Preliminary model of tunicate infestation impacts on seston availability and organic sedimentation in longline mussel farms Thomas Guyondet a, ⁎, Thitiwan Patanasatienkul b , Luc A. Comeau a , Thomas Landry a , Jeff Davidson b a Department of Fisheries and Oceans, Gulf Fisheries Centre, Science Branch, 343 Université Avenue, P.O. Box 5030, Moncton, New Brunswick E1C 9B6, Canada b Department of Health Management, Atlantic Veterinary College, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada abstract article info Article history: Received 22 February 2016 Received in revised form 13 September 2016 Accepted 14 September 2016 Available online 16 September 2016 The productivity of a bivalve farm is largely determined by the availability of organic seston and the level of com- petition for that naturally limited resource. Farm production may also be curtailed by regulatory or certification frameworks concerned with controlling biodeposition, i.e. the sedimentation of organic material. Fouling com- munities dominated by filter-feeding tunicates which both compete for food resources and increase biodeposition levels thus have the potential to further limit bivalve farm productivity. In the present study a farm-scale modelling approach was used to quantify the effects of the tunicate Ciona intestinalis on longline mussel farms. Both cultured and fouling species were simulated using physiological mod- ules that took into account their interactions with organic seston dynamics in terms of filtration and biodeposition, and also predicted their growth over a typical growing season. Various treatment scenarios for re- ducing C. intestinalis infestation levels were also analyzed. Model results showed that C. intestinalis populations can rapidly dominate mussel sleeves in terms of their overall biomass and contribution to organic sedimentation. Early treatments during the tunicate reproductive season were the most effective at controlling the level of infes- tation and its impacts on sestonic food availability, mussel production and organic sedimentation. The proposed generic modelling approach could potentially become an essential aquaculture management tool, especially in the context of biological invasions. Statement of relevance: The growing importance of bivalve aquaculture combined with its vulnerability to envi- ronmental conditions compels to ensure its sustainable development and management. Biofouling can potential- ly disrupt farm productivity and become a nuisance with profound socio-economic consequences. The numerical tool developed in this study provides valuable information for the management and mitigation of fouling by fil- ter-feeding species on mussel farms. Crown Copyright © 2016 Published by Elsevier B.V. All rights reserved. Keywords: Mussel aquaculture Tunicate fouling Biodeposition Numerical modelling 1. Introduction As bivalve aquaculture develops in many places around the world, new challenges arise in maintaining or increasing production levels. Biofouling constitutes one of the major challenges bivalve producers must address on a regular basis. Biofouling potentially impacts both cul- tured animals and infrastructures. Moreover, costs associated with foul- ing prevention or treatment measures can reduce farm profitability (Fitridge et al., 2012). The biological productivity of a bivalve farm is largely determined by food (organic seston) availability and the level of competition for that naturally limited resource. At a local farm scale, seston availability is driven by water transport and cultured bivalve filtration rates (Ferreira et al., 2007). Additional filtering pressure from fouling epibionts may disrupt this delicate balance and lead to food limitation within the cultured population. This reduction in food availability can ultimately lead to a decrease in the growth of the cultured species (Daigle and Herbinger, 2009) and thus undermine farm productivity. In terms of environmental impacts, the sedimentation of organic material or biodeposition represents a major concern for stakeholders. Bivalve biodeposits can disrupt the benthic ecosystem through organic enrichment (Aquaculture Stewardship Council, 2012; Cranford et al., 2009; McKindsey et al., 2011). Thus regulatory or certification frame- works aimed at limiting biodeposition may also curtail farm production, particularly when fouling filter-feeders augment the total biodeposition directed towards the benthic environment beneath farms (McKindsey et al., 2009). Moreover, fouling organisms may themselves constitute an additional source of organic sedimentation when treatment mea- sures are applied. Over the past 15 years, Prince Edward Island, Canada (PEI) coastal embayments have been invaded by several exotic tunicate species. Al- though two colonial species (Botrylloides violaceus and Botryllus schlosseri) are now widespread across the island (Paetzold et al., 2012), two solitary species (Styela clava and Ciona intestinalis) pose the greatest nuisance threat to mussel (Mytilus edulis) farmers. Aquaculture 465 (2016) 387–394 ⁎ Corresponding author. E-mail address: thomas.guyondet@dfo-mpo.gc.ca (T. Guyondet). http://dx.doi.org/10.1016/j.aquaculture.2016.09.026 0044-8486/Crown Copyright © 2016 Published by Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Aquaculture journal homepage: www.elsevier.com/locate/aquaculture