Search

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

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

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

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

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

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

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

Globally, the production of marine bivalves has been steadily increasing over the past several decades. As the effects of human population growth are magnified, bivalves help provide food security as a source of inexpensive protein. However, as climate change alters sea surface temperatures (SST), the physiology, and thus the survival, growth, and distribution of bivalves are being altered. Challenges with managing bivalves may become more pronounced, as the uncertainty associated with climate change makes it difficult to predict future production levels. Modelling techniques, applied to both climate change and bivalve bioenergetics, can be used to predict and explore the impacts of changing ocean temperatures on bivalve physiology, and concomitantly on aquaculture production. This study coupled a previously established high resolution climate model and two dynamic energy budget models to explore the future growth and distribution of two economically and ecologically important species, the eastern oyster (Crassotrea virginica), and the blue mussel (Mytilus edulis) along the Atlantic coast of Canada. SST was extracted from the climate model and used as a forcing variable in the bioenergetic models. This approach was applied across three discreet time periods: the past (1986-1990), the present (2016-2020), and the future (2046-2050), thus permitting a comparison of bivalve performance under different temporal scenarios. Results show that the future growth is variable both spatially and interspecifically. Modelling outcomes suggest that warming ocean temperatures will cause an increase in growth rates of both species as a result of their ectothermic nature. However, as the thermal tolerance of C. virginica is higher than M. edulis, oysters will generally outperform mussels. The predicted effects of temperature on bivalve physiology also provided insight into vulnerabilities (e.g. mortality) under future SST scenarios. Such information is useful for adapting future management strategies for both farmed and wild shellfish. Although this study focused on a geographically specific area, the approach of coupling bioenergetic and climate models is valid for species and environments across the globe.

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

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

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.

A spatially explicit coupled hydrodynamic-biogeochemical model was developed to study a coastal ecosystem under the combined effects of mussel aquaculture, nutrient loading and climate change. The model was applied to St Peter's Bay (SPB), Prince Edward Island, Eastern Canada. Approximately 40 % of the SPB area is dedicated to mussel (Mytilus edulis) longline culture. Results indicate that the two main food sources for mussels, phytoplankton and organic detritus, are most depleted in the central part of the embayment. Results also suggest that the system is near its ultimate capacity, a state where the energy cycle is restricted to nitrogen-phytoplankton-detritus-mussels with few resources left to be transferred to higher trophic levels. Annually, mussel meat harvesting extracts nitrogen (N) resources equivalent to 42 % of river inputs or 46.5 % of the net phytoplankton primary production. Under such extractive pressure, the phytoplankton biomass is being curtailed to 1980's levels when aquaculture was not yet developed and N loading was half the present level. Current mussel stocks also decrease bay-scale sedimentation rates by 14 %. Finally, a climate change scenario (year 2050) predicted a 30 % increase in mussel production, largely driven by more efficient utilization of the phytoplankton spring bloom. However, the predicted elevated summer temperatures (> 25 A degrees C) may also have deleterious physiological effects on mussels and possibly increase summer mortality levels. In conclusion, cultivated bivalves may play an important role in remediating the negative impacts of land-derived nutrient loading. Climate change may lead to increases in production and ecological carrying capacity as long as the cultivated species can tolerate warmer summer conditions.

Póster presentado en el ICES Anuual Science Conference, A Coruña, Spain, 15-19 September 2014, There is a growing interest to understand co-existence processes between marine species in the bio-invasion scenario. Xenostrobus securis is a small mussel endemic to the brackish waters of New Zealand and Australia and has been listed among the “100 Worst Invasive Species”. The mussel Mytilus galloprovincialis is successfully cultivated in Galician Rías. Mussel byssus secretion and its functional strength when subjected to distinct substrate and salinity values were evaluated as the basis to understand dominance patterns within mixed-species beds., This study was funded by the project AGL2010-16464 (Ministerio de Ciencia e Innovación, Spanish Government).

