ICES Journal of Marine Science: Journal du Conseil Advance Access originally published online on March 4, 2008
ICES Journal of Marine Science: Journal du Conseil 2008 65(5):770-774; doi:10.1093/icesjms/fsn020
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Non-indigenous tunicate species in the Bay of Fundy, eastern Canada
1 Biological Station, Fisheries and Oceans Canada, 531 Brandy Cove Road, St Andrews, New Brunswick, Canada E5B 2L9
2 Department of Fisheries, 107 Mount Pleasant Road, St George, New Brunswick, Canada E5C 3S9
Correspondence to M. M. LeGresley: tel: +1 506 5295961; fax: +1 506 5295862; e-mail: legresleym{at}mar.dfo-mpo.gc.ca
LeGresley, M. M., Martin, J. L., McCurdy, P., Thorpe, B., and Chang, B. D. 2008. Non-indigenous tunicate species in the Bay of Fundy, eastern Canada. – ICES Journal of Marine Science, 65: 770–774.The frequency of fouling tunicates is increasing in Atlantic Canada and along the New England coast of the US. Canadian shellfish industries in the Gulf of St Lawrence and along the south shore of Nova Scotia have been affected by the heavy infestation of fouling tunicates. Because little research on tunicates has been conducted in the Bay of Fundy, a Canadian monitoring programme was established to look for the non-indigenous tunicates Ciona intestinalis, Botryllus schlosseri, Didemnum sp. A, Botrylloides violaceus, and Styela clava, in southwest New Brunswick. Collectors were deployed at 11 stations in May/June 2006. Some were retrieved in August 2006; others remained until November of the same year. Ciona intestinalis had established at three survey sites, St Andrews Harbour, St Andrews Biological Station, and Fairhaven, Deer Island, but the heaviest infestation was in the Lime Kiln Bay–Charlie Cove area. The greatest settlement of B. schlosseri was at the Dipper Harbour site, with minimal settlements in St Andrews Harbour and Harbour de Loutre. The other species of interest were not detected during the survey.
Keywords: Bay of Fundy, Botrylloides violaceus, Botryllus schlosseri, Ciona intestinalis, Didemnum sp. A, fouling, non-indigenous, Styela clava, tunicates
Received 18 June 2007; accepted 20 January 2008; advance access publication 4 March 2008.
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Introduction |
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Shellfish industries in the Gulf of St Lawrence and along the south shore of Nova Scotia have been severely affected by fouling tunicates (Carver et al., 2003, 2006a, b; Howes et al., 2007; Locke et al., 2007). Ciona intestinalis biofouling in 1997 in Lunenburg, Nova Scotia (Carver et al., 2003), and Styela clava infestation in 1998 in Prince Edward Island (Clarke and Therriault, 2007) inflicted severe economic losses on the blue mussel (Mytilus edulis) shellfish industry.
Ciona intestinalis and Botryllus schlosseri have both been documented previously in the Bay of Fundy region (Van Name, 1912, 1945; Gosner, 1971; Linkletter et al., 1977). Although Botrylloides violaceus, Didemnum sp. A, and S. clava have not been listed in our study area, B. violaceus has been identified in nearby areas such as Eastport, Maine (Osman and Whitlatch, 1995; Dijkstra et al., 2007), as well as in Nova Scotia and Prince Edward Island (Carver et al., 2006b; Locke et al., 2007), and S. clava in Prince Edward Island (Clarke and Therriault, 2007). Since the first documented appearance of Didemnum sp. A in the Damariscotta River, ME, in 1993 and 2002 on the US portion of Georges Bank (Bullard et al., 2007; Valentine et al., 2007), that species has spread north and south along the New England coast (Dijkstra et al., 2007; Osman and Whitlatch, 2007), and is currently found at a number of locations in Maine as far north as Eastport and Cobscook Bay (Daniel and Therriault, 2007; L. Harris, pers. comm.), which are directly across the St Croix River, which forms the border between Canada and the US. Here, we present the results of a 1-year study to determine the geographic distribution and presence of the non-indigenous tunicates C. intestinalis, B. schlosseri, Didemnum sp. A, B. violaceus, and S. clava, along the New Brunswick coast of the Bay of Fundy, eastern Canada.
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Material and methods |
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During 2006, tunicate collectors were suspended at 11 sites in the Bay of Fundy. Five were suspended from floating docks beside wharves, and six from aquaculture buoys (Figure 1; Table 1). Tunicate collectors consisted of four 100 mm Petri dishes facing downwards and fastened to a horizontal, 23 cm inverted flowerpot base, from which a series of six grey PVC plates (10 cm x 10 cm) were attached at 7.5 cm intervals (Figure 2). In addition, Vemco minilog-T 8k temperature recorders were attached below the Petri dishes at four geographically dispersed sites, St Andrews, Saint John, Charlie Cove, and Seal Cove, New Brunswick (Figure 1). All collector lines were suspended 1 m below the surface and remained submerged at all times. Three collectors were set out at each site in May/June, and two of these remained suspended through October/November. The third collector was retrieved in August 2006, and a fourth was substituted in its place and retrieved in October/November (Table 1).
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Settling plates were retrieved by carefully detaching them from the rope, storing them in queen-sized nylon knee socks, and preserving them in a 4% formaldehyde solution in seawater. Settling plates were photographed digitally before preservation. For analysis, the socked plates were removed from the formaldehyde solution and rinsed with tap water onto a 250-µm wire mesh sieve. Plate and sieve contents were examined under Nikon SMZ1000 dissecting microscopes. Both sides of the settling plates were scanned, and the approximate locations and estimates of the areas covered by the non-indigenous tunicate(s) were drawn onto representative diagrams. The presence of other organisms was also documented, but is not presented here.
