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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. • Indices assessing bivalve culture sustainability rely on key ecosystem turnover rates. • Water renewal time should be assessed using full hydrodynamic models (not tidal prisms). • Bivalve clearance time should account for seasonality and refiltration effects. • Phytoplankton production time does not inform on biomass and community structure. • Interpretative caution is warranted regarding culture sustainability thresholds based on indices. [ABSTRACT FROM AUTHOR]

Abstract 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 <.01). M. galloprovincialis subjected to toxic A. minutum exhibited 20.3 ± 0.4 (x̅ ± SEM) microclosures per 3-h pulse period, whereas those exposed to the control H. triquetra exhibited 7.9 ± 0.4 (x̅ ± SEM) microclosures. This response was detectable over the 3 h following the first inoculation pulse that provided a phytoplankton concentration of 1000 cells l−1. Our findings are consistent with growing evidence that bivalves are sensitive to very low concentrations of harmful microalgae. Deploying in situ valvometry sensors with real-time monitoring capabilities may provide an early warning of harmful algal blooms. Highlights • The behavioral response of mussels to toxic Alexandrium minutum was assessed. • Valve microclosures were more frequent in the presence of these toxic cells. • The response was manifested within 3 h at low cell concentrations. • The response might serve as an early warning of toxic A. minutum proliferations. [ABSTRACT FROM AUTHOR]

While many studies document effects of elevated p CO 2 on coastal organisms, the environmental variability characteristic of coastal regions is often not directly tested. We tested for effects of elevated p CO 2 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 p CO 2 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 p CO 2 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 p CO 2 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 p CO 2 . 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. [ABSTRACT FROM AUTHOR]

This study aims at better understanding of the physiological changes that occur during the winter months in Eastern oysters (Crassostrea virginica) living at their northernmost distributional limit (48°N). It was conducted in northeastern New Brunswick, Canada (47°49'N, 64°46'W). Oysters were held in Vexar® bags on the bottom of a bay and collected before (December) and during (January-April) the ice-cover period. Winter mortality was <5%. A significant decrease in the concentration of lipids stored in the digestive gland (from 42.0 to 22.5mg/g wet tissue) indicated that the animals had access to oxygen, probably through minimal shell openings. Proteins were also used, although less heavily (decrease from 68.0 to 59.1mg/g wet tissue), leading to an accumulation of ammonia in the intrapallial fluid (up to 0.83 μM), which is modest considering the length of time the animals lived as almost closed systems. In contrast, carbohydrates appear to play a minor role in winter energetics. Low pH values of intrapallial fluid were noted in late winter (c. 7.0) as compared with those measured at the onset of winter and in spring (c. 7.7). The animals used more energy substrates in late than in early winter, which might be partly related to the necessity to intensify detoxification mechanisms as toxic metabolites accumulate. Despite the fact that oysters do not filter-feed at temperatures <0 °C, the mass of the digestive gland increased by a factor of 1.5 during early winter, presumably as the result of nutrient transfer from other tissues. The ability of C. virginica to use energy-rich substrates and to minimize the accumulation of catabolic byproducts could partly explain the ability of the species to survive prolonged subzero conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 (< 1 day) exposure, the concentration of marennine found on the gills of both species was positively correlated to the concentration of dissolved marennine in the water medium. However, a behavioral response was detected at the higher marennine concentration (2.0 mg l − 1 ) and both species displayed curtailed valve opening compared to control groups. Under longer-term (8 weeks) exposure, marennine (at 2 mg l − 1 ) significantly decreased scope for growth by 58% and 85% (ANOVA; F 3, 31 = 3.39, P = 0.034 and F 3, 31 = 3.08, P = 0.044) for M. edulis and C. virginica respectively. The greening process had an effect on total fatty acids contained in the digestive gland of mussels only, suggesting that marennine interferes with the accumulation of energy reserves in this bivalve. In the polar lipids of the gills, greening increased the concentration of unsaturated fatty acids of C. virginica but not M. edulis , suggesting a possible regulatory mechanism counteracting the marennine effect in oysters. In conclusion, marennine is currently viewed as a non-toxic compound produced by a non-toxic algae species, yet our results show that the substance impairs the biology of bivalves. Such effects should therefore be taken into consideration before the application of mareninne in aquaculture settings. [ABSTRACT FROM AUTHOR]

