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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)

Copepods are the main natural food of many marine fish larvae. However, enriched rotifers are the most commonly used live prey in larval rearing. Impacts on the feeding behavior, growth, survival, and fatty acid (FA) composition of winter flounder larvae fed with copepods and rotifers were determined and compared to the FA composition of the two live prey. Nauplii of Eurytemora spp. and Acartia sp., two of the main species of copepods present in the St. Lawrence estuary, showed no significant differences in their essential fatty acid profiles, suggesting similar nutritional quality. Thus, only Eurytemora herdmani was compared to enriched rotifers in this study. Copepod nauplii were characterized by higher levels of essential fatty acids, particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). The selective incorporation of essential fatty acids from diets in larval tissues (polar lipids) indicated that nauplii might better fulfill larval nutritional requirements for DHA than rotifers. Furthermore, larval behavior was modified according to the diet: larvae fed with nauplii spent more time swimming with no changes in the occurrence of hunting events.

The objective of this work is to explore a new phycoremediation strategy to convert a dairy by-product into microalgal biomass. A culture strategy involving two different green microalgae species was used to remove lactose from cheese whey permeate. First a co-cultivation experiment involving Scenedesmus obliquus and Chlorella protothecoides showed better utilization of the different sugars (lactose, glucose and galactose) than homogeneous S. obliquus cultures. In a second experiment, sequential cultivation of the two microalgal species allowed to convert 62% of the total lactose into 6.8 ± 0.2 g L − 1 and 6.2 ± 0.4 g L − 1 S. obliquus and C. protothecoides cultures respectively, for a “lactose-to-biomass” yield (Y x/s ) of 0.45. This type of beneficial interaction between two different microbial species represents a simple and sustainable way to improve and diversify the possibilities in the field of industrial microbiology.

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.

Spillages at sea of diluted bitumen (dilbit) from oil sands have received little attention until now. To our best knowledge, there are no reports on the impact of a severe exposure to dilbit on the Blue mussel (Mytilus edulis). In this study, adult Blue mussels were exposed to one conventional crude oil (Heidrun) and two dilbits (Cold Lake Blend and Access Western Blend) for a period of 7 days in an ice-covered environment and then maintained for three months until the spawning season. The exposed mussels were monitored for aromatic hydrocarbon bioaccumulation, physiological energetic budget, cellular stress, byssus production and gametogenesis. In spring, spawning was induced to characterize breeding success. Bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) was detected after three days of exposure, with higher concentrations of PAHs associated to the conventional oil (5.49 ± 0.12 μg·g−1 d.w.) compared to both dilbits (0.91 ± 0.02 μg·g−1; 0.51 ± 0.03 μg·g−1 d.w.). Despite a fast depuration rate and a good resilience of the exposed mussels, significant negative effects were observed at the cellular, physiological and fitness levels, especially in offspring. Our results suggest a higher toxicity of the diluted bitumen compared to the conventional crude despite the lower bioaccumulation of total PAHs. Dilbit treatments caused evident negative transgenerational effects on unexposed F1 generation.

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.

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 (

In the Estuary and Gulf of St. Lawrence, northern shrimp (Pandalus borealis) and Greenland halibut (Reinhardtius hippoglossoides) are usually found at depths > 150 m and thus frequently inhabit hypoxic areas (18–50% saturation). The impact of a one-week exposure to different levels of dissolved oxygen (100, 40, 30, and 20% saturation) at 5 °C was evaluated in adult shrimp and juvenile Greenland halibut; the effect of acute exposure to severe hypoxia was also assessed in Greenland halibut. The activities of key enzymes involved in aerobic (citrate synthase [CS], cytochrome c oxidase [COX]) and anaerobic (pyruvate kinase [PK], phosphoenolpyruvate carboxykinase [PEPCK], lactate dehydrogenase [LDH]) pathways, and of enzymes involved in antioxidant defence (superoxide dismutase, glutathione peroxidase [GPx], and catalase [CAT]) were measured. Quantitative real-time PCR analysis was also performed in Greenland halibut. In northern shrimp exposed to chronic hypoxia, muscle CS activity decreased by ~ 40%. Muscle LDH activity was significantly reduced, with a more intense reduction in males. At the same time, hepatopancreas GPx activity increased under hypoxia, and this response was stronger in males. Overall, the results suggest the presence of a threshold above 40% saturation and higher hypoxia tolerance in males. In juvenile Greenland halibut, exposure to chronic hypoxia elicited a more wide-ranging enzymatic response than did acute exposure to severe hypoxia. Under chronic hypoxia, CS activity decreased and PK and LDH activity were respectively 46% and 57% lower than in normoxia. There were no major changes in the activity of antioxidant enzymes, but activity in normoxia was high compared to other fish species. Interestingly, the relative expression of genes coding for muscle COX (severe hypoxia), liver PEPCK (chronic), and CAT (chronic) activities were triggered in hypoxia. The absence of a corresponding change in enzyme activity makes the interpretation of these results difficult, but clearly there was a response at the transcription level. Overall, the results indicate that these two species are particularly well adapted to withstand severe hypoxia. -- Keywords : Aerobic pathwa ; Anaerobic pathway ; Antioxidant defence ; Metabolic capacity ; Gene expression ; Enzyme activity.

