Development of best practices for more holistic assessments of carrying capacity of aquaculture.

Carrying Capacity (CC) has emerged as a potential tool to sustainably manage human activities such as aquaculture. However, interdisciplinary and integrated frameworks for holistic CC assessments are still missing. The goal of this study was to generate expert consensus on best evaluative practices for holistic CC assessments of ocean-based salmon aquaculture. To achieve this goal, a 3-round Delphi study was conducted with 21 aquaculture and carrying capacity experts from around the world. Experts emphasized that the holistic CC process should i) engage all stakeholders in the process, ii) consider the combination of social, political, ecological, and economic aspects, iii) respond to changes over time, iv) consider multiple spatial and temporal scales, and v) be understandable and clear to all stakeholders involved. Furthermore, the expert panel emphasized the need for a cyclical and dynamic process that allows for the incorporation of feedback in the planning stages, embracing adaptive management. Due to the early stages of truly holistic assessments, the experts recognized challenges related to knowledge uncertainties and lack of approaches to integrate socio-economic data with ecological and physical data, potential conflicts arising from a multi-stakeholder process, and ill-equipped governance structures. The proposed guidelines and framework could help address some of the conceptual and procedural barriers to implementing holistic assessments into decision-making and may position CC as a useful decision-support tool for governments seeking sustainable aquaculture management.

Inferring the potential for nitrogen toxicity on seagrass in the vicinity of an aquaculture site using mathematical models.

Finfish aquaculture is a source of dissolved nutrients, which can impact water quality in the wider environment. Therefore, the potential effects of dissolved nutrient loading must be considered if management is to transition towards an Ecosystem Approach to Aquaculture. In this study, the dissolved nitrogen dispersion pattern from a rainbow trout farm in Port Mouton (Nova Scotia, Canada) was simulated and evaluated in the context of potential toxicity for a foundation seagrass species. A range of scenarios defined under a precautionary approach were simulated using a fully spatial hydrodynamic model. These worst-case scenarios predicted a maximum nitrogen concentration at any moment of the day of 7.5 µM, which is below the expected toxicity threshold for seagrass. Further scenarios demonstrated that the increased dispersion caused by the wind could drop these values by 45-50% in the vicinity of the farm, suggesting the relevant role of wind forcing in nitrogen dispersion. This outcome suggests that the decline of seagrass reported in some parts of Port Mouton bay are unlikely to have been triggered by dissolved nutrients discharged from the farm. This case-study demonstrates the value of ecosystem modelling to make science-based and transparent decisions to implement an ecosystem approach to aquaculture.

The impact of the sea anemone Actinothoe sphyrodeta on Mytilus galloprovincialis mussel cultivation (Galicia, Spain).

Marine mussel aggregations act as a substratum and refuge for many fouling species. Mussel cultivation in Galicia, Spain, is carried out on hanging ropes in subtidal systems. The fauna associated with this cultivation includes a large number of invertebrates that compete for space or food with the mussels, or use their clusters as a refuge from predators or water turbulence. Outbreaks of the epibiont anemone Actinothoe sphyrodeta have been reported in cultivated Galician mussels since 2013, but their impact has not been investigated rigorously. Here, the temporal and spatial variability of Actinothoe sphyrodeta on mussel shells throughout one year is presented. Sampling of mussel size, weight and byssus attachment strength allowed mussel tenacity (attachment strength relative to size) to be calculated. A higher presence of Actinothoe sphyrodeta correlated with lower mussel tenacity and greater biomass losses, suggesting that this species could be an economically important biofouling component.

Bivalve aquaculture-environment interactions in the context of climate change.

Coastal embayments are at risk of impacts by climate change drivers such as ocean warming, sea level rise and alteration in precipitation regimes. The response of the ecosystem to these drivers is highly dependent on their magnitude of change, but also on physical characteristics such as bay morphology and river discharge, which play key roles in water residence time and hence estuarine functioning. These considerations are especially relevant for bivalve aquaculture sites, where the cultured biomass can alter ecosystem dynamics. The combination of climate change, physical and aquaculture drivers can result in synergistic/antagonistic and nonlinear processes. A spatially explicit model was constructed to explore effects of the physical environment (bay geomorphic type, freshwater inputs), climate change drivers (sea level, temperature, precipitation) and aquaculture (bivalve species, stock) on ecosystem functioning. A factorial design led to 336 scenarios (48 hydrodynamic × 7 management). Model outcomes suggest that the physical environment controls estuarine functioning given its influence on primary productivity (bottom-up control dominated by riverine nutrients) and horizontal advection with the open ocean (dominated by bay geomorphic type). The intensity of bivalve aquaculture ultimately determines the bivalve-phytoplankton trophic interaction, which can range from a bottom-up control triggered by ammonia excretion to a top-down control via feeding. Results also suggest that temperature is the strongest climate change driver due to its influence on the metabolism of poikilothermic organisms (e.g. zooplankton and bivalves), which ultimately causes a concomitant increase of top-down pressure on phytoplankton. Given the different thermal tolerance of cultured species, temperature is also critical to sort winners from losers, benefiting Crassostrea virginica over Mytilus edulis under the specific conditions tested in this numerical exercise. In general, it is predicted that bays with large rivers and high exchange with the open ocean will be more resilient under climate change when bivalve aquaculture is present.

