摘要：The conditions for a successful invasion involve the intersection of a species, its vector, and an appropriate receiving environment. Species distribution (biogeography) and availability of a shipping vector were used as filters to reduce a list of 57 tunicates with a history of invasion in marine or estuarine waters worldwide, to a more manageable basis for a �watch list� or �trigger list� for non-indigenous invasive tunicates in Atlantic Canada. Seven species from the worldwide invasives list were already present in Atlantic Canada: the non-indigenous Styela clava , Ciona intestinalis (cryptogenic in southern Nova Scotia but non-indigenous in northern Atlantic Canada), Botryllus schlosseri , Botrylloides violaceus and Molgula manhattensis , and the native Aplidium glabrum and Didemnum candidum . Nine species, not currently present in Atlantic Canada, were removed from the analysis due to insufficient distribution data. All of the remaining 41 species co-occurred in one or more bioregions with species presently found in Atlantic Canada. Examination of distributions relative to shipping patterns eliminated eight species not present in the areas with the most shipping traffic to Atlantic Canada: the eastern seaboard of the USA, the Caribbean Sea, northern Europe and the Mediterranean Sea. A climate zone filter to remove species found only in subtropical or tropical waters eliminated 21 species. Applying both the shipping and climate zone filters resulted in a �watch list� of 17 tunicate species considered the most likely to successfully invade Atlantic Canada: Ascidia sydneiensis , Ascidiella aspersa , Botrylloides leachi , Clavelina lepadiformis , Cnemidocarpa irene , Corella eumyota , Cystodytes dellechiajei , Didemnum vexillum , Diplosoma listerianum , Perophora japonica , Perophora multiclathrata , Phallusia mammillata , Polyandrocarpa zorritensis , Polyclinum constellatum , Styela canopus , Styela plicata , and Symplegma brakenhielmi .
