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Recently, there is a greater interest for the development of mussel Mytilus edulis hatcheries, particularly for the production and commercialization of triploid bivalves. The aims of this study wer...

In North America, studies regarding effects of CO2-induced low pH in bivalve aquaculture are largely restricted to the US Pacific coast. Studies on species from the northwest Atlantic are lacking. Furthermore, information on the roles of intergenerational exposure and biological sex in bivalve responses to low pH, particularly in an aquaculture-specific context, is scant. We tested if short-term (1 month) exposure to CO2-induced reductions in pHNBS affected the reproductive development of male and female eastern oysters (Crassostrea virginica) during hatchery-specific reproductive conditioning and whether maternal and/or paternal exposure influenced larval responses. Reduced pH (7.5–7.7) increased the rate of reproductive development in both males and females. There was no indication of intergenerational effects; adult pH conditions did not affect early larval development. In contrast, low pH conditions experienced by gametes during spawning, fertilization, and embryo incubation (48 h) resulted in higher larval survival (+6–8% from control), reduced shell height (−2 to 3 µm), and increased deformities (abnormal shell shape; +3–5%). We suggest that local adaptation to acidic land runoff may account for the positive effects of low pH observed in this study. Bioeconomic assessments are now needed to understand the implications of reduced pH on aquaculture operations in these regions of Atlantic Canada.

While high levels of siltation are known to be deleterious to eastern oysters (Crassostrea virginica), the collective effect of suspended and bedded sediment is understudied from the perspective of oyster farming and bed restoration. In this study, we used laboratory experiments to explore spat settlement rates on a wild bed proxy substrate (i.e., empty shells on the bottom of experimental tanks) in conditions simulating a siltation event and the presence of suspended spat collectors. Using high-frequency valvometry, we also described the behavioural effects of acute sediment burial on wild adult oysters in situ. The vast majority of larvae settled on bottom substrate as opposed to suspended collectors. Sediment negatively affected overall oyster spat settlement on bottom shell, as spat densities were ≈3 × lower when sediment was present. This negative effect was largely attributed to severely depressed spat densities on the upper side (top) of bottom shells. Settlement on the underside of bottom shell was less affected. Wild adult oyster behaviour was negatively affected by acute burial, which ultimately resulted in death. We suggest that the reduction in settlement in the presence of siltation is likely due to the combined effects of suspended sediment on cue detection and bedded sediment on substrate availability. Given that oysters are ecosystem engineers, the negative effects of siltation on both larval and adult oysters can ultimately result in cascading effects to the surrounding biological community.

11 pages, 6 figures, 1 table, 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, This project was undertaken with the financial support of the Government of Canada, specifically by Environment and Climate Change Canada (FDE-CA-2017i002) and Fisheries and Oceans Canada

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.

16 pages, 4 figures, 2 tables.-- This is an Open Access article distributed under the terms of the Creative Commons Attribution License, The impact of simulated seawater acidification and warming conditions on specimens of the mussel Mytilus galloprovincialis locally adapted to very distinct, widely separated sites in the Mediterranean Sea (Tunisia) and Atlantic Sea (Galicia, NW Spain) was evaluated in relation to key behavioural and eco-physiological parameters. Over the 2-month exposure to the experimental conditions, mussels were fed optimally to ensure that there are no synergistic interactions between climate change drivers and energetic status of the individuals. In general, regardless of origin (Atlantic or Mediterranean), the mussels were rather resilient to acidification for most of the parameters considered and they were able to grow in strongly acidified seawater through an increased feeding activity. However, shell strength decreased (40%) consistently in both mussel populations held in moderately and highly acidified seawater. The observed reduction in shell strength was not explained by slight alterations in organic matter, shell thickness or aragonite:calcite ratio. The combined effects of high acidification and warming on the key response of byssus strength caused a strong decline in mussel performance, although only in Galician mussels, in which the valve opening time decreased sharply as well as condition index (soft tissue state) and shell growth. By contrast, the observed negative effect of highly acidified scenario on the strength of Tunisian mussel shells was (partly but not totally) counterbalanced by the higher seawater temperature. Eco-physiological and behavioural interactions in mussels in relation to climate change are complex, and future scenarios for the ecology of the species and also the feasibility of cultivating them in Atlantic and Mediterranean zones are discussed, This work was supported by the Spanish government through the Ministerio de Economía y Competitividad and European FEDER funds (AGL-2013-45945-R, CTM2016-76146-C3-2-R/CTM2016-76146-C3-1-R) and the Spanish National Research Council (CSIC) through the program I-COOP+ 2016 (ICOOPA20147 to J.L.)

