Mussel Rafts Research Articles

Impact of sediment mobilization on trace elements release in Galician Rías (NW Iberian Peninsula): insights into aquaculture

In the latest years, the concentration levels of certain metals and metalloids in the sediments of the Galician Rías have shown an increasing trend (e.g., As, Zn, Cu, Pb, Hg). These areas are also characterized by their richness in nutrients and their great aquaculture or mariculture activity, with the presence of more than 3500 mussel rafts in the Rías Baixas. The inner areas of the Galician Rías are subjected to activities that resuspend the sediment such as high levels of maritime traffic and dredging or cleaning operations. It is likely that a transfer of these elements to the water column happens during the resuspension of sediments caused by natural events or anthropogenic activities. In this study, selected samples of surface sediments of the Ría de Pontevedra (NW Spain) were subjected to a procedure of aerobic oxidation to determine the concentration of some elements (Fe, Mn, Cu, Cr, Pb, Hg, and Zn) released from the sediment to the aqueous phase. The experiment was carried out within 5 days. Measurements of pH and total concentration were taken both in water and sediment samples. Furthermore, speciation of trace elements was carried out in the sediment samples. Trace element concentrations were lower in the sediments during aerobic oxidation, being released to the aqueous phase. From an environmental point of view, Cu was the only trace element released in quantities that may be toxic for the organisms in the area. This problem of sediment oxidation related to dredging activities or natural storm conditions should be considered in environmental impact studies and transferred to stakeholders.

Functional redundancy as an indicator for evaluating functional diversity of macrobenthos under the mussel raft farm near Gouqi Island

Biological traits analysis (BTA) helps to evaluate the effects of different environmental variables on the traits-based functional composition of macrobenthos. However, research on functional traits of macrobenthos under mussel farming is limited. We investigated the spatial and temporal response of the benthic system in terms of taxonomic and functional diversity to environmental variables of farming and natural stressors resulting from suspended mussel farming near Gouqi Island of eastern China Sea. The functional traits of macrobenthic assemblages under mussel farming were characterized by “medium adult body size”, “vermiform body form”, “high flexibility”, “infauna”, “semi-motile”, “gonochoristic”, “surface deposit-feeders”, “carnivores”, “semi-motile burrowers”, and “tube-dwellers”. Functional redundancy was stable in response to mussel farming stresses among seasons, whereas species diversity showed efficient to evaluate natural variables. Functional diversity was significantly affected by farming stressors rather than natural variables, Further analysis using multivariate methods together with continuous monitoring were highlighted to evaluate the impacts of mussel farming. Our results reinforce the importance of macrobenthic species and functional traits analysis to evaluate human stresses driven impacts in offshore ecosystems. By analysing the environmental variables with different sources, independently, we concluded the main effects of human pressures on macrobenthic community. Such distinction could be particularly effective to isolate variable environmental descriptors and evaluate their effects on functional diversity, making the current approach promising for the evaluation of ecological effects of anthropogenic stressors in aquaculture areas.

The effects of suspended bivalve culture on benthic community structure and sediment fluxes in Saldanha Bay, South Africa

This study provides a follow-up to prior measurements of the impact of mussel Mytilus galloprovincialis farming on benthic macrofauna and biogeochemistry and includes the first measurements of the effect of oyster Crassostrea gigas farming in Saldanha Bay, South Africa. The Shannon–Wiener index was significantly lower for farm than for control sites, indicating reduced diversity at farm sites. The lowest values of the Warwick statistic were recorded at the established farm site (R-old). Nested PERMANOVA showed no significant difference in community composition between farm and control sites. Suspension feeders (the mudprawn Upogebia capensis, clam Venerupis corrugata, and holothurian Thyone aurea) dominated at control sites and were important contributors to dissimilarity. Deposit feeders and predatory/scavenging gastropods tended to be more abundant at the farm sites. nMDS ordination showed a clear separation of the more exposed Big Bay stations. The proportions of mud and very coarse sand were moderately associated with community structure. Biogeochemical fluxes showed insignificant differences in sediment oxygen demand between the farm and control sites. Ammonium (NH4) regeneration dominated nitrogen (N) fluxes and was greater at the farm (313 µmol N m−2 h−1) than at the control (187 µmol N m−2 h−1) sites, and maximum rates were restricted to the established mussel raft (R-old) during winter. In contrast, fluxes of oxidised N were less at farm sites relative to the controls. There was no significant difference in phosphate (PO4) regeneration at farm and control stations, leading to higher inorganic N to PO4 regeneration ratios at farm sites.

