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Supporting information for the article https://doi.org/10.1016/j.scitotenv.2021.145020

Assessing the carbon footprint of marine bivalve aquaculture demands an accurate estimation of the CO2 release associated to capital goods and aquaculture operations but also to the metabolic CO2 budget of the cultured species. Nowadays, there are discrepancies on the processes to include in that budget, how to estimate them, and which scale should be applied, from individual to ecosystem. Site-specific environmental conditions and culture methods also affect significantly the estimates. Here, we have gathered environmental, biochemical and metabolic data from published scientific articles, reports and existing databases to present the metabolic CO2 budget for mussel aquaculture in the coastal inlets of the Northwest Iberian upwelling. We analyse the contribution of mussel flesh and shell production jointly and separately. At the individual scale, the shell CO2 budget is estimated from CO2 removal by shell matrix protein synthesis and CO2 release during calcification and respiration to support shell maintenance. Organic carbon in mussel flesh and CO2 released by respiration to support flesh maintenance contribute to the flesh CO2 budget. Only calcification and respiration processes are considered when estimating the metabolic carbon footprint of individual mussels because organic carbon in mussel flesh and shell returns to the atmosphere as CO2 in a relatively short period. While the metabolic carbon footprint associated to mussel shell remains constant at 365 kg CO2 per ton of shell, it varies from 92 to 578 kg CO2 per ton of mussel flesh. This large variability depends on mussel seeding time and harvesting size, due to the differential seasonal growth patterns of flesh and shell. Inclusion of the CO2 potentially immobilised in mussel faeces buried in the sediments would lead to a reduction of the metabolic carbon footprint estimates by up to 6 % compared with the individual estimates

Flesh yield of commercial mussels cultured in the Ría de Ares-Betanzos (A Coruña, NW Spain). The flesh yield is calculated as the percentage of the total weight of 1 kg of live mussels > 50 mm collected in a mussel raft that is meat weight after opening the valves with water vapour. Flesh yield data have been aggregated monthly and the seasonal cycle of each year has been adjusted to the following harmonic function: FY (%) = A1 + A2* cosine (2*Pi*t/12 + A3) where A1 is the seasonal average value of FY, A2 is half the amplitude of the seasonal cycle of FY; and A3 is the month of the year when FY is halfway between the seasonal minimum and the seasonal maximum. The values of A1, A2 and A3 for years 2002 to 2012 are reported for the two mussel cultivation areas of the Ría de Ares-Betanzos (Arnela and Lorbé) These data have been published in X.A. Álvarez-Salgado, U. Labarta, V. Vinseiro and M.J. Fernández Reiriz (2017). Environmental drivers of mussels flesh yield in a coastal upwelling system. Ecological Indicators 79, 323-329.

Number of days per month that the mussel cultivation areas of the Ría de Areas-Betanzos (A Coruña, NW Spain), Arnela and Lorbé, have been closed to mussel extraction. The toxicity causing the closures (ASP, DSP and PSP) is also indicated. Data covers the period from 2000 to 2007

Forecasting of climate change impacts on marine aquaculture production has become a major research task, which requires taking into account the biases and uncertainties arising from ocean climate models in coastal areas, as well as considering culture management strategies. Focusing on the suspended mussel culture in the NW Iberian coastal upwelling system, we simulated current and future mussel growth by means of a multistructural net production Dynamic Energy Budget (DEB) model. We considered two scenarios and three ocean climate models to account for climate uncertainty, and applied a bias correction to the climate models in coastal areas. Our results show that the predicted impact of climate change on mussel growth is low compared with the role of the seeding time. However, the response of mussels varied across climate models, ranging from a minor growth decline to a moderate growth increase. Therefore, this work confirms that an accurate forecasting of climate change impacts on shellfish aquaculture should take into account the variability linked to both management strategies and climate uncertainty