In coastal environments, fishing and aquaculture may be important sources of disturbance to ecosystem functioning, the quantification of which must be assessed to make them more sustainable. In the Chausey Archipelago, France, recreational fishing and commercial shellfish farming are the only two evident anthropogenic activities, dominated by bivalve hand-raking and 'bouchot' mussel culture, respectively. This study evaluates the impact of both activities on bivalve recruitment dynamics by comparing primary recruitment intensity (short-term effect) and recruitment efficiency (medium-term effect) by sampling bivalves in reference (undisturbed) and disturbed (i.e. subjected to hand-raking or in 'bouchot' mussel culture areas) parcels throughout and at the end of the recruitment season, respectively. Specific hypotheses evaluated were that (H1) bivalve hand-raking negatively affects bivalve recruitment and that (H2) 'bouchot' mussel culture promotes bivalve recruitment. Patterns in bivalve community structure in reference parcels (i.e. natural pattern) differed between initial and final recruitment, underlining the great importance of early post-settlement processes, particularly secondary dispersal. Primary recruitment intensity was inhibited in hand-raking parcels whereas it was promoted in 'bouchot' mussel culture parcels, but the effect on recruitment efficiency was muted for both activities due to post-settlement processes. Nevertheless, the importance of effects that occur during the first step of recruitment should not be ignored as they may affect bivalve communities and induce immediate consequences on the trophic web through a cascade effect. Finally, it is highlighted that hand-raking damages all life stages of the common cockle Cerastoderma edule, one of the major target species, suggesting that this activity should be managed with greater caution than is currently done.

Heterotrophic culture of algal cells is now known as an efficient avenue for lipid production. However, the mechanisms involved are not clearly understood, especially when feeding glucose concurrently to autotrophic culture condition. In this work, the time course dynamics of central carbon metabolites of Chlorella protothecoides was studied in autotrophic, heterotrophic and mixotrophic cultures to elucidate the effect of glucose on the cell metabolic reorganization. Results show that assimilated CO2 mainly goes to the synthesis of upstream carbohydrate-based metabolites under autotrophic condition, while supplementing glucose recalibrates the metabolism towards downstream metabolites and lipids, rather than carbohydrates accumulation. The analysis of the lipid class shows, under glucose supplementation, that cells accumulate neutral lipids as storage rather than as membrane polar lipids, while fatty acid composition changes from polyunsaturated to saturated and monosaturated, which shows improving the quality of biodiesel precursors. The metabolic flux rearrangement seemed being regulated by a high cell energetic state that was maintained by a glucose metabolism. A high initial ATP-to-ADP ratio was observed after adding glucose, suggesting cell energetics as a biomarker of a metabolic shift from starch to lipid accumulation. These findings thus bring novel data on the regulation of carbon flow in microalgal cells, and enhance our understanding of microalgae as a lipid production platform.

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.

In Atlantic Canada, oyster farmers rely on wild oyster spat collections for their main source of seed. In this study, the physiological fitness of oysters originating from four seed producing areas in eastern New Brunswick (NB) was compared. Oysters [50–70 mm shell height (SH)] from Caraquet, Miramichi, Richibucto and Bouctouche, NB were assessed in a laboratory setting using the following parameters: aerobic capacity (metabolic rate), multi-locus heterozygosity (MLH) and stress response (lysosomal destabilization). Field trials were carried out in different environments in the Richibucto estuary with oysters (∼65 mm SH) from Miramichi and Bouctouche. In the laboratory, significant difference in maximum metabolic rates (VO2max) was found for oysters from Caraquet and Bouctouche, compared to those from Richibuctou. The VO2max were 37 % and 45 % lower in Caraquet and Bouctouche oysters, respectively, compared to those from Richibucto. The Miramichi oysters did not differ significantly from the other oyster populations, including Richibucto (P = 0.063). Significant difference in standard metabolic rates (VO2min) also was found for oysters from Bouctouche, compared to Richibucto. However, aerobic capacity (VO2min:VO2max ratio) did not differ among oyster populations, and no significant difference was found in MLH levels or in lysosomal destabilization indices following the thermal stress event. Field trials (August-November 2012) showed low mortality (0–8%) after ∼100 days, regardless of the sampling period—September vs. November or rearing site—downriver vs. upriver and lysosomal destabilisation indices did not differ between Miramichi and Bouctouche oysters. Results suggest that oysters from the major seed producing areas in eastern New Brunswick (Caraquet, Miramichi, Richibuctou and Bouctouche) are similar in physiological performance and quality.

Marine invertebrates inhabiting low-latitude shores are exposed to both extremely hot and highly variable conditions. Further changes in habitat temperature may pose a risk to these populations. In this study, we examined the early life stage response of foundation species from subtropical and tropical latitudes to changes in the thermal habitat. We manipulated the color of settling surfaces for barnacle species that occupy the same ecological niche, Chthamalus bisinuatus (southeastern coast of Brazil), and Chthamalus proteus (northwestern coast of Panama). Using an in situ experimental approach, we assessed: 1) the combined effects of temperature and other abiotic parameters, and 2) the significance of larval and early juvenile traits in determining post-settlement performance for the first three days of benthic life. We found that the biological outcomes differed for the two species, according to the local thermal regime experienced. C. bisinuatus juveniles responded positively to higher temperatures, through a positive interaction between larval energetic condition, post-metamorphic size and temperature on their initial growth. Conversely, C. proteus juveniles grew slower at higher temperatures, although a positive effect of size at settlement was found. Continuous air- and sea-surface temperature measurements revealed that the tropical chthamalids experienced temperatures ≈6 °C higher than their subtropical congeners, as well as harsher thermal conditions during aerial exposure. This suggests that manipulated temperatures likely exceeded the tolerance of the Caribbean population, already living on the edge of their thermal threshold. Our findings contribute to the understanding of the factors underpinning the critical post-settlement events that drive patterns of abundance and distribution of barnacles in low-latitude systems.