This study constitutes a first attempt to quantify processes that govern valve gape dynamics in bivalves. We elected to focus on the scallop, Pecten maximus, not only because of its economic importance but also because it has a complex behaviour and high sensitivity to stress, which can be inferred from valve gape dynamics. The adductor muscle is the primary organ implicated in valve movements. Scallops, as other bivalves, move their valves sharply to ensure basic physiological functions or to respond to stressing conditions; these sharp events can be perceived as discrete events within a continuous dynamic. A biophysical model, originally designed for human muscles, was first selected to simulate the adductor muscle contraction, countering the passive valve opening by the umbo ligament. However, to maintain the possibility of rapid valve movements, described as typical of bivalves behaviour, it was necessary to modify the model and propose an original formulation. The resulting hybrid modelling simulates how valve opening tends to converge continuously toward a stable steady-state angle, while being interspersed with discrete, sharp closing events, deviating values from this equilibrium. The parameters of the new model were estimated by optimization using Hall-Effect Sensor valvometry data recorded in controlled conditions. Equilibrium of the continuous regime (when fiber activation equals deactivation) was estimated for a gape angle close to ca. 15 degrees, which is ca. 45% of the maximum opening angle, hence implying a constant effort produced by the adductor muscle. The distribution of time intervals between two successive discrete events did not differ significantly from a random process, but the peak amplitudes deviated from randomness, suggesting they are regulated physiologically. These results suggest that discrete events interact with continuous dynamic regimes, regulating valve opening to minimize physiological efforts and conserve energy. However, because the overall physiological state of the scallop organism conditions the activity of the adductor muscle, a complete understanding of the physiology of bivalves will require linking a more comprehensive model of valve gape dynamics with experimental observations of physiological energy consumption under different conditions.

Hall-Effect valvometry (HES) is being used to describe bivalve valve gape variations and infer environmental perturbations in a variety of aquatic environments. Surprisingly, the published calibrations in ecological literature ignore both the electromagnetic properties of HES and that the valves rotate around their hinge when they move. The high sensitivity of HES suggests these features should be accounted for explicitly to estimate measurement accurately. To address these issues, two calibration functions were developed based on the electromagnetic properties of the HES: one assumes that the HES and magnet are maintained on the same linear axis, and the second model accounts for the geometric properties of the system (i.e. variations of the angle between HES and the magnet during shell rotation). The great scallop (Pecten maximus) was used as biological model because of its large range of valve openings. HES were installed on the flat valve and magnets installed on the opposing rounded valve; 12 individuals of similar size (10 ± 1(SD) cm), were equipped and placed in controlled experimental conditions. A calibration was done for each individual once time series recordings were completed. The variability of parameter estimates was calculated with a bootstrap method. The second model (with rotatation) improves valve gape distance estimates for larger openings despite the decrease of sensor sensitivity. To infer valve gape dynamics, the reciprocal calculation of the calibration function was formalized and applied to the Hall voltage time series. Our analysis suggests that under controlled laboratory conditions, scallops are partially open most of the time (inter-valve distance equalca. 27 mm on average, or 45 % of the average maximum opening distance). Interspersed in this continuous regime, individual scallops performed closing events at a frequency ofca. 2.5 closings per hour. A closing event is a movement that is fast enough relative to the recording frequency (10 Hz) to qualify as discrete. We find that the inversed calibration model without rotation allows negative value estimates, which indicates that this calibration function is incorrect. In contrast, the inversed calibration model with valve rotation around the hinge constrains gape distance values in their domain of definition which automatically excludes sensor readings that produce negative values from estimated gape time series.

Ocean acidification is expected to affect marine organisms in the near future. Furthermore, abrupt short-term fluctuations in seawater pCO

7 pages, 4 figures, 1 table, The saxitoxin-producing dinoflagellate Alexandrium minutum is a well-known microalga that causes paralytic shellfish poisoning (PSP) in many coastal regions of the world. In this study, we measured the valve movements of cultivated mussels Mytilus galloprovincialis feeding on toxic A. minutum (n = 29 mussels, shell length = 67.1 ± 3.2 mm, x̅ ± SD) or a morphologically-similar, but toxin-free phytoplankton, Heterocapsa triquetra (n = 24 mussels, shell length = 68.3 ± 2.9 mm). Phytoplankton inoculations were conducted in three sequential “pulses” intended to increase microalgal cell concentrations in a stepwise manner up to ~5000 cells l−1 over a 9-h period. M. galloprovincialis was connected to a non-invasive valvometry apparatus that concurrently measured the magnitude of valve openness once every 0.1 s. It was found that M. galloprovincialis tended to keep its valves open over the course of the experiment, regardless of the phytoplankton species present in water. Standard valve opening metrics, such as the opening duration and opening amplitude, were not significantly affected by the species of phytoplankton. However, the frequency of brief and partial valve closures (microclosures) was significantly influenced by phytoplankton species (P, Financial support was provided by Fisheries and Oceans Canada and the Spanish government through the Ministerio de Economía y Competitividad (projects AGL2013-45945-R and CTM2016-76146-C3-2-R)

