Investigating vectors for aquatic invasive species of tunicates in the Canadian shellfish aquaculture industry.

摘要

The potential spread of Didemnum vexillum through aquaculture transfers of Pacific oyster (Crassostrea gigas) was investigated on the Sunshine Coast and the West Coast of Vancouver Island, BC. Pacific oysters from infested areas are regularly transferred for processing to non-infested areas thereby posing a risk of spreading D. vexillum to new areas. This observational study used concepts of the Hazard Analysis Critical Control Point (HACCP) methodology to identify points (control processes, CPs) where the clusters of oysters received manipulations that could alter the amount of epibiont fouling, notably D. vexillum. Three control processes (CPs) were identified: 1) the harvesting procedure, 2) transportation from the harvesting area to the processing plant, and 3) shucking of the oysters and depositing fouled shells in non-infested waters. The percentage coverage of D. vexillum on oyster clusters was evaluated at each CP for product originating from two aquaculture sites, Lemmens Inlet and Okeover Inlet. The results from the assessment demonstrated a significant loss of fouling on C. gigas clusters at both sites from Post-Harvesting (CP1) to Post-Shucking (CP3).;A NR viability assay was developed using Botrylloides violaceus , which is an invasive colonial tunicate in PEI, as a proxy to the colonial tunicate D. vexillum as it is not locally found on PEI. B. violaceus was collected from various locations around PEI and mortality could be determined under light microscopy by assessing filtering and reaction to tactile stimuli as clinical markers. A total of 32 B. violaceus segments (3 cm2) were assessed for viability by comparing a treatment (dead - acetic acid immersion) and a control (alive) group by evaluating NR uptake. Determination of viability in B. violaceus was successful in 100 % of experiments. All of the control group were alive, demonstrating a response to tactile stimulus and a noticeable amount of stain inside the zooids. All treatment groups were dead, demonstrated by the lack of staining and non response to tactile stimulus. A total of 27 fouled clusters containing C. gigas and D. vexillum were collected from an aquaculture lease, Lemmens Inlet, BC, for an aerial exposure comprised of 9 equally divided treatments (0 (control), 0.5, 1.5, 3, 6, 12, 24, 48 and 72 hours). Three segments of D. vexillum were removed from C. gigas and evaluated with the NR stain protocol. Preserved tissues were analyzed and showed no stain uptake for all segments, including the control. This finding demonstrates that D. vexillum has a high tolerance for uncommon situations and may reflect their ability to enter a dormant state during adverse environmental conditions.;In the Montague River estuary, PEI, Ciona intestinalis is the dominant tunicate AIS and is now present in adjacent bays. Removal of C. intestinalis from mussels in processing plants can release gametes into effluent water. Two separate trials in this experimental study focused on the effect of turbidity and flow found in effluent water on C. intestinalis egg fertilization. The first trial evaluated the effect of turbidity (0, 300, 600 and 1200 NTU), and the second evaluated the effect of turbidity (0, 300, 600 and 1200 NTU) combined with water flow (0.9583 L/s). These trials illustrate that regardless of turbidity and flow rate a potential propagule pressure still exists when removing tunicates from mussels within processing plants.;Tunicates have a detrimental effect on the mussel industry by fouling aquaculture gear, product and by increasing labour time and cost of culture. Management to maintain an economically sustainable aquaculture industry via optimized husbandry practices, from a grower and processor perspective, is required to lessen the impact of current tunicates and to reduce the potential impact from new AIS threats. The continued monitoring, education and communication to minimize, if not stop, the ongoing spread is a necessity, especially for shellfish growers in PEI and BC who are already combating tunicate invaders. (Abstract shortened by UMI.).