This study was designed to assess the physiological impact of transferring oysters between upriver and downriver aquaculture sites, a common practice in North America that is primarily aimed at reducing disease infections and predation on cultured stocks. In May 2009, oysters ( Crassostrea virginica) were reciprocally transferred between an upriver and a downriver site in the Richibucto estuary in eastern Canada. Mortality, tissue and cellular stress responses were subsequently evaluated in August and October 2009. Overall, oyster mortality remained low (~5%) throughout the 5-month study period with no significant difference between sites or oyster sources. However, by October oysters reared at the upriver site, regardless of their origin, had significantly higher levels of lysosomal membrane destabilization (63.6%, SE = 1.9) and digestive tubule atrophy (33.3-42.4%, SE = 3.6) than oysters reared at the downriver site (47.5%, SE = 1.8; 15.6-19.1%, SE = 3.8 respectively). They also exhibited a greater salinity differential between their mantle/haemolymph fluids and the ambient seawater, possibly indicating more restricted exchange with the environment. In general, the transfer of upriver oysters to a downriver site had a positive impact, i.e. lower levels of lysosomal destabilization and tubule atrophy, whereas transfer of downriver oysters upriver had the opposite effect. These results suggest that upriver environmental conditions negatively impact cellular and tissue integrity in oysters without leading to mortality during the summer-autumn period. [ABSTRACT FROM AUTHOR]

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 ( CR Area ) for various fouling scenarios. CR Area 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 CR Area , due to self-thinning processes that gradually eliminated 89% of the seed mussels over the 2-year production cycle. CR Area 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 CR Area 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). [ABSTRACT FROM AUTHOR]

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 were to examine the efficiency of inducing triploid mussels by various treatments and to determine the effect of triploidy on larval development. To produce triploids, extrusion of the second polar body of fertilized eggs was inhibited by 6-(dimethylamino)purine (6-DMAP), cold-shock, or heat-shock treatments. Triploidy was detected by flow cytometry for all the treatments. Treatment with 6-DMAP was the most efficient with a rate of triploidy of 90%, followed by heat-shock (56%) and cold-shock (30%) treatments. No survival differences were observed between diploids and 6-DMAP-induced triploid larvae from the D-shape stage up to their settlement. Moreover, increased growth was observed in triploid larvae compared to diploid larvae. Overall, this study showed that 6-DMAP is a highly efficient method to induce triploidy in mussels, with triploid larvae having faster growth compared to diploid. [ABSTRACT FROM AUTHOR]

In the Gulf of St. Lawrence estuaries, mesh bags containing cultured oysters (Crassostrea virginica) are lowered onto the bottom in autumn prior to the formation of a thick ice cover. The oysters remain quiescent and unattended in near-freezing waters for four to five months, during which time they are susceptible to accidental burial by sedimenting particles. The objectives of this study were (1) to gain insight into the mechanism cueing the spring awakening of oysters, (2) to determine the approximate burial depth that oysters can withstand, and (3) to estimate the time it takes for mortality to occur under conditions of excessive siltation. Results indicate that water temperature is the primary factor controlling the timing of awakening, with the majority of oysters suddenly opening their valves when temperatures increased to 2.61±0.66°C. Supplementing the diet to mimic spring bloom conditions had no modulating influence on awakening behaviour. Oysters buried under 20mm of sediment initially exhibited erratic valve movements and sometimes remained closed for days. Within 2weeks, however, they did succeed in expulsing the overlying silt around their valve margins and in resuming normal valve movements, including circadian rhythmicity. By comparison, burial under 40 or 60mm of silt invariably led to death within 11.7±1.3days. It is concluded that oysters should be re-suspended as soon as the ice cover breaks apart and moves offshore in the spring. [ABSTRACT FROM AUTHOR]

The black pygmy mussel Limnoperna securis (Lamarck 1819) is endemic to the brackish waters of New Zealand and Australia, but over the past decade, it has successfully invaded the inner Galician Rias of NW Spain. There is growing concern that L. securis will expand its range to the outer zones of the Rias, where it would pose a threat to the intensive raft culture of the indigenous mussel Mytilus galloprovincialis (Lamarck 1819). In this paper, we compare the valve-opening behaviour of the two mytilids under simulated raft conditions, i.e. full-strength seawater (35 g l) and a low current flow regime (2-5 cm s). Modes of valve-opening amplitudes that were most frequently observed in both species were in the range of 60-90 %, indicating a tendency towards full valve openness. Both species displayed circadian periodicity ( τ = 24 h): maximal gaping was generally observed during periods of darkness and minimum gaping during daylight hours. The only prominent difference in behaviour between the two species was related to the degree of valve opening. The maximum recorded gape angle was 8.2° (SE = 0.9) for L. securis versus 14.8° (SE = 1.4) for M. galloprovincialis. This difference may place L. securis at a competitive disadvantage on substrates, where the two species coexist, such as over rocky shores or potentially mussel culture ropes. [ABSTRACT FROM AUTHOR]

