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Rapid Response for Aquatic Invasive Species; Effect of comprehensive treatment of Violet tunicate biomass on recruitment rates



The spread of two invasive colonial tunicates in the waters of PEI is occurring at a fast pace and the impact of this infestation to the mussel industry is growing rapidly. The violet tunicate (Botrylloides violaceus) and golden star tunicate (Botryllus schlosseri), unlike the solitary clubbed tunicate (Styela clava), are colonial and thus considered a greater fouling challenge for the mussel industry. They not only reproduce sexually spreading larvae through the water column but also can bud or fragment producing new colonies which will drift and easily spread the tunicate further out into the bay/estuary infesting adjacent and distant leases, depending on environmental conditions and/or anthropogenic effects. Of particular concern is the fact that the violet tunicate can encase and smother the crop.

A significant impact of these two colonial tunicates, as well as the solitary clubbed tunicates and vase tunicate (Ciona intestinalis), is the additional cost of operating mussel farms and processing the crop. As well it is possible that the colonial tunicates may significantly impact the ability of the industry to collect mussel seed as it is currently fouling seed collectors in Savage Harbour resulting in a dramatic decrease in the amount of seed collected. The violet tunicate has been established in Savage Harbour since at least the summer of 2004, and has been recently reported in other PEI bays, including Cardigan River which is in close proximity to three other important mussel culture systems (Brudenell River, Montague River and St. Mary's Bay). The estimated landed value of mussel crop in these waters is approximately $10,000,000 annually. At the present time, there are no established rapid response measures for these types of infestations, either from a treatment perspective or from a removal (eradication) perspective. The mussel industry, however, is willing to attempt to reduce the impact and spread of this infestation in Cardigan waters through the removal of a significant amount of the biomass of the violet tunicate by treating all infested mussels leases, including lease gear and mussel crop.

The goal of this project will be to treat all infested leases in Cardigan River in order to reduce the biomass of violet tunicates on mussel socks and culture gear. The main objective of the study will be to assess the effect of this rapid response by evaluating and comparing the recruitment levels in Cardigan Bay utilizing Savage Harbour, as a control bay. A secondary objective will be to monitor the effect of treatment on the infestation levels both on the mussel socks and the bottom under and around the infested leases.

Program Name

Aquaculture Collaborative Research and Development Program (ACRDP)


2005 - 2006


Atlantic: Gulf of St. Lawrence, St. Lawrence Estuary

Principal Investigator(s)

Thomas Landry

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