The mussels industry with a production that accounts for more than twenty five percent of the fresh product landings from the sea, and the full-time employment of more than 8000 people, is by far the largest productive activity of the Galician sea. In the 1980s was noticed an increase in productivity related to processes of innovation in the industry of mussel. Together with it, the first organizational forms of the Galician-based production sector was constituted, with a spatial and administrative reordering for mussel rafts and crops. A new reality of the sector was maintained in both the marketing guidelines and the fact of initiating a vertical integration between the mussel industry and the commercialization. Everything was accompanied by changes in markets and strong tensions: derived from red tides that limit the operating cycle and even its profitability and also from the conflicts between the producing and transforming organizations, added to the competition in the markets of other countries, mainly Chile. The reality of mussel culture and markets leads to a reformulation in the industry, with strategies for territorial diversification of suppliers, new technological improvements in production and even organizational, economic, and bioecological innovations

Determining the magnitude and causes of intrinsic variability is a main issue in the analysis of bivalve growth. Inter-individual variability in bivalve growth has been attributed to differences in the physiological performance. This hypothesis has been commonly tested comparing the physiological rates of fast and slow growers after size differentiation has occurred. This experimental design may detect a link between growth and physiological performance, but we cannot interpret the posterior physiological performance as a driver for the prior growth variability. Considering these limitations, this work introduces a new methodological framework for the analysis of bivalve growth variability. We have conducted sequential measurements of size and physiological performance (feeding, digestion and metabolic rates) in even-sized mussels growing under homogeneous environmental conditions. This experimental design allows us to distinguish between changes over time within individuals, i.e. growth and trends in the physiological rates, from differences between individuals with respect to a baseline level. In addition, Functional Data Analysis provides powerful tools to summarize all the information obtained in the exhaustive sampling scheme and to test whether differences in the physiological performance enhance growth dispersion. Our results report an increasing dispersion in both size and physiological performance over time. Although mussels grew during the experiment, it is difficult to detect any increasing or decreasing temporal pattern in their feeding, digestion and metabolic rates due to the large inter-individual variability. Comparison between the growth and physiological patterns of mussels with final size above (fast growers) and below (slow growers) the median found that fast growers had larger feeding and digestion rates and lower metabolic expenditures during the experimental culture than mussels with slow growth, which agrees with the hypothesis of a physiolog

Under the influence of the Western Iberian upwelling system, the Iberian Atlantic coast holds important hatcheries and recruitment areas for Octopus vulgaris. Recently identified as an octopus hatchery, the Ría de Vigo harbors an important mesozooplankton community that supports O. vulgaris paralarvae during the first days of their planktonic stage. This study represents a preliminary approach to determine the nutritional link between wild O. vulgaris hatchlings, paralarvae and their zooplankton prey in the Ría de Vigo, by analyzing their lipid class content and fatty acid profiles. The results show that octopus hatchlings are richer in structural lipids as phospholipids and cholesterol, while the zooplankton is richer in reserve lipids like triacylglycerol and waxes. Zooplankton samples are also particularly rich in C18:1n9 and 22:6n3 (DHA), that seem to be successfully incorporated by O. vulgaris paralarvae thus resulting in a distinct fatty acid profile to that of the hatchlings. On the other hand, content in C20:4n6 (ARA) is maintained high through development, even though the zooplankton is apparently poorer in this essential fatty acid, confirming its importance for the development of O. vulgaris paralarvae. The content in monounsaturated fatty acids, particularly C18:1n7, and the DHA: EPA ratio are suggested as trophic markers of the diet of O. vulgaris paralarvae.

This study aims to analyze the seasonal variations in seston biochemical compounds (biopolymeric organic carbon (C-BPC), i.e. the sum of proteins, carbohydrates and lipids) in order to infer the bioavailable organic fraction controlling food absorption by mussels cultured in a Galician Ria. Different proxies for high-quality food (including C-BPC) vs. energy absorbed by mussels were explored to elucidate the validity of each proxy in an embayment of intensive mussel cultivation. Our results showed a strong correlation between C-BPC and both the organic fraction (f) and the carbon equivalent of Chloropyll-a (C-Chl-a) in the seston. This fact points to variations in C-BPC (predominantly composed of proteins) are strongly linked with the phytoplankton fluctuations, which in turn are modulated by the seasonal upwelling regime. Maximum total energy absorbed by mussels (about 97%) occurred during the spring phytoplankton bloom, when high-quality organic carbon (high C-BPC) dominated the seston. Minimum energy absorbed (56%) occurred during winter, when continental runoff and local resuspension of surface sediments reintroduce into the water column more refractory organic compounds not favourable to the mussel diet. These results allowed us to establish that parameters such as f, C-Chl-a, and C-BPC have close correlations with physiological responses in mussels and could be used as proxies for food quality. Nonetheless, the use of these high-quality food estimations should be considered according to particularities of each ecosystem.

