2004) Is invasion success explained by the enemy release hypothesis? Ecology Letters 7, 721733.
Currie, D.R., McArthur, M.A. and Cohen, B.F. (1998) Exotic marine pests in the port of Geelong, Victoria. Marine and Freshwater Resources Institute Report 8, 57 pp.
Daigle, R.M. and Herbinger, C.M. (2009) Ecological interactions between the vase tunicate (Ciona intestinalis) and the farmed blue mussel (Mytilus edulis) in Nova Scotia, Canada. Aquatic Invasions 4, 177187.
de Kluijver, M.J. and Ingalsuo, S.S. (2004) Ascidiella aspersa, Macrobenthos of the North Sea-Tunicata, Zoological Museum, University of Amsterdam. Available at
Dybern, B.I. (1969) Distribution and ecology of ascidians in Kviturdvikpollen and Vågsböpollen on the west coast of Norway. Sarsia 37, 2140.
Goodbody, I. (2004) Diversity and distribution of ascidians (Tunicata) at Twin Cays, Belize. Atoll Research Bulletin 524, 119.
Hakodate Fisheries Research Institute (2010) 12th Scallop News in Funka Bay (2010). Available at
Hokkaido Government (2012) Hokkaido fisheries today 2012. Sapporo: Hokkaido Government, 125 pp.
Howes, S., Herbinger, C.M., Darnell, P. and Veraemer, B. (2007) Spatial and temporal patterns of recruitment of the tunicate Ciona intestinalis on a mussel farm in Nova Scotia, Canada. Journal of Experimental Marine Biology and Ecology 342, 8592.
Imai, I., Shimada, H., Shinada, A., Baba, K., Kanamori, M., Sato, M., Kuwahara, Y., Miyoshi, K., Tada, M., Hirano, K., Miyazono, A. and Itakura, S. (2014) Prediction of toxic algal bloom occurrences and adaptation to toxic blooms to minimize economic loss to the scallop aquaculture industry in Hokkaido, Japan. PICES Scientific Report 47, 716.
Japan Meteorological Agency (2010a) The weather of summer (June–August). Available at
Japan Meteorological Agency (2010b) The weather of autumn (September–December). Available at
Japan Meteorological Agency (2012) Report on the 2011 off the Pacific coast of Tohoku earthquake. Technical report of the Japan Meteorological Agency 133, 479 pp.
Kanamori, M., Baba, K., Hasegawa, N. and Nishikawa, T. (2012) Biological characteristics, distinction and identification of Ascidiella aspersa (Müller, 1776), as an alien ascidian in northern Japan (Technical Report). Scientific Reports of Hokkaido Fisheries Research Institutes 81, 151156.
Kanamori, M., Baba, K., Konda, Y. and Goshima, S. (2014) Distribution of the invasive ascidian Ascidiella aspersa (Müller, 1776) (Urochordata, Ascidiacea) in Hokkaido, Japan. Japanese Journal of Benthology 69, 2331.
Keane, R.M. and Crawley, M.J. (2002) Exotic plant invasions and the enemy release hypothesis. Trends in Ecology and Evolution 17, 164170.
Kosaka, Y. and Ito, H. (2006) Japan. In Shumway, S.E. and Parsons, G.J. (eds) Scallops: biology, ecology and aquaculture, 2nd edition. Tokyo: Elsevier, pp. 10931141.
Kott, P. (1985) The Australian Ascidiacea Part I, Phlebobranchia and Stolidobranchia. Memoirs of The Queensland Museum 23, 1440.
Lambert, G. (2005) Ecology and natural history of the protochordates. Canadian Journal of Zoology 83, 3450.
Lambert, G. (2007) Invasive sea squirts: a growing global problem. Journal of Experimental Marine Biology and Ecology 342, 34.
Locke, A. and Carman, M. (2009) An overview of the 2nd International Sea Squirt Conference: what we learned. Aquatic Invasions 4, 14.
Mackenzie, A.B. (2011) Biological synopsis of the European sea squirt Ascidiella aspersa . Canadian Manuscript Report of Fisheries and Aquatic Sciences 2968, 15 pp.
MAFF (2015) The 89th Statistical Yearbook of Ministry of Agriculture, Forestry and Fisheries (2013–2014). Available at
Millar, R.H. (1952) The annual growth and reproductive cycle in four ascidians. Journal of the Marine Biological Association of the United Kingdom 31, 4161.
Millar, R.H. (1971) The biology of ascidians. Advances in Marine Biology 9, 1100.
Nagabhushanam, A.K. and Krishnamoorthy, P. (1992) Occurrence and biology of the solitary ascidian Ascidiella aspersa in Tamil Nadu coastal waters. Journal of the Marine Biological Association of India 34, 19.
