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Biological synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus
Carver, C.E.; Mallet, A.L.; Vercaemer, B. (2006). Biological synopsis of the colonial tunicates, Botryllus schlosseri and Botrylloides violaceus. Canadian Manuscript Report of Fisheries and Aquatic Sciences = Rapport Manuscrit Canadien des Sciences Halieutiques et Aquatiques, 2747. Fisheries and Oceans Canada, Bedford Institute of Oceanography: Dartmouth. v + 45 pp.
Part of: Canadian Manuscript Report of Fisheries and Aquatic Sciences = Rapport Manuscrit Canadien des Sciences Halieutiques et Aquatiques. Government of Canada, Fisheries and Oceans: Ottawa. ISSN 0706-6473; e-ISSN 1488-5387, more
Peer reviewed article  

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  • Carver, C.E.
  • Mallet, A.L.
  • Vercaemer, B.

Abstract
    Two non-indigenous colonial ascidians Botryllus schlosseri (golden star tunicate) and Botrylloides violaceus (violet tunicate) are becoming increasingly abundant on both the east and west coasts of Canada. Their potential for rapid growth allows them to exploit new environments, potentially displacing native species and disrupting community dynamics. In particular, their tendency to colonize floating substrates and overgrow other organisms poses a threat to the viability of marine aquaculture operations. In both species colonies expand via the asexual budding of individual zooids or through fusion with closely-related colonies. This fusion process is controlled by a complex allorecognition system that allows the organism to detect the degree of genetic similarity between adjoining colonies. Both species are hermaphroditic and brood large larvae with a relatively short larval cycle and limited dispersal potential. Both species can tolerate a wide range of environmental conditions but growth rates increase substantially in warmer environments. Localized subpopulations may exhibit variable growth and reproductive patterns depending on the temperature and food regime. Colonial tunicates generally have few predators, particularly B. violaceus which may give it a competitive advantage over B. schlosseri in some environments. Major dispersal mechanisms are rafting on floating debris or hull fouling. No effective control mechanisms have been reported and any strategy that promotes fragmentation may only serve to enhance dispersal rates. Once these colonial tunicate species become established, they are extremely persistent and virtually impossible to eradicate; reducing the rate of dispersal is therefore imperative. More studies are required to document their life-history characteristics in Canadian waters, particularly such aspects as growth rates, spawning patterns, mortality events and overwintering survival strategies. Information on potential control measures and possible predators is also required to devise impact mitigation strategies for the aquaculture industry.

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