Eastern boundary coastal upwelling ecosystems (EBUEs) are highly sensitive to climate variability, particularly to coastal wind change. Here, we test the response of the flesh yield of blue mussels cultured in the northern boundary of the Iberian–Canary current EBUE to climate-related variables. Significant relationships were found between the annual mean, seasonal build-up and phenology of the mussel flesh yield with meteorological variables such as continental runoff, intensity and direction of coastal winds, and solar radiation. Our analysis shows that better flesh yields occur during years characterised by dry winters, accompanied by early springs and followed by summers dominated by strong northerly winds that produce intense upwelling. Compared with other EBUEs, upwelling has weakened in the study area over the last fifty years, implying an overall decrease in mussel flesh yield. However, future climate scenarios suggest that coastal upwelling will intensify over the 21th century, particularly during the summer months, which would lead to a recovery of mussel flesh yield

Understanding biological processes, such as growth, is crucial to development management and sustainability plans for bivalve populations. Von Bertalanffy and Gompertz models have been commonly used to fit bivalve growth. These models assume that individual growth is only determined by size, overlooking the effects of environmental and intrinsic conditions on growth patterns. The comparison between classical models and nonparametric GAM (generalized additive models) fits conducted in this work shows that the latter provide a more realistic approach of mussel growth measured in terms of shell length, and dry weight of hard and soft tissues. GAM fits detected a reduction in growth during the cold season, under unfavourable nutritional conditions. These fits also captured the decoupling between hard and soft tissue growth, widely addressed in the literature but not incorporated in growth models. In addition a GAM fit of condition index allowed us to explain annual changes in resources allocation, identifying the asymptotic growth of shell and the effects of the reproductive cycle on soft tissue fluctuations

Identifying the environmental factors driving larval settlement processes is crucial to understand the population dynamics of marine invertebrates. This work aims to go a step ahead and predict larval presence and intensity. For this purpose we consider the influence of solar irradiance, wind regime and continental runoff on the settlement processes. For the first time, we conducted a 5-years weekly monitoring of Mytilus galloprovincialis settlement on artificial suspended substrates, which allowed us to search for interannual variability in the settlement patterns. Comparison between the seasonal pattern of larval settlement and solar irradiance, as well as the well-known effect of solar irradiance on water temperature and food availability, suggest that solar irradiance indirectly influences the settlement process, and support the use of this meteorological variable to predict settlement occurrence. Our results show that solar irradiance allows predicting the beginning and end of the settlement cycle a month in advance: Particularly we have observed that solar irradiance during late winter indirectly drives the timing and intensity of the settlement onset, Finally, a functional generalise additive model, which considers the influence of solar irradiance and continental runoff on the settlement process, provides an accurate prediction of settlement intensity a fortnight in advance

Allometric relationships between biometric parameters (i.e., soft body and shell weights and shell organic content vs. shell length) as well as for routine and standard metabolic and ammonia excretion rates related to flesh weight and shell length were estimated and compared for subtidal and intertidal populations of Mytilus galloprovincialis in Galicia (NW Spain). This is the first report on allometric size-scaling of excretion and metabolic (both routine and standard) rates in this species. No evidences of differences in size exponent were found between physiological rates or between both populations for any physiological rate. Intercepts of regression lines were significantly higher in subtidal than in intertidal mussels, indicating greater levels of energy expenditure in the former. However, metabolic scope for feeding and growth was about two-fold in intertidal mussels, pointing to a reduced growth efficiency compared with subtidal mussels. Evolution of biometric parameters of body components with size indicated that subtidal mussels allocated energy resources preferably into flesh growth, achieving higher condition indices, while intertidal mussels put more effort on shell calcification and thickening which resulted in heavier shells of reduced organic content. These differentiated growth “strategies” of both populations could be related to their differences in growth efficiencies

