European Estuaries Research Articles

Factors contributing to hypoxia in a highly turbid, macrotidal estuary (the Gironde, France)

Dissolved oxygen (DO) is a fundamental parameter of coastal water quality, as it is necessary to aquatic biota, and it provides an indication of organic matter decomposition in waters and their degree of eutrophication. We present here a 7 year time series of DO concentration and ancillary parameters (river discharge, water level, turbidity, temperature, and salinity) from the MAGEST high-frequency monitoring network, at four automated stations in the central and fluvial regions of the macrotidal Gironde Estuary, one of the largest European estuaries. The spatio-temporal variability of DO at different time scales was first related to the migration and position of the maximum turbidity zone in this extremely turbid estuary. Since 2005, the Gironde Estuary has recorded several borderline hypoxic situations (DO close to 2 mg L(-1)) and a 7 day-long hypoxic event (DO < 2 mg L(-1)) in July 2006. Summer hypoxia occurred exclusively in the fluvial, low salinity, and high turbidity sections of the estuary and was significantly more pronounced in front of the large urban area of Bordeaux (715 000 inhabitants). Detailed analysis of the data at the seasonal, neap-spring and semi-diurnal tidal time scales, reveals that hypoxia in this area occurred: (i) in the maximum turbidity zone; (ii) during the spring to neap tide transition; (iii) at highest water temperature; and (iv) at lowest river discharge; there was also evidence of an additional negative impact of sewage treatment plants of Bordeaux city. Enhancement of respiration by turbidity, temperature and inputs of domestic biodegradable organic matter and ammonia, versus renewal of waters and dispersion of reduced pollutants with the river discharge, appeared as the dominant antagonist processes that controlled the occurrence of summer hypoxia. In the context of long-term environmental changes (increase in temperature and population, decrease in summer river discharge), the occurrence of severe hypoxia could not be excluded in the next decades in the upstream reach of the Gironde Estuary.

PCBs in the fish assemblage of a southern European estuary

The Mondego estuary fish assemblage was studied for the accumulation of PCBs. Three sampling stations were visited along an estuarine salinity gradient, and, in total, 15 species were collected. Analysis of PCBs revealed no significant differences among the sampling stations, although differences were observed among the fish assemblages. Fish assemblages could be divided into three groups. The first group comprised those with higher concentration (more than 10ngg−1, dw), included the species Gobius niger, Sardina pilchardus, Anguilla anguilla, Pomatoschistus microps, Chelidonichthys lucerna and Liza ramada; the second group with medium concentration (5–10ngg−1, dw), included the species Pomatoschistus minutus, Dicentrarchus labrax, Atherina presbyter, Chelon labrosus, Diplodus vulgaris, Platichthys flesus and Cilata mustela; and a third group with low concentration (less than 5ngg−1, dw), included the species Solea solea and Callionymus lyra. A positive correlation was found between lipid content and PCB concentrations. To evaluate the influence of the residence time of species on the accumulation of PCBs, species were divided into two groups: species that spend more than 3years in the estuary, and species that spend less than 3years in the estuary. Species that spend more than 3years in the estuary presented higher concentrations than species that spend less than 3years in the estuary. CBs 138 and 153 had higher concentration, and tended to increase with time spent in the estuary.

Climate Change, Sea-Level Rise and Implications for Coastal and Estuarine Shoreline Management with Particular Reference to the Ecology of Intertidal Benthic Macrofauna in NW Europe.

In many European estuaries, extensive areas of intertidal habitats consist of bare mudflats and sandflats that harbour a very high abundance and biomass of macrobenthic invertebrates. The high stocks of macrobenthos in turn provide important food sources for the higher trophic levels such as fish and shorebirds. Climate change and associated sea-level rise will have potential to cause changes in coastal and estuarine physical properties in a number of ways and thereby influence the ecology of estuarine dependent organisms. Although the mechanisms involved in biological responses resulting from such environmental changes are complex, the ecological effects are likely to be significant for the estuarine benthic macrofauna and hence the consumers they support. This paper reviews the utilisation patterns of estuarine intertidal habitats by shorebirds, fish and crustaceans, as well as factors affecting the distribution, abundance and biomass of estuarine macrobenthos that is known to be important food source for these estuarine predators. This study also provides simple conceptual models of the likely impacts of sea-level rise on the physical and biological elements of estuarine intertidal habitats, and implications of these results are discussed in the context of sustainable long term flood and coastal management in estuarine environments.

