Mussel Growth Research Articles

Dynamics of coastal meta‐ecosystems: the intermittent upwelling hypothesis and a test in rocky intertidal regions

The intermittent upwelling hypothesis (IUH) predicts that the strength of ecological subsidies, organismal growth responses, and species interactions will vary unimodally along a gradient of upwelling from persistent downwelling to persistent upwelling, with maximal levels at an intermediate or “intermittent” state of upwelling. To test this model, we employed the comparative‐experimental method to investigate these processes at 16–44 wave‐exposed rocky intertidal sites in Oregon, California, and New Zealand, varying in average upwelling and/or downwelling during spring–summer. As predicted by the IUH, ecological subsidies (phytoplankton abundance, prey recruitment rates), prey responses (barnacle colonization, mussel growth), and species interactions (competition rate, predation rate and effects) were unimodally related to upwelling. On average, unimodal relationships with upwelling magnitude explained ∼50% of the variance in the various processes, and unimodal and monotonic positive relationships against an index of intermittency explained ∼37% of the variance. Regressions among the ecological subsidies and species interactions were used to infer potential ecological linkages that underpinned these patterns. Abundance of phytoplankton was associated with increases in rates of barnacle colonization, intensity of competition and predation, and predation effects, and rates of barnacle recruitment were associated with increases in mussel growth, barnacle colonization, and species interactions. Positive effects on interactions were also seen for rates of colonization, competition, predation, and predation effects. Several responses were saturating or exponential, suggestive of threshold effects. These results suggest that the IUH has geographic generality and are also consistent with earlier arguments that bottom‐up effects and propagule subsidies are strongly linked to the dynamics of higher trophic levels, or top‐down effects, as well as to nontrophic interactions. The ∼50% of the variance not explained by upwelling is likely due to more regional‐to‐local influences on the processes examined, and future efforts should focus on incorporating such effects into the IUH.

Growth of juvenile blue mussels (Mytilus edulis) on suspended collectors in the Dutch Wadden Sea

In The Netherlands, fishing for juvenile blue mussels (Mytilus edulis) on wild beds is gradually replaced by harvesting of seeds from suspended collectors. Both the relaxation of fishing as well as the up-scaling of the number of seed collectors are expected to result in an increase in the number of mussels in the Wadden Sea. Consequently, an enhanced mussel population will cause an additional filtration impact on the system. The question is raised to what extent collectors can be used without negatively affecting the carrying capacity of an ecosystem. Therefore, a monitoring programme was initiated to study the growth of juvenile mussels on suspended collectors. This growth was related to food availability, measured as chlorophyll-a, and temperature both before and after settlement. Findings will serve as input for mathematical models predicting the carrying capacity for mussel seed collectors in this area.The results for 2010 and 2011 are presented. In 2011 settled mussels achieved a higher growth rate, while phytoplankton concentrations after settlement were lower. This contradicts the general agreement that higher phytoplankton concentrations result in higher growth rates. A positive relation between chlorophyll-a concentrations during the larval period and the growth rate of settled mussels was found.The number of settled larvae was higher in 2011. Results from existing studies on settlement and recruitment on tidal flats combined with estimated settlement date in the current study led to the hypothesis that the number of settled mussels on rope collectors is inversely related to the duration of the larval period (determined by water temperature). Our results indicated that in the Wadden Sea, the intra-annual differences in chlorophyll-a and temperature did not have an impact on the juvenile growth rate, while the interannual differences did. This is an indication that the larval stage is strongly discriminative in terms of juvenile growth rates.Modelling growth of juvenile mussels on collectors should thus include conditions before settlement.

Turbulent mixing limits mussel feeding: direct estimates of feeding rate and vertical diffusivity

Field measurements of physical and biological parameters, together with the estima- tion of mass transport and estimation of clearance rates (for feeding rate) using a biodeposition method (defecation) were combined to improve the understanding of the limiting factors that affect the feeding rate of blue mussels in an intertidal commercial re-laid benthic mussel bed. The study used an in situ feeding rate method to describe one of the mechanisms that underpins mus- sel bed self-patterning. The feeding rate of mussels measured using the in situ method (defeca- tion) closely matched the rate of the measured turbulent transport of chl a. This relationship sug- gested that the supply rate of food limited the growth of mussels in this system. Vertical food depletion ((chl a) <1 µg l �1 ; height <6 cm) was measured above the mussel bed, and horizontal food depletion (at 5 cm above the bed) was measured in the water column at both mussel patches as well as at adjacent bare patches and in between. Mussel size mirrored the measured food gra- dient such that larger mussels occurred at the edge compared with the middle of the patches of mussels. In this system, the high mussel feeding rate (2.9 l ind. �1 h �1 ), despite food depletion near the mussel bed, is due to the interaction of 3 hydrodynamic processes: vertical turbulent mixing, advection and re-suspension. These processes are themselves altered through a positive feedback mechanism associated with the mussel bed morphology. We found that the highest feeding rates are achieved when mussel beds are interspersed with patches of bare mud; thus stocking strate- gies that promote the formation of self-patterning should be encouraged.