The responses of two very distinct populations of the same marine mussel species Mytilus galloprovincialis, and inhabiting the Atlantic and Mediterranean Seas, were evaluated facing climate change scenarios with regard to pCO2 and temperature drivers. The potential threats and resilient behaviour of individuals according to their original habitat were drawn and discussed., The impact of simulated seawater acidification and warming conditions on specimens of the mussel Mytilus galloprovincialis locally adapted to very distinct, widely separated sites in the Mediterranean Sea (Tunisia) and Atlantic Sea (Galicia, NW Spain) was evaluated in relation to key behavioural and eco-physiological parameters. Over the 2-month exposure to the experimental conditions, mussels were fed optimally to ensure that there are no synergistic interactions between climate change drivers and energetic status of the individuals. In general, regardless of origin (Atlantic or Mediterranean), the mussels were rather resilient to acidification for most of the parameters considered and they were able to grow in strongly acidified seawater through an increased feeding activity. However, shell strength decreased (40%) consistently in both mussel populations held in moderately and highly acidified seawater. The observed reduction in shell strength was not explained by slight alterations in organic matter, shell thickness or aragonite:calcite ratio. The combined effects of high acidification and warming on the key response of byssus strength caused a strong decline in mussel performance, although only in Galician mussels, in which the valve opening time decreased sharply as well as condition index (soft tissue state) and shell growth. By contrast, the observed negative effect of highly acidified scenario on the strength of Tunisian mussel shells was (partly but not totally) counterbalanced by the higher seawater temperature. Eco-physiological and behavioural interactions in mussels in relation to climate change are complex, and future scenarios for the ecology of the species and also the feasibility of cultivating them in Atlantic and Mediterranean zones are discussed.

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 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. © 2018. This is the authors’ accepted and refereed manuscript to the article. Locked until 17 July 2020 due to copyright restrictions. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/

In Prince Edward Island, the spring oyster fishery occurs from early May to mid-July. During this time, oysters may be harvested and held for multiple days by harvesters before being brought to oyster processors, who then relay them in seawater at leased sites. Over the past decade, however, processors have reported high mortalities of relayed catch during July. We investigated duration of air exposure as a potential driver for the high July mortalities reported by oyster processors. Wild oysters were removed from fishing beds in June and July 2017 and handled to mimic techniques used by harvesters. After removal, the oysters were exposed to atmospheric conditions (air) for 0, 24, 48, 72, or 96 h and mortality was quantified. The oysters were then placed at a holding site for 60 days and mortality was quantified on days 7, 14, 30 and 60, and condition index was measured on remaining oysters from each air exposure treatment. Increased mortality was associated with increased air exposure duration, and this effect was most pronounced during July. Oysters exposed to air for 72–96 h in June experienced mortality rates of 4–11%, while the same air exposure duration in July yielded mortality rates four times higher than in June (16–44%). Most of the associated mortality occurred during air exposure and within 7 days of placing oysters at the holding site. Condition index was also lower in July; however there was no evidence that oysters had spawned. Higher mortalities and lower condition indices in July were associated with higher average air and seawater temperatures (both ∼3 °C higher than June). These results ultimately suggest that increased air exposure can result in substantial mortality of PEI oysters fished in July, and corroborate the reports of high July mortalities from oyster processors.

While many studies document effects of elevated pCO2 on coastal organisms, the environmental variability characteristic of coastal regions is often not directly tested. We tested for effects of elevated pCO2 on the valve gaping activity of adult eastern oysters ( Crassostrea virginica) in response to acute heat shock that can occur in nearshore shallow coastal waters. In two consecutive experimental trials, oysters (n = 4) wired with Hall Effect biosensors (that measured valve gaping at one-second intervals) were exposed for 10 days at six different pCO2 treatments spanning a range currently observed in nearshore coastal regions, and predicted under near-future ocean acidification . After the 10-day acclimation period, oysters from each pCO2 treatment were exposed to a 3-h heat shock assay (11-12 ➔ 30 °C) and valve gaping activity was monitored continuously. During the heat shock assays, valve gaping activity increased with increasing temperature and then ceased when temperature was reduced back to 11-12 °C; however, these valve gaping rate increases during heat shock were not characteristic of overly-stressed oysters. Exposure to elevated pCO2 had no effect on the valve gaping response of oysters to acute heat shock. Our results suggest that the valve gaping responses of adult eastern oysters to acute temperature increases are unaffected by short-term elevations in seawater pCO2. Future studies incorporating the roles of local adaptation, food availability, and direct functional consequences of valve gaping (e.g. physiological rates, predator avoidance, response to environmental toxins) are warranted.

