Thomas Guyondet | Fisheries and Oceans Canada (original) (raw)

Papers by Thomas Guyondet

Aquaculture

Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, m... more Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, must compete for food resources with three invasive tunicates (Botrylloides violaceus, Ciona intestinalis and Styela clava). Clearance rates determined for each species were used to calculate clearance rate per unit lease area (CRArea) for various fouling scenarios. CRArea for mussels alone was estimated at 338 ± 20 l h− 1 m− 2. Surprisingly, the size of the mussels under cultivation had no significant effect on estimates of CRArea, due to self-thinning processes that gradually eliminated 89% of the seed mussels over the 2-year production cycle. CRArea was also unaffected by the presence of the fouling colonial tunicate B. violaceus. In contrast, the presence of the solitary tunicate C. intestinalis or S. clava significantly increased CRArea by 30—47% compared to non-infested scenarios, even with control/treatment measures in effect. Size fractionation of the available phytoplankton resou...

Aquaculture

Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, m... more Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, must compete for food resources with three invasive tunicates (Botrylloides violaceus, Ciona intestinalis and Styela clava). Clearance rates determined for each species were used to calculate clearance rate per unit lease area (CRArea) for various fouling scenarios. CRArea for mussels alone was estimated at 338 ± 20 l h− 1 m− 2. Surprisingly, the size of the mussels under cultivation had no significant effect on estimates of CRArea, due to self-thinning processes that gradually eliminated 89% of the seed mussels over the 2-year production cycle. CRArea was also unaffected by the presence of the fouling colonial tunicate B. violaceus. In contrast, the presence of the solitary tunicate C. intestinalis or S. clava significantly increased CRArea by 30—47% compared to non-infested scenarios, even with control/treatment measures in effect. Size fractionation of the available phytoplankton resou...

Journal of Marine …, 2008

A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to exam... more A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to examine the impact of suspended mussel culture on phytoplankton biomass in Tracadie Bay, Prince Edward Island, Canada. Due to the extent of mussel culture there, we hypothesised that shellfish filtration would control the concentration and distribution of phytoplankton and other suspended particles in the bay. Circulation was delineated with a tidally-driven 2D numerical model and used to drive an ecosystem model with a focus on pelagic components including phytoplankton production, nutrients, detritus, and mussels. The benthos were treated as a sink. Nutrients and seston were forced by tidal exchange and river input, with phytoplankton additionally forced by light. Boundary conditions of seston and nutrients were derived from field studies with an emphasis on the contrast between spring (high river nutrients, low temperature) and summer (low river inputs and high temperatures). Model output was used to map phytoplankton carbon over the bay for each season and in the presence of mussels and river nutrient input. Results indicate severe depletion effects of mussel culture on overall phytoplankton biomass, but no spatial pattern that can be attributed to grazing alone. Primary production generated by nutrient-rich river water created a mid-bay spike in phytoplankton that dominated the spatial pattern of chlorophyll-based carbon. Model results were validated with surveys from a towed sensor array (Acrobat) that confirmed the river influence and indicated bay-wide depletion of 29% between high and low water. Our model results indicate that the farm-scale depletion emphasised in previous studies cannot simply be extrapolated to seston limitation at the ecosystem level.

The Canadian Geographer / Le Géographe canadien, 2015

Marine Pollution Bulletin, 2015

A moratorium on further bivalve leasing was established in 1999-2000 in Prince Edward Island (Can... more A moratorium on further bivalve leasing was established in 1999-2000 in Prince Edward Island (Canada). Recently, a marine spatial planning process was initiated explore potential mussel culture expansion in Malpeque Bay. This study focuses on the effects of a projected expansion scenario on productivity of existing leases and available suspended food resources. The aim is to provide a robust scientific assessment using available datasets and three modelling approaches ranging in complexity: (1) a connectivity analysis among culture areas; (2) a scenario analysis of organic seston dynamics based on a simplified biogeochemical model; and (3) a scenario analysis of phytoplankton dynamics based on an ecosystem model. These complementary approaches suggest (1) new leases can affect existing culture both through direct connectivity and through bay-scale effects driven by the overall increase in mussel biomass, and (2) a net reduction of phytoplankton within the bounds of its natural variation in the area.