Mussel seed (Mytilusgalloprovincialis) gathered from the intertidal and subtidal environments of a Galician embayment (NW, Spain) were maintained in the laboratory during five months to select fast (F) and slow (S) growing mussels. The physiological basis underlying inter-individual growth variations were compared for F and S mussels from both origins. Fast growing seemed to be a consequence of greater energy intake (20% higher clearance and ingestion rate) and higher food absorption rate coupled with low metabolic costs. The enhanced energy absorption (around 65% higher) resulted in 3 times higher Scope for Growth in F mussels (20.5±4.9 J h−1) than S individuals (7.3±1.1 J h−1). The higher clearance rate of F mussels appears to be linked with larger gill filtration surface compared to S mussels. Intertidal mussels showed higher food acquisition and absorption per mg of organic weight (i.e. mass-specific standardization) than subtidal mussels under the optimal feeding conditions of the laboratory. However, the enhanced feeding and digestive rates were not enough to compensate for the initial differences in tissue weight between mussels of similar shell length collected from the intertidal and subtidal environments. At the end of the experiment, subtidal individuals had higher gill efficiency, which probably lead to higher total feeding and absorption rates relative to intertidal individuals

We aimed to evaluate three defined monoalgal diets, Isochrysis galbana clone T-ISO, Tetraselmis suecica and Rhodomonas lens, as a food source for Mytilus galloprovincialis to ascertain which of the diets maximized the feeding, digestion and the assimilatory balance of nutrients and energy. Mussels fed with Rhodomonas yielded the highest clearance and ingestion rates (CR and IR), suggesting that the dimensions of Tetraselmis and T-ISO might have restricted their capture by the mussels’ gill. Absorption efficiency (AE), an indicator of digestibility, was significantly higher for Rhodomonas (69.6%) than for Tetraselmis (38.4%) or T-ISO (23.6%) diets. This could be explained by the greater proportion of refractive non-digestible material contained in Tetraselmis and T-ISO diets, together with the low digestibility of the cell wall of Tetraselmis. The Rhodomonas diet showed the highest protein content, which was reflected in the highest ingestion and absorption of proteins compared with the other diets. However, the amount of carbohydrates and lipids ingested did not match the amount absorbed, probably owing to inefficient carbohydrate digestion and lipids lost through metabolic fecal losses. The total energy absorbed was higher for Rhodomonas (34.5 Jh− 1) than for T-ISO (20.1 J h− 1) or Tetraselmis (13.9 J h− 1) diet. The optimal feeding and digestive behaviour obtained for mussels fed with Rhodomonas diet, coupled with its ideal size, volume, weight and biochemical composition, might provide a better coverage for the anabolic demands of proteins during the seasonal growth cycle, especially during shell formation, gametogenesis and byssogenesis. Statement of relevance We state that this manuscript is relevant for the field of bivalve aquaculture and hatchery. We recommend that the main criteria in selecting algae for culturing mussels should be based on choosing the suitable dimension (size, volume, weight) of algal cell depending on the feeding capacity of mussels, whi

