Platinum and rhodium in Tagus estuary, SW Europe: sources and spatial distribution.

The spatial distribution of Pt and Rh was assessed in Tagus estuary and their sources discussed. Both elements were analysed in superficial sediment samples (n = 72) by adsorptive cathodic stripping voltammetry. Concentrations varied within the following ranges: 0.18-5.1 ng Pt g-1 and 0.02-1.5 ng Rh g-1. Four distinct areas were established: "reference"; waste- and pluvial water discharge; motorway bridges and industrialised areas. The calculated reference median concentrations were 0.55 ng Pt g-1 and 0.27 ng Rh g-1. Linear relationships were found between Pt and Al, Fe and LOI, whereas Rh depicted scattered patterns. The highest concentrations were found nearby industrialised areas and a motorway bridge, corresponding to the enrichment of 10 and 6 times the background of Pt and Rh, respectively. The main sources of contamination to the Tagus estuary derived from historical and present industrial activities and from automotive catalytic converters. Large variations of Pt/Rh ratio (0.48-39) point to different sources, reactivity and dilution effects.

The Effects of Vessel Traffic on the Behavior Patterns of Common Dolphins in the Tagus Estuary (Portugal).

The impact of vessels on dolphin populations has been extensively studied worldwide. The common dolphin, Delphinus delphis, has been observed in the Tagus estuary for the past two centuries, and during the last several years, these sightings seem to have increased. This area has high levels of maritime traffic throughout the year, both commercial and recreational. To understand the possible effects of vessel traffic on dolphins' behavior, land-based observations were carried out from March 2022 to March 2023. For a total of 67 events (48.9 h of dolphin sightings), differences in behavioral budgets were noted. Although "neutral reaction" was the most observed response when vessels were in the vicinity of dolphins, "negative reaction" was also common and five times more abundant than "positive reaction". The GEE model showed statistical differences between these reaction types (positive, neutral, and negative). Markov chains' analysis revealed distinct patterns in the behavioral transition probabilities, as dolphins were more likely to switch to a traveling state when vessels were nearby. This study is the first step towards understanding a potential impact source in the area since it is expected that tourism companies expand due to the increase in dolphin sightings in the estuary.

Detection of invasive fish species with passive acoustics: Discriminating between native and non-indigenous sciaenids.

Invasive alien species have been rising exponentially in the last decades impacting biodiversity and ecosystem functioning. The soniferous weakfish, Cynoscion regalis, is a recent invasive sciaenid species in the Iberian Peninsula and was first reported in the Tagus estuary in 2015. There is concern about its possible impacts on native species, namely the confamiliar meagre, Argyrosomus regius, as there is overlap in their feeding regime, habitat use, and breeding behaviour. Here, we characterised the sciaenid-like sounds recently recorded in the Tagus estuary and showed that they are made by weakfish as they have similar numbers of pulses and pulse periods to the sounds made by captive breeding weakfish. We further demonstrate that breeding grunts from weakfish and the native sciaenid, recorded either in captivity or Tagus estuary, differ markedly in sound duration, number of pulses and pulse period in the two species, but overlap in their spectral features. Importantly, these differences are easily detected through visual and aural inspections of the recordings, making acoustic recognition easy even for the non-trained person. We propose that passive acoustic monitoring can be a cost-effective tool for in situ mapping of weakfish outside its natural distribution and an invaluable tool for early detection and to monitor its expansion.

Catostylus tagi (Class: Scyphozoa, Order: Discomedusae, Suborder: Rhizostomida, Family: Catostylidae) life cycle and first insight into its ecology.