Marine Ecology Progress Series, 2015

The role of bivalve mariculture in the CO 2 cycle has been commonly evaluated as the balance betw... more The role of bivalve mariculture in the CO 2 cycle has been commonly evaluated as the balance between respiration, shell calcium carbonate sequestration and CO 2 release during biogenic calcification. However, this approach neglects the ecosystem implications of cultivating bivalves at high densities, e.g. the impact on phytoplankton dynamics and benthic−pelagic coupling, which can significantly contribute to the CO 2 cycle. Therefore, an ecosystem approach that accounts for the trophic interactions of bivalve aquaculture, including dissolved and particulate organic and inorganic carbon cycling, is needed to provide a rigorous assessment of the role of bivalve mariculture in the CO 2 cycle. On the other hand, the discussion about the inclusion of shells of cultured bivalves into the carbon trading system should be framed within the context of ecosystem goods and services. Humans culture bivalves with the aim of producing food, not sequestering CO 2 in their shells, therefore the main ecosystem good provided by bivalve aquaculture is meat production, and shells should be considered as by-products of this human activity. This reasoning provides justification for dividing up respired CO 2 between meat and shell when constructing a specific bivalve CO 2 budget for potential use of bivalve shells in the carbon trading system. Thus, an integrated ecosystem approach, as well as an understanding of the ecosystems goods and services of bivalve aquaculture, are 2 essential requisites for providing a reliable assessment of the role of bivalve shells in the CO 2 cycle.

Earth's Future, 2014

ABSTRACT Estuarine ecosystems are highly sensitive to projected effects of climate change such as... more ABSTRACT Estuarine ecosystems are highly sensitive to projected effects of climate change such as ocean warming, acidification and sea level rise but also to the incidence of nor'easter storms and hurricanes. The effects of storms and hurricanes can be extreme, with immediate impact on coastal geomorphology and water circulation, which is integral to estuarine function and consequently to ecosystem services provision. Here we present the results of a natural estuarine-scale experiment on the effects of changes in coastal geomorphology on hydrodynamics and aquaculture production. A bay in Prince Edward Island Canada was altered when a nor'easter storm eroded a second tidal inlet through a barrier island. Previous field and modelling studies allowed a comparison of pre- and post-storm circulation, food limitation by cultured mussels, and aquaculture harvest. Dramatic increases in mussel production occurred in the year following the opening of the new inlet. Model studies showed that post-storm circulation reduced food limitation for cultured mussels allowing greater growth. Climate change is expected to have severe effects on the delivery of marine ecosystem services to human populations, by changing the underlying physical-biological coupling inherent to their functioning.

Reviews in Aquaculture, 2012

Integrated multi-trophic aquaculture (IMTA) seeks to biodiversify fed aquaculture (e.g. finfish o... more Integrated multi-trophic aquaculture (IMTA) seeks to biodiversify fed aquaculture (e.g. finfish or shrimps) with extractive aquaculture, recapturing the inorganic (e.g. seaweeds) and organic (e.g. suspension-and deposit-feeders) nutrients from fed aquaculture for their growth. The combination fed ⁄ extractive aquaculture aims to engineer food production systems providing both biomitigative services to the ecosystem and improved economic farm output through the co-cultivation of complementary species. Major rethinking is needed regarding the definition of an 'aquaculture farm' and how it works within an ecosystem. The economic values of the environmental ⁄ societal services of extractive species should be recognized and accounted for in the evaluation of the full value of these IMTA components. Seaweeds and invertebrates produced in IMTA systems should be considered as candidates for nutrient ⁄ carbon trading credits. While organic loading from aquaculture has been associated with localized benthic impacts, there have also been occurrences of increased biodiversity and abundance of wild species in response to moderate nutrient enrichment and the use of infrastructures as substrates. To develop efficient food production systems, it will be important to understand and use the duality of nutrients (essential when limiting ⁄ polluting when in excess) to engineer systems producing them in moderation so that they can be partially recaptured while maintaining their concentrations optimal for healthy and productive ecosystems. Measures of species diversity, colonization rates, abundance, growth and ecosystem functions with respect to nutrient partitioning and recycling, species interactions and control of diseases could represent valid indicators for the development of robust performance metrics.

Estuaries, 2004

Water renewal in semi-enclosed coastal areas is crucial for the supply of oxygen and seston and f... more Water renewal in semi-enclosed coastal areas is crucial for the supply of oxygen and seston and for the removal of organic loadings from finfish or shellfish aquaculture sites. Water renewal depends on hydrodynamic processes and can have a complex spatial distribution due to irregular topographic features. This study describes some physical oceanography observations gathered in the Richibucto estuary, New Brunswick, Canada, and provides an estimate of the spatial distribution of water renewal in the North Arm, a location in the estuary where the largest American oyster (Crassostrea virginica) aquaculture operation in eastern Canada is located. The estuary changes from a well mixed estuary to a partially stratified estuary depending on runoff conditions. Tides are mixed but mainly diurnal due to the nearby presence of the second M 2 amphidromic point in the Gulf of St. Lawrence. Tidal amplitudes vary from 0.3 to 0.6 m and show a slight increase some 35 km upstream. Currents in the main channel can reach over 0.60 m s Ϫ1 during ebb and 0.3 m s Ϫ1 during flood, with a slack water period of approximately 8 h. Low frequency sea level fluctuations have a range of 0.5 m at the mouth and are coherent within the estuary. Hydrodynamic and advection-dispersion models are used to calculate the spatial distribution of the local renewal time (LRT) in the North Arm for high and low freshwater discharge conditions, using the dissolved tracer method. Results show that the LRT varies from less than 5 d at the downstream end of the North Arm to over 100 d further upstream. When averaged over the entire North Arm, the integral renewal time (IRT) is estimated to vary only from 8 to 21 d depending on the season. The LRT and IRT estimates are major improvements over conventional renewal estimates using tidal prism methods.

