Physiological differences between wild and cultured bivalves in Prince Edward Island, Canada

Bivalve culture in Canada increased by 25% from 2000 to 2016. In Prince Edward Island (PEI), bivalves are cultivated in bays and estuaries and there is limited space for further aquaculture expansion. Thus, there is merit in developing a numerical model determining the abundance of bivalve populations in relation to their food availability in order to assess the carrying capacity of shellfish growing areas. This modelling will take into account the different bivalve species present in the bay, as the cultivated Mytilus edulis and Crassostrea virginica and wild, M. edulis, C. virginica, Mya arenaria and Mercenaria mercenaria. As a first step toward a modelling goal, this study compared the physiological differences of the 6 bivalve groups. Three physiological parameters were measured: clearance rate, oxygen consumption and assimilation to determine the energy budget or scope for growth (SFG). These measurements were carried out on individuals contained in metabolic chamber at summer and autumn temperatures (20 and 8 °C, respectively). Our results show that M. edulis is best adapted to these temperature in PEI as it maintains high SFG at both temperatures. For C. virginica and M. arenaria, high physiological parameters under summer conditions were observed, followed by a decrease in autumn. For M. mercenaria rates were low at both temperatures indicating a persistently low growth potential. These results demonstrate the adaptive physiological capacity of each species and provide insight into the underlying reasons some species such as C. virginica and M. mercenaria are at their northern distribution limit in the Gulf of St. Lawrence. Finally, no differences in the SFG between cultivated and wild bivalves have been observed. These results are discussed within the context of estimating the impact of each bivalve group in bays environment from PEI and particularly on food availability

Revisiting ecological carrying capacity indices for bivalve culture

Ecological carrying capacity (ECC) indices for bivalve culture rely on key ecosystem turnover rates: 1. clearance time (CT), the time needed for the cultured bivalves to filter the entire bay volume; 2. renewal time (RT), the time required to replace the entire bay volume with external water; and 3. production time (PT), the time needed for phytoplankton biomass renewal via local primary production. These turnover rates are conceptually straightforward but lack measurement standardizations in the context of ECC assessments. This study compares simple turnover rate methods with more complex approaches designed to address key assumptions and improve accuracy. Method comparisons were performed across multiple embayments (systems) in Prince Edward Island, Canada. When crop aggregation and system-scale refiltration effects were considered, CT increased by a factor of 14 to 22 depending on the system and species under cultivation. Seasonal temperature considerations further impacted CT by a factor of 38 to 142. Regarding RT, validated hydrodynamic models and tidal prism models produced remarkably different outcomes; the tidal prism approach underestimated RT by 77–94% across the studied systems. Conversely, PT was unaffected by contrasting phytoplankton parameterization; pre-aquaculture (1969–1970) and contemporary (2011−2012) datasets led to similar PT outcomes. However, other metrics revealed a contemporary shift towards low phytoplankton biomass and smaller phytoplankton cells (picophytoplankton); these observations suggest that PT provides insufficient granularity regarding microalgae biomass replacement. Overall, the study rejects a common assumption that the bay-scale turnover rates serving the conventional CT/RT and CT/PT indices can be easily and accurately parameterized; these indices should be used cautiously in assessing the sustainability of farming activities.publishedVersio

The killer within: Endogenous bacteria accelerate oyster mortality during sustained anoxia