Understanding why a species occupies a certain geographic range and predicting how they will be affected by climate change require characterizing physiological traits in geographically-distant populations. The objective of this study was to perform a direct comparison of two eastern oyster ( Crassostrea virginica ) populations that occupy contrasting temperature and salinity habitats, New Brunswick, Canada (47°N – Gulf of St. Lawrence) and Louisiana, USA (29°N – Gulf of Mexico). Specifically, clearance rate, valve opening, and oxygen consumption rate were measured in oysters of both populations following a full factorial design with three temperatures (10, 20, 30 °C) and two salinities (15, 25). New Brunswick oysters had a greater gill area, shell gape angle, and oxygen consumption rate. Temperature was the main driver of clearance rate, valve opening duration and oxygen consumption rate. Clearance rate at 20 °C and 30 °C was significantly higher than at 10 °C, and oysters at 20 °C had their valves opened for a greater percentage of time compared to oysters at 10 °C and 30 °C. Oxygen consumption rate increased gradually from 10 °C to 30 °C and similarly for both populations, with no indications of a thermal breakpoint at 30 °C. Temperature coefficients for the oxygen consumption rate (Q 10) were within the normal ecological range for both populations. No physiological differences were observed between salinity treatments in both populations. No latitudinal compensation in the physiological rates was found. Overall, results showed that C. virginica is tolerant to a broad range of temperatures and salinities. Such physiological plasticity is consistent with the species' extended geographical range.

8 pages, 2 figures, 2 tables, Ocean acidification is expected to affect marine organisms in the near future. Furthermore, abrupt short-term fluctuations in seawater pCO2 characteristic of near-shore coastal regions and high-density aquaculture sites currently have the potential to influence organismal and community functioning by altering animal behaviour. While anti-predator responses in fishes exposed to elevated pCO2 are well documented, such responses in benthic marine invertebrates are poorly studied. We used high frequency, non-invasive biosensors to test whether or not short term (3-week) exposure to elevated pCO2 could impact behavioural responses to the threat of predation in adult Mediterranean mussels from Galicia on the northwestern coast of Spain. Predator alarm cues (crushed conspecifics) resulted in a prolonged (1 h) reduction in the degree of valve opening (−20%) but had no clear effect on overall valve movement activity, while elevated pCO2 did not affect either response. Our results add to the increasing body of evidence suggesting that the effects of end-of-century pCO2 levels on marine animal behaviour are likely weak. Nonetheless, longer-term exposures spanning multiple generations are needed to better understand how ocean acidification might impact behavioural responses to predation in marine bivalves, This project was funded by the Spanish government through the Ministerio de Economía y Competitividad that included European FEDER funds (projects Ref. AGL-2013-45945-R, CTM2016-76146-C3-2-R/CTM2016-76146-C3-1-R)

In response to accidental oil spills at sea, chemical oil dispersants are utilized to limit negative impacts on nearby littoral zones. However, current evidence suggests that such dispersants may be toxic to aquatic organisms. Blue mussels (Mytilus edulis) and giant scallops (Placopecten magellanicus) were exposed to different environmentally relevant concentrations of oil dispersant and their behavioural responses were closely monitored using high frequency (10Hz) valvometry. Behavioural valve responses included rapid closures when oil dispersant was added to the experimental tanks. At higher concentrations, the mussels remained closed throughout the exposure period. The giant scallop displayed escape behaviours (clapping) prior to mortality, suggesting toxicity of the oil dispersant. Relationships between different behavioural indicators and oil dispersant concentrations were observed for both species, but with different trends. While scallops demonstrated positive correlations between gaping behaviours and dispersant concentration, mussels exhibited a concentration threshold beyond which the gaping behaviour was characteristic of longer closure periods. This study highlights behavioural response differences consistent with bivalve-specific biological traits: the continuous valve closure of an intertidal species, M. edulis, firmly attached to the substrate, and the escapement behaviours of a semi-mobile subtidal species, P. magellanicus. From these observations, it appears that valvometry could be used as a tool for environmental assessments.