Heavy metal(loid)s in multiple media within a mussel mariculture area of Shangchuan Island, China: Partition, transfer and health risks

Limited research has been conducted on the heavy metal (loid) (HM) exchanges among seawater, sediments and cultured mussels in mariculture areas. To determine the impacts of mussel mariculture on the transfer and risks of HMs in coastal environments, samples of seawater, sediments and cultured mussels from a typical mariculture area in the South China Sea were analysed. The logarithmic partition coefficients of sediment/water indicated that HMs were preferentially retained by sediments. There were relatively low ecological risks in mussel raft mariculture areas. Principal component analysis and correlation analysis revealed the influences of terrestrial input and ocean circulation on the HMs in seawater, and the bioaccumulation factors reflected the possible accumulation of HMs in seawater by cultured mussels. Mussel farming was the indirect source of HMs in sediments, and the biochemical processes of cultured mussels promoted the transfer and accumulation of HMs into sediments. Health risk assessment revealed that children were more susceptible than adults, and Cd, As and Cr were among the threatening elements. Nonetheless, the health risks that were possibly caused by the daily consumption of farmed mussels were still within safe limits. Thus, the potential pollution remediation and biomonitoring functions of mussel aquaculture in coastal water environments will be further studied in the future.

Influence of aquaculture on fishing strategies: Insights from Galician small-scale fisheries

Marine ecosystems have been traditionally exploited by coastal communities in several ways, especially by fishing. More recently, aquaculture has emerged as an activity through which coastal communities have diversified their economies. Thus, many regions of the world face the challenge of allowing both activities to maximise their yields while complying with conservation objectives. Our study area represents a paradigm of this reality as intensive mussel aquaculture has expanded in the region since the 1950's, forcing small-scale fisheries to adapt to the new scenario. Using a cross-disciplinary approach, we identified two métiers in the studied fleet: a) one composed mostly of queen scallop catches (Queen Scallop Métier - QSM), and b) a more heterogeneous one with a varied composition of Crustacea, Cephalopoda and Fishes (Mixed Composition Métier - MCM). The MCM is strongly spatio-temporally correlated with mussel raft locations, which indicates how the bottom trawl small-scale fleet has adapted its strategies to the presence of aquaculture. Moreover, the rich community associated with mussel rafts is reflected in the heterogeneous catch composition (of valuable species) of the fishing operations carried out near mussel rafts. However, accumulated biodeposits have attracted detritus feeding non-commercial species, creating a new ecological paradigm and posing operational difficulties for the fleet and higher discards.

How can ocean warming at the NW Iberian Peninsula affect mussel aquaculture?

Understanding and forecasting future consequences of climate change in mussel aquaculture industry require the assessment of changes in physical parameters which may affect mussel growth. The FLOW module of Delft3D model forced with climatic data was validated and calibrated for the Rías Baixas (NW Iberian Peninsula), one of the areas with the highest mussel production in the world. This model was used to perform historical (1999–2018) and future (2080–2099) projections. Temperature and stratification water conditions were compared in order to determine at what extent climate change can affect mussel production. Thermal stress will increase in a non-homogeneous throughout the water column and the comfort level of mussels will be reduced by more than 60% in the upper layers and more than 30% in deep layers in most of the mussel raft polygons. Water column stratification will increase ~ 5–10 cycles h−1 in most of the polygons reducing the vertical exchange of nutrients and oxygen. Hereby changes in water temperature and stratification at the end of the century will not be favorable for mussel growth.

