Restoration of degraded estuarine and marine ecosystems: A systematic review of rehabilitation methods in Europe

This article provides a comprehensive study of ecosystem rehabilitation methods widely used in the 21st century, focusing on Europe. The review covers the evolution and trends in scientific article publication, identification of European countries demonstrating high publication outputs, collaboration patterns, leading journals, and thematic areas. Additionally, it examines primary stressors in European aquatic ecosystems, and different methods and treatments commonly employed for remediation purposes. The analysis of selected articles revealed a significant increase in studies over time, driven by public awareness and financial incentives from national, European and global organizations. Italy, Portugal and Spain were the leading countries in degraded ecosystem rehabilitation studies, mainly focusing on remediating contaminated areas where metals were identified as the primary stressor (chemical pollution). Chemical remediation method emerged as the most used, closely followed by biological remediation method, which have gained prominence in recent years due to their ecological, economic, and social combined benefits. Furthermore, recent studies demonstrate a growing trend towards the combined use of more than one treatment/method to rehabilitate ecosystems, particularly with biological treatments. This combined approach has the potential for synergistic effects in achieving more effective rehabilitation and their sustainability in the long term, thus, a focus for future research.

A roadmap to define and select aquatic biological traits at different scales of analysis

Trait-based approaches are a powerful tool, as they not only improve understanding of ecological complexity and functioning but also allow comparison across different ecosystems and biogeographical regions. They may be used to unveil ecosystem processes and assess community structures, but their great potential becomes limited when dealing with scattered trait data and historically unstandardised trait nomenclature. The lack of standardisation allows authors to use the terminology of their preference, which inevitably leads to ambiguous misunderstandings and limits comparison between different studies. There have been some attempts to organise the trait vocabulary, but even these are mostly created from the perspective of a single ecosystem, which limits their applicability. In this work, we conducted a systematic literature review that identified and compiled 1127 traits across 37 datasets of fishes, invertebrates and zooplankton from freshwater, marine and transitional ecosystems. This dataset was then used to build on the Marine Species Traits Wiki and to propose a new, unified approach to a trait vocabulary based directly on readily available trait data. We propose a single standardised designation for all the different traits identified and provide a list of all the different synonyms commonly used for these traits. A roadmap to help the trait selection process is also provided, offering a guide through four main steps and important questions for choosing an adequate set of traits at the beginning of any study, which constitutes one of the main challenges in functional ecology research. Overall, this proposal will provide a solid baseline for tackling gaps in trait nomenclature and ensuring a clearer future for functional ecology studies.

The effect of Zostera noltei recolonization on the sediment mercury vertical profiles of a recovering coastal lagoon

Mercury's extreme toxicity and persistence in the environment justifies a thorough evaluation of its dynamics in ecosystems. Aveiro Lagoon (Portugal) was for decades subject to mercury effluent discharges. A Nature-based Solution (NbS) involving Zostera noltei re-colonization is being tested as an active ecosystem restoration measure. To study the effect of Zostera noltei on the sediment contaminant biogeochemistry, seasonal (summer/winter) sediment, interstitial water and labile mercury vertical profiles were made in vegetated (Transplanted and Natural seagrass meadows) and non-vegetated sites (Bare-bottom area). While no significant differences (p > 0.05) were observed in the sedimentary phase, Zostera noltei presence reduced the reactive/labile mercury concentrations in the top sediment layers by up to 40% when compared to non-vegetated sediment, regardless of season. No differences were found between vegetated meadows, highlighting the fast recovery of the contaminant regulation ecosystem function provided by the plants after re-colonization and its potential for the rehabilitation of historically contaminated ecosystems.

Using seagrass as a nature-based solution: Short-term effects of Zostera noltei transplant in benthic communities of a European Atlantic coastal lagoon

Seagrass meadows provide several ecological functions that improve the overall ecological health of coastal systems and therefore, it is urgent to promote the restoration of such habitats. In Ria de Aveiro, a coastal lagoon in the Atlantic Coast of Portugal, a restoration initiative was responsible for transplanting the dwarf eelgrass Zostera noltei into a highly degraded area. This eelgrass was used as a nature-based solution (NbS) to mitigate some of the impacts of historical mercury contamination. Comparisons of key-species features (density and biomass), and some community-derived indicators (total density and biomass, species richness and Shannon-Wiener index) between the transplanted seagrass patch, their bare vicinities, and their counterpart habitats on the source area, provided signs of the effectiveness of the restoration action on the benthic communities' recovery. Indicators were higher within the restored meadow, and biomass derived indicators of the restored meadow were similar to the source meadow.

