Feeding pressure of Styela clava tunicates on phytoplankton and zooplankton in Malpeque Bay, PEI



To support the sustainable management of the mussel aquaculture industry, Fisheries and Oceans Canada (DFO) and provincial aquaculture managers consider both the farm-scale and ecosystem-scale sustainability of aquaculture activities. Because mussel aquaculture has been impacted by the presence of tunicates and other fouling species in some areas of DFO's Gulf Region, the biology of these species also has to be considered by management as they evaluate proposals for changes in production levels. Shellfish aquaculture production carrying capacity has traditionally been defined as the maximum stocking level for profitability at the farm scale. To ensure sustainability of shellfish aquaculture activities, efforts are focused on characterizing and managing the ecological carrying capacity - that is, the most intensive level of aquaculture activity that can be supported in a particular ecosystem without causing any unacceptable changes in ecological processes. Management decisions for possible increases in mussel aquaculture activity in Malpeque Bay take into consideration both the production and ecological carrying capacities, however, these predictions also need to include estimates of filter feeding pressures from fouling species such as tunicates (Styela clava) that grow on mussel aquaculture lines.

This study investigated the feeding physiology of S. clava so that it can be incorporated into existing ecological carrying capacity models. Specifically this study:

  1. assessed the biomass and size structure of S. clava on mussel socks,
  2. determined S. clava feeding rates on natural phytoplankton communities,
  3. measured S. clava retention efficiency on zooplankton communities,
  4. evaluated S. clava capacity to retain lobster larvae (stages I and IV), and
  5. integrated results into existing carrying capacity models to provide new carrying capacity outputs that included this information.

The outcome of this project supports the development of different mussel production scenarios (present or future) for Malpeque Bay, PEI.


Filter feeding by cultivated blue mussels, Mytilus edulis, and the invasive solitary tunicates, Styela clava, was studied in a portable aquatic laboratory on Prince Edward Island (PEI) using natural seawater. Average standardized clearance rates were 12.5 ± 1.12 Lh-1g-1 dry weight for mussels and 6.7 ± 0.7 Lh-1g-1 dry weight for tunicates. Scaling up these results to a bay scale model that integrated mussel and tunicate feeding pressures on phytoplankton in Malpeque Bay, PEI emphasized the important effect of tunicate mitigations and tunicate treatments on phytoplankton. Without mitigation measures, the feeding capacity by mussels and tunicates increased up to 171 % associated with a maximum reduction in phytoplankton of 1.72 ug chlorophyll a L-1 a reduction of approximately 45 % compared to the current levels (3.83 ug chlorophyll a L-1). Predation on zooplankton by mussels was 35 ± 9.4 % and by tunicates was 28 ± 9.0 %. There was no predation on lobster larvae in either I and IV stages. Mussels and tunicates had no retention or capture of lobster larvae, even at very high lobster densities. These clearance rates and feeding behaviours inform ecosystem carrying capacity modelling.


Sonier, R., Filgueira, R., Douad, D. and Comeau, L.A. 2018. Feeding pressure of Mytilus edulis and Styela clava on phytoplankton and zooplankton, including lobster larvae (stages I and IV). Can. Tech. Rep. Fish. Aquat. Sci. 3263: vi+ 19p.

Comeau, L.A., Filgueira, R., Davidson, J.D.P., Nadeau, A., Sonier, R., Guyondet, T., Ramsay, A., and Davidson, J. 2017. Population structure and grazing capacity of cultivated mussels in Prince Edward Island, Canada. Can. Tech. Rep. Fish. Aquat. Sci. 3228: viii + 23 p.

Comeau, L.A., Filgueira, R., Guyondet, T. and Sonier, R. 2015. The impact of invasive tunicates on the demand for phytoplankton in longline mussel farms. Aquaculture 441: 95-105.

Program Name

Program for Aquaculture Regulatory Research (PARR)


2015 - 2017

Principal Investigator(s)

Rémi Sonier
Research Scientist, Aquaculture and Coastal Ecosystems, Gulf Fisheries Centre, Science Branch
343 Université Avenue, Moncton, New Brunswick
Email: Remi.Sonier@dfo-mpo.gc.ca

Team Member(s)

Luc Comeau

Ramon Filgueira

André Nadeau

Jeffrey Davidson, Aquatic and Ecosystem Health, University of Prince Edward Island