The success of shellfish aquaculture as well as its sustainability relies on adjusting the cultured biomass to local ecosystem characteristics. Oyster filter-feeding activity can control phytoplankton concentration, reaching severe depletion in extreme situations, which can threaten ecological sustainability. A better understanding of oyster–phytoplankton interaction can be achieved by constructing ecosystem models. In this study, a fully-spatial hydrodynamic biogeochemical model has been constructed for the Richibucto Estuary in order to explore oyster carrying capacity. The biogeochemical model was based on a classical nutrient–phytoplankton–zooplankton–detritus (NPZD) approach with the addition of a Dynamic Energy Budget (DEB) model of Crassostrea virginica. Natural variation of chlorophyll was used as a benchmark to define a sustainability threshold based on a resilience framework. Scenario building was applied to explore carrying capacity of the system. However, the complex geomorphology of the Richibucto Estuary and the associated heterogeneity in water residence time, which is integral in estuarine functioning, indicate that the carrying capacity assessment must be specific for each area of the system. The model outcomes suggest that water residence time plays a key role in carrying capacity estimations through its influence on ecological resistance.

The filtration activity of cultured mussels may exert a strong control on phytoplankton populations. Given that phytoplankton constitutes the base of marine food webs, carrying capacity in shellfish aquaculture sites has been commonly studied in terms of phytoplankton depletion. However, spatial and temporal variability of phytoplankton concentration in coastal areas present a methodological constraint for using phytoplankton depletion as an indicator in monitoring programs, and necessitates intensive field campaigns. The main goal of this study is to explore the potential of different bivalve performance indices for use as alternatives to phytoplankton depletion as cost-effective indicators of carrying capacity. For that, a fully spatial hydrodynamic–biogeochemical coupled model of Tracadie Bay, an intensive mussel culture embayment located in Prince of Edward Island (Canada), has been constructed and scenario building has been used to explore the relationship between phytoplankton depletion and bivalve performance. Our underlying premise is that overstocking of bivalves leads to increased competition for food resources, i.e. phytoplankton, which may ultimately have a significant effect on bivalve growth rate and performance. Following this working hypothesis, the relationships among bay-scale phytoplankton depletion and three bivalve physiological indices, one static, condition index, and two dynamic, tissue mass and shell length growth rates, have been simulated. These three metrics present methodological advantages compared to phytoplankton depletion for incorporation into monitoring programs. Although significant correlations among phytoplankton depletion and the three physiological indices have been observed, shell length growth rate is shown as the most sensitive indicator of carrying capacity, followed by tissue mass growth rate and then by condition index. These results demonstrate the potentiality of using bivalve physiological measurements in monitoring programs as indicators of ecosystem status.

Biological interactions between predators and prey constitute a key component of the ecology and evolution of marine systems, and animal behavior can affect the outcome of predator–prey interactions. It has been recently demonstrated that CO2-induced ocean acidification can alter the behavior of marine organisms and potentially alter predator–prey dynamics. This study combines both quantitative (meta-analysis) and qualitative approaches to review the effects of ocean acidification on behavioral prey defenses in marine invertebrates. A systematic literature search identified 34 studies that experimentally assessed behavioral defenses under elevated pCO2 spanning three phyla: crustaceans, echinoderms, and molluscs. A meta-analysis suggested that exposure to elevated seawater pCO2 can negatively affect behavioral defenses in bivalve molluscs and malacostracan crustaceans. By contrast, defenses of cephalopod molluscs seem to be positively impacted by elevated pCO2, whereas gastropods and echinoids appear unaffected. A qualitative assessment of studies on combined effects of ocean acidification and warming revealed that combined effects typically differ from ocean acidification–only effects. Based on a qualitative assessment of three studies to date, neurological interference of GABAA receptors under elevated pCO2 may play a major role in ocean acidification effects on prey defense behaviors; however, more research is needed, and other mechanistic underpinnings are also important to consider. Ultimately, the results of this study suggest that behavioral prey defenses in some shellfish taxa may be vulnerable to ocean acidification, that the effects of ocean acidification are often different under warming scenarios than under present-day temperature scenarios, and that GABAA interference may be an important mechanism underpinning behavioral responses of shellfish prey under ocean acidification. Despite the importance of shellfish behavioral defenses in the ecology and evolution of marine biological communities, however, research to date has only scraped the surface in understanding ocean acidification effects. Increased research efforts on the effects of multiple stressors, acclimation and adaptation, environmental variability, and complex situational and ecological contexts are needed. Studies of fish behavioral defenses under ocean acidification can help streamline hypotheses and experimental approaches, particularly given the similar effects of elevated pCO2 on GABAA function.

13 páginas, 3 figuras, 1 tabla, 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−1) and a low current flow regime (2–5 cm s−1). 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, This study was funded by the project AGL2010-16464 (Ministerio de Ciencia e Innovación, Spanish Government).