Mussel production management: Raft culture without thinning-out

Mussel raft culture as traditionally practiced in Galicia (Spain) represents an extreme case of aggregation, where culture density along growth ropes is maximized to achieve greater commercial yields. However, to maintain high growth rates during the entire cultivation period the initial density must be reduced through a process called “thinning-out” when rope weight increases by a factor of 10.In raft culture, the annual commercial cycle is superimposed on a production cycle that can last up to 18months. For this reason, the thinned-out mussel ropes can only occupy 75% of the usable surface area of the raft. Additionally, the rope handling process has a pronounced impact on production costs, affecting both labor and material costs.With the objective of optimizing economic yields in mussel raft culture, we conducted a study to compare a new technique without thinning-out with the traditional method, and we evaluated the effect of density on mussel growth for both techniques.For this purpose, three different densities were prepared for the no thinning-out ropes (800n, 1000n and 1200n mussels/m), and the other three for the thinning-out ropes (400y, 500y and 600y mussels/m).At the end of the experiment, average length and average live weight for mussels cultured without thinning-out were significantly lower than values observed for mussels cultured with thinning-out. However, the no thinning-out technique did not result in a lower total biomass production.The technique without thinning-out has a production cycle of 12months, which coincides with annual production. On the other hand, the culture with thinning-out technique has a 15-month cycle (seeding and thinning-out processes); thus annual production was 20% lower than total production. Under these conditions, production at the two highest densities (1000n and 1200n) was significantly higher than production at all densities with thinning-out.If we consider economic yield per raft per year, which also takes into account the higher price of mussels with increasing size, the difference between the two culture methods is smaller. Only the 1200n ropes still produced a higher economic yield than the 600y ropes. On the other hand, the shortening of the cultivation time and the elimination of the thinning-out reduce the production costs.In conclusion, the results obtained with the new culture technique without thinning-out at high seed densities enable substantial improvements in terms of biomass, economic yields, and operating costs for mussel production.

Effects of wave exposure, temperature and epibiont fouling on byssal thread production and growth in the blue mussel, Mytilus edulis, in the Gulf of Maine

Blue mussels (Mytilus edulis) need a strong byssal attachment to remain anchored on wave swept shores. Byssogenesis and mussel growth can be affected by abiotic factors, as well as by biotic interactions. Using short- and long-term field deployments of artificially-fouled mussels in coastal New Hampshire, we determined the effects of wave exposure, temperature and epibiont cover on the number and attachment strength of byssal threads produced and on mussel growth. In a factorial experiment, more byssal threads were produced by epibiont-covered mussels located at sheltered sites during summer. With each additional byssal thread that a mussel produced, its total attachment strength to the substrate increased by 3.8%. Furthermore, attachment strength increased by 6.7% when mussels were artificially fouled and by 17.1% during winter. Mussel growth was higher during summer at high wave exposure sites, presumably due to a seasonal increase in nutrients. Epibiont cover had no influence on mussel growth. Our results indicate that wave exposure, temperature, and epibionts influence byssal thread production, whereas wave exposure and temperature affect mussel growth. This study incorporates several different factors simultaneously in a series of field experiments which affect mussel byssal thread production, growth and survival and have an important implication for their population dynamics.