Implementation of marine spatial planning in shellfish aquaculture management: modeling studies in a Norwegian fjord.

Shellfish carrying capacity is determined by the interaction of a cultured species with its ecosystem, which is strongly influenced by hydrodynamics. Water circulation controls the exchange of matter between farms and the adjacent areas, which in turn establishes the nutrient supply that supports phytoplankton populations. The complexity of water circulation makes necessary the use of hydrodynamic models with detailed spatial resolution in carrying capacity estimations. This detailed spatial resolution also allows for the study of processes that depend on specific spatial arrangements, e.g., the most suitable location to place farms, which is crucial for marine spatial planning, and consequently for decision support systems. In the present study, a fully spatial physical-biogeochemical model has been combined with scenario building and optimization techniques as a proof of concept of the use of ecosystem modeling as an objective tool to inform marine spatial planning. The object of this exercise was to generate objective knowledge based on an ecosystem approach to establish new mussel aquaculture areas in a Norwegian fjord. Scenario building was used to determine the best location of a pump that can be used to bring nutrient-rich deep waters to the euphotic layer, increasing primary production, and consequently, carrying capacity for mussel cultivation. In addition, an optimization tool, parameter estimation (PEST), was applied to the optimal location and mussel standing stock biomass that maximize production, according to a preestablished carrying capacity criterion. Optimization tools allow us to make rational and transparent decisions to solve a well-defined question, decisions that are essential for policy makers. The outcomes of combining ecosystem models with scenario building and optimization facilitate planning based on an ecosystem approach, highlighting the capabilities of ecosystem modeling as a tool for marine spatial planning.

Assessing shellfish farming-mediated benthic impacts based on organic carbon flux simulation and composition of macrofaunal community.

Marine benthic environments serve as the ultimate sink for sediment organic matter (SOM), but shellfish farming can potentially disturb the natural sink of seston, altering ecosystem functioning. Understanding the potential disturbance of a shellfish farm and its ecological effects is therefore important for a responsible management of shellfish-mediated marine ecosystem. In this study, the variations in benthic organic carbon flux of a bottom-based Manila clam (Ruditapes philippinarum) farm in Laizhou Bay, China were estimated by using a carbon flux model coupled with hydrodynamic and individual growth models. SOM and macrofaunal community were monitored for 3 years to investigate their changes to the carbon fluxes. Model simulations illustrated that the carbon flux in an area of 247 km2 was altered due to seston depletion and biodeposition, which caused decrease and increase in SOM in different areas, respectively. Cluster analysis based on taxonomic composition of macrofaunal community divided the sites into four groups, which corresponded with predicted changes of carbon flux. Increased carbon flux caused higher disturbance level (indicated by AMBI) to the macrofaunal community but increased species richness, abundance, and Shannon-Wiener index, suggesting the community was both disturbed and benefited from clam farming. This study confirmed that the benthic organic carbon flux is a key factor causing differences in SOM and macrofaunal community outside the farm, and thus can be used as an efficient method for estimating the benthic impacts of shellfish farming both in and outside the farming area.

The role of Dynamic Energy Budgets in conservation physiology.

The contribution of knowledge, concepts and perspectives from physiological ecology to conservation decision-making has become critical for understanding and acting upon threats to the persistence of sensitive species. Here we review applications of dynamic energy budget (DEB) theory to conservation issues and discuss how this theory for metabolic organization of all life on earth (from bacteria to whales) is well equipped to support current and future investigations in conservation research. DEB theory was first invented in 1979 in an applied institution for environmental quality assessment and mitigation. The theory has since undergone extensive development and applications. An increasing number of studies using DEB modelling have provided valuable insights and predictions in areas that pertain to conservation such as species distribution, evolutionary biology, toxicological impacts and ecosystem management. We discuss why DEB theory, through its mechanistic nature, its universality and the wide range of outcomes it can provide represents a valuable tool to tackle some of the current and future challenges linked to maintaining biodiversity, ensuring species survival, ecotoxicology, setting water and soil quality standards and restoring ecosystem structure and functioning in a changing environment under the pressure of anthropogenic driven changes.

Effects of the toxic dinoflagellate Alexandrium catenella on the behaviour and physiology of the blue mussel Mytilus edulis.