Nekton response to freshwater inputs in a temperate European Estuary with regulated riverine inflow

The aim of this 12-year study was to assess the nekton (fish, decapod crustaceans) response to freshwater inputs (rainfall, dam discharges) in a temperate estuary with regulated riverine inflow. Although interannual variability in river discharges to the Guadalquivir estuary has been extremely high since the construction of a dam in 1930, a significant decreasing trend in the dam's discharges has been observed in the last 80years. During this study, an alternation of wet, standard and dry years occurred in the estuarine area but no significant long-term trend was observed. River discharge, in turn, showed a considerable interannual variability and a significantly decreasing long-term trend. Freshwater inputs had an immediate effect on estuarine salinity and turbidity, and consequently on prey availability (mysids). Although 124 nektonic species were collected, only 47 of them (adding up to 99.7% of total abundance) were regularly present in the estuary: 32 marine migrants, 13 estuarine species and 2 diadromous species. Well-defined temporal changes in species composition and abundance yielded clear seasonal patterns in the estuarine nektonic community. Considerable intermonth and interannual changes were occasionally observed relating to freshwater inputs, mainly in winter/autumn of wet years. Thus, within each two-month period, some significant interannual differences in the nektonic community were also observed, with marine migrants tending to be more abundant in dry years. However, changes in the studied nektonic community did not show long-term trends. In conclusion, natural and human-controlled freshwater inputs currently play a significant role in determining the physicochemical conditions and the biota of the Guadalquivir estuary. However, although freshwater input seemed to transitorily affect the estuarine nekton, either directly (flushing out) or indirectly (through changes in salinity, turbidity and prey availability), a quick reestablishment of the estuarine nekton (strong resilience) was observed following freshwater inputs together with the recovery of environmental conditions within the estuary.

Turbidity maxima in four macrotidal estuaries

Hydrodynamic and fine sediment transport characteristics of four major macrotidal Northern European estuaries are compared. The four estuaries (Weser, Seine, Scheldt, Humber) are amongst those key to navigation and shipping in that they are home to several major European ports (e.g. Hull, Antwerp, Le Havre). In particular, the characteristics and behaviour of the estuarine turbidity maximum are described for each system. While this is a complex topic that continues to benefit from ongoing research, some similarities exist between the estuaries in terms of the response of the turbidity maximum to changes in tidal range (during the neap–spring–neap cycle) and fresh water flow (due to seasonal variations in rainfall in the catchments). The hydrodynamics of the four estuaries are very similar, and are characterised by faster, shorter flood tide currents compared with longer, slower ebb tides. Under low fresh water flow conditions, the turbidity maximum is in each case moved upstream, while high fresh water flow conditions cause a net seaward movement of the turbidity maximum. While in general the concentrations of suspended sediment within turbidity maxima are no more than a few hundred milligrams per litre, the particular topography of the Humber estuary system leads to concentrations considerably higher than this.

Grazer avoidance may explain the invasiveness of the red alga Gracilaria vermiculophylla in Scandinavian waters

The invasive red alga Gracilaria vermiculophylla has quickly spread across Europe, but it is unclear whether its success is based on a high tolerance to variations in environmental conditions or to the absence of native grazers that feed on this alga. We tested whether native invertebrate grazers prefer native algae to G. vermiculophylla. Feeding preferences of three common herbivores were quantified when offered G. vermiculophylla and native Fucus vesiculosus, Ceramium virgatum, and Ulva intestinalis in no-, two- and multiple-choice trials. Herbivore growth was measured when fed each of the algae separately. Grazers consumed G. vermiculophylla in no-choice trials, but avoided generally this alga when having a choice. U. intestinalis was always preferred over G. vermiculophylla, and grazers fed with U. intestinalis grew faster than those fed with G. vermiculophylla. We conclude that grazers avoid G. vermiculophylla to most native algae, which may benefit G. vermiculophylla in northern European estuaries.