Highlights: [•] Experimental floating rafts holding oysters were moored in shallow water (1–2m). [•] The oysters were stocked at high densities (16 and 24kgoystersm−2). [•] The oysters produced no discernible biodeposition or benthic enrichment signatures. [•] Rather, the sediment collected under the rafts had relatively low organic content. [•] The rafts possibly impacted local hydrodynamic processes, causing seabed erosion. [ABSTRACT FROM AUTHOR]

The objectives of this study were to compare the stocking density of suspended versus bottom oyster (Crassostrea virginica) culture in Atlantic Canada and to estimate the capacity of these oysters to clear particles from the water column. Surveys of multiple leases indicated that stocking densities for floating bag and floating cage culture techniques were on average 0.3±0.1 and 0.5±0.1kg oystersm−2, respectively. Bottom culture density was estimated at 1.0±0.1kg oystersm−2, whereas natural reef density was assessed at 2.2±1.1kg oystersm−2. In terms of grazing potential, suspended oysters had significantly lower gill areas per unit dry tissue weight than bottom oysters. This result was consistent with power functions relating clearance rate (CR, l h−1) to dry tissue weight (DTW, g). CR increases relative to DTW were significantly lower in the suspended oyster category than in the bottom oyster category, as indicated by the exponent in the relationships CR=6.35±0.59×DTW0.78±0.08 (bottom) and CR=4.34±0.32×DTW0.41±0.08 (suspended). Based on this information it was calculated that CR per unit area (CRArea) in the most heavily exploited leases was 66.5±8.5 (floating bags), 86.5±8.6 (floating cages), and 197.3±144.4 (bottom culture) lh−1 m−2. The CRArea for suspended techniques was on average 10 to 14 times lower than the CRArea for healthy oyster reefs. A bay-scale assessment of an intensive culture site led to the conclusion that cultivated oysters do not exert a dominant top-down control on phytoplankton abundance. [ABSTRACT FROM AUTHOR]

To test the hypothesis that oysters, Crassostrea virginica, from the northernmost part of the species range in the Gulf of St. Lawrence (48°N) open their valves at lower temperatures than those reported for more southern oysters, Hall element sensors were used to monitor their gaping behaviour. These observations were made in a flow-through system and the temperature, salinity and relative fluorescence of unfiltered seawater were monitored. Photoperiod was controlled (15 h dark:9 h light) and light levels were measured but not closely controlled. Gaping behaviour was followed from February to June 2010 (113 days) and from April to May 2011 (34 days) and was classified into three successive phases: quiescent, awakening and active. Although valves were either closed or slightly open during the quiescent phase (maximum gape angle = 0.49°, SE = 0.04), they abruptly opened to maximum angles of about 5.88° (SE = 0.29) during the awakening phase. Moreover, there was noticeable synchrony amongst individuals, since approximately one-half of the monitored population awoke within a 6.6-h period in both study years. Correlative analyses identified temperature as a factor influencing valve movement, and oysters awakened when temperatures were 0.2-4.0 °C (mean = 2.2, SE = 0.2). Oysters exerted their maximal gape angle as soon as temperatures reached 2.8-6.6 °C (mean = 4.8, SE = 0.2). During the active phase, valves remained open 68.6 % (2010) and 79.7 % (2011) of the time. An unexpected result was the observation of a diurnal rhythm in valve openness whereby the openness was greatest near the end of the afternoon and least in the early morning. [ABSTRACT FROM AUTHOR]

Approximately 73 000 Atlantic rock crab ( Cancer irroratus) were captured in coastal waters and transferred to an estuarine mussel aquaculture site in Prince Edward Island, Canada, in an effort to control overgrowth by the invasive tunicate Ciona intestinalis. To assess whether transplanted crabs remained in the vicinity of mussel farms, acoustic tags were attached to 25 resident and 25 transplanted individuals (all males) and their movements were monitored for 1 year, from September 2006 to August 2007. Resident crabs tended to occupy (within 1.6 km) the middle estuary where the majority of mussel farms are located. They left this area during winter, possibly to reach upstream overwintering grounds, and most returned to the middle estuary in spring. In contrast, translocated crabs exhibited a marked downstream movement (<5.5 km distant) in autumn and winter and few returned into the middle estuary in spring. Results suggest that transplanting large numbers of additional rock crabs is not an effective means to reduce the effects of invasive tunicates on mussel farms. [ABSTRACT FROM AUTHOR]