Practical experience in the rearing of freshwater pearl mussels (Margaritifera margaritifera): advantages of a work-saving infection approach, survival, and growth of early life stages

The critically endangered freshwater pearl mussel (Margaritifera margaritifera Linnaeus 1758) is the target species of an Austrian conservation project that involves captive breeding. In order to optimize the operational procedure, controls were conducted at several decisive stages, including infec- tion of host fish (for which a time- and work-saving enclosure approach was tested), larval growth during the parasitic stage, growth of juvenile mussels in climate chambers at different temperatures, and growth and survival of re-introduced juveniles in field cages. High infection rates could be attained under near natural conditions. Distinctive patterns in the way the gill arches of the host fish were infected could be detected. Encysted glochidia showed significantly different successive growth stages, related to water temperature. In all, five distinctive growth stages could be detected in the course of the first 562 days of observation. The stages are described and the respec- tive daily increments given. Very high survival rates were achieved during hibernation in the field as well as at the laboratory. The study suggests a way for saving time in the infection procedure that can more effec- tively be invested in an intensive maintenance of juveniles at the laboratory and during hibernation in the field.

High suspended solids as a factor in reproductive failure of a freshwater mussel

Elevated suspended solids are a widespread stressor of aquatic ecosystems, but their effects on growth and reproduction in freshwater mussels are largely unknown. We fertilized experimental ponds to create a gradient in total suspended solids (TSS) and examined the effects of TSS on growth, nutritional status, reproduction, and clearance rate in Ligumia subrostrata. The number of females that became gravid declined sharply with increasing TSS, and no gravid females were found in the highest TSS treatments. The proportion of gravid females was not related to the TSS organic∶inorganic ratio. Fertilization was an all-or-nothing phenomenon. In all females that did become gravid, 98 to 99% of eggs were fertilized regardless of TSS, and total fecundity was unrelated to TSS. Clearance rates declined sharply as TSS increased but showed a threshold relationship in which clearance was uniformly low at TSS > ∼8 mg/L. Reproductive failure probably was not caused by poor body condition or nutritional status because growth (length and mass) and energetic status (measured as caloric density) were not related to TSS. We propose 2 mechanisms that implicate interference of TSS with fertilization as the cause of reproductive failure. Reduced clearance rate could decrease the chance of females encountering suspended sperm during filter feeding, or an increase in pseudofeces production could bind sperm in mucus and lead to its egestion before fertilization. Interruption of fertilization coincident with high TSS is a potential mechanism to explain the lack of mussel recruitment in many locations. Monitoring and reduction of TSS, especially during the spawning season, may help create conditions necessary for maintenance and recovery of mussel populations. More research is needed to explore the generality of this pattern across a broad range of mussel species including those adapted to lotic environments or that use different brooding strategies.

Comparison of growth and pearl production in males and females of the freshwater mussel, Hyriopsis cumingii, in China

Growth and pearl production were compared for males and females in the freshwater mussel, Hyriopis cumingii, from a full-sib family. The results indicated that there was no significant difference (p > 0.05) on individual weight between male and female mussels of 1- or 2-year-old, while significant difference (p 0.05). Under traditional culture methods, male mussels have a better pearl performance, and artificial separation of females from males can improve the growth and pearl production of female mussels.

Food availability outweighs ocean acidification effects in juvenile Mytilus edulis: laboratory and field experiments

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20gkg(-1) ) and CO2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO2 variability in this habitat and the combined effects of elevated pCO2 and food availability on juvenile M.edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO2 up to 3350μatm. Kiel Fjord was characterized by strong seasonal pCO2 variability. During summer, maximal pCO2 values of 2500μatm were observed at the surface and >3000μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M.edulis at a high pCO2 inner fjord field station (mean pCO2 ca. 1000μatm) in comparison to a low pCO2 outer fjord station (ca. 600μatm). In addition, mussels were able to out-compete the barnacle Amphibalanus improvisus at the high pCO2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO2 . At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus, M.edulis can dominate over a seemingly more acidification resistant species such as A.improvisus. We conclude that benthic stages of M.edulis tolerate high ambient pCO2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification.

Effects of flow restoration on mussel growth in a Wild and Scenic North American River