Ecological Modelling, 2007

Aquaculture Ecosystem model Carrying-capacity Magdalen Islands a

Journal of Marine Systems, 2014

ABSTRACT The success of shellfish aquaculture as well as its sustainability relies on adjusting t... more ABSTRACT The success of shellfish aquaculture as well as its sustainability relies on adjusting the cultured biomass to local ecosystem characteristics. Oyster filter-feeding activity can control phytoplankton concentration, reaching severe depletion in extreme situations, which can threaten ecological sustainability. A better understanding of oyster-phytoplankton interaction can be achieved by constructing ecosystem models. In this study, a fully-spatial hydrodynamic biogeochemical model has been constructed for the Richibucto Estuary in order to explore oyster carrying capacity. The biogeochemical model was based on a classical nutrient–phytoplankton–zooplankton–detritus (NPZD) approach with the addition of a Dynamic Energy Budget (DEB) model of Crassostrea virginica. Natural variation of chlorophyll was used as a benchmark to define a sustainability threshold based on a resilience framework. Scenario building was applied to explore carrying capacity of the system. However, the complex geomorphology of the Richibucto Estuary and the associated heterogeneity in water residence time, which is integral in estuarine functioning, indicates that the carrying capacity assessment must be specific for each area of the system. The model outcomes suggest that water residence time plays a key role in carrying capacity estimations through its influence on ecological resistance.

Ecological Indicators, 2014

ABSTRACT The filtration activity of cultured mussels may exert a strong control on phytoplankton ... more ABSTRACT The filtration activity of cultured mussels may exert a strong control on phytoplankton populations. Given that phytoplankton constitutes the base of marine food webs, carrying capacity in shellfish aquaculture sites has been commonly studied in terms of phytoplankton depletion. However, spatial and temporal variability of phytoplankton concentration in coastal areas present a methodological constraint for using phytoplankton depletion as an indicator in monitoring programs, and necessitates intensive field campaigns. The main goal of this study is to explore the potential of different bivalve performance indices for use as alternatives to phytoplankton depletion as cost-effective indicators of carrying capacity. For that, a fully spatial hydrodynamic–biogeochemical coupled model of Tracadie Bay, an intensive mussel culture embayment located in Prince of Edward Island (Canada), has been constructed and scenario building has been used to explore the relationship between phytoplankton depletion and bivalve performance. Our underlying premise is that overstocking of bivalves leads to increased competition for food resources, i.e. phytoplankton, which may ultimately have a significant effect on bivalve growth rate and performance. Following this working hypothesis, the relationships among bay-scale phytoplankton depletion and three bivalve physiological indices, one static, condition index, and two dynamic, tissue mass and shell length growth rates, have been simulated. These three metrics present methodological advantages compared to phytoplankton depletion for incorporation into monitoring programs. Although significant correlations among phytoplankton depletion and the three physiological indices have been observed, shell length growth rate is shown as the most sensitive indicator of carrying capacity, followed by tissue mass growth rate and then by condition index. These results demonstrate the potentiality of using bivalve physiological measurements in monitoring programs as indicators of ecosystem status.

A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to exam... more A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to examine the impact of suspended mussel culture on phytoplankton biomass in Tracadie Bay, Prince Edward Island, Canada. Due to the extent of mussel culture there, we hypothesised that shellfish filtration would control the concentration and distribution of phytoplankton and other suspended particles in the bay. Circulation was delineated with a tidally-driven 2D numerical model and used to drive an ecosystem model with a focus on pelagic components including phytoplankton production, nutrients, detritus, and mussels. The benthos were treated as a sink. Nutrients and seston were forced by tidal exchange and river input, with phytoplankton additionally forced by light. Boundary conditions of seston and nutrients were derived from field studies with an emphasis on the contrast between spring (high river nutrients, low temperature) and summer (low river inputs and high temperatures). Model output was used to map phytoplankton carbon over the bay for each season and in the presence of mussels and river nutrient input. Results indicate severe depletion effects of mussel culture on overall phytoplankton biomass, but no spatial pattern that can be attributed to grazing alone. Primary production generated by nutrient-rich river water created a mid-bay spike in phytoplankton that dominated the spatial pattern of chlorophyll-based carbon. Model results were validated with surveys from a towed sensor array (Acrobat) that confirmed the river influence and indicated bay-wide depletion of 29% between high and low water. Our model results indicate that the farm-scale depletion emphasised in previous studies cannot simply be extrapolated to seston limitation at the ecosystem level.