An Overview of Rhodoliths: Ecological Importance and Conservation Emergency

Red calcareous algae create bio-aggregations ecosystems constituted by carbonate calcium, with two main morphotypes: geniculate and non-geniculate structures (rhodoliths may form bio-encrustations on hard substrata or unattached nodules). This study presents a bibliographic review of the order Corallinales (specifically, rhodoliths), highlighting on morphology, ecology, diversity, related organisms, major anthropogenic influences on climate change and current conservation initiatives. These habitats are often widespread geographically and bathymetrically, occurring in the photic zone from the intertidal area to depths of 270 m. Due to its diverse morphology, this group offers a special biogenic environment that is favourable to epiphyte algae and a number of marine invertebrates. They also include holobiont microbiota made up of tiny eukaryotes, bacteria and viruses. The morphology of red calcareous algae and outside environmental conditions are thought to be the key forces regulating faunistic communities in algae reefs. The impacts of climate change, particularly those related to acidification, might substantially jeopardise the survival of the Corallinales. Despite the significance of these ecosystems, there are a number of anthropogenic stresses on them. Since there have been few attempts to conserve them, programs aimed at their conservation and management need to closely monitor their habitats, research the communities they are linked with and assess the effects they have on the environment.

Functional threshold responses of benthic macroinvertebrates to environmental stressors in reservoirs

Reservoirs are aquatic ecosystems created by humans to supply water needs. They can impair aquatic diversity due to the lack of connectivity, reduced water volume, and pressures exerted by surrounding human activities. These changes are expected to produce abrupt fluctuations in the reservoirs' environment, thus influencing the structure and functioning of aquatic communities. Therefore, this study aimed to understand the impact of a range of environmental stressors in reservoirs on benthic macroinvertebrates by analyzing their functional threshold response. Biological data were collected in six reservoirs from the semi-arid region of Northeast Brazil, as case study. A total of 37.874 benthic macroinvertebrates belonging to 35 taxa were collected. Nevertheless, almost 90% of this abundance belonged to three species alone, considered generalists, with multivoltine reproduction and from the gatherer-collectors feeding group. Increases in environmental stressors such as salinity, nitrate, ammonia, and dissolved solids led to the selection of macroinvertebrates with specific traits (e.g., protected body, gill respiration, and large body size). These functional traits showed differences in their threshold response depending on the stressors and are indicators of the effects of these stressors on the reservoirs. Some of the potential sensitive traits (with a negative threshold response to the stressor) could also associate with other stressors, demonstrating that tolerance of benthic macroinvertebrates is defined by a set of functional characteristics. Overall, the increase in stressor' gradients selected functionally tolerant organisms with high resistance capacity, but these were represented by dominant species. This resulted in low diversity in the reservoirs, which may compromise ecosystem functioning, and raises concerns about adequate management of the systems.

Extreme drought scenario shapes different patterns of Chironomid coexistence in reservoirs in a semi-arid region

Semi-arid regions are particularly prone to extreme climate events such as droughts, which result in drastic fluctuations in the water volume of aquatic ecosystems, including artificial ones. As these climate extremes intensify, species must adapt, however, not all species can persist under new climate regimes in such a short period of time. In this study, we evaluated how fluctuations in the water levels of reservoirs, caused by drought, affect Chironomidae diversity patterns in a semi-arid region. We studied six reservoirs (256 sites) in two basins in Northeastern Brazil, exposed to different levels of anthropic impact. Sampling was carried out in 2014, 2015 (both extremely dry years) and 2019. A dead water volume was attained during the extreme drought in 2015, consequently affecting the reservoir and resulting in a low diversity, abundance, and functional redundancy of the Chironomidae assemblages. Despite precipitation increases in 2019, some reservoirs continued to be water deficient. These drastic water fluctuations led to different patterns in Chironomidae taxonomic and functional diversity, which were also influenced by anthropic stressors. Thus, the most impacted basin presented lower diversity, with some species and trait turnover between reservoirs. The opposite trend was observed in the least impacted basin. Overall, taxonomic and functional diversity decreased with decreasing water volume, resulting in a community dominated by small-medium sized individuals with multivoltine cycles and hemoglobin and diapause resistant forms, conferring higher tolerance to water stress. The drought and consequent water volume fluctuations throughout the years seemed to exacerbate the water quality due to pre-existing exposure to anthropic impacts (e.g., domestic discharge, fishing activity, agriculture, livestock). This resulted in biotic homogenization, with an observed loss of taxa and traits. This study reinforced the need to implement habitat conservation and water quality improvement strategies to prevent further ecosystem damage in the face of climate change uncertainty.