The migration patterns of marine fishes are poorly known, in part owing to the technical limitations associated with tracking the movements of animals in deep water. Here we document a large-scale, directed, migration of Atlantic cod (Gadus morhua) off eastern Canada. Our approach was based on the acoustic tagging of 126 fish and the deployment of 69 subsurface receivers, stretching over a 160-km distance along the edge of the Laurentian Channel. After 1 year of automated recording, we found that 65% of the fish migrated out of coastal waters in two distinct runs during the summer-autumn period. The offshore-migrating fish overwintered in deep Laurentian Channel waters, returning inshore in April. Individual migration routes and migration timing were variable, indicating that the cod did not aggregate in large schools during the seasonal migration events. [ABSTRACT FROM AUTHOR]

The production of triploid bivalves has elicited great interest because their reproductive investment is known to be lower than that of diploids. Reduced reproductive investment is expected to improve the survival and growth of triploid bivalves compared to diploids as the energy spared from reproduction could be used for other metabolic needs. However, the reduction of triploid fertility varies among species, therefore, its impacts on survival and growth are variable. In this study, we compared the reproductive investment of diploid and triploid mussels between two age and size groups (1-year-old ˂ 30 mm, and 2-years-old ˃ 50 mm). We measured gonadosomatic index (GSI), gonad volume fraction (GVF), gonad maturation, and sex ratio. Results demonstrated that while triploid mussels do invest part of their energy in reproduction, they had lower GSI and GVF than diploids. In all tested groups, triploid gonads were less mature than those of diploids, and their sex ratio was significantly altered, with the absence of female triploids. Furthermore, triploid gonads showed signs of gamete resorption, suggesting that the gametes of triploid mussels could serve as energy reserves. This study reveals that triploid mussels invest less energy in reproduction which suggests that the spared energy could be used to improve other metabolic need and survival. We conclude that triploid mussels could be of great interest for aquaculture because they may have better resistance to post-spawning weakness and better recovery due to gametes resorption. • Triploid mussels invest less in reproduction than diploids do. • Triploid mussels have reduced gonadosomatic index and gonad volume. • Gametes of triploid mussels do not show full maturation. • Triploid mussels have an altered sex ratio, with the absence of females. [ABSTRACT FROM AUTHOR]

An abstract of the study "Determination of the Effects of Seismic Exploration on Fish (Project Seifish)," by Arthur N. Popper et al. is presented.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Shallow coastal environments are becoming more susceptible to marine heatwaves, particularly in Atlantic Canada, which is experiencing higher rates of ocean warming compared with the global average. Understanding bivalves' tolerance to heatwaves in Atlantic Canada is especially important, given the magnitude of bivalve aquaculture in this region. In this study, the physiological state of four commercially important bivalve species—blue mussel (Mytilus edulis Linnaeus, 1758), eastern oyster (Crassostrea virginica (Gmelin, 1791)), soft shell clam (Mya arenaria Linnaeus, 1758), and hard clam (Mercenaria mercenaria (Linnaeus, 1758))—was observed during a naturally occurring heatwave in Prince Edward Island, Canada. The metabolism, feeding physiology, and scope for growth of each species were compared. Results from this study, and comparisons with the literature, show interspecific variability in the metabolic rate and feeding physiology between species, but generally oysters, soft shell clams, and hard clams were less impacted during the heatwave compared with the blue mussels. Additionally, only the scope for growth of mussels declined throughout this experiment, which may be explained by cumulative heat stress, as temperatures experienced during this heatwave exceeded the thermal tolerance limits of mussels. [ABSTRACT FROM AUTHOR]