There are several factors affecting scallops during the metamorphosis process that could explain the relatively low post-larvae yield observed in hatcheries. Competent bivalve larvae respond to different settlement cues to undergo metamorphosis and without adequate cues, larvae delay their metamorphosis. The objective of this study is to improve the settlement ratio of the two scallop species, Placopecten magellanicus and Pecten maximus by physical cues associated with hydrodynamic conditions, stocking density in settlement units and larval size at time of transfer to settling units. For each treatment, physiological condition was determined by fatty acid analysis to determine the energetic reserves and structural lipids. We observed similar results for the two important commercial pectinid species and validate the hypothesis on the positive effect of increased flow rate and larval size after transfer to settlement systems on settlement success. Increasing flow rate also affects positively the physiological condition of settled post-larvae by a higher accumulation of total fatty acids in neutral lipid fractions. Furthermore, no effect of larval stocking density until 90 larvae cm−2 in the downwelling sieves was observed. To our knowledge this study is the first to characterize the effect of seawater flow rate on settlement success of different pectinid species cultured under similar conditions. The experiments were performed in a close to commercial scale and thus are relevant to industry situations.

International audience

article i nfo The practicability of culturing microalgae in mixotrophic mode is evaluated for pilot-scale photobioreactor systems, as a general consideration for new process development: higher biomass production rates, production of (potentially new) high-value products from algae and the transformation (recovery) of other carbon sources are the typical advantages of this production mode. This study is conducted with Scenedesmus obliquus ,a species known for its ability to assimilate a wide variety of carbon sources. Autotrophic experiments are first conducted to obtain the typical behavior (growth curve and nutrient consumption rates) of the alga in standard medium composition. Mixotrophic experiments then follow: aside from productivity aspects, results show that bacterial contaminations can remain an issue at this scale, even for closed systems such as photobioreactors. It is however shown possible to exploit some intrinsic dynamic properties of the algae to limit bacterial growth, with no sig- nificant impact on algal growth and biomass productivity. Anionic analyses on the mixotrophic cultures show that particular attention should be drawn on the phosphate and sulfate ions for further process optimization. © 2015 Elsevier B.V. All rights reserved.

Microalgae are unicellular organisms in which plasma membrane is protected by a complex cell wall. The chemical nature of this barrier is important not only for taxonomic identification, but also for interactions with exogenous molecules such as contaminants. In this work, we have studied freshwater (Chlamydomonas reinhardtii) and marine (Pavlova lutheri and Nannochloropsis oculata) microalgae with different cell wall characteristics. C. reinhardtii is covered by a network of fibrils and glycoproteins, while P. lutheri is protected by small cellulose scales, and the picoplankton N. oculata by a rigid cellulose wall. The objective of this work was to determine to what extent the different components of these microorganisms (proteins, carbohydrates, lipids) can be distinguished by 13C solid-state NMR with an emphasis on isolating the signature of their cell walls and membrane lipid constituents. By using NMR experiments which select rigid or mobile zones, as well as 13C-enriched microalgal cells, we improved the spectral resolution and simplified the highly crowded spectra. Interspecies differences in cell wall constituents, storage sugars and membrane lipid compositions were thus evidenced. Carbohydrates from the cell walls could be distinguished from those incorporated into sugar reserves or glycolipids. Lipids from the plasmalemma and organelle membranes and from storage vacuoles could also be identified. This work establishes a basis for a complete characterization of phytoplankton cells by solid-state NMR.This article is part of a Special Issue entitled: NMR Spectroscopy for Atomistic Views of Biomembranes and Cell Surfaces. Guest Editors: Lynette Cegelski and David P. Weliky.

The aim of this study was to evaluate how variations in total lipids, fatty acids, and total and free amino acids in eggs affect embryonic development throughout the spawning season in cultured walleye ( Sander vitreus ). Eggs were obtained from 4-year-old females and pooled based on spawning time: they were assigned to four consecutive periods during a one-month spawning season according to the first spawning occurrence in the female broodstock. Hatching success was significantly higher at the intermediate spawning period (87.3 ± 2.4%), and no eggs hatched in the late spawning group (p

Microalgae mass cultivation for biodiesel production might very well become the next marketable biofuel. The main challenge to overcome however is the development of high efficiency strategies for the large-scale production of oleaginous microalgae at low costs. In the present work, the use of cheese whey permeate (WP) in mixotrophic microalgae cultures is proposed. Pure lactose, the main constituent of WP (> 80% w/w of the total dissolved solids), can support Scenedesmus growth under heterotrophic culture conditions (absence of light). Substituting 40% (v/v) of the culture medium with WP significantly stimulates Scenedesmus obliquus growth under mixotrophic (μ max = 1.083 ± 0.030 day − 1 ) and heterotrophic (μ max = 0.702 ± 0.025 day − 1 ) conditions, compared to photoautotrophic control cultures (μ max = 0.267 ± 0.083 day − 1 ). As growth occurs in the presence of lactose, a significant reduction of its concentration is observed, while the galactose and glucose concentrations actually increase in the culture medium. Culture medium analyses showed complete exhaustion of extracellular nitrogen (nitrate and ammonium), while intracellular lipid analyses showed neutral lipid (NL) accumulation, particularly under conditions of high pH (> 9.5). Photoautotrophic control cultures accumulated more lipids (per dry weight) than WP-supplemented cultures, an aspect which is discussed in the context of lipid enrichment strategies. A fast and simple method for NL cellular content estimation is also described.