Assessing tropical coastal dynamics across habitats and seasons through different dimensions of fish diversity

Coastal habitat mosaics are among the most productive ecosystems around the globe, with many ecological and social-economic services provided. Their natural challenging conditions have always been a subject of concern for ecologist and conservationist, with a particular interest in understanding how its spatial and temporal dynamics influence ecosystem functioning. In this context, we aimed to assess tropical coastal dynamics using an integrative approach, measuring the different facets of fish diversity across space (habitats) and time (seasons). Three different estuarine systems and their adjacent areas in the southwestern Atlantic were monthly sampled between July 2017 and June 2018, in a sampling design that encompassed three different coastal mosaics with three habitat types (mangroves, seagrass and sandy beaches), and both seasons of the studied region (dry and rainy). Taxonomic, phylogenetic, and functional diversity were then evaluated with equivalent diversity measures to allow comparisons between them. Different patterns of species occurrence and distribution were found between habitats and seasons, which resulted in different effects on the abundance-weighted diversity dimensions. Although taxonomic diversity of habitats was greater during the rainy season (p = 0.03), a seasonal increase in phylogenetic diversity was only observed in the sandy beach habitat (p = 0.04). In contrast for the functional diversity, no significant differences were found among habitats in both seasons (p = 0.15), indicating high levels of redundancy. Our results showed that patterns in the occurrence and abundance of tropical fish species among habitats that comprise a coastal mosaic have different effects on distinct diversity dimensions. More precisely, for tropical coastal systems with marked seasonality, both habitats and season appear to play a synergic role in the maintenance of ecosystem functioning by enhancing functional and phylogenetic redundancy.

Marine invertebrates associated with rhodoliths/maërl beds from northeast Brazil (State of Paraíba)

BACKGROUND

This study investigates the marine macroinvertebrate fauna of rhodolith beds (non-geniculated red corallinaceaous algae) in northeast Brazilian. A total of 57 species were identified, belonging to six phyla (Platyhelminthes, Annelida, Sipuncula, Mollusca, Arthropoda and Echinodermata), of which 50 are considered here as new records for the Paraíba State. Annelids (Class Polychaeta) were the most representative taxa in Miramar and Seixas Beaches, while molluscs were dominant in Maceió Beach.

NEW INFORMATION

This is the first study that includes an identification key, diagnostic features and distribution patterns worldwide and local (including new records) of the marine invertebrate fauna associated with rhodolith beds in northeast Brazil (State of Paraíba). Sampling events were performed in 2018, at low tide in the intertidal to shallow subtidal zones (1.5 and 4.0 m depth), in Miramar, Seixas and Maceió Beaches. A total of 17 species were found for the first time on Seixas Beach, as well as all identified species for Miramar and Maceió. This study tries to contribute to the knowledge of marine invertebrates in northeast Brazilian shallow habitats, providing a baseline for future environmental studies.

Benthic estuarine communities' contribution to bioturbation under the experimental effect of marine heatwaves

Marine heatwaves are increasing worldwide, with several negative impacts on biological communities and ecosystems. This 24-day study tested heatwaves' effect with distinct duration and recovery periods on benthic estuarine communities' diversity and contribution to ecosystem functioning experimentally. The communities were obtained from a temperate estuary, usually subjected to high daily thermal amplitudes. Our goal was to understand the communities' response to the thermal change, including the community descriptors and behavioural changes expected during heat extremes. We measured community composition and structural changes and the bioturbation process and nutrient release as ecosystem functioning measurements. Overall, our findings highlight the potential tolerance of studied estuarine species to the temperature ranges tested in the study, as community composition and structure were similar, independently of the warming effect. We detected a slight trend for bioturbation and nutrient release increase in the communities under warming, yet these responses were not consistent with the heatwaves exposure duration. Overall, we conclude on the complexity of estuarine communities' contribution to functioning under warming, and the importance of scalable experiments with benthic organisms' responses to climate variability, accommodating longer time scales and replication. Such an approach would set more efficient expectations towards climate change mitigation or adaptation in temperate estuarine ecosystems.