A major problem in mussel farming is mussel fall-off from mussel socks due to weakened byssal threads. This weakening is particularly prevalent following spawning events. During the last decades, significant work has been devoted to the production of triploid bivalves, which have a lower reproductive investment. In this study, we compared the byssal properties and energetic rates of triploid and diploid 1-year-old mussels (˂30-mm). To determine the effect of triploidy on byssal threads, diploid and triploid mussels were placed in a recirculating flume to induce the production of byssal filaments. Our results showed that triploid mussels produced up to 65% more threads than the diploids. Furthermore, tensile measurements showed that byssal threads from triploid mussels had higher Young's modulus values (45% increase) and had multiple yield points. Energetic rates and metabolic investments were measured through food assimilation and oxygen consumption. The results showed that triploid mussels had a higher clearance rate (40% increase) and scope for growth (260% increase) when compared to diploids. Morphological comparisons showed variations between the two groups, with triploid mussels having a larger shell height than diploids of the same length. • Triploid mussels produce more byssal threads than diploids. • Byssal threads from triploid mussels have a higher Young's modulus than diploids. • Byssal threads from triploid mussels have more yield points than diploids • Triploid mussels have a higher scope for growth than diploids • Triploid shells have a larger shell height than diploids of the same length [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This study compares the effect of two anti-fouling treatments, hot water immersion (15 s at 60°C) and air drying (72 h) on the physiological status of the Eastern oyster Crassostrea virginica. The negative impact of hot water immersion was greater than that of air drying, but varied depending on the initial size of the oysters (40 vs. 60 mm shell height) and the time of the year (June vs. August). Groups treated with hot water exhibited a higher proportion of haemocytes with destabilized lysosomal membranes ( HDLM; 47.5 ± 3.1%) than those exposed to air drying (37.5 ± 2.9%). This suggests that the oyster immunocompetency may be lowered by hot water immersion. Overall, the large oysters had lower HDLM values (32.9 ± 3.5%) than the small individuals in June (45.7 ± 2.8%) but similar values in August (46.6 ± 3.5%). Small oysters subjected to hot water immersion in June exhibited a 50% reduction in shell growth and a 50% mortality rate after one month. Our results indicate that air drying is more suitable than hot water immersion as an anti-fouling treatment for <45 mm oysters. [ABSTRACT FROM AUTHOR]

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 1 0 - 2 0% 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. [ABSTRACT FROM AUTHOR]

We compared lipid dynamics and the physiological responses of blue mussels Mytilus edulis, a cold-adapted species, and oysters Crassostrea virginica, a warmer-water species, during simulated overwintering and passage to spring conditions. To simulate overwintering, animals were held at 0°C, 4°C and 9°C for 3 months and then gradually brought to and maintained at 20°C for 5 weeks to simulate spring-summer conditions. Changes in lipid class and fatty acid composition were related to clearance rate and oxygen consumption. We found major differences between species in triglyceride (TAG) metabolism during overwintering. Mussels used digestive gland TAG stores for energy metabolism or reproductive processes during the winter, whereas oysters did not accumulate large TAG stores prior to overwintering. Mussel TAG contained high levels of 20:5n-3 compared to levels in oysters and in the diet. This may help to counteract the effect of low temperature by reducing the melting point of TAG and thus increasing the availability of storage fats at low temperature. Mussels seemed better able to mobilise 20:5n-3 and 18:4n-3 than other fatty acids. We also found that both bivalves underwent a major remodelling of membrane phospholipids. The unsaturation index decreased in the gills and digestive glands of both species during the early stages of warming, principally due to decreases in 22:6n-3 and 20:5n-3. In digestive glands, the unsaturation index did not increase with decreasing temperature beyond a threshold attained at 9°C whereas a perfect negative relationship was observed in gills, as predicted by homeoviscous adaptation. The presence of digestive enzymes and acids in the digestive gland microenvironment may lead to specific requirements for membrane stability. That oysters had lower metabolic rates than mussels coincides with a lower unsaturation index of their lipids, as predicted by Hulbert's theory of membranes as metabolic pacemakers. Both species showed increased 20:4n-6 levels in their tissues as temperature rose, suggesting an increasing availability of this fatty acid for eicosanoid biosynthesis during stress responses. The contrast between the species in TAG dynamics and the similarity of their phospholipid remodelling emphasises the essential functional role of membrane phospholipid structure and the contrasting use of TAG by oysters and mussels during overwintering. [ABSTRACT FROM AUTHOR]