Monitoring of trace metal accumulation in two South African farmed mussel species, Mytilus galloprovincialis and Choromytilus meridionalis

Mussels pose health risks to consumers through accumulation of trace metals from the ocean. Saldanha Bay, South Africa, has heavy industry and international shipping, creating concerns over pollution levels for aquaculture facilities. Samples of C. meridionalis and M. galloprovincialis were collected from mussel rafts over two-years and analysed for trace metal content using Inductively Coupled Plasma Mass Spectrometry. Aluminium, Cr, Fe, Zn, Cd and Pb were higher in M. galloprovincialis, while C. meridionalis accumulated more Cu and Mn. Temporal fluctuations occurred for Fe and As concentrations in C. meridionalis, and Fe, As, Hg and Pb in M. galloprovincialis. Arsenic exceeded South African regulatory limits (3 mg/kg) once in each species (max = 3.4 mg/kg w.w.). Lead concentrations in M. galloprovincialis were within EU regulatory limits for bivalves (1.5 mg/kg) but exceeded SA regulatory limits for fish (0.5 mg/kg) four times. Overall, farmed mussels from Saldanha Bay were determined to be safe for human consumption.

Study of ceramic membrane behavior for okadaic acid and heavy-metal determination in filtered seawater

The performance of several MF and UF ceramic membranes that filter the seawater surrounding mussel rafts is studied for preventive detection of toxic episodes. The modified fouling index applied to UF membranes (MFI-UF) is used to compare fouling rates and membrane fouling levels. The reduction of several quality parameters such as turbidity, alkalinity, chemical oxygen demand (COD), and chlorophyll content is explained by the higher quality of the UF rather than the MF permeates. Membrane rejection rates of Pb+2 and okadaic acid, the main toxin that provokes toxic episodes due to bloom-forming algae, are measured under different pH and pressures. Measurements are taken particularly at filtration times before and after the formation of stable caking on the membrane surface. The results indicated that trace concentrations of heavy ions were mainly rejected by the membrane charge, until the saturation point was reached, and that no rejections occurred when the pH was lower than the isoelectric point of the membranes. However, most of the okadaic acid was rejected due to the formation of cake on the membrane surface. The rejection of okadaic acid depended on the membrane pore size and transmembrane pressure, yielding negative rejections under specific filtration conditions.

The Galician mussel industry: Innovation and changes in the last forty years

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.

Occurrence and toxicological assessment of polycyclic aromatic hydrocarbons (PAHs) in marine sediments under mussel farming influence.

The use of marine resources for mussel culture has become increasingly important, particularly on the European Atlantic coast and notably in the Galician Rías in the northwest of Spain. Despite its importance, there is a lack of research and analysis in this area and of the potential problems that it could cause to the environment. This paper details the findings of a study that aimed to find the probable environmental impact of mussel culture activities and to evaluate the polycyclic aromatic hydrocarbon (PAH) content derived from this activity. The Ría de Arousa, where you can find over 70% of all installed rafts in Galicia, was selected for the present study, and nearly 40 marine sediment samples were collected there. The sediments were extracted by ASE (accelerated solvent extraction) procedure, and the quantification of PAHs was performed using gas chromatography coupled to mass spectrometry (GC-MS), with the aid of deuterated PAH internal standards. The total concentration of parental PAHs ranged from 11.66 to 30,272-ngg-1 dry weight (d.w.), with a mean value of 3907-ngg-1 d.w.; the concentration of alkyl PAHs varied from 3.72 to 1187-ngg-1 d.w., with a mean value of 205.1-ngg-1 d.w. Compositional patterns, principal component analysis (PCA) and hieratical cluster association (HCA) yielded a sediment classification where the mussel raft impact is pointed out. PAH ratios indicated a predominance of combustion sources, except in two samples, located in small harbors. Only one station showed total potential carcinogenic PAH values in the range that would frequently cause negative biological effects, and the toxic equivalent concentrations based on BaP equivalents identified another ten positions where biological effects would occur occasionally.

Mussel farming impact on pelagic production and respiration rates in a coastal upwelling embayment (Ría de Vigo, NW Spain)

This paper provides the first diagnosis of the impact of mussel farming on the primary production (PP) and the metabolic balance in a coastal upwelling region (Ría de Vigo). Measurements of size-fractionated PP and microbial plankton metabolism were performed outside (reference station; ReS) and inside the farming area (raft station; RaS). At ReS, integrated PP was higher during upwelling (1.05 ± 0.45 g C m−2 d−1) with microphytoplankton dominating carbon fixation (74 ± 14%). The significance of nanophytoplankton and picophytoplankton increased during winter linked to lower PP (0.24 ± 0.03 g C m−2 d−1). Water column at ReS was always autotrophic with net community production (NCP) ranging from 186 ± 67 mmol O2 m−2 d−1 during upwelling to 43 ± 22 mmol O2 m−2 d−1 in winter. At RaS, there was a decrease in PP attributable not only to mussel consumption but also to the lower irradiance under mussel rafts. Concomitant decrease in NCP was also observed (by 56%), yet remained autotrophic, supporting the view that under current conditions food does not limit mussel growth in the Ría, thus securing the carrying capacity of the system in terms of production.