This paper provides the first continuous assessment of behavioural quiescence in Eastern oysters (Crassostrea virginica) overwintered at their northernmost (48°N) distribution range. The paper also describes how quiescent oysters respond to sediment burial, which may occur inadvertently when cultured stocks are lowered onto soft-sediment seabeds. Long term monitoring of valve opening indicated that quiescence persisted for 164.9 ± 1.8 days (mean ± SE, n = 14 oysters) in 2014–2015. Quiescence was initiated in mid-November 2014 when the water temperature fell to 2.7 ± 0.2 °C and ended in early May 2015 when the water temperature rose to 4.4 ± 0.4 °C. The low mortality rate (3.4 ± 1.9%) of the control groups indicated that this species is well-adapted to such overwintering conditions. When buried in late October, oysters initially exhibited low-amplitude and sporadic shell movements, possibly in an attempt to clear the sediment covering their valve margins. Following a period of quiescence, behavioural morbidity ensued, with lethargic opening of valves beginning 153.3 ± 9.9 days after burial (n = 16 oysters). Death occurred 186.5 ± 3.6 days following burial (n = 16 oysters). Removing buried quiescent oysters from the sediment in late winter accelerated the depletion of energy reserves, particularly lipids and proteins, thereby advancing death. In conclusion, detrimental health effects associated with the burial of oysters in autumn cannot be mitigated through winter or spring desiltation. Thus, reducing the risk of burial by avoiding soft estuarine sediment whenever possible remains the best husbandry practice.

Haslea ostrearia is a marine diatom that synthesizes and releases marennine, a water-soluble blue-green pigment responsible for the greening of the gills and labial palps of bivalves. The present study evaluated the effect of different marennine concentrations (0, 0.5, 1.0 and 2.0 mg l− 1) on the behavior (valve opening), physiology (clearance rates, oxygen consumption, assimilation efficiency and scope for growth) and biochemistry (fatty acid composition of neutral and polar lipids) of two commercially important bivalves, the blue mussel Mytilus edulis and the eastern oyster Crassostrea virginica. Under short-term (

Blue mussels ( Mytilus edulis ) that are cultivated in the marine area around Prince Edward Island, Eastern Canada, are susceptible to the heavy biofouling of their shells by an invasive solitary tunicate, Styela clava , which rapidly proliferates. To mitigate this issue, mussel farmers periodically lift the longlines on which the mussels are suspended out of the water to spray a highly alkaline (~ 12.7 pH units) calcium hydroxide solution onto fouled individuals. Here, we tested the hypothesis that calcium hydroxide exerts behavioural stress on mussels and other bivalves. Field surveys revealed that the alkalinity of the seawater in the vicinity of longlines increased (9.3–11.7 pH units) immediately after treated mussel sleeves were returned into the water column. Thereafter, pH values declined rapidly, and met federal water quality guidelines (7.0–8.7 pH units) within 3.1 ± 0.5 min (range 0.3–10.5 min, n = 31 sleeves). Cultivated mussels challenged to both emersion and calcium hydroxide closed their valves for 14.0 ± 3.3 min ( n = 18) compared to 6.5 ± 1.6 min ( n = 17) by control mussels (emersion only). We subsequently assessed how three benthic bivalve species ( M. edulis , Crassostrea virginica (eastern oyster) and Argopecten irradians (bay scallop)) respond to weak (pH ≤ 9.2) but sustained (3-h daily for 3 days) alkalinity conditions. All three species consistently responded by completely or partially closing their valves. However, all behavioural responses were short-lived (0.2–4.7 h), and were generally confined to the treatment period. In conclusion, spraying calcium hydroxide onto cultivated mussels has limited impact on seawater alkalinity and the behaviour of nearby bivalves.

The productivity of a bivalve farm is largely determined by the availability of organic seston and the level of competition for that naturally limited resource. Farm production may also be curtailed by regulatory or certification frameworks concerned with controlling biodeposition, i.e. the sedimentation of organic material. Fouling communities dominated by filter-feeding tunicates which both compete for food resources and increase biodeposition levels thus have the potential to further limit bivalve farm productivity. In the present study a farm-scale modelling approach was used to quantify the effects of the tunicate Ciona intestinalis on longline mussel farms. Both cultured and fouling species were simulated using physiological modules that took into account their interactions with organic seston dynamics in terms of filtration and biodeposition, and also predicted their growth over a typical growing season. Various treatment scenarios for reducing C. intestinalis infestation levels were also analyzed. Model results showed that C. intestinalis populations can rapidly dominate mussel sleeves in terms of their overall biomass and contribution to organic sedimentation. Early treatments during the tunicate reproductive season were the most effective at controlling the level of infestation and its impacts on sestonic food availability, mussel production and organic sedimentation. The proposed generic modelling approach could potentially become an essential aquaculture management tool, especially in the context of biological invasions. Statement of relevance The growing importance of bivalve aquaculture combined with its vulnerability to environmental conditions compels to ensure its sustainable development and management. Biofouling can potentially disrupt farm productivity and become a nuisance with profound socio-economic consequences. The numerical tool developed in this study provides valuable information for the management and mitigation of fouling by filter-feeding species on mussel farms.

