A model of aquaculture biodeposition for multiple estuaries and field validation at blue mussel (Mytilus edulis) culture sites in eastern Canada

Abstract

Development of mariculture in Canadian waters has outpaced the ability of regulators to adequately assess environmental impacts and coexistence with other resource users. In eastern Canada, suspended longline culture of blue mussels (Mytilus edulis) leads to depletion of seston and subsequent biodeposition of feces and pseudofeces. Based on the need to evaluate aquaculture effects over multiple farms, a model was developed to compare the rate of mussel egestion with the scale of culture and tidal flushing of particulate waste from estuarine waters. Egestion was calculated using a bioenergetic submodel, and tidal flushing was determined with a tidal prism method. A short-term field program of particle sensing and sediment trapping was undertaken in Tracadie Bay and Savage Harbour (Prince Edward Island) to examine model assumptions and for validation. A finite element model was used to verify tidal prism calculations. Expressing model output as sedimentation rate, predicted biodeposition in Tracadie Bay was less than that estimated from field results but within the range of estuary-wide variation. In Savage Harbour, the egestion model overestimated biodeposition, likely because culture density on leased areas was sparse. A ranking of sites based on susceptibility to culture impacts was devised for multiple culture sites.

Local enhancement of epibenthic macrofauna by aquaculture activities

“…The overall influence of mussel aquaculture on benthic communities is likely to be affected by a number of factors such as local primary production, hydrodynamic features of the site, size, biomass and age of the shellfish farm (Grant et al 2005, Miron et al 2005. Results from our study showed significant differences in the composition and structure of the epibenthic macrofaunal component of benthic communities at the different mussel farms.…”

“…The scales over which bivalve aquaculture influence the environment may then depend on the precise variable studied (e.g. physicochemical features, biodeposition, infaunal or epibenthic assemblages) (Hartstein & Rowden 2004, Grant et al 2005, Miron et al 2005, Richard et al 2007). For example, the effects of sediment enrichment on infaunal assemblages may be limited to tens of meters whereas the effects on more mobile invertebrates may extend to hundreds of meters.…”

Sedimentation rates in a suspended mussel farm (Great-Entry Lagoon, Canada): biodeposit production and dispersion

“…In the Gulf of St. Lawrence region, mussel farms are usually established in relatively shallow coastal areas (e.g. 3 to 5 m; Grant et al 2005) as compared to other areas (e.g. 8 to 42 m in New Zealand; Hartstein & Stevens 2005) and characterised by low current velocities.…”

Modeling the impact of floating oyster (Crassostrea virginica) aquaculture on sediment-water nutrient and oxygen fluxes

“…mussels, oysters) located at sites with slower currents and less resuspension suffered measurable degradation (e.g. sulfide production, nutrient release) with high POM accumulation (Grant et al 2005, Holyoke 2008). …”

“…Many types of models have been used to compute biodeposition associated with shellfish aquaculture (Grant et al 2005, Weise et al 2009), stock production (Gangnery et al 2001, Duarte et al 2003, carrying capacity (Byron et al 2011), and ecosystem effects and linkages (Ren et al 2012). From a biogeochemical perspective, numerical models can be used to quantify the spatial and temporal impacts of aquaculture-derived POM deposition on underlying sediments and how these impacts are related to farm size, culture intensity, and the physical environment of the aquaculture site.…”