Cultivation of the Ribbed Mussel (Geukensia demissa) for Nutrient Bioextraction in an Urban Estuary.

Shellfish aquaculture is gaining acceptance as a tool to reduce nutrient over enrichment in coastal and estuarine ecosystems through the feeding activity of the animals and assimilation of filtered particles in shellfish tissues. This ecosystem service, provided by the ribbed mussel (Geukensia demissa), was studied in animals suspended from a commercial mussel raft in the urban Bronx River Estuary, NY, in waters closed to shellfish harvest due to bacterial contamination. Naturally occurring populations of ribbed mussels were observed to be healthy and resilient in this highly urbanized environment. Furthermore, mussels grown suspended in the water column contained substantially lower concentrations of heavy metals and organic contaminants in their tissues than blue mussels (Mytilus edulis) collected at a nearby benthic site. Spat collection efforts from shore and within the water column were unsuccessful; this was identified as a key bottleneck to future large-scale implementation. Filtration experiments indicated that a fully stocked G. demissa raft would clear an average 1.2 × 107 L of Bronx River Estuary water daily, removing 160 kg of particulate matter from the water column, of which 12 kg would be absorbed into mussel digestive systems. At harvest, 62.6 kg of nitrogen would be sequestered in mussel tissue and shell. These values compare favorably to other resource management recovery methods targeting agricultural and stormwater nitrogen sources.

Reduction of diarrhetic shellfish poisoning (DSP) toxins accumulation in cultured mussels by means of rope clustering and hydrodynamic barriers

Accumulation of marine toxins in the organisms is one of the most important problems of the bivalve aquaculture. Mitigation methods are difficult to implement especially in species, as the mussel Mytilus galloprovincialis, which have a relatively low commercial value. For this species, one possible way of decreasing the toxin accumulation is to restrict the availability of toxic cells to the mussels by means of the reduction of the water flow around the perimeter of the culture ropes. We have checked the effectivity to decrease the accumulation of DSP toxins (okadaic acid) in mussels of two ways of obtaining that reduction: surrounding the ropes with a fishing net (1cm mesh); and grouping the ropes (groups of four). During a four week period – with relatively high concentrations of particulate matter – those two ways were tested and shown to effectively reduce both, toxin concentration and toxin burden of cultured mussels exposed to toxic populations of Dinophysis acuminata. The observed reductions were important, 41% and 37% for grouping and surrounding with a net, respectively. Both methods can be used for mussel rafts and long lines and it is very likely they could be also effective with other kinds of toxicity and with other environmental conditions. Statement of relevanceIt would allow a substantial reduction of toxin accumulation.

The impact of shellfish farming on common bottlenose dolphins’ use of habitat

Shellfish farming is an expanding segment of marine aquaculture, but the impact of this industry on coastal cetacean species is only beginning to be considered. The interaction between mussel farming and coastal cetaceans in one of the world’s leading producers of this bivalve (Galicia, NW Spain) was studied. Specifically, the habitat use of common bottlenose dolphins (Tursiops truncatus) was evaluated in relation to environmental, geographical, and anthropogenic variables. Over a period of 22 months spent in the field, 154 daily boat surveys and 353 common bottlenose dolphin encounters were done. Results of this study confirm that areas of mussel production are frequently utilized by common bottlenose dolphins. Of the investigated factors, shellfish farms appeared to have a clear effect, with increased bottlenose dolphin occurrence at mussel farm locations and in waters close to the aquaculture zones. These observations contrast with previous studies where the occurrence and distribution of coastal cetacean species decreased in association with shellfish aquaculture representing a source of habitat loss and causing potentially negative effects. These differences suggest that the interactions between shellfish aquaculture and cetaceans are affected by the culture method and cetacean species involved. The positive relationships between dolphins’ occurrence and mussel aquaculture zones are presumably the result of large aggregations of fish species around mussel rafts, which provide high densities of high-quality prey for dolphins. This study provides new insights into the understanding of how shellfish aquaculture influences coastal dolphins and hence support the design of policies aimed at implementing ecosystem management principles.