BackgroundFreshwater mussels remain among the most imperiled species in North America due primarily to habitat loss or degradation. Understanding how mussels respond to habitat changes can improve conservation efforts. Mussels deposit rings in their shell in which age and growth information can be read, and thus used to evaluate how mussels respond to changes in habitat. However, discrepancies between methodological approaches to obtain life history information from growth rings has led to considerable uncertainty regarding the life history characteristics of many mussel species. In this study we compared two processing methods, internal and external ring examination, to obtain age and growth information of two populations of mussels in the St. Croix River, MN, and evaluated how mussel growth responded to changes in the operation of a hydroelectric dam.ResultsExternal ring counts consistently underestimated internal ring counts by 4 years. Despite this difference, internal and external growth patterns were consistent. In 2000, the hydroelectric dam switched from operating on a peaking schedule to run-of-the-river/partial peaking. Growth patterns between an upstream and downstream site of the dam were similar both before and after the change in operation. At the downstream site, however, older mussels had higher growth rates after the change in operation than the same sized mussels collected before the change.ConclusionsBecause growth patterns between internal and external processing methods were consistent, we suggest that external processing is an effective method to obtain growth information despite providing inaccurate age information. External processing is advantageous over internal processing due to its non-destructive nature. Applying this information to analyze the influence of the operation change in the hydroelectric dam, we suggest that changing to run-of-the-river/partial peaking operation has benefited the growth of older mussels below the dam.

Biofouling leads to reduced shell growth and flesh weight in the cultured mussel Mytilus galloprovincialis

Competitive interactions between cultured mussels and fouling organisms may result in growth and weight reductions in mussels, and compromised aquaculture productivity. Mussel ropes were inoculated with Ciona intestinalis, Ectopleura crocea or Styela clava, and growth parameters of fouled and unfouled Mytilus galloprovincialis were compared after two months. Small mussels (≈50 mm) fouled by C. intestinalis and E. crocea were 4.0 and 3.2% shorter in shell length and had 21 and 13% reduced flesh weight, respectively, compared to the controls. Large mussels (≈68 mm) fouled by S. clava, C. intestinalis and E. crocea were 4.4, 3.9 and 2.1% shorter than control mussels, respectively, but flesh weights were not significantly reduced. A series of competitive feeding experiments indicated that S. clava and C. intestinalis did not reduce mussels’ food consumption, but that E. crocea, through interference competition, did. Fouling by these species at the densities used here reduced mussel growth and flesh weight, likely resulting in economic losses for the industry, and requires consideration when developing biofouling mitigation strategies.

Area-intensive bottom culture of blue mussels Mytilus edulis in a micro-tidal estuary

Dredge fishery for blue mussels Mytilus edulis (L.) impacts the benthic ecosystem, and substitution by area-intensive bottom culture production may reduce adverse effects on the ecosystem. Two different field studies in 2007 and 2009 tested the productivity of bottom culture of blue mussels, and whether a shift from dredging of full-grown blue mussels to production of blue mussels in bottom culture could reduce the area of impacted sea bottom. In the first study, the macrostructure of a commercial bottom culture was analysed by side scan mapping, and the growth of blue mussels was recorded on a transect from the edge to the central part of the bottom culture. In the second study, we analysed the effect of seeding density (1.5 and 3.5 kg m −2 ) on mus- sel production. The measured production was used to model the affected area when producing blue mussels in bottom culture. The macrostructure of the culture bed formed during the trans- plantation of mussel seed was not changed 1 yr after transplantation, indicating that transplanta- tion supported the formation of a robust blue mussel bed. Shell growth showed no spatial variabil- ity from the edge to the central part of the commercial bottom culture, suggesting that growth was not reduced by density-dependent food limitation. The population production:biomass ratio (P/B) of the experimental bottom cultures was 1.0 and showed no significant effect of seeding density. Model simulations indicated that the impacted area was smaller when producing blue mussels in bottom culture than in a fishery of full-grown mussels if P/B was higher than 0.5.

Screening for negative effects of candidate ascidian antifoulant compounds on a target aquaculture species, Perna canaliculus Gmelin

The natural chemical compounds radicicol, polygodial and ubiquinone-10 (Q10) have previously been identified as inhibitors of metamorphosis in ascidian larvae. Accordingly, they have potential as a specific remedy for the costly problem of fouling ascidians in bivalve aquaculture. In this study, these compounds were screened for their effects on the physiological health of an aquaculture species, the green-lipped mussel, Perna canaliculus Gmelin, at or above the 99% effective dose (IC99) in ascidians. Three physiological biomarkers of mussel health were screened: growth (increases in shell height and wet weight), condition (condition index) and mitochondrial respirational function (Complex I-mediated respiration, Complex II-mediated respiration, maximum uncoupled respiration, leak respiration, respiratory control ratios and phosphorylation system control ratios). While polygodial and Q10 had no effect on mussel growth or the condition index, radicicol retarded growth and decreased the condition index. Mitochondrial respirational function was unaffected by radicicol and polygodial. Conversely, Q10 enhanced Complex I-mediated respiration, highlighting the fundamental role of this compound in the electron transport system. The present study suggests that polygodial and Q10 do not negatively affect the physiological health of P. canaliculus at the IC99 in ascidians, while radicicol is toxic. Moreover, Q10 is of benefit in biomedical settings as a cellular antioxidant and therefore may also benefit P. canaliculus. Accordingly, polygodial and Q10 should be progressed to the next stage of testing where possible negative effects on bivalves will be further explored, followed by development of application techniques and testing in a laboratory and aquaculture setting.