Long-Term Changes in Population Dynamics of the Shrimp Palaemon longirostris in the Gironde Estuary

Spanning 20 years (1979–2007), this study is the longest time series pertaining to the resident shrimp species Palaemon longirostris in a European estuary. Data from monthly faunal surveys undertaken across the middle part of the Gironde estuary from April 1979 along with data from a statistical analysis of the commercial catches throughout the entire estuary and river were considered in order to explore their inter and intra-annual variability and long-term trends. Long-term densities series as well as environmental series (salinity, discharge, temperature and NAO) were decomposed and the effects of environmental variables were also examined using statistical models (GAMs). This revealed important spatio-temporal variability and a significant overall decrease in abundance of this species in the Gironde estuary since the beginning of the 1980s. This long-term decrease in abundance corresponded significantly to long-term decreases in both discharge and the NAO index, as well a long-term increase in temperature and salinity in the middle part of the estuary. However, models showed that environmental factors explained only a small part of the variability. The upstream shift of the population highlighted in this study, probably due to the intrusion of marine waters into the middle section of the estuary, may also have contributed to its decrease in abundance. Inter-annual variability of densities was also significantly linked with inter-annual fecundity fluctuations, and a significant decrease in both mean female size and fecundity was shown for preserved samples from 1992. Moreover, the breeding period has been temporally stretched out and began earlier in more recent years, potentially due to the increase in spring temperature.

Oceanic and local environmental conditions as forcing mechanisms of the glass eel recruitment to the southernmost European estuary

The main oceanic and local environmental traits forcing the glass eel Anguilla anguilla (L., 1758) recruitment to the southernmost European estuary, the Guadalquivir (SW Spain), were studied during nine successive migration seasons (June 1997–December 2006) using a fishery-independent experimental survey at three sampling sites in the estuary. A clear seasonal pattern was observed: density was highest between late autumn and spring with two migration peaks, and lowest during summer. Short-term (inter-month) changes in glass eel density were partially driven by local environmental variables, such as estuarine turbidity, local rainfall and water temperature. Long-term (inter-annual) changes were positively correlated with oceanic factors related to recruitment success (NAO index and primary production at the spawning area) as well as local environmental factors (westerly and southerly wind mixing indices and rainfall). Spatial changes in glass eel density within the estuary depended on tidal and light situations although maximum densities were mainly observed at diurnal and/or nocturnal flood tides. Although the decrease in the abundance of European glass eels has been widely known since the 1980s, during this study there was no evidence of a declining trend, probably because of an insufficiently long time series.

Physiological status and intersex in the endobenthic bivalve Scrobicularia plana from thirteen estuaries in northwest France

The bivalve Scrobicularia plana, an important species for the structure and functioning of estuarine and coastal mudflats, was studied in thirteen sites from NW France differing by their degree of contamination to document the presence of reproduction impairments (intersex, sex ratio, gonadosomatic indices) in relation to the condition revealed by using hepatosomatic and condition indices. In agreement with recent studies in other European estuaries, intersex was revealed in all the studied estuaries, including sites the chemical and ecological status of which is considered “good” according to the criteria of the European Water Framework Directive. The presence of endocrine disrupting chemicals (EDCs) could result in such disturbances. Our results re-inforce the concern linked to the subtle effects of EDCs, which are active at very low doses, often in the absence of any major sign of toxicity. However at this stage, no clear link may be established between intersex and population effects.

URGORRI COMPLANATUS GEN. ET SP. NOV. (CRYPTOPHYCEAE), A RED-TIDE-FORMING SPECIES IN BRACKISH WATERS(1).