A calibrated fine resolution physical-biogeochemical model coupled with a dynamic energy budget (... more A calibrated fine resolution physical-biogeochemical model coupled with a dynamic energy budget (DEB) is used to investigate the local and system scale interactions between a mussel farm and the receiving coastal ecosystem. Using a set of published parameters for the DEB, the coupled model reproduces quite accurately both the local mussel growth and its spatial distribution over the farm area. Mussel related process rates are also well reproduced, allowing the study of mussel/environment interactions. Results show the local importance of cultured mussels in the cycling of nitrogen within the cultivation area. Despite the strongly reduced influence exerted by the mussel farm at the scale of the entire system, the culture activity still has the ability to alter the structure of Grande-Entrée lagoon's ecosystem. The coupled model results show that the mussel stock could be greatly increased before reaching the maximum production capacity of Grande-Entrée lagoon. However, when the ecological aspect is accounted for, using model results along with objective criteria such as the depletion footprint curve, the overall carrying capacity of Grande-Entrée lagoon must be significantly reduced. The coupled fine scale numerical model developed for this study gives the opportunity to assess the ecological carrying capacity of a coastal region for shellfish culture accounting for both local and system scale processes.

Tidal and wind renewal of water in the coastal zone is important in the transport of natural and ... more Tidal and wind renewal of water in the coastal zone is important in the transport of natural and anthropogenic particles and solutes. Models of these systems require detailed parameterization of exchange processes. Renewal of seston food supplies for cultured suspension-feeding shellfish is one such application. This study examines the sensitivity of food limitation estimates of an inshore region for shellfish aquaculture to the methods used in calculating the region's water renewal time. The region is the Indian Island oyster culture site in the Richibucto estuary, New Brunswick, Canada, and the methods considered are the volume advection and the local conservative tracer methods. In both cases, water renewal is calculated from field time series measurements of hydrodynamic parameters and outputs of coupled hydrodynamic and advection-dispersion three-dimensional (3D) numerical models. A comparison of oyster food demand and supply is then made to estimate the food limitation risk in the region using field measurements of biological parameters and the renewal times previously estimated. It is found that water renewal by tides is efficient but it can be cancelled altogether by meteorological forcing. Contrary to the conservative tracer method, the tidal prism method proves to be inadequate when estimating water renewal in estuarine tidal channels and was replaced by another volume advection method. The preliminary results obtained using the depletion index estimates indicate that the Indian Island region could sustain a high oyster biomass. These simple calculations also show the importance of water renewal estimate for carrying capacity studies. Hence, the tidal prism method or other volume advection estimates should be used with great caution or be avoided altogether in such studies. D

Finite element numerical modelling based on field data is used to study the tidal and tidally ind... more Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled ''restricted'' and ''leaky'' coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a ''restricted'' nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a ''leaky'' nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.

Estuarine, Coastal and Shelf Science, 2008

Finite element numerical modelling based on field data is used to study the tidal and tidally ind... more Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled ''restricted'' and ''leaky'' coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a ''restricted'' nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a ''leaky'' nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.

Aquacultural Engineering, 2014

Benthic impacts that may ultimately result from further intensification of suspended oyster cultu... more Benthic impacts that may ultimately result from further intensification of suspended oyster culture in eastern Canada were proactively investigated. Eastern oysters (Crassostrea virginica) were placed in experimental floating rafts (12.1 m 2 ) designed to hold densities 2-3 times higher than those presently found in floating bag operations. Experimental rafts were moored in shallow water (1-2 m) at fixed positions where no aquaculture had been practiced. A biodeposition model predicted that the majority of feces released by suspended oysters would fall onto the seabed area directly beneath the rafts. However, field measurements over a 132 d period indicated that the fecal deposition from the highly aggregated oysters was not reflected in higher organic sedimentation rates or seabed sulfide levels. Rather, the proportion of organic matter in the top sediment layer was significantly lower in samples collected underneath rafts (5.1 ± 1.5%) than in samples taken at reference sites (10.5 ± 3.2%). This same pattern was observed for control rafts holding shells only. It is suggested that the floating raft impacted local hydrodynamic processes, forcing water to move underneath the structure, thereby amplifying turbulence and resuspending low shear strength particles such as biodeposits.