Jellyfish proliferations, which are conspicuous and natural events, cause blooms that may lead to severe consequences for anthropogenic activities and ecosystem structure and functioning. Although research during the last decade has focused on factors influencing the different jellyfish life stages, few species currently have their full life cycle known. In this context, we describe for the first time the developmental stages in the life cycle of Catostylus tagi, from planula to young medusa, reared in the laboratory. The species displays the typical Rhizostomida metagenetic life cycle. Mature scyphistomae display 16 tentacles and a total body length of 1.5 ± 0.2 mm. Only podocyst production and strobilation were observed. Strobilation, occurring continuously under laboratory conditions, was mainly polydisc. The eight-rayed typical ephyrae, with a total body diameter of 2.4 ± 0.4 mm at detachment, showed development typical of the Rhizostomida. As a first step in studying this species' ecology, we also present preliminary assessments of: (i) the influence of different temperature and salinity regimes on planulae survival, settlement and metamorphosis and (ii) the effect of temperature and diet on asexual reproduction. The results showed a high tolerance of planulae to a wide range of salinities (15‰ to 25‰), while polyp development was significantly faster at higher temperature (20-25 °C). Strobilation onset was 2-3 times faster at 20 °C (10.6 ± 5.4 to 15 ± 6.6 day at various tested diet) than at 15 °C (32.2 ± 3 day). Feeding was a key factor as unfed polyps never underwent strobilation during the trial. Finally, we present the spatial and seasonal distribution of C. tagi in the Tagus estuary (Portugal) in 2019, showing its occurrence throughout the year (except in April), with most observations recorded on the northern shoreline. As C. tagi shows the ability to form blooms and a wide tolerance for temperature and salinity (for planulae and medusae stage), it is essential to understand its life cycle.

Mercury and methylmercury transport and fate in the water column of Tagus estuary (Portugal).

Six campaigns were performed in North Channel (CNOR), Barcas Channel (BC) and lower zones (EZ) of Tagus estuary to better understand methylmercury (MMHg) and mercury (Hg) transport and fate. Highest concentrations of particulate and dissolved MMHg were observed in CNOR in bottom waters and in the warmest months. The MMHg distribution coefficients between particulate and dissolved fractions were mainly influenced by particulate matter and dissolved organic carbon. The values were slightly higher in summer than in winter and in CNOR. Overall, results established that the tidal effect is a main driver on the transport and fate of Hg and MMHg from CNOR to outer areas, evidenced by the exportation of the Hg species from CNOR to the upstream station in high tide and to the downstream one in low tide. Therefore, CNOR may be considered a source of Hg and MMHg to the outer estuary.

Sources and distribution of yttrium and rare earth elements in surface sediments from Tagus estuary, Portugal.

The distribution and sources of yttrium and rare-earth elements (YREE) in surface sediments were studied on 78 samples collected in the Tagus estuary (SW Portugal, SW Europe). Yttrium and total REE contents ranged from 2.4 to 32mg·kg-1 and 18 to 210mg·kg-1, respectively, and exhibited significant correlations with sediment grain-size, Al, Fe, Mg and Mn, suggesting a preferential association to fine-grained material (e.g. aluminosilicates but also Al hydroxides and Fe oxyhydroxides). The PAAS (Post-Archean Australian Shale) normalized patterns display three distinct YREE fractionation pattern groups along the Tagus estuary: a first group, characterized by medium to coarse-grained material, a depleted and almost flat PAAS-normalized pattern, with a positive anomaly of Eu, representing one of the lithogenic components; a second group, characterized mainly by fine-grained sediment, with higher shale-normalized ratios and an enrichment of LREE relative to HREE, associated with waste water treatment plant (WWTP) outfalls, located in the northern margin; and, a third group, of fine-grained material, marked by a significant enrichment of Y, a depletion of Ce and an enrichment of HREE over LREE, located near an inactive chemical-industrial complex (e.g. pyrite roast plant, chemical and phosphorous fertilizer industries), in the southern margin. The data allow the quantification of the YREE contents and its spatial distribution in the surface sediments of the Tagus estuary, identifying the main potential sources and confirming the use of rare earth elements as tracers of anthropogenic activities in highly hydrodynamic estuaries.

Metals and As content in sediments and Manila clam Ruditapes philippinarum in the Tagus estuary (Portugal): Impacts and risk for human consumption.