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.

Picophytoplankton (PPP) may contribute to the bulk of primary production in nutrient-rich marine ecosystems. In this study, we quantified the capacity of blue mussels (Mytilus edulis) and clubbed tunicates (Styela clava) to exploit PPP. In the water, we introduced PPP cells that were isotopically labelled with 13C and using the same enrichment approach, we measured the secondary transfer (recycling) of carbon via the assimilation of pseudofeces and feces. Results show that both M. edulis and S. clava assimilate PPP carbon by ingesting PPP cells directly from water. In addition, PPP assimilation rates were similar in both species. Most interesting was our observation that both species assimilated PPP carbon contained in pseudofeces and feces, including large fecal pellets produced by S. clava. We conclude that within cultured and invasive filter feeders, PPP carbon is recycled via ingestion of feces and pseudofeces among individuals growing in close proximity. In aquaculture settings, cultured bivalves and fouling tunicates may provide an ecological service by removing excess PPP in nutrient-rich systems via direct and secondary ingestion.

Through physical manipulation, oyster growers can modify the morphological features of young oysters in order to improve their robustness and resiliency to predation. In this study, the efficacy of a novel passive culturing technique using floating buckets that “bounce” oysters prior to the benthic grow-out phase for enhancing shell thickness and strength, while not compromising oyster shape, was investigated. Using a field experiment, we quantified and compared the shell thickness (mm), compressive strength (Newtons), and shape (fan ratios and cup ratios) of juvenile oysters subjected to this bouncing technique with oysters grown in floating bags, the current industry standard. Results indicated that bouncing increased shell thickness and strength for oysters >45 mm shell height compared to control oysters, but also decreased shell thickness and strength for oysters

The carbon dioxide taken up by the ocean is increasing as levels of atmospheric carbon dioxide increase, thus lowering the ocean pH and altering the carbonate system. In this laboratory study, we evaluated the physiological responses of juvenile mussels Mytilus galloprovincialis from Galician waters (NW Iberian Peninsula) exposed to control (500 µatm) and elevated (800 or 1200 µatm) seawater pCO2 conditions under 2 different feeding regimes (optimal and suboptimal). Shell properties such as compressive strength and composition (organic matter and aragonite:calcite ratio) were negatively affected by high seawater pCO2, regardless of food availability. This result suggests that water chemistry is a main driver for shell development. Under the optimal feeding regime, mussel feeding rates increased in response to elevated pCO2, presumably as a strategy to maintain a high strength of attachment. In contrast, mussels on the suboptimal diet showed weak attachment and narrow valve opening at the highest pCO2 condition. Thus, our results suggest that with optimal food availability, mussels were resilient to water acidification with respect to feeding activity, valve opening and attachment strength. Under a suboptimal diet, however, the ability of mussels to respond to acidification was compromised. These results highlight complex ecophysiological interactions for calcifying organisms subjected to climate change, This study was funded by the Spanish government through the Ministerio de Economía y Competitividad that included European FEDER funds (projects Ref. AGL-2013-45945-R, CTM2016-76146-C3-2-R/ CTM2016- 76146-C3-1-R). J.L. acknowledges funding from the Spanish National Research Council (CSIC) through the Program ICOOP+ 2016 (Ref. ICOOPA20147)

Bivalve farming can contribute to nutrient removal in coastal and estuarine systems, as bivalves directly incorporate nutrients into their tissues and shells. We conducted a meta-analysis to compare the nitrogen removal potential (NRP; i.e., percentage of nitrogen in tissues and shells) of mussels, Mytilus edulis, and oysters, Crassostrea virginica. We then used species-specific NRPs to determine and compare the total and per-hectare NRPs for four shellfish aquaculture methods used in two Atlantic Canadian provinces – New Brunswick (NB) and Prince Edward Island (PEI) – based on current harvest biomasses. Finally, we determined the contribution of current shellfish farming to nitrogen load mitigation for a subset of bays in NB and PEI. Results revealed that on a per-weight basis, NRP was similar for the tissues of mussels and oysters, while mussel shells had a significantly higher percentage of nitrogen than oyster shells. Collectively, shellfish harvesting has the capacity to remove a mean annual total of 99088 kg and 204571 kg of nitrogen from NB and PEI, respectively. Given current harvesting practices for four culture methods employed in the region, suspended mussel culture provides the greatest NRP per hectare of farm area, followed in sequence by suspended mussel and oyster mixed culture, suspended oyster culture, and bottom oyster culture. Preliminary analysis suggested that harvests in the region typically remove

