Management of Biological Invasions (2015) Volume 6, Issue 4: 385–394 doi: http://dx.doi.org/10.3391/mbi.2015.6.4.07 Open Access © 2015 The Author(s). Journal compilation © 2015 REABIC Research Article Distribution of the non-indigenous colonial ascidian Didemnum vexillum (Kott, 2002) in the Bay of Fundy and on offshore banks, eastern Canada 1 1 1 2 3 Bénédikte Vercaemer *, Dawn Sephton , Pierre Clément , Adam Harman , Sarah Stewart-Clark 1 and Claudio DiBacco 1Coastal Ecosystem Science Division, Fisheries and Oceans Canada, Bedford Institute of Oceanography, 1 Challenger Drive, Dartmouth, NS, B2Y 4A2, Canada 2Dalhousie University, Department of Biology, Life Science Centre, 1355 Oxford Street, Halifax, NS Canada, B3H 4R2, Canada 3Dalhousie University, Department of Plant and Animal Sciences, Aquaculture Genomics Laboratory, 58 River Road, Truro, NS, B2N 5E3, Canada E-mail: [email protected] (BV), [email protected] (DS), [email protected] (AH), [email protected] (PC), [email protected] (SS-C), [email protected] (CDB) *Corresponding author Received: 17 December 2015 / Accepted: 29 June 2015 / Published online: 21 July 2015 Handling editor: Katherine Dafforn Abstract The invasive colonial ascidian Didemnum vexillum (Kott, 2002) was initially discovered in the fall of 2013 near Parrsboro, Nova Scotia. A rapid response survey was conducted in April 2014 to confirm the presence of the species and to determine its distribution near the original detection site. Subsequent surveys between May and August 2014 examined the dredge contents collected during sea scallop stock assessment surveys on German Bank, northern Browns Bank, eastern Georges Bank and in the Bay of Fundy region. The presence of D. vexillum was confirmed at 22 of 30 stations sampled in four areas of the Minas Basin and Minas Channel region in the northern Bay of Fundy during the rapid response survey. The scallop surveys confirmed the presence of D. vexillum at 9 of 829 stations sampled in the Bay of Fundy region, including 7 in the Minas Basin, 1 off Digby Gut and another off the coast of Yarmouth. Due to the presence of a native species, D. albidum, in the region, a PCR assay was developed to distinguish D. vexillum from all other species in the region. Once the PCR assay was validated this assay was used to confirm all positive identifications in this study. Colonies overgrew rocks, bivalve shells and seaweeds or were retrieved as large dislodged fragments. They were in an overwintering state in April, but healthy, and observed to grow into dense mats in summer. In other regions of the world, D. vexillum has been reported to foul shellfish and aquaculture gear, smother benthic organisms such as the sea scallop (Placopecten magellanicus), and overgrow substrates, suggesting this new colonial invasive ascidian poses a potential threat to Eastern Canada aquaculture and commercial benthic fisheries. Key words: Didemnum vexillum, Bay of Fundy, Eastern Canada, colonial ascidian, fouling, scallop fishery, invasive species Introduction Tagliapietra et al. 2012). In Canada, D. vexillum has been present in British Columbia since 2003 The colonial ascidian Didemnum vexillum (Kott, (Daniel and Therriault 2007), mainly on artificial 2002) can rapidly colonize natural and artificial structures such as aquaculture cages (Lambert hard substrates and overgrow other benthic 2009). In New England, where it was introduced organisms such as bivalves (Valentine et al. 2007a, in the 1980s, D. vexillum is commonly found on b). In the last two decades, non-indigenous popu- both natural (e.g., gravel, eel grass) and artificial lations of D. vexillum have been reported from substrates (e.g., docks, pontoons) in coastal marine many regions worldwide. Originally from the habitats (Bullard et al. 2007; Carman et al. 2014; northwest Pacific ocean (Stefaniak et al. 2012), Valentine et al. 2007a). It has also been reported the species has been reported in temperate waters on gravel substrata offshore on the Northern off New Zealand, Europe, and both coasts of Edge of Georges Bank near the Canadian/US North America (Bullard et al. 2007; Valentine et boundary (Valentine et al. 2007b) where it occupied al. 2007a; Lambert 2009; Griffith et al. 2009; 50 to 90% of available space over a 230 km2 area 385 B. Vercaemer et al. Figure 1. Sample sites and distribution of Didemnum vexillum in the Minas Channel and Minas Basin, Nova Scotia, including the initial detection location (Moore et al. 2014). CCGS Hudson 2013 survey sampling locations (B. Law, pers. comm.). Rapid response survey (April 2014). Scallop stock assessment surveys (May-August 2014). Open symbols represent stations with no tissue collected. Green and red symbols represent stations from which collected tissue tested negative and positive for D. vexillum via molecular screening protocols, respectively. (Bullard et al. 2007; Valentine et al. 2007b). (Moore