Aquaculture

Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, m... more Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, must compete for food resources with three invasive tunicates (Botrylloides violaceus, Ciona intestinalis and Styela clava). Clearance rates determined for each species were used to calculate clearance rate per unit lease area (CRArea) for various fouling scenarios. CRArea for mussels alone was estimated at 338 ± 20 l h− 1 m− 2. Surprisingly, the size of the mussels under cultivation had no significant effect on estimates of CRArea, due to self-thinning processes that gradually eliminated 89% of the seed mussels over the 2-year production cycle. CRArea was also unaffected by the presence of the fouling colonial tunicate B. violaceus. In contrast, the presence of the solitary tunicate C. intestinalis or S. clava significantly increased CRArea by 30—47% compared to non-infested scenarios, even with control/treatment measures in effect. Size fractionation of the available phytoplankton resou...

Aquaculture

Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, m... more Mussels (Mytilus edulis) cultivated on the eastern coast of Prince Edward Island (PEI), Canada, must compete for food resources with three invasive tunicates (Botrylloides violaceus, Ciona intestinalis and Styela clava). Clearance rates determined for each species were used to calculate clearance rate per unit lease area (CRArea) for various fouling scenarios. CRArea for mussels alone was estimated at 338 ± 20 l h− 1 m− 2. Surprisingly, the size of the mussels under cultivation had no significant effect on estimates of CRArea, due to self-thinning processes that gradually eliminated 89% of the seed mussels over the 2-year production cycle. CRArea was also unaffected by the presence of the fouling colonial tunicate B. violaceus. In contrast, the presence of the solitary tunicate C. intestinalis or S. clava significantly increased CRArea by 30—47% compared to non-infested scenarios, even with control/treatment measures in effect. Size fractionation of the available phytoplankton resou...

Journal of Marine …, 2008

A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to exam... more A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to examine the impact of suspended mussel culture on phytoplankton biomass in Tracadie Bay, Prince Edward Island, Canada. Due to the extent of mussel culture there, we hypothesised that shellfish filtration would control the concentration and distribution of phytoplankton and other suspended particles in the bay. Circulation was delineated with a tidally-driven 2D numerical model and used to drive an ecosystem model with a focus on pelagic components including phytoplankton production, nutrients, detritus, and mussels. The benthos were treated as a sink. Nutrients and seston were forced by tidal exchange and river input, with phytoplankton additionally forced by light. Boundary conditions of seston and nutrients were derived from field studies with an emphasis on the contrast between spring (high river nutrients, low temperature) and summer (low river inputs and high temperatures). Model output was used to map phytoplankton carbon over the bay for each season and in the presence of mussels and river nutrient input. Results indicate severe depletion effects of mussel culture on overall phytoplankton biomass, but no spatial pattern that can be attributed to grazing alone. Primary production generated by nutrient-rich river water created a mid-bay spike in phytoplankton that dominated the spatial pattern of chlorophyll-based carbon. Model results were validated with surveys from a towed sensor array (Acrobat) that confirmed the river influence and indicated bay-wide depletion of 29% between high and low water. Our model results indicate that the farm-scale depletion emphasised in previous studies cannot simply be extrapolated to seston limitation at the ecosystem level.

The Canadian Geographer / Le Géographe canadien, 2015

Marine Pollution Bulletin, 2015

A moratorium on further bivalve leasing was established in 1999-2000 in Prince Edward Island (Can... more A moratorium on further bivalve leasing was established in 1999-2000 in Prince Edward Island (Canada). Recently, a marine spatial planning process was initiated explore potential mussel culture expansion in Malpeque Bay. This study focuses on the effects of a projected expansion scenario on productivity of existing leases and available suspended food resources. The aim is to provide a robust scientific assessment using available datasets and three modelling approaches ranging in complexity: (1) a connectivity analysis among culture areas; (2) a scenario analysis of organic seston dynamics based on a simplified biogeochemical model; and (3) a scenario analysis of phytoplankton dynamics based on an ecosystem model. These complementary approaches suggest (1) new leases can affect existing culture both through direct connectivity and through bay-scale effects driven by the overall increase in mussel biomass, and (2) a net reduction of phytoplankton within the bounds of its natural variation in the area.

Marine Ecology Progress Series, 2015

The role of bivalve mariculture in the CO 2 cycle has been commonly evaluated as the balance betw... more The role of bivalve mariculture in the CO 2 cycle has been commonly evaluated as the balance between respiration, shell calcium carbonate sequestration and CO 2 release during biogenic calcification. However, this approach neglects the ecosystem implications of cultivating bivalves at high densities, e.g. the impact on phytoplankton dynamics and benthic−pelagic coupling, which can significantly contribute to the CO 2 cycle. Therefore, an ecosystem approach that accounts for the trophic interactions of bivalve aquaculture, including dissolved and particulate organic and inorganic carbon cycling, is needed to provide a rigorous assessment of the role of bivalve mariculture in the CO 2 cycle. On the other hand, the discussion about the inclusion of shells of cultured bivalves into the carbon trading system should be framed within the context of ecosystem goods and services. Humans culture bivalves with the aim of producing food, not sequestering CO 2 in their shells, therefore the main ecosystem good provided by bivalve aquaculture is meat production, and shells should be considered as by-products of this human activity. This reasoning provides justification for dividing up respired CO 2 between meat and shell when constructing a specific bivalve CO 2 budget for potential use of bivalve shells in the carbon trading system. Thus, an integrated ecosystem approach, as well as an understanding of the ecosystems goods and services of bivalve aquaculture, are 2 essential requisites for providing a reliable assessment of the role of bivalve shells in the CO 2 cycle.