The morphology, ultrastructure, phylogeny, and ecology of a new red-tide-forming cryptomonad, Urgorri complanatus Laza-Martínez gen. et sp. nov., is described. U. complanatus has been collected in southwestern European estuaries, blooming in the inner reaches of several of them. The estuarine character of the species is also supported by its in vitro salinity preferences, showing a maximum growth rate at 10 psu. U. complanatus is a distinctive species and can be easily distinguished by LM from other known brackish and marine species. Cells are dorsoventrally flattened. The plastid has two anterior lobes. One pyrenoid is located in each of the lobes, and a third one on the posterior part. Thylakoids are arranged in pairs and do not penetrate pyrenoids. The plastid is reddish due to the presence of the phycoerythrin Cr-PE545. An orange discoidal eyespot lies beneath the nucleus, in the posterior ventral face of the plastid. A long furrow runs from the vestibulum, and a gullet is lacking. The periplast is composed of an inner sheet. The nuclear 18S rDNA based molecular analysis reveals U. complanatus is not related to any of the main cryptomonad lineages. Based on ultrastructural and pigment data, the most probable relatives are those merged under the family Geminigeraceae. Its lack of derived characters, together with the presence of characters proposed in previous studies to be primitive, suggests Urgorri could be considered representative of the cryptophycean ancestral character state.

Carbon dioxide emissions from Indian monsoonal estuaries

Estuaries are known to be strong source for atmospheric CO2, however, little information is available from Indian estuaries. In order to quantify CO2 emissions from the Indian estuaries, samples were collected at 27 estuaries all along the Indian coast during discharge (wet) period. The emissions of CO2 to the atmosphere from Indian estuaries were 4–5 times higher during wet than dry period. The pCO2 ranged between ∼300 and 18492 μatm which are within the range of world estuaries. The mean pCO2 and particulate organic carbon (POC) showed positive relation with rate of discharge suggesting availability of high quantities of organic matter that led to enhanced microbial decomposition. The annual CO2 fluxes from the Indian estuaries, together with dry period data available in the literature, amounts to 1.92 TgC which is &gt;10 times less than that from the European estuaries. The low CO2 fluxes from the Indian estuaries are attributed to low flushing rates and less human settlements along the banks of the Indian estuaries.

Environmental factors influencing the dynamics of Chinese mitten crab zoeae in the San Francisco Bay-Delta

Abstract The Chinese mitten crab is an invasive catadromous species that has populated many European estuaries. However, despite repeated ‘introductions’, the only known established North American population is in the San Francisco Bay Delta, along with recent populations discovered in Chesapeake Bay and the Hudson River. In established populations, adult mitten crab numbers oscillate dramatically, and large numbers of crabs can have severe environmental impacts. Extremely little is known about the biology and ecology of juvenile stages, but understanding the factors behind new cohort survival is crucial for understanding the dynamics of newly-established populations. In this study, we use the only known long-term life-history data set to assess the relative importance of reproductive potential and environmental factors in regulating mitten crab population dynamics in San Francisco Bay. Both exploratory regression tree and bivariate data analyses support the hypotheses that concentrations of planktonic zoeae are strongly influenced by interactions between the number of breeding female crabs, the timing of reproduction, and water temperature. Additional studies are needed in other estuaries invaded by mitten crabs to test the generalities of these relationships and further evaluate the potential of these relationships to inform predictions about the extent and magnitude of mitten crab populations.

Land–ocean contributions of arsenic through a river–estuary–ria system (SW Europe) under the influence of arsenopyrite deposits in the fluvial basin