Influence of Mussel Culture on the Vertical Export of Phytoplankton Carbon in a Coastal Upwelling Embayment (Ría de Vigo, NW Iberia)

The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ria de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564 ± 1936 mg m−2 day−1) was four times higher than at ReS (731 ± 276 mg m−2 day−1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.

Dynamics of submersible mussel rafts in waves and current

To investigate the dynamics of submersible mussel rafts, the finite element program Aqua-FE™, developed by the University of New Hampshire (UNH), was applied to rafts moored at the surface and submerged. The submerged configuration is used to reduce wave forcing and to avoid contact with floating ice during winters in northern waters. Each raft consists of three pontoons connected by a grid framework. Rafts are intended to support densely spaced mussel ropes hung from the framework. When submerged, the pontoons are flooded, and the raft is held vertically by floats attached by lines. The computer models were developed in Aqua-FE™ to simulate the effects of waves and current. They were validated by comparison with wave tank results by use of a 1/10 scale raft physical model. Comparisons showed good agreement for the important heave (vertical) and pitch (rotational) motions, though there was a tendency towards conservative results for wave and current drag. Full-scale simulations of surface and submerged single raft and two rafts connected in tandem were performed. Submerged raft wave response was found to be reduced relative to that at the surface for both the single and two-raft configurations. In particular, the vertical motion of mussel rope connection points was significantly reduced by submergence, resulting in reduced potential for mussel drop-off. For example, the maximum vertical velocities of mussel rope attachment points in the submerged two raft case were 7%–20% of the corresponding velocities when at the surface.

Circulation of water through a mussel raft: clearance area vs. idealized linear flows

AbstractThis study suggests revision of ecological concepts as food depletions and/or water flow reductions based on idealized linear flows through mussel rafts. We offer an alternative based on the extension of the clearance area, defined as the area affected by the nonlinear effects produced by each raft and surroundings ones. These conclusions are supported by our results, which indicate that (i) the preferential entry of water through a mussel raft does not occur through the bow, contrary to previously thought, and (ii) the intraraft circulation is strongly influenced by the orientation of the raft relative to the background current direction and does not follow a defined pattern. Intraraft circulation is assessed by means of four current metres installed at each side of the raft and the dimensions of the clearance area using long‐term data provided by GPS and compass. While both intraraft circulation and clearance area dimensions are mainly controlled by tide, the net water exchange through the raft is reasonably explained by wind (velocity and direction) and river discharges.

Saccharina latissima (Laminariales, Ochrophyta) farming in an industrial IMTA system in Galicia (Spain)

The development of integrated multitrophic aquaculture (IMTA) systems in Spain has been rather limited so far. However, trials carried out in recent years at experimental and at small industrial scale have been very promising. One of the most encouraging experiences involves the development of seaweed farming for human consumption in combination with mussel rafts in Galicia (NW Spain). Here, we describe a new and more productive marine farming system of Saccharina latissima (“sugar kelp”) combined with mussel rafts. We show its level of integration in terms of harvest and protein content as well as an assessment of the sources of assimilated nitrogen through the analysis of δ15N isotope ratios. Oceanographic conditions in Northwest Spain make S. latissima behave like a winter-spring species in culture with a growing period of just 5–6 months. Nonetheless, production values in our experiment equalled or exceeded those recorded in northern parts of the Atlantic where the culturing period is almost twice as long. Compared to natural populations, S. latissima from mussel-integrated culture systems had almost twice as much protein content, giving greater added value to the species both as food and feed.

Biodeposit contribution to natural sedimentation in a suspended Mytilus galloprovincialis Lmk mussel farm in a Galician Ría (NW Iberian Peninsula)

Abstract 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 Ria de Ares–Betanzos (NW Iberian Peninsula). Our results showed that seston content are below the pseudofeces threshold ( − 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 Ria 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.

Fatty acids as tracers of trophic interactions between seston, mussels and biodeposits in a coastal embayment of mussel rafts in the proximity of fish cages.

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 170 m distant from the fish cages incorporated fish feed FA markers compared with samples obtained 550 m 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.