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Effects of husbandry practices and mitigation treatments on the long-term control of tunicate infestation in PEI mussel farms



Tunicate infestations have severely impacted the shellfish aquaculture industry in Atlantic Canada, particularly the mussel aquaculture industry in PEI. Floating or submerged substrate such as shellfish aquaculture structures, gear, and mussel lines provide ideal surfaces for the colonization of invasive tunicates. While mitigation practices (e.g., pressure washing) address the immediate removal of tunicates from mussel lines and substrate, they do not prevent re-infestation. Past research had focused primarily on the timing, frequency, and ecological sustainability of these practices; however, there had been no long-term assessments of these treatments or of alternative measures. Examining the role of bay-wide mussel stocking densities and related effects on tunicate recruitment provided insights into alternative options for managing tunicates on shellfish farms.

In the case of tunicates it is recognized that unused space or substrate availability facilitates the settling of these invasive species in a new environment. This project investigateed the relationship between available recruitment space and levels of infestation by the invasive tunicate, Ciona intestinalis, on PEI mussel culture sites. The study was conducted at the scale of a typical mussel aquaculture site, and will entailed multi-year simulations to assess the overwintering potential of tunicates. The effect of different mussel stocking densities on infestation levels was assessed, and numerical models developed to simulate the effects of fallowing of culture leases. The results from this study inform long-term tunicate management strategies at both farm and bay-scale levels.


Numerical modelling of the tunicate population dynamics of C. intestinalis was informed by in situ tunicate observations. A combination of tunicate treatment and mussel stock scenarios were reproduced to provide information on the long-term management of bay-scale level infestations. The potential recruitment surface area for Ciona intestinalis in PEI embayments was mostly provided by cultivated mussels. Model scenarios tested did not provide clear management options to eradicate Ciona populations from these systems.



Program Name

Program for Aquaculture Regulatory Research (PARR)


2014 - 2017

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

Principal Investigator(s)

Thomas Landry
Research Scientist, Aquaculture and Coastal Ecosystems, Gulf Fisheries Centre
343 Ave Université Ave, Moncton, New Brunswick

Thomas Guyondet
Research Scientist, Aquaculture and Coastal Ecosystems, Gulf Fisheries Centre
343 Ave Université Ave., Moncton, New Brunswick

Collaborative Partner(s)

Aaron Ramsay, PEI Department of Fisheries, Aquaculture and Rural Development

Jeffrey Davidson, Atlantic Veterinary College

Thitiwan Patanasatienkul, Atlantic Veterinary College

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