Water was sampled monthly from September 2005 to August 2006 at 14 stations distributed throughout the coastal system of Anllóns–Laxe, from where 30 surface sediment samples were also taken. After filtration through 0.22 μm polycarbonate filters, dissolved inorganic and total arsenic (UV oxidation) concentration was determined by HG-AFS. After microwave digestion, the arsenic in SPM and sediment was determined by AAS. Ultra-clean procedures were adopted during sampling, handling and analysis and the analytical accuracy was checked using certified reference material. Spatial distribution of As in water (0.2–4.0 μg L − 1 ), SPM (21–169 mg kg − 1 ) and sediment of the river reservoir was altered by the presence of arsenopyrite deposits in the middle fluvial basin that increases 2.1 ± 0.5 and 1.7 ± 0.5 times the concentrations of inorganic dissolved (DI-As) and particulate (P-As) arsenic, respectively. At the termination fluvial zone As fluxes can be calculated to be: [DI-As] = 7.09 · Q − 0.69 . The Anllóns River exports to its estuary 460 kg a − 1 of dissolved (< 7% as organic) arsenic annually. It is higher (i.e. 0.83 kg s − 1 km − 2 of DI-As) than that of most of European rivers. In the estuary reservoir, the influence of arsenopyrite is also evident as the river concentration of DI-As, which was lower than in seawater during the wet season and higher during the dry season. Arsenic has non-conservative behaviour, as in other European estuaries, but the Anllóns shows an ambivalent pattern: as it usually gains DI-As during the wet season and loses it during the dry season, whilst P-As seems to behave contrary to the DI-As. When the fluvial arsenic reaches the ria its concentration varies due to the estuarine processes. In the wet season DI-As increases its concentration by one third whilst in the dry season it decreases by one fifth and the annual contribution to the ria is 10% higher than the fluvial output. In the case of P-As more data are necessary to quantify its behaviour; however, the estuarine sediments are contaminated by arsenic. In the ria reservoir DI-As levels were similar to those of the ocean, DO-As comprises 9–22% of the inorganic, P-As ranges from 3 to 40 mg kg − 1 , and As-sedimentary can be classified as uncontaminated (4–18 mg kg − 1 ), except in the fishing ports. The ria circulation, reinforced by upwelling favours the exportation of arsenic to the ocean. In the Anllóns–Laxe system as a whole, the freshwater–saline interface processes do not lead to a decrease in the dissolved fluvial arsenic flux to the ocean.

Is parasitism in fish a good metric to assess ecological water quality in transitional waters? What can be learned from two estuarine resident species?

Fish-based indices are becoming important bioassessment tools for estuaries since the European Water Framework Directive included fish as a biological quality element to be monitored for the assessment of ecological status of those systems. In particular, data on species composition and abundance of the ichthyofauna must be used to evaluate the ecological status of European estuaries, but other factors like measures of fish health are also considered important metrics. These indicators of fish health include infections by parasites. The common goby, Pomastoschistus microps, and the Lusitanian toadfish, Halobatrachus didactylus, are fairly sedentary fish, very abundant in Portuguese estuaries, and were used to investigate if parasitism in fishes in transitional waters is a good metric to reflect anthropogenic impacts in the environment. No significant relationships were observed between the parasite levels in these two species and the intensity of human pressures, either at a large or small spatial scale. Results obtained also are contrary to the generalized idea that a higher proportion of parasitized fish necessarily reflects a decrease in their condition as a result of habitat degradation. A high degree of temporal and ontogenetic variability in the parasite levels of both P. microps and H. didactylus was detected, which make it difficult to establish the scores for this hypothetical metric even if significant relationships between parasite levels and human pressures are identified in the future. Therefore, the present work does not uphold the hypothesis that parasitism in fish is a good metric to assess ecological water quality in transitional waters.

Monitoring of hexabromocyclododecane diastereomers in fish from European freshwaters and estuaries