16 pages, 5 figures, 2 tablesSustained periods of anoxia, driven by eutrophication, threaten coastal marine systems and can lead to mass mortalities of even resilient animals such as bivalves. While mortality rates under anoxia are well-studied, the specific mechanism(s) of mortality are less clear. We used a suite of complementary techniques (LT50, histology, 16S rRNA amplicon sequencing, and valvometry) to show that the proliferation of anaerobic bacteria within eastern oysters (Crassostrea virginica) accelerates mortality rate under anoxic conditions. Manipulative laboratory experiments revealed that oyster survival under anoxic conditions was halved when bacteria were present compared to when they were excluded by the broad-spectrum antibiotic chloramphenicol. Histological assessments supported this mechanism and showed infiltration of bacteria in oysters that were not treated with antibiotics compared to a general lack of bacteria when oysters were treated with antibiotics. 16S rRNA amplicon sequencing failed to identify any particular genera of bacteria responsible for mortality, rather a diversity of endogenous anaerobic and/or sulfate-reducing bacteria were common among oysters. In addition, monitoring of oyster valve gaping behavior in the field revealed that oysters showed remarkable valve closure synchrony when first exposed to anoxia. However, oysters periodically opened throughout anoxia/hypoxia in both the lab and field, suggesting that the infiltration of exogenous bacteria from the environment may also influence mortality rates under natural settings. Coupled with previous studies, we posit that mass mortality events in a wide range of coastal bivalves are likely the result of co-morbidity from asphyxiation and bacterial processesThis study was funded by L'Étang Ruisseau Bar Ltd. in partnership with the Department of Fisheries and Oceans of Canada (Aquaculture Collaborative Research and Development Program, project 17-G-02 led by M.R.S.C.), a NSERC Discovery Grant to R.F. (RGPIN-2017-04294), and a Total Development Fund from the New Brunswick Department of Agriculture, Aquaculture and Fisheries to R.F.Peer reviewe

Ecosystem models of bivalve aquaculture: Implications for supporting goods and services

In this paper we focus on the role of ecosystem models in improving our understanding of the complex relationships between bivalve farming and the dynamics of lower trophic levels. To this aim, we review spatially explicit models of phytoplankton impacted by bivalve grazing and discuss the results of three case studies concerning an estuary (Baie des Veys, France), a bay, (Tracadie Bay, Prince Edward Island, Canada) and an open coastal area (Adriatic Sea, Emilia-Romagna coastal area, Italy). These models are intended to provide insight for aquaculture management, but their results also shed light on the spatial distribution of phytoplankton and environmental forcings of primary production. Even though new remote sensing technologies and remotely operated in situ sensors are likely to provide relevant data for assessing some the impacts of bivalve farming at an ecosystem scale, the results here summarized indicate that ecosystem modelling will remain the main tool for assessing ecological carrying capacity and providing management scenarios in the context of global drivers, such as climate change

Mytiliculture écosystème côtier : modélisation intégrée de leurs interactions dans la lagune de Grande-Entrée (Îles-de-la-Madeleine, Québec)