The Manila clam is emerging as a relevant species for the Portuguese market. The present work was conducted in the Tagus estuary to evaluate 1) the metals and As content in the sediments of the Tagus estuary, especially on those areas subjected to Manila clam harvesting 2) the metals and As content in clams, and the risk associated with their consumption 3) the physiological and biochemical responses of the clam to metals and As contamination, and its possible role as a pollution bioindicator in the estuarine environment. The most contaminated sediments were identified nearby industrial areas, nevertheless clams collected in low contaminated areas showed high metals and As concentrations. The condition index, glycogen content, membrane oxidative damage, biotransformation enzymes and metallothioneins showed consistent responses to metals and As content in clams. Results emphasize the need for the development of a management plan for the species exploitation in the Tagus estuary.

Dissolved gaseous mercury formation and mercury volatilization in intertidal sediments.

Intertidal sediments of Tagus estuary regularly experiences complex redistribution due to tidal forcing, which affects the cycling of mercury (Hg) between sediments and the water column. This study quantifies total mercury (Hg) and methylmercury (MMHg) concentrations and fluxes in a flooded mudflat as well as the effects on water-level fluctuations on the air-surface exchange of mercury. A fast increase in dissolved Hg and MMHg concentrations was observed in overlying water in the first 10min of inundation and corresponded to a decrease in pore waters, suggesting a rapid export of Hg and MMHg from sediments to the water column. Estimations of daily advective transport exceeded the predicted diffusive fluxes by 5 orders of magnitude. A fast increase in dissolved gaseous mercury (DGM) concentration was also observed in the first 20-30min of inundation (maximum of 40pg L-1). Suspended particulate matter (SPM) concentrations were inversely correlated with DGM concentrations. Dissolved Hg variation suggested that biotic DGM production in pore waters is a significant factor in addition to the photochemical reduction of Hg. Mercury volatilization (ranged from 1.1 to 3.3ngm-2h-1; average of 2.1ngm-2h-1) and DGM production exhibited the same pattern with no significant time-lag suggesting a fast release of the produced DGM. These results indicate that Hg sediment/water exchanges in the physical dominated estuaries can be underestimated when the tidal effect is not considered.

Effects of metal contamination on the gene expression profile of two benthic species: Cerastoderma edule and Ruditapes philippinarum.

This study aimed to identify new biomarkers for metal exposure in two bivalve species. Suppressive Subtractive Hybridization (SSH) was employed to evaluate the transcriptomic response of Cerastoderma edule and Ruditapes philippinarum to metal pollution. Protein synthesis and catalytic activity were the most affected metabolic processes in C. edule and R. philippinarum, respectively. Also, different genes responded to the effect of contamination in each species. The different response observed in both species reinforces the importance of including more than one bioindicator species in risk assessment studies. These results provide the basis for new studies, which are necessary for further validation of the use of the identified genes as molecular biomarkers for metal exposure.

Seasonal variation of methylmercury in sediment cores from the Tagus Estuary (Portugal).

Seasonal and spatial variations of dissolved and particulate methylmercury were evaluated for the first time in sediment cores from the Tagus Estuary. Results showed the highest MeHg concentrations in summer months indicating that the "seasonally" methylation process occurs not only at the topmost layers of the sediments but also in the deeper layers of the sediment column. The proportion of MeHg (up to 92%) in some of our pore water samples was higher than values reported in the literature for other estuaries suggesting that the sedimentary environment in the Tagus tends to favour Hg methylation. This work points to the importance of seasonal variation of the MeHg production in sediment cores. In physically dominated estuaries this enhances seasonal MeHg production in deeper sediments that can have serious ecological impacts due to resuspension or advection processes under extreme events by the increase of MeHg transported to the water column.

Occurrence of plastic debris in the stomach of the invasive crab Eriocheir sinensis.

The Chinese mitten crab is known as a pest causing damage to fishing gears and fish. On the other hand, this highly invasive species is considered a delicacy by Asian migrants and therefore commercially fished and sold in many countries. The ingestion of plastic by the Chinese mitten crab Eriocheir sinensis from the Baltic coastal waters (Poland) and the Tagus Estuary (Portugal) was studied based on stomach content analysis. As many as 13% of the 302 analysed males and females (38.07-89.07mm carapace width) from both regions, contained microplastic in the form of strands and balls. Most of them were transparent. Ingested plastic particles were identified as fragments of fishing gears. Contamination with plastic may have a negative impact on this species as well as on higher trophic levels feeding on crabs.