The fatty acid (FA) profiles in neutral lipids (NLs) and polar lipids (PLs) of the gills, digestive gland and mantle of female and male mussels Mytilus galloprovincialis (cultured in Ría de Arousa, Galicia, NW Spain, and studied during an annual seasonal cycle) reflected dietary, sexual and functional differences. Seasonal differences arose from variations in the trophic environment, with diatom FA biomarkers dominating during the spring bloom, biomarkers from dinoflagellate-rich diets dominating during winter mixing, and a combination of both sources apparent during the summer and autumn transitory periods. The influence of diet was more pronounced in the NL (energetic reserves) than in the PL (structural membrane components) FA signatures of all organs, although dietary changes were mirrored more clearly in the digestive gland. Differences between males and females were restricted to the mantle and probably resulted from gonadal ripeness during spring. The NL and PL FA profile of the mantle was characterized by the abundance of 14:0, 16:0 and 16:1n-7 in females and predominance of 18:0, 18:3n-3 and 22:6n-3 in males, suggesting that each gender has distinct energetic and structural requirements during gametogenesis. Lipids containing alkenyl ethers or non-methylene interrupted (NMI) FAs were mostly found in the PLs of the gills and the mantle, supporting their role as structural and functional components in the membranes of organs directly exposed to physicochemical fluctuations. Competition between NMI and polyunsaturated fatty acids (PUFAs) was only evident in the mantle, suggesting that deficiencies in PUFAs might provoke de novo biosynthesis of NMI to satisfy reproductive demands

We compared the seasonal variations in Condition Index (CI) and proximate composition of the mantle and the digestive gland of mussels (Mytilus galloprovincialis) cultivated at outer and inner regions of a raft polygon. The results are discussed in the context of the energy balance. The proximate composition and CI varied with the seasonal fluctuations in seston composition and the reproductive cycle described for the Galician Rías. Seston's nutritional quality peaked during the spring bloom and descended during winter downwelling. Proteins were first depleted in the gland during autumn, while the mantle maintained high levels until summer. Similarly, lipids were highest in the mantle during winter and decreased following the spring spawning, suggesting transference of reserves from the gland to the mantle to support gametogenesis. In contrast, glycogen was stored in the mantle during the summer and exhausted during winter, when food % POM was lowest. This opposite pattern suggested that glycogen was probably converted to lipids during gamete development. The variations in CI significantly correlated with the accumulation and expenditure of reserves. Mussels harvested in autumn had the highest CI and biochemical reserves, while minimum CI was in winter, when mussels had a low energy balance. Resuspension events in autumn–winter significantly diluted the particulate organic matter suspended at the innermost raft (38.91% POM) compared with the outer raft (60.52% POM). This was reflected in short-term reductions in CI, proteins' and lipids' reserves in innermost mussels. These temporal increases in turbidity did not seem to significantly affect bivalves' proximate composition and meat yield over a longer time scale

We analyzed the spatial and temporal variability of seston parameters at 4 locations in the Ría de Ares-Betanzos (NW Spain) over 5 yr. Seston content was higher in the inner part of the ría and during winter, while seston quality was higher in the outer part of the ría with maximum values during summer, and exhibited a marked relationship with water circulation. Inter-annual differences were detected only in the organic content of seston (which was not always well-correlated with chlorophyll a), and only at some locations. Seston quality had the strongest relationship with meteorological factors, and was the only variable that was consistent at the 4 sites within the embayment. This led us to develop an empirical model that explains the spatial-temporal variability of seston quality in terms of wind stress and river discharge

This study describes the physiological performance of two populations of the razor clam Tagelus dombeii from two geographic areas with different histories of exposure to paralytic shellfish poisoning (PSP) linked to the toxic dinoflagellate Alexandrium catenella. Clams from Melinka-Aysén, which are frequently exposed to PSP, were not affected by the presence of toxins in the diet. However, clams from Corral-Valdivia, which have never been exposed to PSP, exhibited significantly reduced filtration activity and absorption, affecting the energy allocated to scope for growth (SFG). Ammonia excretion and oxygen uptake were not affected significantly by the presence of A. catenella in the diet. Measurements of energy acquisition and expenditure were performed during a 12-day intoxication period. According to three-way repeated measure ANOVAs, the origin of the clams had a highly significant effect on all physiological variables, and the interaction between diet and origin was significant for the clearance and absorption rates and for the scope for growth. The scope for growth index showed similar positive values for both the toxic and non-toxic individuals from the Melinka-Aysén population. However, it was significantly reduced in individuals from Corral-Valdivia when exposed to the diet containing A. catenella. The absence of differences between the physiological response of the toxic and non-toxic clams from Melinka-Aysén may be related to the frequent presence of A. catenella in the environment, indicating that this bivalve does not suffer negative consequences from PSP. By contrast, A. catenella has a negative effect on the physiological performance, primarily on the energy gained from the environment, on T. dombeii from Corral-Valdivia. This study supports the hypothesis that the history of PSP exposure plays an important role in the physiological performance and fitness of filter feeding bivalves.