Mild Effects of Sunscreen Agents on a Marine Flatfish: Oxidative Stress, Energetic Profiles, Neurotoxicity and Behaviour in Response to Titanium Dioxide Nanoparticles and Oxybenzone

UV filters are potentially harmful to marine organisms. Given their worldwide dissemination and the scarcity of studies on marine fish, we evaluated the toxicity of an organic (oxybenzone) and an inorganic (titanium dioxide nanoparticles) UV filter, individually and in a binary mixture, in the turbot (Scophthalmus maximus). Fish were intraperitoneally injected and a multi-level assessment was carried out 3 and 7 days later. Oxybenzone and titanium dioxide nanoparticles induced mild effects on turbot, both isolated and in mixture. Neither oxidative stress (intestine, liver and kidney) nor neurotoxicity (brain) was found. However, liver metabolic function was altered after 7 days, suggesting the impairment of the aerobic metabolism. An increased motility rate in oxybenzone treatment was the only behavioural alteration (day 7). The intestine and liver were preferentially targeted, while kidney and brain were unaffected. Both infra- and supra-additive interactions were perceived, with a toxicodynamic nature, resulting either in favourable or unfavourable toxicological outcomes, which were markedly dependent on the organ, parameter and post-injection time. The combined exposure to the UV filters did not show a consistent increment in toxicity in comparison with the isolated exposures, which is an ecologically relevant finding providing key information towards the formulation of environmentally safe sunscreen products.

Immunological and oxidative stress responses of the bivalve Scrobicularia plana to distinct patterns of heatwaves

As a consequence of global warming, extreme events, such as marine heatwaves (MHW), have been increasing in frequency and intensity with negative effects on aquatic organisms. This innovative study evaluated for the first time, the immunological and physiological response of the estuarine edible bivalve Scrobicularia plana to different heatwaves, with distinct duration and recovery periods. So, extensive immune (total haemocyte count - THC, haemocyte viability, phagocytosis rate, respiratory oxidative burst of haemocytes, total protein, protease activity, nitric oxide and bactericidal activity of plasma) and oxidative stress (lipid peroxidation - LPO, superoxide dismutase - SOD, catalase - CAT and glutathione-S-Transferase - GST) analyses were performed in an experimental study that tested the impact of heatwaves during 25 days. The survival and condition of S. plana were not affected by the exposure to the extreme events. However, our data suggested that longer heatwaves with shorter recovery periods can be more challenging for the species, since THC and phagocytic activity were most affected under the temperature increase conditions. Regarding the oxidative status, the species increased its SOD activity while MDA production slightly declined to the increase of temperature, protecting the organism from cellular damage. These results indicate that S. plana has a great capacity to adapt to environmental temperature changes, however, the expected higher frequency/duration of heatwaves with climate change trends can cause some debility of the species face to other stressors, which can compromise its success in the future.

Is tourism affecting polychaete assemblages associated with rhodolith beds in Northeastern Brazil?

ABSTRACT. Introduction: Rhodoliths are biogenic structures distributed worldwide, formed by several types of calcareous algae. They may host a great diversity of marine invertebrates, among which polychaetes are conspicuous and diversified representatives. Rhodolith beds are notwithstanding vulnerable to several human activities (e.g. exploitation of commercial species associated with rhodoliths, petroleum exploration, fishing activities, effluent discharges, and tourism), which may compromise that diversity. Tourism is presently increasing its impact on rhodolith beds. Global warming and ocean acidification are also determinant factors in faunal change. Objective: to analyse the polychaete assemblages associated with rhodolith beds subject to different intensities of touristic pressure at Seixas Beach (NE Brazil), where tourism is gradually increasing over time. Methods: Effects were evaluated at two depths, 1.5 m and 4.0 m. Sampling was done every two months during 2015, encompassing the two marked seasons of the year in the region (rainy and dry). Quadrats of 15 x 15 cm were placed in each depth during sampling. All rhodoliths present within the quadrat were collected (usually four to five rhodoliths). Our hypothesis was that the deeper depth and the samples from the dry season months would be increasingly subject to the impact of tourism. Results: Overall, 49 species were found (from 21 different families), and a total of 733 individuals were collected. The most abundant species was Eunice wasinensis (280 individuals, 38.2% of total abundance). The species Eurythoe complanata, Eunice biannulata, E. wasinensis, Lysidice ninetta, Oxydromus pugettensis and Ceratonereis (Ceratonereis) singularis appeared in all months. The study detected a tendency for higher diversity to occur at the depth of 1.5 m for all indices, but only the Shannon-Wiener values were significantly higher there (p < 0.05). No clear differences were found regarding months or season. Conclusions: These results suggest that a higher potential pressure due to tourism may occur at 4.0 m due to more intense craft shipping activities (traffic of catamaran boats transporting tourists to and from the reefs) in that area.  

