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It is important to be able to predict the growth of filter-feeding bivalves, as they grow in dense populations both naturally and for commercial production. To understand the growth of bivalves it is necessary to have a mechanistic understanding of how they acquire energy through ingestion. This study was designed to understand if capture efficiency (CE), a primary step in ingestion for filter-feeders, is variable in the blue mussel Mytilus edulis. CE was measured using natural seston in 3 populations of naturally occurring M. edulis and within 2 populations along a fjord gradient. Differences in CE were found within a single population as well as along the fjord gradient. To determine if these differences were driven by short- or long-term changes, a single population of mussels was reciprocally transplanted between 2 locations along a fjord. This study is the first time CE has been measured within a population of M. edulis using a regional transplant experiment. Results showed that CE may vary between populations and change within populations, indicating that CE seems primarily driven by environmental cues. Pumping and overall ingestion rates differed between populations and varied within populations. For widely distributed species in changing environments, it is increasingly relevant to understand the limits of plasticity of specific traits to be able to predict their growth, survival, and distribution. Here, we aimed to provide a more mechanistic description of CE, pumping rate, and overall ingestion in M. edulis.

Climate change, observed as warming sea surface temperatures, is expected to impact the Eastern coast of Canada at a rate higher than the global average. Changes in marine abiotic conditions will impact the growth and performance of economically important bivalve species, creating an increasingly uncertain future for the bivalve aquaculture industry. Site-selection for new farms, and the management of extant ones could mitigate these potential impacts, but the implementation of this planning process is dependent on stakeholder support and engagement. Recognizing the importance of stakeholder input in management decisions, this research analyzed the perspectives of farmers, researchers, and managers from Nova Scotia (NS) and Prince Edward Island (PEI) on the relationship between climate change and bivalve aquaculture. Stakeholder perspectives were analyzed using a semi-quantitative interview method (Q methodology). These perspectives indicated the need for a higher level of integration both between stakeholder groups, namely farmers and managers, and management tools and climate change. Increased understanding between farmers and managers could be achieved through the use of researchers as knowledge brokers, collaborating and communicating with both groups. Making use of management tools, such as the ecosystem approach to aquaculture, required insurance, and adaptive management, governmental bodies on both a federal and provincial level can act as channels by which uncertainty generated by climate change can be further reduced. In summary, stakeholder perception can be used by marine planners to adapt to these foreseen changes, and to promote the expansion of this industry.

16 pages, 5 figures, 2 tables, Sustained 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 processes, This 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.

Aquaculture for finfish, bivalves, and seaweed is an important and growing food producing sector globally. However, culturing of species in the marine environment implies multiple interactions between farmed species and their environment. This has led to concerns over the ecological effects of aquaculture, which include benthic organic loading, changes to water quality, habitat modification, disease spread, and introduction of exotic or invasive species, interaction with wild species, coastal eutrophication, and marine litter. Over the years, governments and international organizations have recognized the need to identify, mitigate, and reduce these ecological effects. The Food and Agriculture Organization of the United Nations proposes an Ecosystem Approach to Aquaculture (EAA), which implies recognizing its effects at multiple spatial scales, including near-field effect (farm scale) and far-field (bay scale and global scale) effect. This chapter reviews ecological effects of finfish, bivalve, and seaweed aquaculture in marine coastal waters, and describes the mitigation efforts currently used to improve its sustainable management.

Macroalgae can incorporate the isotopic signature (δ15N) of their external environment and be used as ‘bioindicators’ to map and identify between multiple sources of anthropogenic nitrogen. However, evidence suggests that the isotopic signature of their tissues can also be influenced by a range of other factors, which could confound their use as a monitoring tool. Hence, this study aimed to better understand the factors affecting macroalgae isotopic signatures, using Chondrus crispus as a model species. This was achieved by exposing C. crispus to 15N-enriched NO3− and/or NH4+ at varying concentrations, temperatures and incubation times under controlled laboratory conditions. Longer incubation times promoted macroalgae δ15N values closer to that of the external nitrogen source. However, even after 28 days incubation, macroalgae δ15N was still >30‰ lower than the source. This suggests that the δ15N of C. crispus is unlikely to reach isotopic equilibrium with its external environment within a time frame that is feasible for most field studies. However, C. crispus can be used to highlight relative isotopic differences between sources even at very low nitrogen concentrations (

Macroalgal blooms in eutrophic coastal waters around the globe constitute a rising issue for ecosystems and economic activities. Sometimes leading to anoxic events, a better understanding of its growth dynamics is necessary to develop mitigation strategies and inform policies on nutrient runoff management. The development of a Dynamic Energy Budget (DEB) model for the sea lettuce, Ulva lactuca, provides a generic mechanistic description of energy and matter fluxes within the macroalgae and between macroalgae and the environment. Forcing variables consist of seawater temperature, light intensity, and seawater concentrations of dissolved carbon and nitrogen. The model includes a self-shading module for light reduction under heavy biomass and simulation outputs consist of (but are not limited to) total algae biomass, nutrient uptake (carbon and nitrogen), photosynthetic rate, and state of nutrient reserve. Model parameters were estimated using data-sets from the literature and laboratory experiments, then validated using an independent field study in two estuaries with contrasting nutrient loads that feed into Malpeque Bay, PEI (Canada). The validation step yielded accurate temporal predictions of sea lettuce biomass in both of these estuaries. These results indicate that the present mechanistic modelling approach for predicting sea lettuce dynamics captures salient patterns along a spectrum of nutrient loading and could therefore be of use for managing across diverse ecological conditions, which is particularly relevant for a widespread species like Ulva lactuca.

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. Modelling 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. Modelling 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.