Lobsters and crabs as potential vectors for tunicate dispersal in the southern Gulf of St. Lawrence, Canada Renée Bernier, Andrea Locke and J. Mark Hanson Fisheries and Oceans Canada, P.O. Box 5030, Moncton, NB, E1C 9B6 Canada Introduction The spread of several non-indigenous tunicates along Prince Edward Island’s coast has prompted further investigation into the vectors facilitating their dispersal. Ballast water discharge from international shipping, recreational and commercial boating, introduction and transfers of live shellfish and commercial fisheries are vectors to consider in this area. Most of the emphasis has been put on introduction and transfers of shellfish and recreational and commercial boating for wide-range dispersal, but little attention has been given to the possibility of migrating crustaceans as vectors. Anecdotal reports suggest tunicates occasionally occur on crabs and lobsters caught in commercial fisheries in these waters. To further investigate the importance of this vector, a pilot project was conducted in November 2005 in tunicate-infested estuaries (St. Peters Bay and Savage Harbour, PE) and in the Northumberland Strait in August 2006 to determine the presence/absence of invasive tunicates on American lobsters (Homarus americanus), rock crabs (Cancer irroratus) and lady crabs (Ovalipes ocellatus). Materials and methods Sampling for this project was conducted in part through coordination with the Prince Edward Island’s Fishermen’s Association (PEIFA) on the northern shore of Prince Edward Island in St. Peters Bay and Savage Harbour (Fig. 1) where the golden star tunicate (Botryllus schlosseri) and the violet tunicate (Botrylloïdes violaceus) ranged from moderate to high infestation on November 3-4, A total of 10 lobster traps were set in two sampling sites per bay (inner and outer bay) to fish for twenty-four hours. Carapace length, sex, presence or absence of tunicates and other epibionts and percent coverage of the latter (if present) were determined in the field for both rock crabs and lobsters. Lobsters and lady crabs from the Northumberland Strait (Fig. 1) were also inspected for possible tunicates and other epibionts during a DFO lobster survey on August 4-5, Further identification of epibionts was conducted at the Gulf Fisheries Centre laboratory in Moncton, NB. Results A total of 112 rock crabs and 66 lobsters were examined on November 3, 2005 in St. Peters Bay. Two hundred and seventy-five rock crabs and 6 lobsters were inspected on November 4, 2005 in Savage Harbour. No invasive tunicates were found on rock crabs examined from St. Peters Bay. However, small patches of Botrylloides violaceus were found on 1.8% of rock crabs sampled from Savage Harbour (Fig. 2). The most common epibionts were green, red and brown algae, which were found on 58% and 64% of rock crabs (Fig. 3) examined from St. Peters Bay and Savage Harbour, respectively. Small sea grapes (Molgula sp.) were discovered on 5.4% of rock crabs from St Peters Bay and on 5.5% of those from Savage Harbour (Fig. 4). All other epibionts, including Anomia simplex, Crepidula fornicata, Crepidula plana, and various sponges and bryozoans, occurred on 6.3% and 4.7% of rock crabs from Savage Harbour and St. Peters Bay, respectively. The lobsters sampled and examined from Savage Harbour were free of epibionts, whereas 14% of lobsters from St. Peters Bay had bryozoans on them and a small colony of Botryllus schlosseri was found on the ventral side of one female lobster (92 mm carapace length) from St. Peters Bay (Fig. 5). On August 4 & , 199 lobsters and 126 lady crabs were examined in the Northumberland Strait. No rock crabs were caught in fishing gear during these two days. Invasive tunicates were not found on any lobsters or lady crabs from this area. Only 2.5% (n=5) of lobsters had Molgula sp. attached on their ventral surface, between pereopods 2 and 4. Most Molgula could not be identified to species, but Molgula citrina was identified on one of the males (144 mm carapace length) (Fig. 6). Fig. 2. Small patch of Botrylloides violaceus (3 mm width X 2 mm height) on Cancer irroratus from Savage Harbour (PE). Fig. 3. Green algae growing on Cancer irroratus from Savage Harbour (PE). Fig. 5. Colony of Botryllus schlosseri (14mm width X 15 mm height) on female lobster from St. Peters Bay (PE). Conclusion The movement of lobsters and rock crabs may vary by area within the southern Gulf of St. Lawrence. Lobsters have been reported to travel up to a maximum of 86 km in the Northumberland Strait (Bowlby et al., 2007) and at an average of 10 km off the northern shore of Prince Edward Island (Comeau and Savoie, 2002). Information on movement of rock crab in the southern Gulf is sparse. Preliminary data from an acoustic tagging study conducted in Montague (PE) suggests that rock crabs can travel several kilometers within a few months (M. Ouellette, DFO, pers. comm.). Based on our preliminary sampling and results, lobsters and rock crabs should be considered as important potential vectors for regional transport and spread of tunicates within the southern Gulf of St. Lawrence. Although the molting process might delay the dispersal of tunicates by lobsters and rock crabs, it would most likely not eliminate it. As molting frequency decreases with age, older lobsters and rock crabs might pose more of a threat for tunicate dispersal than younger individuals (Fig. 7). Fig. 6. Molgula citrina (4mm width X 4 mm height) on male lobster from Northumberland Strait. Fig. 7. A clubbed tunicate (Styela clava) on an adult rock crab from Murray Harbour (PE). References Bowlby, H.D., J. M. Hanson and J. A. Hutchings Resident and dispersal behavior among individuals within a population of American lobster Homarus americanus. Mar. Ecol. Prog. Ser. 331: Comeau, M. and F. Savoie Movement of American lobster (Homarus americanus) in the southwestern Gulf of St. Lawrence. Fish. Bull. 100: Fig. 1. Map of southern Gulf of St. Lawrence showing locations sampled in November 2005 (Savage Harbour and St. Peters Bay, PE), general area sampled within the Northumberland Strait (highlighted in yellow) on August 4-5, 2006 and other place names mentioned in the text. Fig. 4. Patch of 10 Molgula sp. clustered together on Cancer irroratus from St. Peters Bay (PE). Close-up of individuals are shown with and without tunic.