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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 physiological basis for bivalve growth variability. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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, which might vary between species and life stages (larvae, adult). The second main criteria should be based on selecting algae with high digestibility and balanced biochemical composition, to obtain a high absorption of energy that covers the nutritional requirements of each life stage of the mussels. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract: We traced the food sources of mussel Mytilus galloprovincialis cultured in suspension in Ría Ares-Betanzos (N.W. Spain) by means of fatty acid (FA) biomarkers. The FA profile of seston, mussels' mantle, digestive gland and feces was analyzed during five seasons. Due to the proximity of a fish farm to the bivalve aquaculture site, we also tested if mussels and seston situated 170m distant from the fish cages incorporated fish feed FA markers compared with samples obtained 550m away. The principal FA in the mussels' organs were 16:0, 16:1ω7, EPA (20:5ω3) and DHA (22:6ω3), while 16:0 predominated in the feces. Seasonal fluctuations in the seston composition were mirrored in the FA signature of mussels' organs and feces, although the digestive gland had the closest resemblance to the seston FA profile. In general, diatom and bacteria derived-biomarkers predominated in mussels' organs and feces during the upwelling period (spring–summer), while dinoflagellates were the dominant dietary source during downwelling (autumn–winter). The higher concentration of EPA and DHA in both organs and the feces compared with the seston suggested a preferential accumulation of these ω3 FA in the mussels' tissues. The results showed a lack of assimilation of fish feed FA biomarkers in the seston and mussel samples. This might be due to the dispersion of uneaten feed particles by high current velocity, substantial distance between the fish and mussel culture, the limited amount of nutrient waste released by the fish farm and dilution of feed particles in the large mussel standing stock. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

The seasonal variability of the physiological components of the Scope for Growth (SFG) of mussels Mytilus galloprovincialis was investigated in a raft adjacent (170m) to fish net-pens and compared with a raft 550m distant from the cages in Ría Ares-Betanzos (Galicia, Spain). Chlorophyll and phytoplankton size-classes were determined in the field, simultaneously with SFG. Average chlorophyll-a was 0.65±0.24μgl−1, while nanophytoplankton (2–20μm) was the most abundant size-class, ranging from 50 to 70% of the total chlorophyll. The temporal pattern found for chlorophyll-a and phytoplankton size-classes reflected the upwelling–downwelling events and were correlated with the feeding, digestive and metabolic rates. Nanophytoplankton and microphytoplankton were preferentially cleared and ingested by mussels. There were no significant differences between the chlorophyll and phytoplankton size-classes among rafts. The lack of any enhancement in food availability resulted in no significant increase in the SFG of mussels beside the fish cages. Maximum SFG corresponded with the autumn (16.60±7.90Jh−1) and spring (12.72±9.32Jh−1) chlorophyll maximums. An abnormally hot summer and reduced chlorophyll levels resulted in lower energy intake, significantly higher metabolic expenditure and a negative SFG (−34.57±12.55Jh−1). Any particulate wastes and potential fish-derived chlorophyll enhancement would be rapidly diluted by the currents, while the placement of bivalves too distant from the fish farm in an environment with high supplies of natural seston may explain the lack of an augmented SFG of the co-cultured mussels. [ABSTRACT FROM AUTHOR]

Abstract: Integrated Multi-Trophic Aquaculture (IMTA) is a recycling concept in which waste nutrient discharges from high trophic levels become an additional energetic input for extractive organisms such as bivalves. The aim of this study was to measure the seston levels and absorption efficiency of mussels reared in the proximity of fish net-pens. The absorption efficiency of mussels Mytilus galloprovincialis and Mytilus edulis cultured at sites adjacent to red sea bream (Pagellus bogaraveo) and salmon (Salmo salar) cages was assessed on site, using natural seston diets and compared with mussels reared distant from the cages in the Ría de Ares-Betanzos (Galicia, N.W. Spain) and the Bay of Fundy (S.W. New Brunswick, Canada), respectively. Total particulate matter and the organic and the inorganic fractions of the seston were measured simultaneously. Seston parameters were generally similar at the mussel sites close to the fish cages and at the reference sites. However, significantly higher particulate inorganic matter coupled with lower food quality (seston organic content) observed at the sites close to the fish cages suggested occasional sediment resuspension events in the Ría de Ares-Betanzos and the Bay of Fundy. Owing to the reduced food quality, 20% lower absorption efficiency was measured for mussels in the proximity to the cages during the resuspension events. No significant differences in absorption efficiency were detected between the fish cages and the reference sites outside the resuspension events. Consequently, differences in absorption efficiency were attributed to natural variations in seston organic content, and absorption increased with increasing food quality. The results showed no evidence of increased organic content of the seston resulting from proximity to the fish-farm. It was concluded that proximity of cultured mussels to the fish cages did not result in an enhancement of the absorption efficiency. [Copyright &y& Elsevier]