et al. 2014; Figure 1). Following this This species is a notorious global rapid invader initial detection, the Canadian rapid response (Lambert 2007, 2009) and will likely continue to framework (Locke et al. 2011) was implemented spread via natural and anthropogenic vectors by the Department of Fisheries and Oceans (Herborg et al. 2009). Furthermore, to date D. (DFO) Aquatic Invasive Species (AIS) Monitoring vexillum has been demonstrated particularly Program. A rapid response survey of the Minas difficult to eradicate without effective response Basin off Parrsboro was conducted in April 2014, tools (e.g. New Zealand, Coutts and Forrest 2007; and further sampling to delineate its distribution Wales, Sambrook et al. 2014). was undertaken from May to August 2014 during There is considerable suitable habitat for D. scallop stock assessment surveys throughout the vexillum throughout eastern Canadian waters based Bay of Fundy as well as regions of the Scotian on the species’ temperature and salinity tolerances, Shelf including, German Bank, northern Browns including the Bay of Fundy, the southwestern Bank and eastern Georges Bank. waters of Nova Scotia (NS) and locations around Several PCR based assays have been developed Cape Breton Island (Therriault and Herborg 2007). to assist in monitoring for invasive species in At least one morphologically similar native environmental water samples and species identi- species, D. albidum (Verrill, 1871), is present in fication of tunicate tissue samples in Atlantic the area and complicates the identification of D. Canada. These assays have been used to assist vexillum. The northernmost location of D. DFO in monitoring for Diplosoma listerianum vexillum in the northwest Atlantic was Eastport, (Willis et al. 2011) and Botryllus schlosseri, Maine until 2013 when the species was confirmed Ciona intestinalis, Styela clava and Botrylloides to occur in the Bay of Fundy off Parrsboro, NS violaceus in the region (Stewart-Clark et al. 2009). 386 Distribution of Didemnum vexillum in the Bay of Fundy Since D. albidum is a native species in the the geographic extent of D. vexillum. An AIS region, and not a fouling concern, it is imperative observer sampled didemnid-like tissues from scallop that scientists be able to confidently distinguish dredge contents collected on Georges, Browns between these two species. As a result, a PCR and German Banks and inshore throughout the based species-specific assay was designed based Bay of Fundy (Figure 2A). A total of 236 scallop on a section of the Cytochrome Oxidase 1(COI) tows were completed on offshore banks between gene that had variation between D. vexillum and May 22 and June 6, and 593 tows were completed D. albidum. during the inshore surveys in the upper, middle and outer Bay of Fundy between June 16 and Methods August 28. Offshore surveys used a New Bedford scallop dredge (l × w × h = 7.5 × 8 × 1 ft). Rapid response survey - April 2014 Standardized tows were performed for 8 min on The Aquatic Invasive Species (AIS) group at BIO average at a minimum speed of 2.5–3.5 kn. The 2 (Bedford Institute of Oceanography) conducted a offshore surveys dredged a total area of 0.83 km . rapid response survey in the Minas Basin and For inshore surveys, sampling gear consisted in a Minas Channel region in the upper Bay of Fundy series of Miracle bucket dredges (l × w × h = 2 × to collect samples in order to confirm the 2 × 1 ft) in a nine-gang configuration and tows presence of D. vexillum beyond the area of its were performed for 8 min on average at minimum initial discovery (Figure 1). Prior to the rapid speed (2.5–3.5 kn). The inshore survey dredged a 2 response survey, bottom images obtained from a total area of 2.49 km . Didemnid-like encrusted CCGS Hudson scientific cruise conducted in material and colony fragments were photographed June 2013 in the Minas Basin showed didemnid- and logged. Tissue from colonies resembling D. like colonies at an approximate depth of 20 m vexillum was sampled and preserved in 100% depth off Clarke Head near Parrsboro and in ethanol, which was drained and replenished within Scots Bay, south of the Minas Channel in the 48–72 hours, for subsequent molecular screening. upper Bay of Fundy (Figure 1). These areas were targeted for investigation during the rapid Molecular screening response survey along with two additional areas off West Bay and Cape Spencer, north of Minas Assay development Channel, where anecdotal reports described the presence of a bottom growth resembling didemnid NCBI Primer-Blast was used to generate multiple colonies (Figure 1). primer sets for D. vexillum. These primers were The rapid response survey was conducted on then evaluated for specificity to ensure that no 10 and 11 April 2014. A small scallop dredge false positives would occur if the native D. (l × w × h = 1 × 1 × 0.5 m) was used to survey a albidum was present.