Realistic scenarios of environmental disturbance lead to functionally important changes in benthic species-environment interactions

Changes in community structure concurrent with environmental forcing often form a precursor to changes in species diversity, and can have substantive consequences for ecosystem functioning. Here, we assess the effects of altered levels of evenness that are representative of different levels of eutrophication and changes in salinity associated with altered precipitation patterns, on the mediation of nutrient release by sediment-dwelling invertebrate communities. We find that an adjustment towards a more even distribution of species corresponds with an increase in sediment particle reworking that, in general, translates to increased levels of nutrient release. This response, however, is dependent on the functional role of each species in the community and is influenced by concomitant changes in salinity, especially when salinity extends beyond the range typically experienced by the community. Overall, our findings highlight the dynamic nature of species contributions to functioning and reinforce the importance of understanding when, and how, the mechanistic basis of species-environment interactions are modified as the influence of abiotic and biotic factors flex under periods of directional forcing.

Ecological consequences of invasion across the freshwater-marine transition in a warming world

The freshwater-marine transition that characterizes an estuarine system can provide multiple entry options for invading species, yet the relative importance of this gradient in determining the functional contribution of invading species has received little attention. The ecological consequences of species invasion are routinely evaluated within a freshwater versus marine context, even though many invasive species can inhabit a wide range of salinities. We investigate the functional consequences of different sizes of Corbicula fluminea-an invasive species able to adapt to a wide range of temperatures and salinity-across the freshwater-marine transition in the presence versus absence of warming. Specifically, we characterize how C. fluminea affect fluid and particle transport, important processes in mediating nutrient cycling (NH ₄-N, NO ₃-N, PO ₄-P). Results showed that sediment particle reworking (bioturbation) tends to be influenced by size and to a lesser extent, temperature and salinity; nutrient concentrations are influenced by different interactions between all variables (salinity, temperature, and size class). Our findings demonstrate the highly context-dependent nature of the ecosystem consequences of invasion and highlight the potential for species to simultaneously occupy multiple components of an ecosystem. Recognizing of this aspect of invasibility is fundamental to management and conservation efforts, particularly as freshwater and marine systems tend to be compartmentalized rather than be treated as a contiguous unit. We conclude that more comprehensive appreciation of the distribution of invasive species across adjacent habitats and different seasons is urgently needed to allow the true extent of biological introductions, and their ecological consequences, to be fully realized.

New climatic targets against global warming: will the maximum 2 °C temperature rise affect estuarine benthic communities?

The Paris Agreement signed by 195 countries in 2015 sets out a global action plan to avoid dangerous climate change by limiting global warming to remain below 2 °C. Under that premise, in situ experiments were run to test the effects of 2 °C temperature increase on the benthic communities in a seagrass bed and adjacent bare sediment, from a temperate European estuary. Temperature was artificially increased in situ and diversity and ecosystem functioning components measured after 10 and 30 days. Despite some warmness effects on the analysed components, significant impacts were not verified on macro and microfauna structure, bioturbation or in the fluxes of nutrients. The effect of site/habitat seemed more important than the effects of the warmness, with the seagrass habitat providing more homogenous results and being less impacted by warmness than the adjacent bare sediment. The results reinforce that most ecological responses to global changes are context dependent and that ecosystem stability depends not only on biological diversity but also on the availability of different habitats and niches, highlighting the role of coastal wetlands. In the context of the Paris Agreement it seems that estuarine benthic ecosystems will be able to cope if global warming remains below 2 °C.