Results from microscopic analysis using the downward side of the settling plates were assigned to five categories, reflecting the estimate of the area covered by the species of interest. Although the original intent was to report results of the study in a presence–absence format, we felt that, although subjective, more information could be obtained by assigning the following categories: 0 (absence), <25% (minimal presence), 25–50% (moderate presence), 51–75% (abundant), and >75% (very abundant). Following analyses, we resocked the plates and archived them in 70% alcohol. Results were compiled from the settling plates left in the field from May to November 2006. However, because the collector lines at the Harbour de Loutre and North Head sites were lost during the study, only the plates left in the field from August to November 2006 and from May to August 2006, respectively, were analysed and included in the results for those two sites (Table 1).
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Results and discussion |
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From the 147 settling plates analysed, only C. intestinalis and B. schlosseri (of the five species of interest) were found. Tunicates were in the abundant to very abundant categories at two locations: Lime Kiln Bay (C. intestinalis) and Dipper Harbour (B. schlosseri). St Andrews Harbour and Harbour de Loutre were the only sites where both C. intestinalis and B. schlosseri were found together on the settling plates. We realize that wharves and structures adjacent to our suspended collectors are also vectors for settlement (Lambert, 2005); they were not investigated in this study but will be considered in future work. All floating docks, except Saint John Harbour, had some non-indigenous tunicate recruitment.
The settling plates from Lime Kiln Bay were 50–100% covered with C. intestinalis, whereas plates from Charlie Cove, Fairhaven, Harbour de Loutre, St Andrews Harbour, and the Biological Station had minimal to moderate presence (Table 2). Infestation of C. intestinalis on mussel lines from the Lime Kiln area supports these results (MML, pers. obs.). The prevalence of C. intestinalis in the Lime Kiln–Charlie Cove area may be the result of its proximity to salmon and experimental mussel aquaculture sites, which enhance the availability of settling substrata (Tyrrell and Byers, 2007), and provide high nutrient loads and particulate organic matter (Lander et al., 2004). Lambert (2005) indicated that high faecal matter and nutrient load in areas of low turbulence may contribute to the growth of non-indigenous tunicate biomass.
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Botryllus schlosseri cover varied considerably between locations, with minimal to very abundant cover on plates at Dipper Harbour, but only in minimal to moderate levels on plates at St Andrews Harbour, Harbour de Loutre, and Seal Cove. It was also observed on ropes, tags, labels, and the flowerpot bases (Table 3).
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Although Didemnum sp. A was not observed on our settling plates, it has been observed at Eastport, Maine (Daniel and Therriault, 2007; L. Harris, pers. comm.). The species normally attaches to gravel or hard substratum, and occurs in both shallow water on floating docks and in the deeper waters of Georges Bank, and was found on settling plates 1 m above the seabed at a depth of 5–6 m in a study by Osman and Whitlatch (2007). One opportunistic scallop trawl on a gravel bottom at a depth of 35 m within the US–Canadian border and proximate to Eastport yielded neither Didemnum sp. A nor any non-indigenous tunicates (MML, pers. obs.).
A temperature difference of 4–5°C was recorded between Saint John Harbour and Seal Cove throughout the season, Saint John Harbour having the maximum water temperature (18.4°C on 3 August 2006), despite it being the more northern sampling location (Figure 3). This high temperature might be the result of the substantial discharge of fresh water from the Saint John River, and its elevated summer water temperatures. Although the highest temperature was at Saint John, that site is located in an area of strong tides and currents, and fluctuating salinity, which may contribute to the scarcity of organisms on the settling plates after 5 months. The maximum temperature at St Andrews also occurred on 3 August 2006 (16.8°C), whereas at Charlie Cove it reached 13.1°C on 8 August. Seal Cove (Grand Manan Island) temperature peaked (13.1°C) the following month, on 3 September (Figure 3).
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We recognize that the timing of deployment is important, but because of logistic limitations, collectors were not deployed and retrieved synoptically. The sites on Grand Manan Island were the last to be set out and retrieved, because they were managed on an opportunistic basis. The absence of non-native tunicate species on Grand Manan may be the result of the late deployment, on 5 July 2006.
The Petri dishes appeared slightly better indicators of minimal presence than the PVC plates, especially for B. schlosseri, because it appeared on the dishes at St Andrews Harbour and Harbour de Loutre. However, where B. schlosseri was at higher concentrations at the Dipper Harbour site, the difference between settling plate types was not as apparent. Ciona intestinalis was found at most locations equally on the PVC plates and Petri dishes, except at Harbour de Loutre, where it was only found on the Petri dishes. One explanation for the apparent preference for Petri dishes might be the sheltered position provided by the lip of the flowerpot base.
The 2006 tunicate survey determined that C. intestinalis is established in three areas: (i) St Andrews Harbour and St Andrews Biological Station; (ii) Fairhaven; (iii) the heaviest infestation in the Lime Kiln Bay–Charlie Cove area. Botryllus schlosseri is concentrated in the Dipper Harbour area, with minimal settlement in St Andrews and Harbour de Loutre. This non-indigenous tunicate survey will be expanded further in 2007 to cover a wider geographic area and to continue searching for Didemnum sp. A along the US–Canadian border in the Bay of Fundy.
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Acknowledgements |
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We thank Wayne Miner and Danny Loveless of the CCGC "Pandalus III", and Renée Bernier, Andrea Locke, Jim Martin, Shawn Robinson, Dawn Sephton, and Bénédikte Vercaemer for assistance with sample collection, species identification, design, and providing the collectors.
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