• Sediment mobilization and temperature increase impacted distinctly on clams behaviour. • Valve opening and filtration rates declined significantly due to physical disturbance. • Combination of stressors caused increase in metabolism and nitric oxide production. • Clams were reported to be highly resilient after physical disturbance. • Energy uptake might be compromised during physical disturbance in a highly heterogenous environment. Infaunal organisms living within marine sediments can provide valuable information about the effect of key environmental factors, acting as ecological indicators e.g. species composition and diversity, tolerance to pollution, or resilience degree facing abiotic stressors such as wave storm events. These organisms may modify their environment through burrowing behavior, enhancing mixing, and nutrient and oxygen cycling, which are crucial for ecosystem health. Simultaneously, such high-energy events (wave storms) may impair the ecophysiology of organisms, altering trophic interactions in this particular food web. A set of behavioral, ecophysiological, and stress/immune responses were monitored for the infaunal clam Polititapes rhomboides exposed to key abiotic stressors identified in our coasts (Rías Baixas, NW Iberian Peninsula) as drivers of massive mortality events in the past: sediment mobilization disturbance (SM) in the bottom seafloor, and seawater warming (SW). Valve opening was clearly reduced during physical disturbance while minor effects were observed for temperature increase (+3 °C, from 15 °C to 18 °C). Nevertheless, a highly resilient behavior was noted for the shell opening of clams (crucial for vital physiological functions) after each physical disturbance cycle, with similar profiles to organisms kept under control calm scenarios. The physiology of clams was also altered by sediment mobilization, resulting in a decline of clearance rates (feeding activity) but only with regard to short-term periods after disturbance (e.g. hours). In contrast, temperature increase caused clearance rates to also increase significantly, linked to the optimal diet supplemented during the experiment. The combination of both stressors (sediment mobilization and temperature increase simultaneously) resulted in elevated oxygen consumption rates and nitric oxide production by the clams as activated responses to stress. Again, the ability of the clams to recover from physical disturbance and re-burrow after each disturbance cycle was notorious, most likely escaping from warmer seawater. Clams were able to increase feeding activities (clearance rates) when sediment mobilization ceased based on optimal food availability that counterbalanced the increase in metabolic expenditure during disturbance, although far from the energetic uptake capacity of undisturbed clams. Neither mortality nor dramatic metabolic changes were reported for P. rhomboides subjected to physical disturbance and warming proposed in this survey. Optimal food resource availability has been crucial for the clams to recover from abiotic stressors despite the reported energetic vulnerability index (SFG). The stressors investigated here would act at a greater magnitude in the natural environment, with much more heterogeneity regarding to trophic conditions. Changes in the dynamics of coastal areas driven by heterogeneous (high-energy) environments linked to hydrodynamics would affect not only biodiversity maintenance but also the socioeconomic sectors involved and therefore, its comprehension would be crucial for the resilience of natural systems under Agenda 2030 and the Sustainable Development Goals (SDGs). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 p CO 2 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) p CO 2 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 p CO 2 , 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Bivalve aquaculture has rapidly expanded in shallow coastal habitats, leading to substantial changes in the natural environment. While the grazing pressure of mussels (Mytilus edulis) on phytoplankton and zooplankton has been well documented, cascading effects of plankton depletion on the development and survival of resident fish and invertebrate larvae remains largely unexplored. This study experimentally assessed the impact of control (no mussel grazing), low (20 mussels·m−3) and high (80 mussels·m−3) mussel densities on a model community composed of various phytoplankton and zooplankton and how changes in plankton characteristics influence the development and survival of lobster (Homarus americanus) larvae. Mussels fed primarily on nanophytoplankton, while the picophytoplankton experienced significantly less grazing. Zooplankton was readily ingested by mussels, showing a sharp decline under low mussel density, whereas it was eliminated from the plankton under high density of mussels. A 65% decrease of polyunsaturated fatty acids (∑ PUFA) was observed in the plankton under mussel filtration compared to control. Lobster larvae reared under control plankton conditions exhibited the fastest development, highest survival rate, carapace length, total lipid and ∑ PUFA contents, and TAG/ST (triacylglycerols/sterols) ratio, indicating the best nutritional condition. Larvae reared under low mussel density showed longer developmental time, lower survival rate and carapace length than that for controls. In addition, these larvae showed a significant reduction in total lipid, ∑ PUFA, and TAG/ST, which collectively suggests poor nutritional status due to limited dietary intake. Under high mussel density, larvae did not molt to stage II and died within 14 days, suggesting that the depleted plankton community was unable to sustain physiological requirements for survival and development of the larvae. Overall, mussel grazing altered the meroplankton community structure and its biochemical composition, ultimately impacting the development, survival, and quality of lobster larvae. These findings provide novel information on complex trophic interactions between bivalves and a meroplankton species and adds a new perspective to fuel discussions on energy and nutrient pathways, particularly long-chain PUFA, in ecosystem carrying capacity studies for shellfish aquaculture in shallow coastal habitats. • Mussel grazing reduced the availability of both plankton and ∑ PUFA to meroplankton. • Under no mussel influence, plankton was abundant and yielded the best quality lobster larvae. • Mussels fed primarily on nanophytoplankton and zooplankton. • Low mussel density reduced plankton and ∑ PUFA, yielding low quality lobster larvae. • High mussel density filtered out zooplankton, starved lobster larvae and led to severe mortality. [ABSTRACT FROM AUTHOR]