Climate influence on juvenile European sea bass (Dicentrarchus labrax, L.) populations in an estuarine nursery: A decadal overview

Estuarine systems support the life cycle stages of commercially important marine fish and are influenced by large and local-scale climatic patterns. In this study, performed in the Mondego estuary, Portugal, we used an 11-year database (2003-2013) for analyzing the variability in the population of a marine juvenile migrant fish, the European sea bass Dicentrarchus labrax, regarding changes in abundance, population structure, growth rates, secondary production and annual day of peak abundance. Higher densities and production occurred in 2003, but no differences in 0-group growth could be observed. In order to detect change points in both biological and climatic data, the cumulative sum (CUSUM) of the deviations from the mean for the 2003-2013 period were determined for each parameter. The relationship between large and local-scale drivers and 0-group biological attributes were evaluated using a Spearman rank correlation analysis of CUSUM of biological and environmental data, considering the correspondent yearly values and with a time-lag of 1 year. The North Atlantic Oscillation (NAO) index, sea surface temperature (SST) and their respective winter values were tested as large-scale factors, while river runoff, salinity and estuarine water temperature were considered as local climate patterns. The significant factors explaining D. labrax 0-group abundance and production were salinity and the NAO, the latter being also a significant predictor considering the 1-year lag. The NAO with 1-year lag was also positively correlated with the day of peak abundance. The early stages of European sea bass were demonstrated to have a climate-dependent life cycle, controlled by variations in both large-scale climatic patterns and local features. In southern European marine populations, the effects of the NAO seem less direct, and dependent on the magnitude of its expressions and on the time scale considered.

Changes in the fish assemblages of a coastal lagoon subjected to gradual salinity increases

This study analyses fish data to understand how the gradual increase of salinity registered in a coastal lagoon and consequently, anthropogenic disturbance, affected the fish communities. For that, fish assemblages of the Ria de Aveiro were sampled monthly in 3 years from different decades (1988, 1997 and 2012). Dominant species were Atherina boyeri, A. presbyter, Sardina pilchardus, Dicentrarchus labrax, Liza aurata and L. ramada. Significant differences in fish communities were detected among years in both terms of density and biomass. Results pointed out to a taxonomic and functional homogenization of fish assemblages in 2012, when salinity was higher and its range of variation across the whole lagoon more uniform. Marine species were clearly associated with 2012, while some freshwater species only appeared in 1988, reflecting the gradual salinity increase in the lagoon. Overall, both the structure and function of fish assemblages of Ria de Aveiro have changed over the time, which was attributed to human activities to maintain the lagoon operational.

Functional diversity of fish communities in two tropical estuaries subjected to anthropogenic disturbance

The functional diversity of fish communities was studied along the salinity gradient of two estuaries in Northeast Brazil subjected to different anthropogenic pressures, to gain a better understanding of the response of fish communities to disturbance. We evaluated functional complementarity indices, redundancy and analysed functional composition through functional groups based on combinations of different traits. The fish communities in both estuaries share similar functions performed by few functional groups. The upstream areas had generally lower taxonomic, functional diversity and lower redundancy, suggesting greater vulnerability to impacts caused by human activities. Biomass was slightly more evenly distributed among functional groups in the less disturbed estuary, but total biomass and redundancy were lower in comparison to the urbanized estuary. The present findings lend strength to the notion that the less disturbed estuary may be more susceptible to anthropogenic impacts, underscoring the need for more effective conservation measures directed at this estuary.

Effect of historical contamination in the fish community structure of a recovering temperate coastal lagoon

This study aimed to assess the impact of trace element concentrations in fish assemblages of a recovering coastal lagoon. Fish, water and sediment were sampled in winter and summer in the Ria de Aveiro (Portugal). Multivariate analyses were used to examine the relationship between fish assemblages and environmental variables (physical-chemical parameters, contaminants and sediment grain size). In winter, fish density and biomass were mainly affected by the water turbidity, while Li concentration in the water column was found to be significant for fish biomass. During summer, a significant relationship was found between fish density and temperature, Hg, Li and Zn concentration in the sediment. These contaminants were mainly associated with the historically contaminated area, were Liza spp. and Dicentrarchus labrax appeared as dominant species. Environmental variables were not significant for fish biomass. The historical contamination in the Ria de Aveiro still seems to exert some influence on fish community structure.

Do different degrees of human activity affect the diet of Brazilian silverside Atherinella brasiliensis?