Earth's Future, 2014

ABSTRACT Estuarine ecosystems are highly sensitive to projected effects of climate change such as... more ABSTRACT Estuarine ecosystems are highly sensitive to projected effects of climate change such as ocean warming, acidification and sea level rise but also to the incidence of nor'easter storms and hurricanes. The effects of storms and hurricanes can be extreme, with immediate impact on coastal geomorphology and water circulation, which is integral to estuarine function and consequently to ecosystem services provision. Here we present the results of a natural estuarine-scale experiment on the effects of changes in coastal geomorphology on hydrodynamics and aquaculture production. A bay in Prince Edward Island Canada was altered when a nor'easter storm eroded a second tidal inlet through a barrier island. Previous field and modelling studies allowed a comparison of pre- and post-storm circulation, food limitation by cultured mussels, and aquaculture harvest. Dramatic increases in mussel production occurred in the year following the opening of the new inlet. Model studies showed that post-storm circulation reduced food limitation for cultured mussels allowing greater growth. Climate change is expected to have severe effects on the delivery of marine ecosystem services to human populations, by changing the underlying physical-biological coupling inherent to their functioning.

Reviews in Aquaculture, 2012

Integrated multi-trophic aquaculture (IMTA) seeks to biodiversify fed aquaculture (e.g. finfish o... more Integrated multi-trophic aquaculture (IMTA) seeks to biodiversify fed aquaculture (e.g. finfish or shrimps) with extractive aquaculture, recapturing the inorganic (e.g. seaweeds) and organic (e.g. suspension-and deposit-feeders) nutrients from fed aquaculture for their growth. The combination fed ⁄ extractive aquaculture aims to engineer food production systems providing both biomitigative services to the ecosystem and improved economic farm output through the co-cultivation of complementary species. Major rethinking is needed regarding the definition of an 'aquaculture farm' and how it works within an ecosystem. The economic values of the environmental ⁄ societal services of extractive species should be recognized and accounted for in the evaluation of the full value of these IMTA components. Seaweeds and invertebrates produced in IMTA systems should be considered as candidates for nutrient ⁄ carbon trading credits. While organic loading from aquaculture has been associated with localized benthic impacts, there have also been occurrences of increased biodiversity and abundance of wild species in response to moderate nutrient enrichment and the use of infrastructures as substrates. To develop efficient food production systems, it will be important to understand and use the duality of nutrients (essential when limiting ⁄ polluting when in excess) to engineer systems producing them in moderation so that they can be partially recaptured while maintaining their concentrations optimal for healthy and productive ecosystems. Measures of species diversity, colonization rates, abundance, growth and ecosystem functions with respect to nutrient partitioning and recycling, species interactions and control of diseases could represent valid indicators for the development of robust performance metrics.

Estuaries, 2004

Water renewal in semi-enclosed coastal areas is crucial for the supply of oxygen and seston and f... more Water renewal in semi-enclosed coastal areas is crucial for the supply of oxygen and seston and for the removal of organic loadings from finfish or shellfish aquaculture sites. Water renewal depends on hydrodynamic processes and can have a complex spatial distribution due to irregular topographic features. This study describes some physical oceanography observations gathered in the Richibucto estuary, New Brunswick, Canada, and provides an estimate of the spatial distribution of water renewal in the North Arm, a location in the estuary where the largest American oyster (Crassostrea virginica) aquaculture operation in eastern Canada is located. The estuary changes from a well mixed estuary to a partially stratified estuary depending on runoff conditions. Tides are mixed but mainly diurnal due to the nearby presence of the second M 2 amphidromic point in the Gulf of St. Lawrence. Tidal amplitudes vary from 0.3 to 0.6 m and show a slight increase some 35 km upstream. Currents in the main channel can reach over 0.60 m s Ϫ1 during ebb and 0.3 m s Ϫ1 during flood, with a slack water period of approximately 8 h. Low frequency sea level fluctuations have a range of 0.5 m at the mouth and are coherent within the estuary. Hydrodynamic and advection-dispersion models are used to calculate the spatial distribution of the local renewal time (LRT) in the North Arm for high and low freshwater discharge conditions, using the dissolved tracer method. Results show that the LRT varies from less than 5 d at the downstream end of the North Arm to over 100 d further upstream. When averaged over the entire North Arm, the integral renewal time (IRT) is estimated to vary only from 8 to 21 d depending on the season. The LRT and IRT estimates are major improvements over conventional renewal estimates using tidal prism methods.