Offshore and open sea suspension-culture of mussels is largely in development but, in this particular environment, sleeved mussels are submitted to high-energy oceanographic conditions which could increase fall-offs. In this study, we compared the performance of open sea mussel culture to that of culture in a lagoon environment. Byssus attachment strength, condition index, mechanical properties of individual byssal threads, metal content of the filaments for mussels from both the open sea and the semi-closed lagoon sites were monitored as well as the environmental characteristics of these sites. The spawning event occurred approximately one month earlier for mussels in the open sea than in the lagoon, probably due to a difference in temperature and food availability. The attachment strength of the mussels was weaker in the open sea, even if individual threads were bigger and stronger than in the lagoon. This lower attachment strength seems related to a lower production of byssal threads.

Krill, as forage species, play a pivotal role in marine food webs by linking lower to upper trophic levels. Despite their ecological relevance, processes affecting their physiological condition and their feeding selectivity remain not well known. Here, we hypothesize that significant spatial fluctuations of environmental conditions in a Subarctic region affect the energy reserve content and feeding strategies of krill. To test this hypothesis, we assessed the fatty acid content and composition of two dominant northern krill species Meganyctiphanes norvegica and Thysanoessa inermis on a seasonal basis over more than 1000 km in the Estuary and Gulf of St. Lawrence (eastern Canada) and for the first time during the ice covered winter. M. norvegica exhibited large spatial variation of its energy reserve lipids, which were similar to seasonal variations found in a previous study in the same environment. In contrast, lipid content of T. inermis was much less affected by the spatial variations of environmental conditions but showed high seasonal variability. Feeding preferences assessed using fatty acid trophic markers highlight that the zooplankton standing stock could be more critical than phytoplankton to fulfill the metabolic requirements of these krill species and to build lipid energy reserves. In addition, diet comparison between both species highlights that trophic niche partitioning is present in the Gulf of St. Lawrence, however, modulated by spatial differences in food supply and oceanographic conditions.

Microalgae are potentially a sustainable biofuel source, however commercial algal biofuel production is presently expensive. Two major factors, energy efficient harvesting and recycling of the harvested medium, need to be addressed to reduce costs and facilitate profitable biofuel production using algae as feedstock. To address these barriers to sustainable use of the promising oleaginous marine microalgae Parachlorella kessleri-I grown in standard the f/2 culture medium, we evaluated the optimal flocculant concentration and pH for six inorganic, one organic and integrated flocculation processes using chemo-magnetic nanoparticle (Che-MNP) and chitosan-magnetic nanoparticle (CS-MNP) composites. The harvesting efficiency, and reusability of the medium for algal culture along the corresponding lipid and fatty acid composition of algae were evaluated. This study shows that CS-MNP and Che-MNP considered being a promising flocculation process due to its high efficiency, low dosage of chemical requirement, short harvesting time, total reusability of the flocculant (MNP) and flocculated medium without affecting the lipid and fatty acid profile of algae. The integrated harvesting processes offer an effective, sustainable and rapid harvesting of P. kessleri-I for sustainable biofuel production or others potential biotechnological needs.

The release of hatchery-reared American lobster ( Homarus americanus ) is used, on some occasions, as a tool to enhance depleted lobster stocks. Current Canadian lobster enhancement programs rely on the release of postlarvae (stages IV and V), which are still vulnerable to high mortality. We hypothesized that larvae enriched in triglycerides (TAG) and polyunsaturated fatty acids (PUFA) during their development from stage I to stage IV have higher survival and growth rates. We assessed the condition, growth and survival of lobster postlarvae (stage IV) fed during their larval stages with live natural zooplankton, to maximise TAG and PUFA enrichment, compared to those fed a standard Artemia diet. Stage I larvae obtained from ovigerous wild females were cultured in the hatchery on either an Artemia or a zooplankton diet until stage IV (7 d old), when they were transferred to the field (i) individually in small boxes for 3 months or (ii) communally in large enclosures for 3–4 months to assess survival and growth in situ. Our results show that a diet of natural zooplankton significantly increases the TAG and PUFA content of larvae compared to a diet of live Artemia . Stage IV lobsters fed natural zooplankton had a better condition index (TAG/ST) and a higher activity of the enzyme regulating osmoregulation than those fed Artemia . Larvae fed zooplankton had a significantly higher growth rate than larvae fed Artemia , (655 vs 507 μm dry mass d − 1 , respectively). Despite these differences, survival was similar for both diets, in the hatchery as well as in situ, in predator-free situations. Nevertheless, a higher growth rate may be a potential survival advantage for newly released lobsters, allowing them to reach a size refuge from predation more rapidly. We conclude that even if live Artemia remains the best and most reliable source of live food for the production of American lobster larvae, it needs to be considerably enriched with PUFA, at levels comparable to that of natural zooplankton, to increase osmoregulation potential and growth.