Eastern oysters (Crassostrea virginica) are ecosystem engineers that are important to the ecological and economic sustainability of Atlantic Canada’s estuarine resources. Recently, there has been an increased industry demand for oyster spat (i.e., newly-settled larvae), which is often collected using artificial spat collectors suspended in the water column. Little is known, however, about the interactions between artificial spat collectors and naturally occurring substrates, and whether or not such collectors can affect oyster recruitment to wild beds which are simultaneously fished. In the laboratory, we mimicked the typical set-up of artificial spat collectors used in Atlantic Canada to measure differences in spat recruitment between locally-used artificial collectors and natural shell substrate under real-life spat-collection scenarios. Larvae were allowed to settle on various substrates where they occur in a natural system and were subsequently counted. In both single substrate and choice experiments, results indicated that oyster larvae recruited in higher numbers to natural shell substrate located on the benthic surface compared to suspended shell; and there were no significant differences among suspended substrates. This experiment provides evidence supporting existing theories around recruitment behaviour by oyster larvae, mainly that settling oysters tend to sink before they settle, suggesting that spat collectors in the wild may have little effect on wild recruitment. With increasing densities of artificial collectors in estuarine systems to meet system demands, however, further research is needed to investigate the potential draw of oyster larvae away from benthic oyster beds under more realistic natural conditions before broad conclusions regarding spat collector effects on wild oyster populations can be achieved. Crown Copyright © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

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.

There are few data on Crassostrea virginica physiological rates across the range of salinities and temperatures to which they are regularly exposed, and this limits the applicability of growth and production models using these data. The objectives of this study were to quantify, in winter (17 °C) and summer (27 °C), the clearance and oxygen consumption rates of C. virginica from Louisiana across a range of salinities typical of the region (3, 6, 9, 15 and 25). Salinity and season (temperature and reproduction) affected C. virginica physiology differently; salinity impacted clearance rates with reduced feeding rates at low salinities, while season had a strong effect on respiration rates. Highest clearance rates were found at salinities of 9–25, with reductions ranging from 50 to 80 and 90 to 95% at salinities of 6 and 3, respectively. Oxygen consumption rates in summer were four times higher than in winter. Oxygen consumption rates were within a narrow range and similar among salinities in winter, but varied greatly among individuals and salinities in summer. This likely reflected varying stages of gonad development. Valve movements measured at the five salinities indicated oysters were open 50–60% of the time in the 6–25 salinity range and ~ 30% at a salinity of 3. Reduced opening periods, concomitant with narrower valve gap amplitudes, are in accord with the limited feeding at the lowest salinity (3). These data indicate the need for increased focus on experimental determination of optimal ranges and thresholds to better quantify oyster population responses to environmental changes.

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 resources indicated that picophytoplankton (0.2–3.0 μm) accounted for a major proportion of the primary production (61.5 ± 4.0%) and standing stock biomass (75.8 ± 3.6%). M. edulis was much less efficient at retaining this picophytoplankton component (18.1 ± 2.2%) than were the invasive tunicates (59.0 ± 2.6%). Carrying capacity calculations indicated a balanced state of demand versus supply for nanophytoplankton (> 3.0 μm) when mussel leases occupy 33% of the spatial area of a bay. The presence of solitary tunicates effectively lowered this bay-scale occupancy threshold to 23–26% (treated sleeves) or 10–11% (non-treated sleeves).