Hexabromocyclododecane (HBCD) is a brominated flame retardant used mainly in polystyrene foam as well as in textile applications. In recent years, measures were taken to reduce HBCD emissions during its production and use. To evaluate the efficacy of these measures, a monitoring project was initiated with fish as bioaccumulation indicators. Since 2007 bream was sampled annually at several European freshwater sites applying standardized methods. Muscle samples were analyzed by a validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) method which allows the quantification of α-, β-, and γ-diastereomers of HBCD. In most samples, α-HBCD was predominant. The lowest HBCD levels (11 μg/kg lipid weight (lw), sum of three HBCD diastereomers) were detected in bream sampled in 2009 from Lake Belau which is situated in a rural area of Northern Germany. During the 4-year study period, statistical significant decreases of HBCD concentrations were detected in bream from the rivers Rhone (France; -85%, level 2010, 205 μg/kg lw) and Western Scheldt (the Netherlands; -60%, level 2010, 36 μg/kg lw). High HBCD concentrations (9,480-14,500 μg/kg lw) without a clear time trend were observed in bream from the river Tees (UK). These high levels are in line with published data for fish from contaminated regions. Overall, the results indicate that environmental burdens of HBCD are decreasing at those locations where point sources and more diffuse emissions are expected.

Acute toxic effects of pyrene on Pomatoschistus microps (Teleostei, Gobiidae): Mortality, biomarkers and swimming performance

Pyrene has been reported as one of the most important polycyclic aromatic hydrocarbons (PAHs) found as environmental contaminant in estuaries and coastal areas. Therefore, in the present study, the acute effects (96h) of pyrene on the common goby Pomatoschistus microps, a key species in several European estuaries and lagoons, were assessed through individual exposure of juveniles to 0.125, 0.25, 0.5 or 1mgL−1 of pyrene. Mortality, swimming performance and several biomarkers were used as effect criteria. The 96h median lethal concentration (LC50) was 0.871mgL−1 and the swimming performance of fish was significantly decreased at all the pyrene concentrations tested. A significant increase of bile metabolites was found at increasing concentrations of pyrene (LOEC=0.125mgL−1) indicating the production of metabolites during the biotransformation of the toxicant. Pyrene significantly inhibited the activity of head acetylcholinesterase at 0.5mgL−1 and muscle cholinesterases at 1mgL−1. A bell-shape pattern response in the activity of muscle lactate dehydrogenase and isocitrate dehydrogenase (IDH) was found, with a significant increase of IDH at 0.25mgL−1, suggesting changes in the pathways of energy production. A bell-shape response for the antioxidant enzyme glutathione peroxidase and a less evident bell-shape response of glutathione S-transferase and glutathione reductase were also found. Lipid peroxidative damage was found in liver (0.25mgL−1) and gills (0.50mgL−1). It should be noted that although the concentrations of pyrene tested in the present study are higher than those that have been found in estuarine water and sediments, the occurrence of pyrene as single environmental contaminant is rare; in fact, the most common situation is the contamination by several PAHs, a considerable part of them sharing toxicological properties with pyrene and thus with a high probability of inducing additive or synergistic effects in simultaneous exposures. The findings of the present study are ecologically relevant and should be taken into consideration in the management of estuaries contaminated by petrochemical products. Moreover, effects of pyrene in this species should be further investigated.

Presence of Palaemon macrodactylus in a European estuary: evidence for a successful invasion of the Gironde (SW France)

Palaemon macrodactylus, an exotic shrimp native to the northwest Pacific Ocean, has been recorded in many estuaries along the Atlantic coast of Europe since the late 1990’s. In this study, a regular monthly survey, held since 1992 of the middle section of the Gironde estuary, revealed this species’ rapid and full colonization of the system since its appearance in samples during summer 1998. In the Gironde, the population of P. macrodactylus is self-sustaining and the species is now established there. Our study highlights two important elements that might explain its successful colonization: its ability to quickly invade a niche under-exploited by the similar native species and its greater reproductive output. The species’spatio-temporal distribution in relation to environmental variables was studied and compared with that of the native species P. longirostris. The exotic species was shown to mainly inhabit the polyhaline and mesohaline section of the estuary, which are sections generally under-exploited by females of the native species. Furthermore, fecundity analysis and larval abundance survey results revealed a higher potential fecundity and a greater proportion of larvae and juvenile stages for P. macrodactylus in the natural environment.