Mudworm ( Polydora websteri) parasitism is known to result in unsightly mud blisters in eastern oysters ( Crassostrea virginica), resulting in reduced product quality and increased vulnerability to illness and environmental stress. While typically a concern only for bottom-grown oysters, an abnormal severe outbreak of P. websteri in surface-cultured oysters in New Brunswick, Canada, was reported in 2013, along with an anecdotally reported concurrent increase in siltation. Although heavier loads of silt are reported to increase P. websteri infestations in oysters, studies report mixed effects of siltation to this regard. Here, we report the results of a field experiment testing the effect of siltation on P. websteri recruitment in surface-grown oysters at an aquaculture site in Richibucto, New Brunswick. Live oysters of similar size were deployed at the aquaculture site and were left to collect P. websteri recruits under one of two siltation treatments (high vs. low) for 50 days. Results suggested that P. websteri recruitment correlated with metrics of oyster size (shell weight, length, width, depth and surface area). When P. websteri counts were standardized for oyster shell morphometry, P. websteri recruitment was significantly higher in oysters exposed to the high siltation treatment, accumulating approximately 1.5× as many P. websteri as oysters exposed to the low siltation treatment. Our results suggest that higher amounts of siltation on surface-cultured oysters can result in increased rates of P. websteri parasitism. Enhanced cleaning regimes may help to alleviate the impacts of P. websteri in surface-grown oysters, although other mitigation strategies exist. [ABSTRACT FROM AUTHOR]

šIn this study, we investigated the food sources of eastern oysters Crassostrea virginica cultivated in Atlantic Canada. Stable isotopes (13Cand 15N) and fatty acid biomarkerswere used to identify these sources under in situ conditions for suspended (~0.5mbelow surface) and bottom(~2m) culture stocks. It was found that particulate organic matter represented the main food source, with major contributions from live phytoplankton. Higher lipid contents were detected in the digestive glands of suspended oysters compared to bottom oysters (p<0.05). Bottom oysters did not show significant preference for detrital or bacterial organic matter. Near-surface waters contained an elevated picophytoplankton biomass (PPP, 0.2-2mm, 1.93 ± 0.16µg l-1, mean ± SEM) compared to nanophytoplankton biomass (NPP, >2mm, 1.05 ± 0.15µg l-1, mean ± SEM). To determine whether the small size PPP was captured and assimilated by C. virginica, feeding trials were conducted in the laboratory using three PPP/NPP diets (20%, 50%, and 80% PPP), consisting of isotopically-labelled (d13C) PPP cells (Nannochloropsis oculata) and non-labelled NPP cells (Tisochrysis lutea). An isotopically-labelled fatty acids analysis indicated PPP assimilation in various tissues (digestive gland, gills, mantle, and abductor muscle), including from oysters fed the reduced (20%) PPP diet. Isotopic enrichment (13C) in the FA22:2 (non-methylene-interrupted orNMI) showed that precursors of NMIs utilized PPP carbon in its biosynthesis process. In conclusion, C. virginica assimilated primarily particulate organic matter (POM), including PPP, which dominated the phytoplankton community in near surface waters. C. virginica can exploit PPP carbon during fatty acid production and further biosynthesis. [ABSTRACT FROM AUTHOR]

Different combinations of behavioural and physiological responses may play a crucial role in the ecological success of species, notably in the context of biological invasions. The invasive mussel Xenostrobus securis has successfully colonised the inner part of the Galician Rias Baixas (NW Spain), where it co-occurs with the commercially-important mussel Mytilus galloprovincialis. This study investigated the effect of a heatwave on the physiological and behavioural responses in monospecific or mixed aggregations of these species. In a mesocosm experiment, mussels were exposed to simulated tidal cycles and similar temperature conditions to those experienced in the field during a heat-wave that occurred in the summer of 2013, when field robo-mussels registered temperatures up to 44.5°C at low tide. The overall responses to stress differed markedly between the two species. In monospecific aggregations M. galloprovincialis was more vulnerable than X. securis to heat exposure during emersion. However, in mixed aggregations, the presence of the invader was associated with lower mortality in M. galloprovincialis. The greater sensitivity of M. galloprovincialis to heat exposure was reflected in a higher mortality level, greater induction of Hsp70 protein and higher rates of respiration and gaping activity, which were accompanied by a lower heart rate (bradycardia). The findings show that the invader enhanced the physiological performance of M. galloprovincialis, highlighting the importance of species interactions in regulating responses to environmental stress. Understanding the complex interactions between ecological factors and physiological and behavioural responses of closely-related species is essential for predicting the impacts of invasions in the context of future climate change. [ABSTRACT FROM AUTHOR]