Northern shrimp is an important commercial species in the Estuary and Gulf of St. Lawrence. It is usually found at depths > 150 m and thus frequently inhabits hypoxic areas (18–40% saturation) in this region. To evaluate the impact of hypoxia on adult shrimp, males and females were exposed to different levels of dissolved oxygen at two temperatures (5 and 8 °C). Standard and maximal metabolic rates as well as the critical oxygen threshold were measured. In addition, metabolic and antioxidant enzyme activities were measured at 5 °C. Females had a higher critical oxygen threshold than males at both temperatures (15.5 and 22.2 vs. 9.0 and 13.8 at 5 and 8 °C respectively), indicating that they were less tolerant of hypoxia. A decrease in glycolytic and fermentation enzyme activities confirmed this result: in females, severe hypoxia significantly decreased the specific activities of citrate synthase and of enzymes involved in anaerobic biochemical pathways (lactate dehydrogenase, pyruvate kinase, and phosphoenolpyruvate carboxykinase (PEPCK)); in males, only the PEPCK activity decreased significantly while glutathione peroxidase (antioxidant defense) activity increased significantly. In females, severe hypoxia (22% sat.) did not affect the standard metabolic rate but significantly reduced (by ~ 43%) the maximum metabolic rate compared to normoxia. Consequently, aerobic scope was reduced by ~ 58% at 22% sat. compared to normoxia. This suggests that the shrimp's flexibility to respond to metabolic demands, including such activities as vertical migration, foraging, and egg production, could be reduced in hypoxic conditions, especially in females.

The blue mussels Mytilus edulis are widely cultured in the coastal regions of Canada. However, their production on sleeves attached to long lines in the water column suffers from fall-offs due to byssus weakening, especially during the spawning period. Thus, we tested in laboratory the hypothesis that the spawning event changes the chemical and biochemical composition of byssal threads, resulting in a significant modification of their mechanical properties. Metal composition of byssus is interesting, as the proteins are cross-linked by complexation with metals influencing the breaking force. Our results show that the filaments' diameter and breaking force significantly decreased after spawning, as compared to unspawned individuals. However, no differences in the stress-at-break and strain-at-break were observed between the two experimental groups. Analysis of the lipid composition of the fibers' distal region indicates a very low concentration of total lipids, i.e. M. edulis in laboratory conditions was mainly due to a reduction of the fiber diameter, and cannot be related to changes in lipids, amino acid or metal composition.

Through biological flume experiments, we studied the effect of shear velocity and attachment period on the percent detachment of Pecten maximus post-larvae of different sizes reared on two experimental diets. The first diet, (Pavlova lutheri, Isochrysis galbana, Chaetoceros calcitrans), which served as a reference diet (PTC), is commonly used in bivalve hatcheries; the second is the PTC diet with the addition of Rhodomonas salina (PTCR). Our results indicate that the detachment of post-larvae fed PTCR diet showed significant interactions between scallop length, attachment period and shear stress, while the post-larvae feed with the PTC diet showed only effect of shear stress factor. Furthermore, post-larvae exposed to various flume velocities showed different percentages of detachment according to diet (PTC=36% and PTCR=57%) for flow velocities between 1.42 to 2.45 cm s(-1) after 12 h attachment periods. This result could be related to differences in the biochemical composition of post-larvae as discussed. (C) 2012 Elsevier B. V. All rights reserved.

International audience; Quantification of mRNA of genes related to metabolism, immunity and cellular stress was examined in relation to a massive mortality event during the culture of American oyster larvae. Crassostrea virginica which was probably, in regard to previous microbiological analysis, induced by Vibrio infection. To document molecular changes associated with the mortality event, mRNA levels were compared to biochemical and physiological data, previously described in a companion paper. Among the 18 genes studied, comparatively to the antibiotic control, 10 showed a lower relative gene expression when the massive mortality occurred. Six of them are presumed to be related to metabolism, corroborating the metabolic depression associated with the mortality event suggested by biochemical and physiological analyses. Relationships between the regulation of antioxidant enzyme activities, lipid peroxidation, and the mRNA abundance of genes linked to oxidative stress, cytoprotection, and immune response are also discussed. Finally, we observed an increase in the transcript abundance of two genes involved in apoptosis and cell regulation simultaneously with mortality, suggesting that these processes might be linked. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.

Extremum seeking control is applied to batch cultures of microalgae Nannochloropsis Oculata with the objective of maximizing the growth rate through manipulation of the pH. A commercial biomass monitor (BugEye from BugLab) using on-line optical density (OD) measurements at 725 nm is used to provide signals relative to both biomass density and growth. Parameters for the optimization algorithm are derived from system identification data and simulation results on a phenomenological simulator built specifically to represent the system. A summary of the simulator development and validation on available data from the physical system, a pre-industrial scale photobioreactor, are also presented.

The main objective of this study was to evaluate the effect of the addition of Rhodomonas salina in the diet of Pecten maximus on growth, survival and metamorphosis success in relation to biochemical content. Food quality is an essential factor in the success of larval, post-larval and juvenile development. A diet rich in polyunsaturated fatty acids present an advantage for growth, survival and metamorphosis success. Larvae and post-larvae fed with the diet containing R. sauna showed a higher accumulation of arachidonic acid (20:4n-6) and generally a lower concentration of docosahexaenoic acid (22:6n-3). Addition of R. sauna in diet was related with higher level of eicosapentaenoic acid (20:5n-3) in larval stages, but lower level in post-larvae. Addition of R. salina seemed to be advantageous during larval stages by a higher accumulation of triacylglycerol associated with an earlier appearance of metamorphosis. The composition of sterol observed in larvae fed with an addition of R. sauna showed a high level of brassicasterol. Advantage of the preferential accumulation of brassicasterol with the addition of R. salina is not clear but other studies suggest that brassicasterol can replace cholesterol in some functions. Our results suggest that addition of R. salina at larval stages could be advantageous in the aquaculture hatchery by a more rapid passage of P. maximus in the nursery. (C) 2010 Elsevier B.V. All rights reserved.