Byssogenesis rate and attachment strength of the mussel Mytilus galloprovincialis were investigated in the laboratory considering different body sizes and feeding conditions. Byssal thread secretion was significantly higher in juveniles as compared to larger mussels of approximately 87 mm shell length. Asymptotic number of threads attached was obtained from approximately 72 hours onwards within a range of 42–46 and 27–31 for juveniles and larger experimental mussels, respectively (P < 0.05 ANOVA). Absorption efficiency values of control fed individuals dropped significantly from 0.78 in juveniles to 0.70 in larger mussels (P < 0.001 ANOVA) which pointed out energetic constraints of mussels with regard to their size and its probable effect on byssus secretion rates. Attachment force was 2.8 times higher in larger mussels than in juveniles (2.21 versus 0.78 N for both sizes, respectively; P < 0.001 ANOVA) which in turn followed the same order of magnitude than differences in the thread's thickness values of both experimental mussel sizes. Tenacity followed a reverse pattern with juveniles presenting two-fold higher values than larger mussels (P < 0.001 ANOVA) based on a lower increment of attachment force (x2.8) as compared to shell area (x6) for the comparison larger versus juvenile mussel size, which in turn might suggest that larger specimens secreted weaker threads. When animals were maintained unfed for a week, a significant drop in both byssus secretion and attachment force were observed in juveniles but was not the case for larger mussels most likely as a consequence of a relatively short period of maintenance under food availability stress for the latter individuals that showed significantly higher initial condition and/or energetic store values. Accordingly, the use of energetic reserves in juveniles kept unfed for a week together with a significant drop in byssus secretion and attachment force might suggest a link, i.e. transfer of energy between soft tissues and byssus under stress. Quantitative values of byssal threads, based on the significance of the byssus versus attachment force relationship, together with its morphometric value, i.e. thread's thickness, represented a primary mechanism to explain variability in attachment strength of M. galloprovincialis of the different body sizes studied here. [ABSTRACT FROM PUBLISHER]

Abstract: Variability of taurine (2-aminoethane sulfonic acid) was studied as a function of size in the mussel Mytilus galloprovincialis and tissue specificity. Isometric and/or allometric relationships were established with regard to total soft mass of the mussels between 20 and 60 mm shell length. Relative amounts of taurine dropped significantly with increasing mass of whole soft tissues with an allometric coefficient value of −0.15. The inverse relationship between taurine and increasing size of mussels was confirmed for gill epithelium and labial palp (allometric coefficient values of −0.16 and −0.10, respectively), tissues that, in turn, represented isometric functions with regard to total soft mass. Although relative amounts of taurine were significantly different in digestive gland, mantle and foot, relationships with increasing size of mussels remained unchanged in these tissues. Gill area of mussels was related to soft mass with an allometric coefficient of 0.70 by 2D Image Analysis, but increased to 0.85 when introducing a third dimension, i.e. gill thickness. Results are discussed according to gill structure analysis and taurine functionality. [Copyright &y& Elsevier]

Growth of mussel Mytilus galloprovincialis using raft culture was investigated for the first cultured generation following the Prestige oil spill off northwestern Spain. Seed from three natural populations along the Galician coastline, Pindo, Miranda, and Redes, was transplanted to a raft culture system in Ría de Ares-Betanzos. The physiological and biochemical status of mussels at the onset of culture and the degree of oil exposure three months after the spill (February 2003) have been described already, but here growth patterns of three populations sampled monthly from seeding to thinning-out (March/August 2003) and from thinning-out to harvest (August 2003/February 2004) were assessed. Mussels from Pindo (the area most affected by the oil spill) showed significantly less growth by weight than the other populations, resulting in a lower yield at harvest. The percentage of mussels classified as “large” in the Pindo population at harvest was also significantly less than that of the other two mussel populations. [Copyright &y& Elsevier]