Influence of UV-B radiation on lead speciation in the presence of natural particles of estuarine waters.

The influence of UV-B irradiation on filtered and non-filtered water samples collected in a non-polluted area of Tagus estuary was evaluated in this study. In the laboratory, both samples were titrated with lead (Pb(+2)) followed by differential pulse anodic stripping voltammetry (DPASV), before and after 1 and 10 days under UV-B irradiation. Metal-ligand complexing parameters were obtained based on a macromolecular heterogeneous ligand described by two distinct sites with a labile behavior, and a third small homogeneous weaker group, which concentration was determined from a potentiometric titration. Under UV-B radiation, the complexing strength decreased with time in both (filtered and non-filtered) irradiated samples, but this effect was more pronounced in the non-filtered water, which might be due to some adsorption of dissolved macromolecular ligands on the particles and/or to further degradation of dissolved organic matter (DOM). Furthermore, the presence of particles favored the break-down of the macromolecular ligand under long UV-B exposure time. These results present ecological implications for the estuarine ecosystems such as bioavailability and toxicity.

Genetic diversity and antimicrobial resistance of Escherichia coli from Tagus estuary (Portugal).

Fecal pollution of surface waters is a current world-wide public health concern and may contribute for the dissemination of antibiotic resistance. The Tagus estuary located in the south of Portugal is one of the largest wetlands in the west coast of Europe. In this study, water samples were collected from seven stations with different anthropic pressures along the estuary and evaluated for water quality indicator bacteria. Escherichia coli isolates (n=350) were typed by REP-PCR. Representatives of each REP profile (n=220) were evaluated phenotypically for resistance to 17 antibiotics and characterized in terms of phylogenetic group. Resistant isolates were screened for the presence of antibiotic resistance genes (tet(A), tet(B), sul1, sul2, qnrA, qnrB, qnrS, aacA4-cr, bla(TEM), bla(SHV), bla(CTX-M), bla(CMY-like), bla(IMP), bla(VIM)) and integrase genes (intI1 and intI2). The highest antibiotic resistance prevalence was observed for streptomycin and tetracycline followed by ß-lactams and sulphonamides. Among E. coli isolates, 65.16% were resistant to at least one of the 17 antibiotics tested and approximately 19% were multiresistant. In our E. coli population phylo-groups A and D were predominant and characterized by higher prevalence of the antibiotic resistance. intI1 and intI2 genes were found in 12% of the isolates with prevalence of class 1 integrons. A strong correlation between the prevalence of integrons and multiresistance was observed. Differences in terms of antibiotic resistance between phylogenetic groups and between sampling sites were statistically significant. The results demonstrate a high prevalence of antibiotic resistance among E. coli circulating in the Tagus estuary with emphasis on the occurrence of resistance to last-resort antibiotics and on the high incidence of multiresistance.

Intertidal macrofauna and environmental stress at a riverine-marine boundary.

A field experiment was carried out to test the effect of pore water salinity on the macrobenthic assemblages in an estuarine region of the Tagus estuary (Portugal) subjected to wide fluctuations in salinity. The conditions at the experimental site ranged from freshwater (minimum salinity 0.2) to mesohaline (maximum salinity 15.3). The experimental site was affected by an unexpected deposition of fluid mud during summer. Redundancy Analysis discriminated the experimental treatments along the first canonical ordination axis. The analysis also revealed an experimental gradient of increasing environmental stress, in which the minimal presence of organisms corresponded to treatments representing a high level of environmental stress. Sediment dynamics and saline fluctuations were the major factors that, together, determined the low macrofaunal abundance and species diversity at the experimental site. The most abundant macrofaunal species in this harsh environment were the polychaetes Hediste diversicolor and Streblospio shrubsolii.