Soft-shell clam, Mya arenaria, culture on the east coast of Canada is characterized by high loss following seeding. To evaluate the importance of passive transport due to currents, an experimental flume study was designed. The purpose was to measure the effects of hydrodynamic conditions, substrate, and clam size on dispersal in controlled laboratory condition and to interpret these results in relation to field measurements. Unidirectional currents with gradual increasing velocities (0 to 60 cm s(-1)) were applied to three substrates (muddy sand, medium sand, and coarse sand) in which clams from one of three size classes (10, 15, and 20 mm) had burrowed. We also examined the resulting effects of turbulent kinetic energy on the erosion of medium-grain sand and clams from the three size classes. Turbulent energy was created with a homemade device acting on the unidirectional currents. Nearly 95% of buried clams (all substrates and size classes together) were unaffected by unidirectional currents of up to 60 cm s(-1), but only 10% withstood turbulent kinetic energy of 10.1 J m(-3), a level that is lower than that measured in the field during an autumnal storm. The transport of clams was found to be directly related to substrate erosion-levels. (C) 2010 Elsevier B.V. All rights reserved.

The mean multi-locus heterozygosity (MLH) of suspension-cultured mussels has been reported to decrease within a few months after traditional sleeving in previous studies. Two experiments were carried out to determine if this decrease could be attributed to the more rapid migration of the more heterozygous mussels out of the mesh tubes after sleeving. Since these individuals occur in greater numbers at the periphery of the sleeves, they are more susceptible to fall-offs. In the first experiment, the mean MLH of the mussels emerging from the mesh tubes was significantly higher than the MLH of the spat used for sleeving two weeks before. In a second experiment with caged and free sleeves under field conditions, a significant decrease in MLH was observed, but only for the mussels from the free sleeves. This decrease occurred in late December, only one month after sleeving. It is hypothesized that the experimental cages limited turbulence and thus fall-offs during the weeks following sleeving. As a consequence, the slower moving homozygotes were able to catch up with the faster heterozygotes at the sleeve's periphery. In contrast, mussels in the free sleeves may have experienced more turbulent conditions leading to high fall-offs of the more heterozygous mussels at the sleeve's periphery during the crucial period following sleeving. These losses could impact mussel production since MLH explained 32% of the variation in individual dry tissue weight in this study. Furthermore, the total fresh weight of mussels with high MLH (5–7 heterozygous loci) was almost twice that of the mussels with low MLH (0–2 heterozygous loci) about one year after sleeving: 11.38 vs. 5.95 g. In addition, there were 3.7 times more commercial-sized mussels (>50 mm) with a high MLH than with a low MLH (80% vs. 21.5%). In contrast to traditional sleeving with plastic mesh tubes, a new method of mechanical sleeving provides continuous sleeves wrapped in cotton cloth. This biodegradable cloth helps retain the heterozygotes on the sleeves before it disintegrates.

Previous studies have suggested that a large proportion of the more heterozygous mussels are lost while in suspension culture. Such a reduction in multi-locus heterozygosity (MLH) could impact mussel production because more heterozygous individuals have better growth and survival than more homozygous ones. The present study followed the changes in MLH over a year in two different cohorts and found a reduction in MLH during the culture cycle for both cohorts. This reduction did not occur during the early phases of the culture operations, such as sleeving (= socking), or during the first weeks in suspension culture, but took place during the following growing season starting in early summer for both cohorts. The MLH decrease was not associated with different environmental conditions at the growing site. It is hypothesized that mussels characterized by high MLH are more mobile than those with lower MLH and migrate out of the mesh tubes faster after sleeving to get access to better growing conditions (space and food). However, being at the periphery of the sleeves, these more heterozygous individuals are more vulnerable to fall-offs due to turbulence and/or self-thinning. We suggest that the MLH decrease on the sleeves is not caused by the selective mortality of more heterozygous individuals but rather by higher losses through fall-offs.

The aetiology of haemic neoplasia (HN) is unknown, so far but many causative factors are suggested such as viral, pollution and genetics. The aim of this study was to determine if, under chronic exposure, two major pesticides (chlorothalonil and mancozeb) which are used in potato production could induce HN in soft-shell clams (Mya arenaria). Short-term experiments with acute exposure were also performed. Clams were collected from an epizootic site (North River, PEI) and from a site free of the disease (Magdalen Islands, Quebec). The tetraploid level of haemocytes was assessed by flow cytometry for each clam to determine the HN status. The bioaccumulation of pesticides in tissues was quantified by gas chromatography/mass spectrometry (GC/MS) for chlorothalonil while mancozeb and manganese were quantified by inductively coupled plasma-mass spectrometer (ICP/MS). Long term exposure to fungicide Bravo 500((R)) did not induce high tetraploid levels on negative calm from North River and the analysis of the digestive gland and the mantle did not reveal any detectable level of chlorothalonil. In the Manzate 200 DF((R)), some clams revealed high level of tetraploid cells but no difference were observed between the treatments and the control. The analysis of the digestive gland and the mantle for manganese did not highlight any significant difference in tissue concentration (p=0.05). For the acute exposure, chlorothalonil analysis showed that the active ingredient is distributed between four chlorinated compounds: 99.5% for chlorothalonil isomers, 0.4% for pentachlorothalonil and 0.1% for trichlorothalonil isomers. For a 72 h experiment, the accumulation was within 4h; the higher tissue concentration of chlorothalonil was 59.2 microg g(-1) in the mantle after 48 h, following by a decrease to an undetectable level at the end. For the manganese, the accumulation was detected after 4h; the higher tissue concentration was 48.8 microg g(-1) in the mantle after 24h and, over the following 48 h, the accumulation decreased until the end of the trial. Based on the data, the accumulation of these fungicides seems to be transitory. Chlorothalonil and mancozeb are both oxidative-stress promoters and could have induced cell dysfunction while in the tissue. Study on the effect of these fungicides on the p53 protein system is an example of strategy that would provide information on cellular events promoting neoplasia.