The aim of the present study was to test whether different degrees of human activity affect the diet of the Brazilian silverside Atherinella brasiliensis in two tropical estuaries. Fish were collected along the salinity gradient of two Brazilian estuaries, the heavily impacted Paraiba Estuary and the less impacted Mamanguape Estuary, in the dry and wet seasons. The findings confirm that A. brasiliensis has generalist feeding habits and is able to change its diet under different environmental conditions. The results indicate clear spatial (i.e. along the estuarine gradient) changes in diet composition in both estuaries, but diet was also influenced by the degree of anthropogenic disturbance. During the wet season in the nutrient enriched Paraiba Estuary, when human activity was higher, the diet of A. brasiliensis was poorer and dominated by few dietary items, reflecting the potential impoverishment of prey items in this heavily disturbed system. The specimens collected in the most affected estuary also had a greater frequency of micro-plastics and parasites in their stomachs, reflecting the greater degree of human disturbance in the estuary. The present findings suggest that the diet of A. brasiliensis could be a useful indicator of changes in the ecological quality of these and other tropical estuaries of the western Atlantic Ocean.

Long-term functional changes in an estuarine fish assemblage

The functional diversity of the fish assemblages of the Mondego estuary was studied for a discontinuous 30-year period (1988-2012). During this time, hydrological changes occurred due to man-induced alterations and weather extremes. These changes led to alterations in the structure and function of the fish community. Species richness and functional richness decreased over time and the fish community started to explore new micro-habitats and food resources. Before severe hydrological changes, the community was dominated by pelagic, detritivorous and species with wider salinity ranges. After, the community became dominated by demersal, benthic, piscivorous and marine species. During a drought, omnivorous became increasingly important, reflecting greater possibilities of using available feeding resources. We have also found an increase in sub-tropical species throughout the years, which might be related to gradual temperature increases at a global scale. This study also confirmed estuaries as extremely important for restocking several commercial species.

Mercury accumulation and tissue-specific antioxidant efficiency in the wild European sea bass (Dicentrarchus labrax) with emphasis on seasonality

The main goal of this study was to assess both mercury (Hg) accumulation and organs' specific oxidative stress responses of gills, liver and kidney of Dicentrarchus labrax with emphasis on seasonality. Fish were collected in cold and warm periods in three stations: reference, moderated and highly contaminated sites. Our results showed that seasonal factors slightly influenced Hg accumulation between year periods (cold and warm) and strongly affected organs' response basal levels. In contrast, seasonality seemed not to influence oxidative stress responses, since similar response patterns were obtained for both year periods, and moderate degree of antioxidant responses was obtained. Moreover, the oxidative stress profile may be attributed to Hg contamination degree, which showed organ-specific response and accumulation patterns. Hence, gills showed to be able to adapt to Hg contamination, and in opposition, kidney and liver demonstrated some vulnerability to Hg toxicity. The critical Hg concentrations indicated specific threshold limits for each organ. Overall, seasonality should be taken into account in monitoring programmes, helping to characterize the individuals' reference values of response and thus to discriminate between the effects induced by natural causes or by contamination.

Recovery trends of Scrobicularia plana populations after restoration measures, affected by extreme climate events

The Mondego estuary (Portugal) went through different ecological scenarios over the last decades. An eutrophication process led to a decline in the ecosystem quality. The ensuing restoration plan resulted into a gradual ecological recovery, which was impaired by the occurrence of successive extreme climate events that affected dynamics and productivity of key species. In this study we assess the response of the bivalve Scrobicularia plana to the impacts of these events in a recovery scenario, by comparing populations in two different intertidal habitats: a seagrass bed and a sandflat area. As a general tendency, S. plana, which was negatively affected by eutrophication, responded positively to restoration. However, the occurrence of extreme climate events seemed to affect recruitment success, biomass and production, impairing the recovery process. In the seagrass bed, S. plana maintained a stable and structured population, while in the sandflat area recovery clearly reverted into a decline, mainly concerning biomass and production values. This sequence of multiple stressors might have reduced S. plana resilience to further impacts and therefore, understanding the behavior of biological populations following restoration initiatives requires acknowledgement that some changes may not be easily reversible.

Drivers of estuarine benthic species distribution patterns following a restoration of a seagrass bed: a functional trait analyses

We integrate information on functional diversity (FD) patterns from estuarine intertidal benthic communities from different habitats and along a temporal disturbance gradient, to understand the drivers of species coexistence patterns. Species and traits' biomass levels seemed to be first determined by habitat filtering, selecting those traits better adapted to the biologically challenging estuarine environment. Within that subset of traits and within each habitat, biotic interactions were probably high, as evidenced by high α-diversity and community weighted mean differences. The former patterns hold for the disturbance/recovery scenario considered. However, as the estuary recovered, biomass became more distributed among different trait categories, consistent with increases in FD when the seagrass started to increase. Policy towards the restoration of seagrass bed and other biogenic structures, and improving the connectivity within adjacent systems were confirmed and suggested, as this would imply higher FD and potentially higher resilience to disturbance within the estuarine intertidal system.