Toxicity of sediments potentially contaminated by coal mining and natural gas extraction to unionid mussels and commonly tested benthic invertebrates

Sediment toxicity tests were conducted to assess potential effects of contaminants associated with coal mining or natural gas extraction activities in the upper Tennessee River basin and eastern Cumberland River basin in the United States. Test species included two unionid mussels (rainbow mussel, Villosa iris, and wavy-rayed lampmussel, Lampsilis fasciola, 28-d exposures), and the commonly tested amphipod, Hyalella azteca (28-d exposure) and midge, Chironomus dilutus (10-d exposure). Sediments were collected from seven test sites with mussel communities classified as impacted and in proximity to coal mining or gas extraction activities, and from five reference sites with mussel communities classified as not impacted and no or limited coal mining or gas extraction activities. Additional samples were collected from six test sites potentially with high concentrations of polycyclic aromatic hydrocarbons (PAHs) and from a test site contaminated by a coal ash spill. Mean survival, length, or biomass of one or more test species was reduced in 10 of 14 test samples (71%) from impacted areas relative to the response of organisms in the five reference samples. A higher proportion of samples was classified as toxic to mussels (63% for rainbow mussels, 50% for wavy-rayed lampmussels) compared with amphipods (38%) or midge (38%). Concentrations of total recoverable metals and total PAHs in sediments did not exceed effects-based probable effect concentrations (PECs). However, the survival, length, or biomasses of the mussels were reduced significantly with increasing PEC quotients for metals and for total PAHs, or with increasing sum equilibrium-partitioning sediment benchmark toxic units for PAHs. The growth of the rainbow mussel also significantly decreased with increasing concentrations of a major anion (chloride) and major cations (calcium and magnesium) in sediment pore water. Results of the present study indicated that (1) the findings from laboratory tests were generally consistent with the field observations of impacts on mussel populations; (2) total recoverable metals, PAHs, or major ions, or all three in sediments might have contributed to the sediment toxicity; (3) the mussels were more sensitive to the contaminants in sediments than the commonly tested amphipod and midge; and (4) a sediment toxicity benchmark of 1.0 based on PECs may not be protective of mussels.

Numerical modelling of spatio-temporal variability of growth of Mytilus edulis (L.) and influence of its cultivation on ecosystem functioning

One of the key needs of the aquaculture industry is the implementation of effective management methods to ensure the sustainability, economic viability and minimization of negative impacts on both human and ecosystem well-being. The authors developed a Fortran 90 implementation of the dynamic energy budget (DEB) model for Mytilus edulis. The model has been further developed to include physiological interactions with the ecosystem and coupled to a biogeochemical nutrient–phytoplankton–zooplankton–detritus (NPZD) model. Phytoplankton and detritus uptakes, oxygen utilisation, CO2 production, NH4 excretion, egestion of faeces, and assimilation of food are modelled. A novel approach was derived that accounts for the allocation of C and N in mussel flesh and shell organic fraction. The DEB–NPZD model has been subsequently coupled to a high resolution three dimensional numerical coastal ocean model of the south–west coast of Ireland, where approximately 80% of national rope mussel is produced annually. Simulations have been carried out for the time period July 2010–June 2011, for which the field data on mussel biometrics and ambient seawater properties were collated. The model accurately reproduced the spatio-temporal variability in blue mussel growth. It is also shown that the ecosystem dynamics is affected by the presence of aquaculture farms. The modelling system presented allows for the assessment of the impacts of aquaculture activities on water quality, quantification of the production and ecological carrying capacities and improvement of our understanding of the ecosystem functioning with particular emphasis on interactions between various trophic levels.