The Grande-Entree Lagoon (Magdalen Islands, Canada) has supported mussel ( Mytilus edulis ) cultivation for the last 25 years. Algal biomass in this lagoon is relatively low while heterotrophic plankton biomass is high. Although often considered herbivorous, it is known that filter-feeding bivalves can consume various types of food, from bacteria to zooplankton. We hypothesize that along with phytoplankton, heterotrophs constitute an important food resource for the Grande-Entree mussels. In situ mesocosm experiments were undertaken at different seasons using short socks filled with mussels from the same cohort taken from an aquaculture farm, in order to determine the impact of cultured mussels on local plankton communities and assess the role of heterotrophs. Filtration activity by the mussels and associated epibionts present in the socks was expressed as clearance rates (CR). The average CR over all taxa was lowest in June and highest in October. Diatoms, dinoflagellates and heterotrophic protists constituted the bulk of planktonic carbon removed by mussels. While smaller-sized taxa contributed little (

A major problem for the mussel aquaculture industry on Prince Edward Island, Canada surfaced in the late 1990s with the introduction of a fouling organism commonly known as the clubbed tunicate, Styela clava. This organism has the ability to infest mussel cultivation equipment to the point where productivity is severely compromised. This study examined the effects two anti-fouling treatments, air exposure and acetic acid, had on experimental mussel populations. Socked mussel seed obtained from a mussel farm on Prince Edward Island was exposed to three treatment regimes and subsequently placed on a long-line in New London Bay, P.E.I. The treatments were a 40-h air exposure, 30-s 5% acetic acid immersion and a 2-min 5% acetic acid immersion. Treatment effects on mussels were measured after seven months in the field, along with untreated controls. Mussel quality was assessed using mussel sock weights, length, condition index and changes in genetic characteristics measured at allozyme loci. A significant decrease in mean sock weights was found for all three treatments compared to control sock weights (p

When contaminated, most molluscs destined for human consumption require a depuration regime lasting 48 h at a minimum temperature of 5 °C to ensure elimination of coliforms. However, this regime is unsatisfactory in northern temperate regions, where temperatures are frequently below 5 °C. A series of tests were undertaken to determine the filtration activity of mussels (Mytilus spp.) under cold temperatures. We used physiological measures rather than the more traditional method of bacterial analysis to evaluate mussel acclimation to cold temperatures. Mussels were acclimated for 4 weeks at three different temperatures (8, 4, and − 1 °C) and their scope for growth was evaluated each week to determine the level of acclimation. Mussels were then exposed to a thermal shock and clearance rates were measured after 2 h and 72 h. We observed a clearance rate of 2.45 l h− 1 g− 1 (g DW) for the 8 °C control group. Thus, within a 48-h depuration period, Mytilus spp. could filter a standard volume of 117.47 l. We used a von Bertalanffy exponential model to estimate the time required for an individual from each thermal shock treatment to filter that standard volume. We found that thermal shock had an important effect on the volume filtered by a mussel in 48 h. For example, mussels acclimated at 8 °C were able to filter the standard volume of 117.47 l in an average of 75 h at 4 °C, whereas those acclimated at 4 °C and transferred to 8 °C required only 23 h on average.

Mussel aquaculture on Prince Edward Island (PEI), Canada, is an important but relatively new industry. Although seed manipulation using hatcheries for mussel culture occurs on the west coast of North America, seed supply on the east coast of Canada, including Prince Edward Island (PEI), is based solely on wild collection. Two techniques for culling seed (

This study investigated the biological effects of various dietary essential fatty acids levels to sea scallop larvae, Placopecten magellanicus . Scallop larvae were fed three diets from D-veliger to settlement. Diet A consisted of Isochrysis sp. and Pavlova lutheri , diet B was a mix of Isochrysis sp. and Chaetoceros muelleri and diet C consisted of the same two species, but C. muelleri was grown under silicate deprivation to alter the fatty acid composition. Pediveligers (28 days old) were sampled prior to settlement for fatty acid analysis, growth measurement and survival assessment. Survival and settlement success were measured at the end of the experiment (day 40). Our results show that feeding regime greatly influenced larval size, settlement and fatty acid composition. Diet A was severely deficient in arachidonic acid (20:4n-6, AA), leading to the poorest larval growth, survival and lipid content. Nevertheless, larvae fed diet A selectively accumulate AA by a factor three compared to the dietary amount. Shell size of 28-day-old larvae was positively correlated with AA content and negatively correlated with eicosapentaenoic acid (20:5n-3, EPA)–AA ratio, thus suggesting that these two variables are of major interest for the optimisation of larval growth in sea scallops. Finally, larvae fed diet C displayed 20% higher shell size at day 28 than larvae fed diet A and B, likely in relation to the dietary amount of saturated fatty acid (SFA). However, the moderate survival and settlement success of these groups of larvae might be associated with a relative deficiency in docosahexaenoic acid (22:6n-3, DHA). This study underlines that the overall balance between polyunsaturated fatty acid (PUFA) needs to be considered to adequately fed sea scallop larvae.