Argopecten purpuratus was exposed to two different diets which reflected short term variations in quantity and quality of the natural food supply typical in bays of southern Chile. No significant differences of clearance rate were observed over different time periods at either of two food concentrations. The scallop reduced its clearance rate significantly when it was exposed to the higher food concentration. Pseudofaeces production occurred only at this high diet and the time factor had no significant effect on this process. The organic content of pseudofaeces was significantly lower than the organic content of the food, suggesting a pre-ingestive selection mechanism. Based on this capacity for particle selection, A. purpuratus was able to compensate for the differences in food quality of the experimental diets and ingesting particulate material containing 38% organic matter as a result of the selection process when fed at the higher food concentration. Absorption efficiency was lower following exposure to the high food concentration, suggesting that the experimental time of 72 h was not sufficient to acclimate the digestive response to a food supply significantly different from that of its habitat of origin. Phytoplankton form the principal nutritional source for this epibenthic species, and resuspended detritus, although occurring in large quantities, may only be of importance once digestive processes become acclimated to processing them. [ABSTRACT FROM PUBLISHER]

Submersion time of collector ropes influences settlement and larval metamorphosis of Mytilus galloprovincialis, which might be related to the biofilm development. In the present study, the effect of submersion time of collector ropes on the settlement of mussel seed was studied. The results of two experiments performed in an experimental long-line in the Ría de Ares-Betanzos have established a minimum submersion time of 41–46 days. [ABSTRACT FROM AUTHOR]

Abstract: Crowding conditions in bivalve populations cause intraspecific competition processes, resulting in individual growth reduction. In aquaculture, density is usually maximized to obtain a greater commercial yield. Commercial farms provide an ideal scenario for studying the effect of density on mussel growth in suspended culture systems. In this study, different growth indicators for Mytilus galloprovincialis (growth rates, length and weight growth curves and size frequency distributions) were measured along a cultivation density gradient. Ropes cultured at different densities (220, 370, 500, 570, 700, 800 and 1150ind/m) were hanged from a commercial raft and growth indicators were monitored monthly over the second phase of traditional culture in Galicia, from thinning-out to harvest (April to October 2008). A negative effect of density on individual growth was observed. Individuals cultured at lower densities presented higher growth rates and consequently reached greater weight and length values at the end of the experimental period than those cultured at higher densities. Differences in growth related to the cultivation density may suggest differences in intraspecific competition for limiting resources (space/food). Effects of density on growth started after 4months of culture (August) when individuals reached sizes around 66±1.3mm. The increase in size of individuals in a population implies an increment of their food and space requirements, which in turn intensifies intraspecific competition. This fact should be considered in aquaculture management, since higher densities could be supported without effects on growth performance if cultured mussels are limited to a lower size. [Copyright &y& Elsevier]

Abstract: Bivalve molluscs are characterized by high morphological plasticity in response to variations in local environmental conditions. In the present study, we evaluate this capacity in the mussel Mytilus galloprovincialis with regard to intra-specific competition caused by cultivation density. Suspended cultivation ropes at different initial densities (220, 370, 500, 570, 800 and 1150 individuals per meter of rope) were placed on a raft in the Ría Ares-Betanzos, following standard cultivation techniques. From May to October, covering the period from thinning out to harvest, various morphological indicators (length/width, length/height and height/width ratios) and allometric relationships (Volume-Length and Projected area-Length) in addition to energy distribution (dry tissue weight/dry valve weight) were analyzed. Differences in morphological indicators due to cultivation density were observed while no influence on the energy distribution was detected. From the second cultivation month (June), a decrease was recorded in the length/height ratio of individuals due to cultivation density. Similarly, there was also a decrease in the length/width ratio, although this decrease only became statistically significant from September. In addition, the allometric relationships studied (Volume-Length and Projected area-Length) suggested asymmetric competition processes. Differences in volume or projected area between densities were only detected at the end of the experimental culture (October) and only in the smaller individuals. These morphological adaptations can be understood as a strategy to mitigate the effects of intra-specific competition, palliating the consequences of physical interference at high densities. [Copyright &y& Elsevier]