Natsuike, M., Kanamori, M., Baba, K., Moribe, K., Yamaguchi, A. and Imai, I. (2014) Changes in abundances of Alexandrium tamarense resting cysts after the tsunami caused by Great East Japan Earthquake in Funka Bay, Hokkaido, Japan. Harmful Algae 39, 271279.
Niermann-Kerkenberg, E. and Hoffman, D. K. (1989) Fertilization and normal development in Ascidiella aspersa (Tunicata) studied with Nomarski-optics. Helgoländer Meeresuntersuchungen 43, 245258.
Nishikawa, T., Kajiwara, Y. and Kawamura, K. (1993) Probable introduction of Polyandrocarpa zorritensis (Van Name) to Kitakyushu and Kochi, Japan. Zoological Science 10 (Supplement), 176.
Nishikawa, T., Oohara, I., Saitoh, K., Shigenobu, Y., Hasegawa, N., Kanamori, M., Baba, K., Turon, X. and Bishop, J.D.D. (2014) Molecular and morphological discrimination between an invasive ascidian, Ascidiella aspersa, and its congener A. scabra (Urochordata: Ascidiacea). Zoological Science 31, 180185.
Ohtani, K., Akiba, Y., Ito, E. and Onoda, M. (1971a) Studies on the change of the hydrographic conditions in the Funka Bay IV. Oceanographic conditions of the Funka Bay occupied by the Tsugaru Warm Waters. Bulletin of the Faculty of Fisheries Hokkaido University 22, 221230.
Ohtani, K., Akiba, Y., Yoshida, K. and Ohtuki, T. (1971b) Studies on the change of the hydrographic conditions in the Funka Bay III. Oceanographic conditions of the Funka Bay occupied by the Oyashio water. Bulletin of the Faculty of Fisheries Hokkaido University 22, 129142.
Osman, R.W. and Whitlatch, P.B. (2000) Ecological interactions of invading ascidians within epifaunal communities of southern New England. In Pederson, J. (ed.), Marine bioinvasions: Proceedings of the First National Conference, January 24–27, 1999. Cambridge, MA: Massachusetts Institute of Technology, pp. 164174.
Pyo, J., Lee, T. and Shin, S. (2012) Two newly recorded invasive alien ascidians (Chordata, Tunicata, Ascidiacea) based on morphological and molecular phylogenetic analysis in Korea. Zootaxa 3368, 211228.
R Development Core Team (2013) R: A language and environment for statistical computing. Vienna: R Foundation for Statistical Computing. Available at
Rius, M., Carmen, M. and Turon, X. (2009) Population dynamics and life cycle of the introduced ascidian Microcosmus squamiger in the Mediterranean Sea. Biological Invasions 11, 21812194.
Robinson, T.B., Griffiths, C.L. and Kruger, N. (2004) Distribution and status of marine invasive species in and bordering the West Coast National Park. Koedoe 47, 7987.
Shenkar, N. and Loya, Y. (2008) The solitary ascidian Herdmani momus: native (Red Sea) versus non-indigenous (Mediterranean) populations. Biological Invasions 10, 14311439.
Shenkar, N. and Loya, Y. (2009) Non-indigenous ascidians (Chordata: Tunicata) along the Mediterranean coast of Israel. Marine Biodiversity Records 2, 17.
Shenkar, N. and Swalla, B.J. (2011) Global diversity of Ascidiacea. PLoS ONE 6, e20657.
Stachowicz, J.J., Terwin, J.R., Whitlatch, R.B. and Osman, R.W. (2002) Linking climate change and biological invasions: ocean warming facilitates nonindigenous species invasions. Proceedings of the National Academy of Sciences USA 99, 1549715500.
Svane, I.B. and Young, C.M. (1989) The ecology and behaviour of ascidian larvae. In Barnes, M. (ed.) Oceanography and marine biology, an annual review 27. Aberdeen: Aberdeen University Press, pp. 4590.
Tatián, M., Schwindt, E., Lagger, C. and Varela, M.M. (2010) Colonization of Patagonian harbours (SW Atlantic) by an invasive sea squirt (Chordata, Ascidiacea). Spixiana 33, 111117.
The Plankton Society of Japan and The Japanese Association of Benthology (2009) Marine aliens introduced by human activities and their impacts on ecosystems and industries. Hadano: Tokai University Press.
Tokioka, T. and Kado, Y. (1972) The occurrence of Molgula manhattensis (De Kay) in brackish water near Hiroshima, Japan. Publications of the Seto Marine Biological Laboratory 21, 2129.
Vicente, C.S. and Sorbe, J.C. (2013) Comparative life-histories, population dynamics and productivity of Schistomysis population (Crustacea, Mysida) in European shelf environments. Journal of Sea Research 81, 1332.
Whitlatch, R.B. and Bullard, S.G. (2007) Introduction to the Proceedings of the 1st International Invasive Sea Squirt Conference. Journal of Experimental Marine Biology and Ecology 342, 12.
World Sea Temperatures (2015) Saltcoats sea temperature. Available at



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