Ecological Modelling, 2007

Aquaculture Ecosystem model Carrying-capacity Magdalen Islands a

Journal of Marine Systems, 2014

ABSTRACT The success of shellfish aquaculture as well as its sustainability relies on adjusting t... more ABSTRACT The success of shellfish aquaculture as well as its sustainability relies on adjusting the cultured biomass to local ecosystem characteristics. Oyster filter-feeding activity can control phytoplankton concentration, reaching severe depletion in extreme situations, which can threaten ecological sustainability. A better understanding of oyster-phytoplankton interaction can be achieved by constructing ecosystem models. In this study, a fully-spatial hydrodynamic biogeochemical model has been constructed for the Richibucto Estuary in order to explore oyster carrying capacity. The biogeochemical model was based on a classical nutrient–phytoplankton–zooplankton–detritus (NPZD) approach with the addition of a Dynamic Energy Budget (DEB) model of Crassostrea virginica. Natural variation of chlorophyll was used as a benchmark to define a sustainability threshold based on a resilience framework. Scenario building was applied to explore carrying capacity of the system. However, the complex geomorphology of the Richibucto Estuary and the associated heterogeneity in water residence time, which is integral in estuarine functioning, indicates that the carrying capacity assessment must be specific for each area of the system. The model outcomes suggest that water residence time plays a key role in carrying capacity estimations through its influence on ecological resistance.

Ecological Indicators, 2014

ABSTRACT The filtration activity of cultured mussels may exert a strong control on phytoplankton ... more ABSTRACT The filtration activity of cultured mussels may exert a strong control on phytoplankton populations. Given that phytoplankton constitutes the base of marine food webs, carrying capacity in shellfish aquaculture sites has been commonly studied in terms of phytoplankton depletion. However, spatial and temporal variability of phytoplankton concentration in coastal areas present a methodological constraint for using phytoplankton depletion as an indicator in monitoring programs, and necessitates intensive field campaigns. The main goal of this study is to explore the potential of different bivalve performance indices for use as alternatives to phytoplankton depletion as cost-effective indicators of carrying capacity. For that, a fully spatial hydrodynamic–biogeochemical coupled model of Tracadie Bay, an intensive mussel culture embayment located in Prince of Edward Island (Canada), has been constructed and scenario building has been used to explore the relationship between phytoplankton depletion and bivalve performance. Our underlying premise is that overstocking of bivalves leads to increased competition for food resources, i.e. phytoplankton, which may ultimately have a significant effect on bivalve growth rate and performance. Following this working hypothesis, the relationships among bay-scale phytoplankton depletion and three bivalve physiological indices, one static, condition index, and two dynamic, tissue mass and shell length growth rates, have been simulated. These three metrics present methodological advantages compared to phytoplankton depletion for incorporation into monitoring programs. Although significant correlations among phytoplankton depletion and the three physiological indices have been observed, shell length growth rate is shown as the most sensitive indicator of carrying capacity, followed by tissue mass growth rate and then by condition index. These results demonstrate the potentiality of using bivalve physiological measurements in monitoring programs as indicators of ecosystem status.

A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to exam... more A fully-coupled biological-physical-chemical model of a coastal ecosystem was constructed to examine the impact of suspended mussel culture on phytoplankton biomass in Tracadie Bay, Prince Edward Island, Canada. Due to the extent of mussel culture there, we hypothesised that shellfish filtration would control the concentration and distribution of phytoplankton and other suspended particles in the bay. Circulation was delineated with a tidally-driven 2D numerical model and used to drive an ecosystem model with a focus on pelagic components including phytoplankton production, nutrients, detritus, and mussels. The benthos were treated as a sink. Nutrients and seston were forced by tidal exchange and river input, with phytoplankton additionally forced by light. Boundary conditions of seston and nutrients were derived from field studies with an emphasis on the contrast between spring (high river nutrients, low temperature) and summer (low river inputs and high temperatures). Model output was used to map phytoplankton carbon over the bay for each season and in the presence of mussels and river nutrient input. Results indicate severe depletion effects of mussel culture on overall phytoplankton biomass, but no spatial pattern that can be attributed to grazing alone. Primary production generated by nutrient-rich river water created a mid-bay spike in phytoplankton that dominated the spatial pattern of chlorophyll-based carbon. Model results were validated with surveys from a towed sensor array (Acrobat) that confirmed the river influence and indicated bay-wide depletion of 29% between high and low water. Our model results indicate that the farm-scale depletion emphasised in previous studies cannot simply be extrapolated to seston limitation at the ecosystem level.