Abstract: The biochemical composition (proteins, carbohydrates, glycogen, total lipids and lipid classes) of the mussel Mytilus galloprovincialis was investigated during an experimental culture using mussel seed from areas with different degree of exposure to the Prestige oil spill. The aim of the study was to identify alterations in the biochemical composition of mussel seed from natural populations commonly used in Galicia for mussel raft culture that might be linked to previous oil exposure. We have selected three mussel seed populations from Pindo, Miranda and Redes, that were characterised in a previous study according to the oil exposure three months after the spill. These populations were transplanted to a raft culture system in the Ría de Ares-Betanzos where our experimental culture followed standard commercial techniques from March 2003 to February 2004. Mussels from Pindo (characterised as the most affected area by the oil spill) showed marked differences in lipid composition with regard to other populations in the content of triacylglycerols, (P <0.001), free fatty acids (P <0.001) and phospholipids (P <0.05) at the onset of the culture. Although these differences in lipid composition might reflect their previous exposition to hydrocarbons, this pattern did not last longer most likely due to depuration of hydrocarbons stored in the tissues or by the development of certain tolerance to PAHs. These significant differences were not detected between Miranda (designed as hardly affected area) and Redes (designed as reference area) which may reflect that Miranda mussels were not affected or only hardly affected by the spill. With the exception of the onset of the culture, biochemical composition showed similar patterns in all mussel populations. Then, the fact of being cultured in a common environment seemed to be more responsible for the long-term variability in the energetic reserve than the origin of the populations or their previous biochemical status. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: Fish predation interferes with mussel seed population dynamic and is an important limiting factor on seed supply in several areas of mussel farming production. In the present study we assessed the impact of fish predation in a mussel farm sited in the Ría de Ares-Betanzos (Galicia, NW Spain). To assess fish impact on recruitment, we have quantified mussel recruitment densities with or without excluding fish predation. The experiment was carried out using four different collector rope designs that could contribute to decrease the fish predation impact on the amount of mussel seed collected for cultivation. The unprotected long-line (fish exposed treatment) showed lower recruitment densities than the protected one (fish exclusion treatment) for every collector design tested (between 38 and 58%; ANOVA, p <0.001) with the exception of non-filamentous loop complement ropes (NF-L), which showed similar density values (9104±316 and 7855±375indiv/m in the protected and unprotected long-line, respectively; Tukey p >0.05). In addition, in the protected long-line recruitment densities were homogeneous between collector designs (8820±635indiv/m; ANOVA p >0.05) whereas in the unprotected one statistically significant differences between collectors were observed. These results pointed out the influence of fish predation in the amount of mussel seed collected and its different effect between collector designs. The homogeneous density recorded in the protected long-line between collector designs would suggest the presence of another regulation factor of population size when fish predation is excluded. This regulation factor could be the intra-specific competition derived by space and food limitations of the studied area. With regard to the collector design, differences in recruitment density in the unprotected long-line would suggest different degree of protection from predators depending on collector texture and lacing complexity which could enhance the strength of seed attachment and create space refuges from fish. [Copyright &y& Elsevier]

Abstract: The large amount of mussel seed required to support the present mussel farming production levels in Galicia (NW Spain) forces the development of new designs in artificial spat collectors for continual improvement of mussel seed gathering. In the present study, we have assessed both settlement and recruitment of Mytilus galloprovincialis on four different collector ropes in the Ría de Ares-Betanzos (Galicia). Besides the traditional collector ropes (lacing without loops and non-filamentous structure; NF-NL), three new rope designs with different lacing and structures were evaluated; ropes with a filamentous loop complement (F-L), ropes with a non-filamentous loop complement (NF-L) and filamentous ropes without loops (F-NL). Ropes with loops showed higher settlement densities (53,925±4625 and 42,433±5525 indiv./m for F-L and NF-L, respectively) than ropes without loops (26,475±3875 and 13,033±1136 indiv./m for F-NL and NF-NL, respectively). This may be explained by the increase in available surface area provided by the loops. Several studies recognized the importance of filamentous substrata for mussel spat settlement, which may help to explain greater settlement densities on filamentous structures between ropes with the same lacing. In recruitment evaluation, ropes with filamentous loops showed the highest densities expressed in indiv./m (5493±587) as was the case of settlement. However, when density was expressed in kg/m, the ropes with non-filamentous loops had a higher yield (8.48±0.22kg/m), that could be a result of differences in adjusted shell length between ropes. Intra-specific competition and predation were identified as important factors affecting post-settlement mortality. The latter factors could also influence population length distribution. Ropes with rigid loops (NF-L) may supply refuges for spat from predators and therefore, enhance the recruitment of larger individuals, although other factors like size selective settlement could play a significant role in this result. [Copyright &y& Elsevier]