The present study seeks to establish industry management strategies based on ecosystem-based indicators in an intensive mussel culture area. Spatial differences in the environmental conditions and in the productivity of mussels cultured on hanging ropes were examined at five locations in Ría de Arousa (NW Spain). The environmental conditions of the ecosystem were described on basis of the next ecosystem-based indicators: hydrography (salinity, temperature and chlorophyll a), dynamics (current velocity) and food availability (FA). Mussel productivity was assessed by measuring the biomass per rope, total fresh weight, and length of cultured mussels. Mussel productivity was successfully modeled from empirical relationships with current velocity, chlorophyll a and culture density. Commercial production (in kg) was evaluated from biomass and translated into economic value taking into account mussel commercial category. Finally, economic gross yield of each location was related with environmental conditions and culture densities by means of empirical relationships

The main drawback of the traditional self-thinning model is how time is handled. Self-thinning (ST) has been formally recognized as a dynamic process, while the current ST models have not included the temporal effect. This restricts the analysis to the average competitive behaviour of the population and produces a biased estimation of the self-thinning parameters. In this study, we extend the dynamic ST model introduced by Roderick and Barnes (2004) to the analysis of multilayered sessile animal populations. For this purpose, we incorporate the number of layers and the density per layer into the dynamical approach. The performance of the dynamic model was checked and compared with the classical ST model through the analysis of mussel populations grown at different density treatments. Unlike the traditional model, the dynamical approach detected the effect of culture density on the competitive behaviour of individuals and allowed to analyse the temporal evolution of intraspecific competition by estimating the ST exponent trajectory. Moreover, this approach provided an ecological interpretation of any possible value of the ST exponent. Thus, our results support the use of the dynamic model in the analysis of self-thinning in sessile animal multilayered populations. The estimation of the ST exponent trajectory reflects the dynamic nature of the ST process, providing a more realistic description of population dynamics than the traditional model.

This work aimed to study how mussel culture of Mytilus galloprovincialis Lmk modulates the natural sedimentation rates through the water column as key controlling factor of the potential organic load reaching the bottom sediments. To achieve this objective, seston, feces production and natural sedimentation dynamics were characterized during 4 seasonal campaigns at two mussel rafts and at a reference station not affected by the mussel culture in the Ría de Ares–Betanzos (NW Iberian Peninsula). Our results showed that seston content are below the pseudofeces threshold (< 4 mg L− 1) with inorganic contents ranging between maximum values of 76 ± 4% in winter and minimum values of 6 ± 4% in spring. These seasonal variations controlled the feces (biodeposits) production by mussels (11–221 mg ind− 1 d− 1) that increased with seston content, in particular under winter stormy conditions, when intense continental runoff and resuspension processes represented an important source of non-digestive inorganic particles for mussels. Natural sedimentation fluxes recorded by means of sediment traps under the rafts (84–536 g m− 2 d− 1) seasonally varied with mussel biodeposition being 6–7 folds the rates at the reference site. This fact corroborates that mussel feeding activity throughout the production of feces increased natural sedimentation rates in the Ría de Ares–Betanzos. However, the relatively energetic water column conditions and the potentially high degradation rates of feces in the culture area reduced up to 55–90% the biodeposits' organic carbon potentially arriving at the seafloor. This indicates that in highly hydrodynamic environments the impact derived from shellfish culture may be reduced, attenuating a possible impact on the benthic communities