A calibrated fine resolution physical-biogeochemical model coupled with a dynamic energy budget (... more A calibrated fine resolution physical-biogeochemical model coupled with a dynamic energy budget (DEB) is used to investigate the local and system scale interactions between a mussel farm and the receiving coastal ecosystem. Using a set of published parameters for the DEB, the coupled model reproduces quite accurately both the local mussel growth and its spatial distribution over the farm area. Mussel related process rates are also well reproduced, allowing the study of mussel/environment interactions. Results show the local importance of cultured mussels in the cycling of nitrogen within the cultivation area. Despite the strongly reduced influence exerted by the mussel farm at the scale of the entire system, the culture activity still has the ability to alter the structure of Grande-Entrée lagoon's ecosystem. The coupled model results show that the mussel stock could be greatly increased before reaching the maximum production capacity of Grande-Entrée lagoon. However, when the ecological aspect is accounted for, using model results along with objective criteria such as the depletion footprint curve, the overall carrying capacity of Grande-Entrée lagoon must be significantly reduced. The coupled fine scale numerical model developed for this study gives the opportunity to assess the ecological carrying capacity of a coastal region for shellfish culture accounting for both local and system scale processes.

Tidal and wind renewal of water in the coastal zone is important in the transport of natural and ... more Tidal and wind renewal of water in the coastal zone is important in the transport of natural and anthropogenic particles and solutes. Models of these systems require detailed parameterization of exchange processes. Renewal of seston food supplies for cultured suspension-feeding shellfish is one such application. This study examines the sensitivity of food limitation estimates of an inshore region for shellfish aquaculture to the methods used in calculating the region's water renewal time. The region is the Indian Island oyster culture site in the Richibucto estuary, New Brunswick, Canada, and the methods considered are the volume advection and the local conservative tracer methods. In both cases, water renewal is calculated from field time series measurements of hydrodynamic parameters and outputs of coupled hydrodynamic and advection-dispersion three-dimensional (3D) numerical models. A comparison of oyster food demand and supply is then made to estimate the food limitation risk in the region using field measurements of biological parameters and the renewal times previously estimated. It is found that water renewal by tides is efficient but it can be cancelled altogether by meteorological forcing. Contrary to the conservative tracer method, the tidal prism method proves to be inadequate when estimating water renewal in estuarine tidal channels and was replaced by another volume advection method. The preliminary results obtained using the depletion index estimates indicate that the Indian Island region could sustain a high oyster biomass. These simple calculations also show the importance of water renewal estimate for carrying capacity studies. Hence, the tidal prism method or other volume advection estimates should be used with great caution or be avoided altogether in such studies. D

Finite element numerical modelling based on field data is used to study the tidal and tidally ind... more Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled ''restricted'' and ''leaky'' coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a ''restricted'' nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a ''leaky'' nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.

Estuarine, Coastal and Shelf Science, 2008

Finite element numerical modelling based on field data is used to study the tidal and tidally ind... more Finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of a coupled ''restricted'' and ''leaky'' coastal lagoon system located in the Magdalen Islands, Gulf of Saint-Lawrence. Havre-aux-Maisons Lagoon (HML) is of a ''restricted'' nature with a neutral inlet in terms of tidal asymmetry. Grande-Entrée Lagoon (GEL) is of a ''leaky'' nature with a marked ebb dominance at the inlet due to direct interactions between the main astronomical tidal constituents. The imbalance caused by the different tidal filtering characteristics of both inlets combines with the internal morphological asymmetries of the system to produce a residual throughflow from HML to GEL. The residual circulation is also characterized by strongest values at both inlets, very weak residual currents in HML deep basin and a dipole of residual eddies over the deeper areas of GEL. Further investigations including numerical tracer experiments will be necessary to achieve a full understanding of the long term circulation of this lagoonal system.

Aquacultural Engineering, 2014

Benthic impacts that may ultimately result from further intensification of suspended oyster cultu... more Benthic impacts that may ultimately result from further intensification of suspended oyster culture in eastern Canada were proactively investigated. Eastern oysters (Crassostrea virginica) were placed in experimental floating rafts (12.1 m 2 ) designed to hold densities 2-3 times higher than those presently found in floating bag operations. Experimental rafts were moored in shallow water (1-2 m) at fixed positions where no aquaculture had been practiced. A biodeposition model predicted that the majority of feces released by suspended oysters would fall onto the seabed area directly beneath the rafts. However, field measurements over a 132 d period indicated that the fecal deposition from the highly aggregated oysters was not reflected in higher organic sedimentation rates or seabed sulfide levels. Rather, the proportion of organic matter in the top sediment layer was significantly lower in samples collected underneath rafts (5.1 ± 1.5%) than in samples taken at reference sites (10.5 ± 3.2%). This same pattern was observed for control rafts holding shells only. It is suggested that the floating raft impacted local hydrodynamic processes, forcing water to move underneath the structure, thereby amplifying turbulence and resuspending low shear strength particles such as biodeposits.