Effects of extreme climate events on the macrobenthic communities' structure and functioning of a temperate estuary

The Mondego estuary (Portugal) experienced profound structural and functional modifications due to eutrophication, which was exacerbated by consecutive weather extremes that compromised a previous restoration project. This work explores multiple climate impacts on macrobenthic communities' structure and functioning and its implications on ecosystem's recovery. Floods and heat waves had a stronger negative effect on macrobenthic assemblages than the droughts, imposing a total abundance decline. Contrarily, biomass was not so affected by climate events, being stable and even increased in a mudflat area, where seagrass is re-colonizing. Bivalves and oligochaetes decreased with the flooding episodes, likewise subsurface-deposit feeders and suspension feeders, while crustaceans were particularly sensitive to heat waves. Species richness declined with the floods and heat waves, whilst evenness increased in sandflat area, constituting a positive sign towards recovery. Succession of different climate extremes affected ecosystem structure and functioning, delaying its recovery with possible consequent effects at higher trophic levels.

Assessing estuarine environmental quality using fish-based indices: performance evaluation under climatic instability

The seasonal variation of five selected multimetric indices for the determination of the Ecological Quality Status (EQS) of transitional waters was evaluated, as well as the indices' responses to an extreme drought event that occurred in 2005. The database used regards the Mondego River estuary, which was sampled from June 2003 to August 2006 on a monthly basis. Among the selected indices (EBI-Deegan et al. [Deegan, L., Finn, J.T., Ayvazlan, S.G., Ryder-Kieffer, C.A., Buonaccoesi, J., 1997. Development and validation of an Estuarine Biotic Integrity Index. Estuaries 30(3), 601-617], EDI-Borja et al. [Borja, A., Franco, J., Valencia, V., Bald, J., Muxika, I., Belzunce, M.J., Solaun, O., 2004. Implementation of the European Water Framework Directive from the Basque Country (northern Spain): a methodological approach. Marine Pollution Bulletin 48(3-4), 209-218], EFCI-Harrison and Whitfield [Harrison, T.D., Whitfield, A.K., 2004. A multi-metric fish index to assess the environmental condition of estuaries. Journal of Fish Biology 65, 683-710], EBI-Breine et al. [Breine, J.J., Maes, J., Quataert, P., Van den Bergh, E., Simoens, I., Van Thuyne, G., Belpaire, C., 2007. A fish-based assessment tool for the ecological quality of the brackish Scheldt estuary in Flanders (Belgium). Hydrobiologia 575, 141-159] and TFCI - Coates et al. [Coates, S., Waugh, A., Anwar, A., Robson, M., 2007. Efficacy of a multi-metric fish index as an analysis tool for the transitional fish component of the Water Framework Directive. Marine Pollution Bulletin 55, 225-240]), the EBI by Breine et al. (2007) was the only that evidenced clear interannual and seasonal variations. The EQS by the several indices ranged from "Low" to "High", depending on the index considered, evidencing the high level of mismatch between indices. The results are discussed in the scope of the EU Water Framework Directive, regarding monitoring strategies, application of indices and EQS assessment.

Anthropogenic and natural disturbance effects on a macrobenthic estuarine community over a 10-year period

For some decades, the Mondego estuary has been under severe ecological stress, mainly caused by eutrophication. The most visible effect was the occurrence of macroalgal blooms and the concomitant decrease of the area occupied by Zostera noltii beds. Since the end of 1998, mitigation measures were implemented in the estuary to promote the recovery of the seagrass beds and the entire surrounding environment. The present study offers a unique opportunity to evaluate the impact of disturbance and the success of the initial recovery process (before and after implementation of the management measures), over a 10-year period, having secondary production as the descriptor. Before the implementation of the mitigation measures, in parallel with the decrease of the Z. noltii beds, species richness, mean biomass and production also decreased, lowering the carrying capacity of the whole Mondego's south arm. Yet, after the introduction of management measures, the seagrass bed seemed to recover. Consequently, the biomass and production also increased substantially, for the whole intertidal area. Nevertheless, even after the mitigation measures implementation, natural-induced stressors, such as strong flood events induced a drastic reduction of annual production, not seen before the implementation of those measures. This shows that the resilience of the populations may have been lowered by a prior disturbance history (eutrophication) and consequent interactions of multiple stressors.