Fish farming releases extensive amounts of particulate organic waste that can be exploited by bivalves in integrated culture. We tested if mussels Mytilus galloprovincialis cultured at two depths (1 and 6 m) in a raft, moored 170 m from a fish farm had greater growth than bivalves held 550 m from the fish cages. Mussel growth was monitored monthly, covering the second phase of the culture, from thinning-out to harvest (March to November 2011). We also studied if fish solid and dissolved nutrients increased the organic content of the seston and chlorophyll-a levels near the fish cages through weekly samples. Results showed no differences in seston, chlorophyll and physiochemical characteristics of the water among rafts. Maximum growth and Condition Index (CI) occurred during spring–summer (April–August), when mussels had access to greater food quality and quantity. Mussels cultivated close to the cages showed similar shell length, weight and CI compared with mussels distant from the fish farm. Average shell length, meat dry weight and CI at harvest were 76.31 mm, 2.51 g and 23%. Bivalves cultured distant from the fish cages displayed 26% higher biomass than the other raft at the end of the experiment. Differences in biomass were explained by the significantly higher recruitment of mussel seed observed at the raft distant from the fish cages from June to November. The lack of a significant enhancement in growth of the bivalves cultured next to finfish is discussed.

Knowledge of water flows through mussel rafts and their controlling factors is required for an ecosystem approach to the sustainable management of this culture in the Galician rías. With this aim, 4 acoustic 2D-ACM current meters were hung from the bow of 4 rafts located in the mussel cultivation areas of the Ría de Ares-Betanzos (NW Spain) during autumn 2007. Simultaneously, an Aanderaa DCM12 Doppler profiler was moored in an area free of rafts in the middle ría. There were differences in the subtidal and tidal dynamics of the middle channel and mussel farm areas. The tide explained 51.5% of the total variance of the surface current in the middle ría. The explained variance in the seed collection areas of Redes (inner ría) and Miranda (outer ría), where only 2–3 rafts are anchored, were 64.1% and 16.8%, respectively. In the cultivation areas of Arnela (inner ría) and Lorbé (middle ría), where 101 and 40 rafts are anchored, 14.3% and 53.4% of the total variance was explained by the tide. These disparities in the contribution of the tide are likely due to a combination of topographic and bathymetric differences among sites and distortions of the natural flow by the rafts and their hanging ropes. Furthermore, there was a marked influence of winds on the subtidal currents within the rafts; contrasting correlation coefficients and lag times between wind speed and currents were observed for the outer and inner sides of the embayment. The filtration rate of the growing mussels and the number of mussels per raft allow an efficient clearing of the particles transported across the hanging ropes by the measured subtidal currents of 2–3 cm s–1 characteristic of the cultivation areas of Arnela and Lorbé

The effects of seawater acidification caused by increasing concentrations of atmospheric carbon dioxide (CO2), combined with other climatic stressors, were studied on 3 coastal Mediterranean bivalve species: the mussel Mytilus galloprovincialis and the clams Chamelea gallina and Ruditapes decussatus. CO2 perturbation experiments produced contrasting responses on growth and calcification of juvenile shells, according to species and location. In the Northern Adriatic (Italy), long-term exposure to reduced pH severely damaged the shells of M. galloprovincialis and C. gallina and reduced growth for the latter species. Seawater in the Ria Formosa lagoon (Portugal) was consistently saturated in carbonates, which buffered the impacts on calcification and growth. After 80 days, no shell damage was observed in Portugal, but mussels in the acidified treatments were less calcified. Reduced clearance, ingestion and respiration rates and increased ammonia excretion were observed for R. decussatus under reduced pH. Clearance rates of juvenile mussels were significantly reduced by acidification in Italy, but not in Portugal. Both locations showed a consistent trend for increased ammonia excretion with decreasing pH, suggesting increased protein catabolism. Respiratory rates were generally not affected. Short-term factorial experiments done in Italy revealed that acidification caused alterations in immunological parameters of adult bivalves, particularly at temperature and salinity values far from the optimal for the species in the Mediterranean. Overall, our results showed large variations in the sensitivities of bivalves to climatic changes, among different species and between local populations of the same species. Expectations of impacts, mitigation and adaptation strategies have to consider such local variability.