The effects of harmful algae on bivalve physiology are complex and involve both physiological and behavioural responses. Studying those responses is essential to better describe and predict their impact on shellfish aquaculture and health risk for humans. In this study we recorded for two months the physiological response of the blue mussel Mytilus edulis from Eastern Canada to a one-week exposure to a paralytic shellfish poisoning producing dinoflagellate strain of Alexandrium catenella, isolated from the St Lawrence estuary, Canada. Mussels in a 'control' treatment were fed continuously with a non-toxic diet, while mussels in a 'starvation' treatment were fed the same non-toxic diet the first week and subsequently starved for seven weeks. Mussels in a 'toxic' treatment received A. catenella for one week before being starved until the end of the experiment. Over a two-month experiment we monitored shell and tissue growth, filtration capacity, respiration rate, byssal attachment strength, valve opening behaviour, and toxin content in tissues. Mussels fed normally on the toxic dinoflagellate and accumulated an average of 51.6 µg STXeq 100 g-1 after one week of exposure. After seven weeks of depuration, about half of the specimen showed levels around 18 µg STXeq 100 g-1. The condition index of exposed mussels ('toxic' treatment) decreased rapidly from the start as compared to mussels that received a one-week non-toxic diet ('starvation' treatment). Oxygen consumption rates increased in the 'toxic' treatment before leveling out with that of mussels from the 'starvation' treatment. Valve opening amplitude was lower in the 'toxic' treatment during and following the exposure. Average valve closure duration was higher right after the exposure, during the peak of mussel tissue intoxication. No significant change in byssal thread strength was observed through time in each treatment but less force was required to detach mussels from the 'toxic' and 'starvation' treatments. The number of byssus threads produced by mussels exposed to the toxic dinoflagellate was also lower than in the control group. These results represent advancements in our understanding of the impacts of harmful algae on bivalves and contribute to the development of mitigation measures necessary to both the safety of consumers and the sustainability of aquaculture operations.

Modelling bivalve culture - Eutrophication interactions in shallow coastal ecosystems.

Assessing the carrying capacity of ecosystems is crucial to the selection of suitable and sustainable locations for aquaculture farms. In Malpeque Bay (PEI, Canada), the potential expansion of mussel farms has driven a series of numerical modelling studies. We coupled sub-models for sea lettuce, wild and cultured oysters and wild softshell clams to an existing ecosystem model to better understand nutrient dynamics and the carrying capacity of Malpeque Bay. Simulations suggested that competition for nutrients between phytoplankton and sea lettuce and filtration by cultured bivalves predominantly mitigate eutrophication effects. The addition of sea lettuce reduced mussel growth by 2% on average and up to 9% near eutrophic estuaries favouring macroalgae growth. Projected new mussel farms reduced current mussel growth by 2% also, suggesting that the carrying capacity of the bay may not be reached yet. Both current and projected aquaculture activities seemed to have limited effects on natural bivalve growth.

The Use of Kernel Density Estimation With a Bio-Physical Model Provides a Method to Quantify Connectivity Among Salmon Farms: Spatial Planning and Management With Epidemiological Relevance.

Connectivity in an aquatic setting is determined by a combination of hydrodynamic circulation and the biology of the organisms driving linkages. These complex processes can be simulated in coupled biological-physical models. The physical model refers to an underlying circulation model defined by spatially-explicit nodes, often incorporating a particle-tracking model. The particles can then be given biological parameters or behaviors (such as maturity and/or survivability rates, diel vertical migrations, avoidance, or seeking behaviors). The output of the bio-physical models can then be used to quantify connectivity among the nodes emitting and/or receiving the particles. Here we propose a method that makes use of kernel density estimation (KDE) on the output of a particle-tracking model, to quantify the infection or infestation pressure (IP) that each node causes on the surrounding area. Because IP is the product of both exposure time and the concentration of infectious agent particles, using KDE (which also combine elements of time and space), more accurately captures IP. This method is especially useful for those interested in infectious agent networks, a situation where IP is a superior measure of connectivity than the probability of particles from each node reaching other nodes. Here we illustrate the method by modeling the connectivity of salmon farms via sea lice larvae in the Broughton Archipelago, British Columbia, Canada. Analysis revealed evidence of two sub-networks of farms connected via a single farm, and evidence that the highest IP from a given emitting farm was often tens of kilometers or more away from that farm. We also classified farms as net emitters, receivers, or balanced, based on their structural role within the network. By better understanding how these salmon farms are connected to each other via their sea lice larvae, we can effectively focus management efforts to minimize the spread of sea lice between farms, advise on future site locations and coordinated treatment efforts, and minimize any impact of farms on juvenile wild salmon. The method has wide applicability for any system where capturing infectious agent networks can provide useful guidance for management or preventative planning decisions.

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.