RÉSUMÉ : Dans le contexte de ressources marines surexploitées, l'aquaculture est appelée à fournir une part croissante des besoins nutritionnels de la population mondiale. De plus la culture de bivalves nécessite des techniques simples et des investissements restreints ce qui explique son essor actuel. Le développement de cette pratique majoritairement en zone côtière se heurte déjà à la question de la capacité de support des écosystèmes récepteurs. La complexité de ce type de problème, qui fait intervenir aussi bien l' hydrodynamique de la région concernée, les processus biogéochimiques régissant la production et la consommation de la nourriture des bivalves et l'écophysiologie de ces mollusques, nécessite le développement d'outils adaptés. La modélisation numérique fournit un cadre adéquat pour la réalisation de ce type d'études. L'objectif de cette thèse est de développer un outil numérique permettant d'intégrer les trois aspects du problème de capacité de support et de considérer dans une même étude les différentes échelles spatiales mises en jeu, ce qui faisait défaut jusqu'alors. Le modèle ainsi développé sera mis à contribution pour étudier les interactions entre l'élevage mytilicole et l'écosystème de la lagune de Grande-Entrée, Îles-de-Ia-Madeleine, Golfe du Saint-Laurent. Dans un premier temps, la modélisation numérique en éléments finis basée sur des données de terrain est utilisée pour étudier la dynamique des circulations tidale et résiduelle du système couplé de lagune "restreinte" et "coulante" des Îles-de-Ia-Madeleine. La lagune de Havre-aux-Maisons (HML) est considérée comme "restreinte" et présente une embouchure neutre en terme d 'asymétrie tidale. La lagune de Grande-Entrée (GEL) est, elle, de nature "coulante" avec une dominance de jusant bien marquée au niveau de son embouchure, due aux interactions directes entre les principales composantes astronomiques de la marée. Le déséquilibre causé par les différentes caractéristiques d'absorption de l'onde de marée des deux embouchures se combine avec l'asymétrie morphologique interne du système pour produire un flux résiduel de HML vers GEL. La circulation résiduelle est aussi caractérisée par de plus fortes valeurs aux deux embouchures, de très faibles courants résiduels dans le bassin profond de HML et un dipôle de tourbillons résiduels couvrant les zones profondes de GEL. Dans la deuxième partie de cette étude un modèle biogéochimique, couplé au moteur hydrodynamique mis au point précédemment, est développé pour étudier la dynamique de l'écosystème de la lagune Grande-Entrée, qui abrite un élevage commercial de moules. La calibration du modèle est basée sur la comparaison objective des résultats du modèle avec les observations récoltées lors d'une campagne d'échantillonnage sur le terrain, à la fois en terme de concentrations des variables d'état et de la magnitude des différents processus. Une analyse de sensibilité est ensuite réalisée pour tester les capacités prédictives du modèle. Les résultats du processus de calibration et de l'analyse de sensibilité établissent clairement la capacité du modèle à reproduire avec précision la dynamique de l'écosystème lagunaire, y compris les effets de l'élevage mytilicole. Cette dynamique se caractérise en été par la dominance des processus de recyclage parmi les mécanismes d'apport en azote et également par le rôle dominant du réseau microbien, en particulier le microzooplancton, dans la détermination du niveau de productivité de ce système. L'activité mytilicole à son stade actuel de développement ne semble pas exercer d'influences majeures sur la dynamique du système à l'échelle globale. Enfin, le modèle calibré physique-biogéochimique de la section précédente est amélioré par l'ajout d'un modèle écophysiologique de type budget d 'énergie dynamique (DEB) et est utilisé pour étudier les interactions entre la ferme mytilicole de GEL et l'écosystème côtier qui l'abrite, aussi bien à l'échelle locale qu 'à celle du système au complet. En utilisant un jeu de paramètres de la littérature pour le DEB, le modèle couplé reproduit assez précisément la croissance locale des moules ainsi que sa répartition spatiale sur toute la ferme. Les flux métaboliques des moules sont également bien reproduits, ce qui autorise l'étude des relations moules/environnement. Les résultats montrent l' importance des moules dans le cycle de l'azote à l'échelle locale dans la zone d'élevage. Malgré l'influence réduite qu'exerce la ferme mytilicole à l'échelle du système complet, elle possède toutefois la capacité de modifier la structure de l'écosystème de la lagune de Grande-Entrée. Selon les résultats du modèle couplé, le stock de moules en élevage pourrait être considérablement augmenté avant d 'atteindre la capacité de production maximale de la GEL. Toutefois, si l'aspect écologique est pris en compte les résultats obtenus utilisés conjointement avec des critères objectifs tels que les empreintes de déplétion, montrent que la capacité de support de la GEL est beaucoup plus restreinte. Cette estimation peut néanmoins être qualifiée de conservatrice puisqu'elle s'appuie uniquement sur la période estivale où l'influence des moules est maximale. L'outil numérique développé lors de ce doctorat offre la possibilité d 'estimer la capacité de support écologique d'une région côtière pour l'aquaculture de bivalves en incluant à la fois les processus à l'échelle locale et de toute la lagune. ABSTRACT : ln the context of over-exploited marine resources, aquaculture should provide an increasing part of the food demand worldwide. Thanks to the simple technical level and the low investments it requires, shellfish culture is developing rapidly. This development takes place mainly in coastal areas where it already raises the question of the carrying capacity of the receiving ecosystems. The complexity of su ch a problem, mixing aspects of the hydrodynamics of the system, the biogeochemical processes influencing the production and consumption of bivalve food and the ecophysiology of these molluscs, requires the set up of adequate tools. Nwnerical modelling provides the ideal framework for this kind of study. The main goal of the present thesis is to develop a numerical tool integrating the three aspects of the carrying capacity problem and to consider the diverse spatial scales involved, which is lacking from previous studies. The model will then be used to investigate the interactions between the mussel farm and the ecosystem of Grande-Entrée lagoon, Magdalen Islands, Gulf of Saint-Lawrence. In the first part of the work, finite element numerical modelling based on field data is used to study the tidal and tidally induced residual circulation dynamics of the coupled "restricted" and "Ieaky" coastal lagoon system of the Magdalen Islands. 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 internai 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. In the second step of the study, a biogeochemical model coupled to the hydrodynamic model of the previous section is developed to study the dynamics of GEL's ecosystem sheltering a commercial mussel aquaculture farm. The model calibration is based on the objective comparison of model results and observations from a field sampling pro gram both in terms of state variable concentrations and process rate magnitudes. A sensitivity analysis is th en carried out to test the predictive ability of the mode!. The results of both the calibration process and the sensitivity analysis strongly establish the capacity of the model to accurately reproduce the lagoon 's ecosystem dynamics, including the effects of cultured mussels. These dynamics are characterized in summer by the dominance of recycling processes among inorganic nitrogen input mechanisms and the dominant role of the microbial food web, especially the microzooplankton, in setting the productivity level of the system. The mussel culture activity in its present state does not seem to exert any major influence on the system dynamics at the global scale. Finally, the calibrated fine resolution physical-biogeochemical model is improved with the addition of a dynamic energy budget (DEB) and used to investigate the local and system scale interactions between the mussel farm and the receiving coastal ecosystem. Using a set of published parameters for the DEB, the coupled model reproduces both the local mussel growth and its spatial repartition over the farm area quite accurately. Mussel related process rates are also weil reproduced, allowing the study of musseVenvironment 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 resuIts show that the mussel stock could be greatly increased before reaching the maximum production capacity of GEL. 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 GEL must be significantly reduced. The coupled fine scale numerical model developed for this study gives the opportunity to assess the ecological carrying capa city of a coastal region for shellfish culture accounting for both local and system scale processes