Crecimiento del mejillón verde &lt;i&gt;Perna viridis&lt;/i&gt; (Bivalvia: Mytilidae) bajo sistema de cultivo de fondo en la ensenada de Turpialito, Golfo de Cariaco, Venezuela

Mussels represent one of the most important mollusk species for culture activities around the world, and their growth may depend on the culture system used and locality. In this study, we evaluated the growth of Perna viridis in bottom culture to test its performance when using natural food, and to decide its use as a culture species in the Gulf of Cariaco. For this, mussel seeds (35.81 +/- 1.41 mm in length) were obtained in the locality of Guaca (North coast of Sucre state) and transferred to the Hydrobiological Station of Turpialito, Gulf of Cariaco, Sucre state, Venezuela, where they were planted in "Spanish baskets" to evaluate their growth between July 2007 and February 2008. Monthly survival was determined and the maximum shell length, dry mass of muscle and remains tissues of the gonad. The environmental parameters (water temperature, salinity, dissolved oxygen, chlorophyll a, total seston and organic fraction), in the cultivation area were determined every 15 days. Monthly measurements were made of proteins, lipids and carbohydrates to seston. During the entire study the mussels showed continued growth, ultimately reaching a maximum length of 78.7 +/- 4.43 mm. However, the growth rate of the dry mass of somatic (muscle, other tissue) and reproductive tissues showed variability throughout the study, and observed a significant increase by the end of the experiment. The observed variations in the growth rate of the reproductive tissue mass depended on the reserves accumulated and food offered by the environment. The organic seston throughout the experience showed an independence of temperature and chlorophyll a values; this one maintained values above 1 mg/L, thus forming the main food resource for mussels. The high content of proteins, lipids and carbohydrates observed in the seston at the end of the study, might be mainly associated with coastal upwelling, which provides a great food contribution of phytoplankton and organic type. The high survival rate (>80%), increase in the length of the shell and the high gonad production, suggests an excellent physiological condition of P. viridis, related to the availability and quality of food particularly the organic type present in the medium. We concluded that the bottom culture can provide an alternative aquaculture production in the Gulf of Cariaco.

Sediment accumulation predicts the distribution of a unionid mussel (Elliptio complanata) in nearshore areas of a Canadian Shield lake

Summary1. The importance of native freshwater mussels for ecosystem processes depends on their density, size distribution and activity. In lakes, many of the factors that affect mussels (fish hosts, habitat, food) could be directly or indirectly related to wind‐driven physical processes.2. We tested whether the abundance and size of Elliptio complanata in the shallow, nearshore areas of a medium‐sized lake were related to site exposure, substratum type and fish distribution. To disentangle some of the correlated variables known to affect mussel distribution, we used paired exposed and sheltered sampling sites along the 7‐km fetch of the lake basin.3. The distribution of sediment characteristics in nearshore areas was highly predictable. The mean depth of accumulated soft sediments decreased with increasing fetch at wind‐exposed sites, but increased with increasing fetch at sheltered sites. Sediments were deeper along the main shoreline than around islands. Deeper sediments tended to be finer and higher in silt content and organic fraction.4. The density and proportion of juvenile mussels along the main shoreline varied in a unimodal way with sediment depth. These results suggest that wind‐driven physical forces affect the transport of young juveniles to sediment depositional areas and create sediment conditions that influence their growth and survival. In contrast, the proportion of juvenile mussels around islands was not related to sediment characteristics, but decreased with remoteness of the island, suggesting that the distribution of juvenile mussels may be limited by fish movements. These results are tentative since they do not include buried juvenile mussels.5. We also found a unimodal relationship between total mussel density (juveniles and adults) and sediment depth but, in contrast to the relationship for juveniles only, it applied to all sites with soft sediments, including islands. We conclude that factors related to sediment depth affect the growth and survival of adult mussels around islands and that these factors are strong enough to modify the pattern of distribution established via dispersal during earlier life stages.6. The mean shell length of adults at different sites within the lake basin ranged from 60 to 85 mm. Mussel shell length decreased with increasing fetch at sites exposed to the prevalent winds, but was relatively constant on the sheltered side of peninsulas and islands. The size of unionid mussels in different parts of the lake seems to be determined both by their exposure to physical forces and by sediments.7. The local distribution of E. complanata is determined, directly and indirectly, by wind‐driven forces. These processes are likely to be important for other benthic organisms affected by similar habitat conditions (e.g. sediment characteristics, physical disturbance).