The lipid class and the fatty acid composition of microalgae are of primary importance in feeding filter-feeding animals properly and variations of those parameters have never been investigated in a cultivation system applied to hatcheries. The objective of this study was to document the lipid class and fatty acid composition of the diatom Chaetoceros muelleri (CHGRA) and the flagellate Isochrysis sp. (Clone TISO) during the entire process of hatchery cultivation in relation to the period of the year (summer vs. winter). At the beginning of the cultivation process of CHGRA, in a small volume of culture, triacylglycerol (TAG), sterol, saturated, monounsaturated, and polyunsaturated fatty acids (particularly 20:5n3) were high, sharply dropping when volume was increased. An inverse relationship has been observed for acetone mobile polar lipids (AMPLs; pigment) and phospholipids (PLs), thus leading to no significant effect of the volume of culture on the total lipid (TL) content of CHGRA. The total lipid content of TISO increased with the volume of culture due to AMPL and PL classes and saturated and polyunsaturated fatty acids. The short- and long-term variability of lipid class composition has been observed for both species. Such results highlight the high variability of marine microalgae lipid content during the culture process and season as well. Hatchery implication is discussed. D 2003 Elsevier Science B.V. All rights reserved.

Our study examined whether the differences in susceptibility to summer mass mortality of two stocks of mussels from the Magdalen Islands (Quebec, Canada) are related to bioenergetic and/or genetic factors. The relative importance of maintenance and maximal metabolic rates, scope for growth (SFG) and the O:N ratio were followed over time to assess whether the increased incidence of mortality in late summer reflects a decrease in bioenergetic status at this period. The stock of mussels which was more susceptible to summer mortality had higher values of V O 2 . Furthermore this stock had a more negative scope for growth and lower O/N ratio in early August. These parameters are likely to reflect unfavourable environmental conditions, which led the mussels to rely upon protein catabolism. We also observed a negative correlation between multiple-locus heterozygosity and standard V O 2 . The more susceptible stock of mussels had a lower degree of multiple-locus heterozygosity. Thus, we suggest that the periodic, but irregular, outbreaks of summer mortality are the result of a synergistic interaction involving dietary deficiencies, temperature, a possible post-spawning stress and the genetic characteristics of the stock. The higher metabolic demand associated with a reduced degree of heterozygosity will impose a supplementary stress and render such stocks more vulnerable to summer mortality. The results are in agreement with the hypothesis that high levels of heterozygosity are related with lower costs of maintenance.

For the correct use of a stress index in the assessment of disturbances due to pollution, it is indispensable to know whether the response investigated exhibits natural fluctuations which could subsequently bring biases to the interpretations. Stability of the lysosomal membrane was measured at short time intervals during two full tidal cycles in the digestive gland of Mytilus edulis L. and Mya arenaria . In both species, destabilisation of the lysosomal membrane was observed during emersion periods. There was no indication of membrane destabilisation in the soft-shelled clams when they were submerged. In mussels, the destabilisation of the lysosomal membrane was observed occasionally during the immersion period. Air exposure and the associated hypoxia appeared to be the factors explaining the lysosomal responses in these two species. The physiological importance of these findings seems closely linked to the role of lysosomes in the well known process of proteolysis via controlled autophagy and to phasic digestive rhythms, two strategies for a maximal utilisation of limited food resources during the tidal cycle. These results demonstrate for the first time to our knowledge, under natural conditions, the differences of lysosomal responses between two bivalve species inhabiting the intertidal zone. It appeared finally, that the infaunal bivalve M. arenaria is most suitable as a sentinel species when the lysosomal membrane destabilisation is chosen as a biomarker of stress in field conditions.

The cell membrane is an important biological interface often targeted by bioactive molecules such as antimicrobial peptides (AMPs) which can disrupt the bacterial lipid barrier. Identification and study of AMPs is a dynamic research field motivated by the emergence of antibiotic-resistant pathogens. To develop new efficient therapies, the action mechanism of membrane-disrupting antimicrobial agents should thus be studied. 2H solid-state NMR is a useful method to monitor changes in organization and dynamics of phospholipids in bilayers. Usually carried out with model systems, the complex composition of bacterial membranes - especially the presence of lipopolysaccharides (LPS) - encourages such studies on intact organisms. We have therefore developed a protocol to 2H-label phospholipids in Escherichia coli membranes without mutating. About 75% of the phospholipids had deuterated acyl chains. We have thus investigated in vivo the interaction mechanism of antimicrobial agents, i.e., the antibiotic polymyxin B (PxB), the detergent cetyltrimethylammonium chloride (CTAC) and fullerenol nanoparticles. 2H NMR spectra and spectral moment analysis support the insertion of the PxB's lipid tail in the bacterial membrane. Our results also suggest that membrane rigidification could play a role in the biocide activity of the detergent. The use of intact bacteria seems important in cases where the antibiotic action relies on an interaction with LPS. This is shown with fullerenol nanoparticles for which a different effect is seen on intact cells as compared to model DPPC/DPPG membranes, as will be detailed. This is further demonstrated with the blue pigment marennine produced by marine microalgae which would also interact with LPS. A different perturbation of the bacterial membranes by the intra- and extracellular forms of this pigment was also evidenced, thus shedding light on the action mechanism of this potential natural antibiotic.