Will improving wastewater treatment impact shorebirds? Effects of sewage discharges on estuarine invertebrates and birds

AbstractHuman communities often discharge wastewaters into estuaries, influencing their organic and pollutant loading, benthic community and trophic structure. The implementation of the Water Framework Directive has encouraged the treatment of wastewater discharges across European estuaries, but the implications for invertebrate and waterbird communities are poorly understood. We explore the effects of untreated sewage discharges on the distribution and abundance of foraging black‐tailed godwits Limosa limosa and their main benthic prey (bivalves and polychaetes) on the Tejo estuary in Portugal, a major European Special Protection Area with ongoing wastewater improvements. Patches of mudflat in close proximity to sewage streams (&lt;30 m) can support polychaete densities and biomass that are an order of magnitude higher than more distant sites (&gt;70 m), and godwits foraging in these areas can attain the highest intake rates recorded for the estuary. However, high intake rates can also be attained on bivalve prey, and bivalve biomass and density increase slightly with distance from sewage streams. As the organic input from sewage outfalls influences invertebrate abundance and godwit foraging rates over relatively small areas, the ongoing implementation of a sewage treatment network on the Tejo estuary seems likely to have only a limited impact on the wintering godwit population. The localized effect of untreated sewage discharges on benthic communities suggests that the implications for predatory birds are relatively minor where alternative prey are available, but may be more severe in locations with more depauperate, polychaete‐dominated invertebrate communities.

Lifespan mercury accumulation pattern in Liza aurata: Evidence from two southern European estuaries

Mercury accumulation throughout the lifespan of Liza aurata (Risso, 1810) was analysed in four tissues (muscle, gills, liver and brain) in two southern European coastal ecosystems with distinct mercury contamination. Specimens from four to five age classes were captured in two sampling sites in the Ria de Aveiro (Laranjo bay and Mira), a system historically contaminated by industrial mercury, and in one site in the Mondego estuary, assumed as a mercury-free ecosystem. Mercury concentration in all tissues was found to be significantly higher in the Ria de Aveiro (Laranjo bay) compared to the Mondego, in accordance with the environmental contamination (water, sediments and suspended particulate matter). Significant differences inside the Ria de Aveiro (between the Mira and Laranjo bay) were only detected in the liver. This tissue registered the highest levels of mercury (ranging from 0.11 to 4.2 μg g −1) in all sampling sites, followed by muscle, brain, and gills. In all sampling sites and tissues was denoted a mercury dilution pattern along the lifecycle (except in liver at the Mondego, the reference area where the concentrations are always very low). An exponential trend was found in the metal age variation patterns in Laranjo (the most contaminated area) and a linear trend in the Mira and the Mondego (the least contaminated areas). Organic mercury concentration in muscle generally accounted for over 95% of total mercury concentration, and followed the same accumulation pattern of total mercury. This fish species is of lesser importance in mercury transfer to adjacent coastal areas and although the consumption of fish from Laranjo may present some risk for the humans, this risk decreases with fish age/size.

Organochlorine pesticides, polychlorinated biphenyls and trace elements in wild European sea bass ( Dicentrarchus labrax) off European estuaries

Polychlorinated biphenyls (PCBs) and organochlorine pesticides like dichloro-diphenyl-trichloroethane (DDTs), hexachlorocyclohexanes (HCHs), aldrin, dieldrin and trace elements (Cd, Cu, Se, Pb, Zn and Hg) were analysed in the muscle of European sea bass ( Dicentrarchus labrax) sampled in Atlantic coastal regions near several important European river mouths (Gironde, Charente, Loire, Seine and Scheldt). High contamination levels were measured in the muscles of European sea bass sampled in the coastal regions near those river mouths (e.g. Σ ICES PCB = 133–10,478 μg kg − 1 lw and Hg = 250–2000 μg kg − 1 dw). The Scheldt and the Seine are still among the most contaminated estuaries in Europe. Each region presented their specific contamination patterns reflecting different sources due to the input of the respective rivers. As fish and fishery products are the main contributors of the total dietary intake of organochlorinated pollutants, regular consumption of European sea bass with the reported contamination levels may represent a significant exposure route for the general human population.