First measurements of the scope for growth (SFG) in mussels from a large scale survey in the North-Atlantic Spanish coast

SFG and physiological rates were measured in wild mussels from the Spanish Marine Pollution monitoring program (SMP) in order to determine seawater quality. It consists of 41 stations, covering almost 2500km of coast, making the SMP the widest-ranging monitoring network in the Iberian Peninsula's Atlantic region. Results of the 2007 and 2008 surveys when 39 sites were sampled: (20 in 2007 and 19 in 2008, being 8 sites sampled both years) were presented. Chemical analyses were carried out to determine the relationships between physiological rates and the accumulation of toxic compounds. Data presented are the first to become available on the use of SFG as a biomarker of the marine environment on a large spatial scale (>1000km) along Spain's Atlantic seaboard.SFG values enable significant differences to be established between the areas sampled and between the two years surveyed. The integration of biological and chemical data suggests that certain organochlorine compounds, namely chlordanes and DDTs, may have a negative effect on SFG, although such an effect is of a lesser magnitude than that associated with certain biological parameters such as condition index and mussel age. These variables act as confounding factors when attempting to determine the effect of chemical compounds present in the marine environment on mussel SFG. Further research is therefore needed on the relation between these confounding factors and SFG in order to apply the relevant corrective strategies to enable this index to be used in monitoring programs. The effect of these confounding factors is more clearly revealed in studies that cover a wide-ranging spatial and time scale, such as those carried out within the SMP. These results do not invalidate the use of biological data in monitoring programs, but rather point to the need to analyze all the factors affecting each biological process.

Mussel selectivity for high-quality food drives carbon inputs into open-coast intertidal ecosystems

Filter-feeding invertebrates consume phytoplankton and detritus and therefore serve as important mediators of the exchange of materials from nearshore pelagic to intertidal benthic ecosystems. Here, we evaluated the linkages between nearshore and intertidal systems on tem- perate rocky reefs on the coasts of Oregon, USA, and New Zealand's South Island. We used dif- ferences in the concentrations of both nearshore particulate organic carbon and chlorophyll a (chl a), a proxy for phytoplankton availability, at different sites in Oregon and New Zealand to evaluate the influences of suspended particulate organic material (POM) quality and quantity on the rates of carbon inputs associated with intertidal mussels (Mytilus californianus in Oregon and Mytilus galloprovincialis in New Zealand). We also analyzed the carbon stable isotope ratios (δ 13 C) of intertidal mussels and nearshore POM to examine changes in mussel growth in carbon relative to changes in their potential food sources along gradients of POM quality (i.e. carbon-to- chlorophyll ratios, C:chl a). In both Oregon and New Zealand, the δ 13 C in mussel tissues did not change along a gradient of food quality, whereas the δ 13 C of the POM declined as food quality declined (i.e. C:chl a increased), suggesting that mussels were selectively consuming high-quality food. We also found that the availability of phytoplankton, a high-quality component of the POM, was a better predictor of mussel growth in carbon (mg C g �1 d �1 ) than the total concentration of particulate organic carbon, which includes both higher-quality phytoplankton and lower-quality detrital material. Our results highlight the necessity of considering POM quality while evaluating the role of filter-feeders as mediators of carbon inputs into intertidal systems.

Seawater acidification by CO2 in a coastal lagoon environment: Effects on life history traits of juvenile mussels Mytilus galloprovincialis

The carbonate chemistry of seawater from the Ria Formosa lagoon was experimentally manipulated, by diffusing pure CO2, to attain two reduced pH levels, by −0.3 and −0.6 pH units, relative to unmanipulated seawater. After 84days of exposure, no differences were detected in terms of growth (somatic or shell) or mortality of juvenile mussels Mytilus galloprovincialis. The naturally elevated total alkalinity of the seawater (≈3550μmolkg−1) prevented under-saturation of CaCO3, even under pCO2 values exceeding 4000μatm, attenuating the detrimental effects on the carbonate supply-side. Even so, variations in shell weight showed that net calcification was reduced under elevated CO2 and reduced pH, although the magnitude and significance of this effect varied among size-classes. Most of the loss of shell material probably occurred as post-deposition dissolution in the internal aragonitic nacre layer. Our results show that, even when reared under extreme levels of CO2-induced acidification, juvenile M. galloprovincialis can continue to calcify and grow in this coastal lagoon environment. The complex responses of bivalves to ocean acidification suggest a large degree of interspecific and intraspecific variability in their sensitivity to this type of perturbation. Further research is needed to assess the generality of these patterns and to disentangle the relative contributions of acclimation to local variations in seawater chemistry and genetic adaptation.