Pre-spawning blue mussels (Mytilus edulis) appear sensitive to elevated temperature and robust to elevated pCO2; however, the effects of these stressors soon after investing energy into spawning remain unknown. Furthermore, while studies suggest that elevated pCO2 affects the byssal attachment strength of Mytilus trossulus from southern latitudes, pCO2 and temperature impacts on the byssus strength of other species at higher latitudes remain undocumented. In a 90 day laboratory experiment, we exposed post-spawning adult blue mussels (M. edulis) from Atlantic Canada to three pCO2 levels (pCO2 ~625, 1295 and 2440 μatm) at two different temperatures (16°C and 22°C) and assessed energetic reserves on Day 90, byssal attachment strength on Days 30 and 60, and condition index and mortality on Days 30, 60 and 90. Results indicated that glycogen content was negatively affected under elevated temperature, but protein, lipid, and overall energy content were unaffected. Reduced glycogen content under elevated temperature was associated with reduced condition index, reduced byssal thread attachment strength, and increased mortality; elevated pCO2 had no effects. Overall, these results suggest that the glycogen reserves of post-spawning adult M. edulis are sensitive to elevated temperature, and can result in reduced health and byssal attachment strength, leading to increased mortality. These results are similar to those reported for pre-spawning mussels and suggest that post-spawning blue mussels are tolerant to elevated pCO2 and sensitive to elevated temperature. In contrast to previous studies, however, elevated pCO2 did not affect byssus strength, suggesting that negative effects of elevated pCO2 on byssus strength are not universal.

6 pages, 5 figures, 1 table.-- This is an open access article under the CC BY-NC-ND license, We describe the valve-opening behavior of raft-cultivated mussels (Mytilus galloprovincialis) in the Ría de Arousa (Arousa estuary), Spain. Eight rope-grown mussels [mean ± standard error (SEM), shell length 61.6 ± 2.1 mm] were connected to a non-invasive valvometry apparatus that monitored (one measurement min−1) the magnitude of valve openness systematically over a 10 day period. It was found that valves were open 97.5 ± 1.3% percent of the time. Valve closures were not synchronized among the eight monitored mussels, suggesting that feeding cessation was physiologically-regulated rather than environmentally-mediated. The opening amplitudes that were most frequently observed were in the range of 60–90%, indicating that, when open, valves are usually opened relatively close to their maximum possible extent. The majority (7/8) of mussels displayed a circadian rhythm (τ = 24.0 h) in valve opening amplitude. They tended to exhibit maximum valve opening during nighttime and minimum opening during daytime. It is possible that the light:dark cycle represents an environmental zeitgeber entraining an endogenous gaping rhythm in this bivalve, This study was funded by the Spanish government through the Ministerio de Economía y Competitividad (project Mytiga AGL2013- 45945-R)

Temperature affects nearly all biological rates and consequently is fundamental to individual development time and timing of phenological events. One example is the duration of the pelagic larval stage of mussels, which is crucial for determining the magnitude and timing of recruitment, as well as population dispersal patterns. Understanding the impact of temperature on the rate of larval development is key to predicting the timing of settlement and optimizing mussel seed collection. Advising mussel farmers on Prince Edward Island about the ideal timing for collector deployment is one of the goals of the Mussel Monitoring Program (MMP). In this study we examine the relationship between the phenology of larval development based on MMP data, and satellite measurements of sea surface temperature. The analyses indicated that the first day of the year on which 10 –20% of the pool of mussel larvae reached 250 mm could be predicted using the thermal integral measure growing degree-days. While this finding confirmed the importance of temperature for mussel larval phenology, the effect of other environmental variables such as phytoplankton quantity and quality cannot be dismissed.

Pre-spawning blue mussels (Mytilus edulis) appear sensitive to elevated temperature and robust to elevated pCO2; however, the effects of these stressors soon after investing energy into spawning remain unknown. Furthermore, while studies suggest that elevated pCO2 affects the byssal attachment strength of Mytilus trossulus from southern latitudes, pCO2 and temperature impacts on the byssus strength of other species at higher latitudes remain undocumented. In a 90 day laboratory experiment, we exposed post-spawning adult blue mussels (M. edulis) from Atlantic Canada to three pCO2 levels (pCO2 ~625, 1295 and 2440 μatm) at two different temperatures (16°C and 22°C) and assessed energetic reserves on Day 90, byssal attachment strength on Days 30 and 60, and condition index and mortality on Days 30, 60 and 90. Results indicated that glycogen content was negatively affected under elevated temperature, but protein, lipid, and overall energy content were unaffected. Reduced glycogen content under elevated temperature was associated with reduced condition index, reduced byssal thread attachment strength, and increased mortality; elevated pCO2 had no effects. Overall, these results suggest that the glycogen reserves of post-spawning adult M. edulis are sensitive to elevated temperature, and can result in reduced health and byssal attachment strength, leading to increased mortality. These results are similar to those reported for pre-spawning mussels and suggest that post-spawning blue mussels are tolerant to elevated pCO2 and sensitive to elevated temperature. In contrast to previous studies, however, elevated pCO2 did not affect byssus strength, suggesting that negative effects of elevated pCO2 on byssus strength are not universal.

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.