Physiological differences between wild and cultured bivalves in Prince Edward Island, Canada

Bivalve culture in Canada increased by 25% from 2000 to 2016. In Prince Edward Island (PEI), bivalves are cultivated in bays and estuaries and there is limited space for further aquaculture expansion. Thus, there is merit in developing a numerical model determining the abundance of bivalve populations in relation to their food availability in order to assess the carrying capacity of shellfish growing areas. This modelling will take into account the different bivalve species present in the bay, as the cultivated Mytilus edulis and Crassostrea virginica and wild, M. edulis, C. virginica, Mya arenaria and Mercenaria mercenaria. As a first step toward a modelling goal, this study compared the physiological differences of the 6 bivalve groups. Three physiological parameters were measured: clearance rate, oxygen consumption and assimilation to determine the energy budget or scope for growth (SFG). These measurements were carried out on individuals contained in metabolic chamber at summer and autumn temperatures (20 and 8 °C, respectively). Our results show that M. edulis is best adapted to these temperature in PEI as it maintains high SFG at both temperatures. For C. virginica and M. arenaria, high physiological parameters under summer conditions were observed, followed by a decrease in autumn. For M. mercenaria rates were low at both temperatures indicating a persistently low growth potential. These results demonstrate the adaptive physiological capacity of each species and provide insight into the underlying reasons some species such as C. virginica and M. mercenaria are at their northern distribution limit in the Gulf of St. Lawrence. Finally, no differences in the SFG between cultivated and wild bivalves have been observed. These results are discussed within the context of estimating the impact of each bivalve group in bays environment from PEI and particularly on food availability

Informing Marine Spatial Planning (MSP) with numerical modelling: A case-study on shellfish aquaculture in Malpeque Bay (Eastern Canada)

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

Past, Present, and Future: Performance of Two Bivalve Species Under Changing Environmental Conditions