The incidence of nutrient-induced hypoxia or anoxia-related mortality of aquatic species is becoming more prevalent in coastal systems worldwide. One such instance in an estuary of New Brunswick, Canada, resulted in the loss of approximately 75% of cultured oysters in certain farms. Field observations revealed that, although the occurrence of summer hypoxia in north Tracadie Bay was linked with anthropogenic stressors, changes in the morphology of one of the bay's inlets were likely to play a significant role in escalating the eutrophic conditions. However, adequate information on the circulation dynamics of Tracadie Bay was lacking. To address this knowledge gap, a high-resolution spatially explicit hydrodynamic model was developed for Tracadie Bay to evaluate the possible physical processes involved in the generation of hypoxia leading to oyster mortality. Further, the model was coupled with a volume advection-dispersion tracer module to track the dissemination of effluent. The model showed high skill in south Tracadie Bay in simulating water level elevations and slightly lower skill in north Tracadie Bay. Residual flow estimates revealed poorly-circulated stagnant areas, consistent with hot spots in sediment organic matter content. Findings from modeling scenarios based on past, present, and future inlet morphology suggest that inlets have strong consequences on intricate circulation patterns, renewal of water, and transport. Outcomes from this study will be of relevance for managing water quality and aquaculture practices. • Bay's flushing potential responds to inlet geomorphic setting. • Long water renewal time indicates poor flushing. • Stagnant areas coincides with hot spots of sediment organic content. • Feeble outgoing fluxes likely to escalate eutrophic conditions. [ABSTRACT FROM AUTHOR]

• Experimental study of the effects of A. catenella on M. edulis physiology and behaviour. • Average saxitoxin accumulation in tissues reached 52 µg STXeq 100 g–1 after one week. • Short-term responses include significant weight loss, increased oxygen consumption. • Valve opening amplitude was also lower and closure duration longer in exposed mussels. • No clear long-term differences were observed in comparison to non-exposed mussels. 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. [ABSTRACT FROM AUTHOR]

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. • Tested effect of silt on oyster larval settlement to artificial collectors and natural shell substrate. • Compared settlement on upper and under side of benthic shell substrate. • Examined adult oyster health during an acute siltation event. • Settlement higher on benthic shell than suspended substrate; silt negatively affected settlement and adult health. • Negative effects of siltation were less severe on underside of benthic shell. [ABSTRACT FROM AUTHOR]

• Behavioural effects of an oil dispersant on M. edulis and P. magellanicus valve gaping were explored. • M. edulis continuously closed their valves following the addition of higher oil dispersant concentrations. • P. magellanicus mortality was rapidly detected though abnormal valve movements at the higher oil dispersant concentration. • Valvometry represents a potential tool for environmental assessments. 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. [ABSTRACT FROM AUTHOR]

Ocean acidification is expected to affect marine organisms in the near future. Furthermore, abrupt short-term fluctuations in seawater p CO 2 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 p CO 2 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 p CO 2 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 p CO 2 did not affect either response. Our results add to the increasing body of evidence suggesting that the effects of end-of-century p CO 2 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. • Tested effects of elevated CO 2 on valve gaping responses to predator alarm cues in Mediterranean mussels. • Mussels reduced valve gaping in response to predator alarm cues; no change in valve movement activity. • Elevated CO 2 had no effect on baseline behaviour nor responses to predator cues. • Behavioural responses to predator cues in bivalves appear robust to high CO 2. [ABSTRACT FROM AUTHOR]

• Investigated efficacy of "bouncing" technique to increase shell thickness and strength for on-bottom cultured oysters. • Bouncing increased shell thickness and strength for oysters >45 mm shell height compared to control oysters. • Bouncing decreased shell thickness and strength for oysters <45 mm shell height compared to control oysters. • Bouncing had no effect on shell shape. • The size at which bounced oysters are released after grow out will dictate usefulness of bouncing technique. 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 <45 mm shell height compared to control oysters. There was no difference in shell shape between bounced and control oysters, with both groups having similar fan and cup ratios. Ultimately, our results suggest that the size at which bounced oysters are released to the benthos for grow out will dictate the usefulness of bouncing technique for reducing predation-related mortality. [ABSTRACT FROM AUTHOR]