Shellfish aquaculture implies the placement of artificial structures in the coastal environment and the alteration of natural bivalve populations, which calls for the establishment of legislative regulatory frameworks based on an ecosystem approach. One of the challenges for policy makers is the need to monitor the effectiveness of management actions. In this study, a meta-analysis across different bays, covering a large spatial scale in Atlantic Canada, was performed to test the response of two potential indicators of aquaculture intensity: (1) the bivalve growth using both Dynamic Energy Budget (DEB) and Scope For Growth (SFG) approaches, and (2) the bivalve condition index (CI = (meat weight/shell weight) × 100). Our underlying premise was that overstocking of bivalves leads to increased competition for food resources, which might ultimately have a significant effect on bivalve growth performance and the CI. Bivalve growth performance for cohorts of Mytilus edulis and Crassostrea virginica were simulated by combining satellite remote sensing (temperature and chlorophyll) with individual based models using both DEB and SFG approaches. These models were calibrated for each cohort, by adjusting the half-saturation coefficient of the food ingestion function term ( X K ), which is a common parameter related to feeding behavior in both approaches. A significant correlation between X K and lease coverage (lease area/bay area, dimensionless) was found for M. edulis . However, because of unrealistic X K values in some M. edulis cohorts and the lack of consistent simulations for C. virginica precluded using X K as a reliable indicator of aquaculture intensity. By contrast, according to the observed results CI emerged as a good indicator of aquaculture intensity for both species. A General Additive Model (GAM) for C. virginica provided a regression that included the initial dry meat weight as a linear term and the lease area as a non-linear term, explaining a total deviance of 59.9% in describing final CI values. The GAM for M. edulis included only non-linear terms, lease coverage, and lease area, explaining a total deviance of 61.0%. Since the CI theoretically integrates the effects of changing trophic conditions over time, the good relationship between the CI and lease/bay characteristics provides a scientific framework for its use as a reliable ecological indicator of aquaculture intensity. From an applied perspective, this finding is of relevance because the CI is easy to measure and is widely available in government and industry datasets.

Autotrophic picoplankton (≤2.0 µm) is one of the most abundant phytoplankton components in marine ecosystems. The contribution of picophytoplankton to blue mussel (Mytilus edulis) growth was investigated in eastern Prince Edward Island, where the bulk of the Canadian suspended mussel industry is located. Field trials using flow cytometry were used to determine the ability of mussels to retain picophytoplankton (0.2–2.0 µm) and nanophytoplankton (2.0–20.0 µm). Size-fractionated phytoplankton biomass (chl-a) and mussel growth (shell height and tissue weight) were also measured. Mussel retention efficiencies (RE) for picophytoplankton and nanophytoplankton averaged 20 ± 2.0 and 60 ± 3.5 %, respectively. Estimates of RE and phytoplankton biomass were integrated into a dynamic energy budget (DEB) model to investigate the contribution of picophytoplankton to mussel growth during the post-spring bloom period. When DEB simulations excluded picophytoplankton (RE = 0 %), the predicted reduction in mussel growth ranged between 14 and 29 %. It is concluded that the contribution of

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.

23 páginas, 6 figuras, 3 tablas.-- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited, 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, This research was supported by the Autonomous government Xunta de Galicia-FEDER (GRC2013-004) and the Spanish government (AGL2010-16464 and AGL2013-45945-R). IG was supported by a pre-doctoral contract funded by the University of Vigo (P.P. 00VI 131H 64103). FPL

Serum testosterone, estradiol-17β (E2), L-thyroxine (T4), 3,5,3'-triiodo-L-thyronine (T3), and free (protein-unbound) T3 concentrations were examined in relation to the extensive (up to 650 km) seasonal migrations undertaken by southern Gulf of St. Lawrence cod Gadus morhua L.. Testosterone levels were low as the stock moved out of the Gulf of St. Lawrence in autumn, and increased only during the final stages of the return migration in spring. E2 in females peaked near the onset of the spring migration, and remained elevated until this migration was completed in early summer. However, we suggest that the changes in E2 levels are functionally tied with egg develop- ment and not with spring migratory behaviour. Free T3 showed no consistent pattern in relation to seasonal migrations, whereas T4 and T3 levels increased at the start of the autumn migration. We con- clude that thyroid hormones may facilitate the onset of the autumn migration by enhancing metabo- lism, sensory physiology and swimming capacity.