Globally, the production of marine bivalves has been steadily increasing over the past several decades. As the effects of human population growth are magnified, bivalves help provide food security as a source of inexpensive protein. However, as climate change alters sea surface temperatures (SST), the physiology, and thus the survival, growth, and distribution of bivalves are being altered. Challenges with managing bivalves may become more pronounced, as the uncertainty associated with climate change makes it difficult to predict future production levels. Modeling techniques, applied to both climate change and bivalve bioenergetics, can be used to predict and explore the impacts of changing ocean temperatures on bivalve physiology, and concomitantly on aquaculture production. This study coupled a previously established high resolution climate model and two dynamic energy budget models to explore the future growth and distribution of two economically and ecologically important species, the eastern oyster (Crassotrea virginica), and the blue mussel (Mytilus edulis) along the Atlantic coast of Canada. SST was extracted from the climate model and used as a forcing variable in the bioenergetic models. This approach was applied across three discreet time periods: the past (1986–1990), the present (2016–2020), and the future (2046–2050), thus permitting a comparison of bivalve performance under different temporal scenarios. Results show that the future growth is variable both spatially and interspecifically. Modeling outcomes suggest that warming ocean temperatures will cause an increase in growth rates of both species as a result of their ectothermic nature. However, as the thermal tolerance of C. virginica is higher than M. edulis, oysters will generally outperform mussels. The predicted effects of temperature on bivalve physiology also provided insight into vulnerabilities (e.g., mortality) under future SST scenarios. Such information is useful for adapting future management strategies for both farmed and wild shellfish. Although this study focused on a geographically specific area, the approach of coupling bioenergetic and climate models is valid for species and environments across the globe

Modeling the impact of hypoxia on the energy budget of Atlantic cod in two populations of the Gulf of Saint-Lawrence, Canada

International audienceLike many marine species around the globe, several stocks of Atlantic cod (Gadus morhua) live in increasingly hypoxic waters. In the Gulf of Saint Lawrence (GSL) in Canada, the deep channels traversing the semi-enclosed sea exhibit year-round hypoxia, identified as one of the limiting factor for the recovery of GSL cod in its northern part. While many individuals in the northern GSL are known to venture in deeper, warmer, and more hypoxic waters of the Gulf channels, those in the southern GSL live in a shallower, colder, and more oxygenated environment. In this study, we use the modeling framework of the Dynamic Energy Budget (DEB) theory to disentangle the effects of hypoxia, temperature and food on the life-history traits of these two populations of cod in the GSL. Following recent advances by Thomas et al. (2018, this issue) on the mechanisms for the effects of hypoxia within the context of DEB theory, we implemented a correction of ingestion depending on dissolved oxygen (DO) saturation. We successfully developed and validated a set of parameters for a GSL Atlantic cod DEB model. Using simulations of historical growth trajectories from 1990 until 2004 estimated from data collected through fisheries research surveys, we found that temperature explained about half (48%) of the difference in length and 59% of the difference in mass between the two populations. The remaining proportion was attributed to exposure to hypoxia and food input. We also used our model to explore scenarios of duration, frequency, and intensity of hypoxia on cod's life-history traits, which showed that decreasing DO linearly reduces growth and reproduction while young cod seem to avoid impairing conditions resulting in limiting effects on developmental stages

Ocean acidification and molluscan shell taphonomy: Can elevated seawater pCO2 influence taphonomy in a naticid predator–prey system?

The size and frequency of gastropod drill holes in shells of their prey are common indicators of predator-prey ecology in the fossil record. Taphonomic processes occurring after predation, however, can influence the preservation of shells in a given fossil assemblage and can thus influence ecological inferences based on preserved shells. To determine if ocean acidification (OA) has the capacity to influence prey shell taphonomy in a gastropod drilling predation system, we tested for effects of elevated pCO2 on dissolution rates, breakage force, and drill hole diameters in non-fragmented shells of two prey species of the cannibalistic naticid gastropod, Euspira heros. Drilled and non-drilled shells of Littorina littorea and E. heros were exposed to control (~300 μatm) and elevated (~800 and 4000 μatm) pCO2 treatments for five weeks. Dry shell weight and drill hole diameter (outer and inner) were recorded for individual shells before and after exposure; the force required for shell breakage was recorded at the end of the exposure period. Shell mass loss in 800 and 4000 μatm, respectively, were ~1 and 7% for E. heros, and ~0 and 4% for L. littorea, compared to ~0% in the control for both species. Shell breakage force was unaffected by elevated pCO2, but was affected by species and drill hole presence, with E. heros shells requiring a force of ~220 and 269 Newtons in drilled and non-drilled shells, respectively, compared to ~294 and 415 Newtons in L. littorea. At 4000 μatm, outer drill hole diameter significantly increased by ~12% for E. heros, while inner drill hole diameter significantly increased by ~13% in E. heros and ~10% in L. littorea. Ultimately, this study provides the first documentation of molluscan shell taphonomy in the context of OA for a gastropod drilling predation system and sets the stage for future research