Due to their nature as transition systems, fishes in estuaries have affinities with both marine a... more Due to their nature as transition systems, fishes in estuaries have affinities with both marine and freshwater faunas. Estuarine fish assemblages face physicochemical dynamics and instability, as well as human-induced changes. These systems represent
a fundamental link in the life cycle of numerous species, which use them in specific life stages (in an obligatory or opportunistic manner). Many of these species represent important coastal fisheries and it is paramount to address the importance of estuaries as nurseries and their connectivity with the marine environment. Integrative approaches, as ecohydrology, may provide tools toward sustainability and restoration of estuarine ecological functions.
The relative importance of nursery areas and their relationships with several environmental varia... more The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but ...
The subtidal fish assemblage of Tagus estuary coastal area was sampled in order to infer about it... more The subtidal fish assemblage of Tagus estuary coastal area was sampled in order to infer about its relationship to environmental conditions and its possible nursery function for marine species. Fish sampling took place between May 2001 and February 2002 with an otter trawl. In addition to fish sampling, a physical, chemical and biological characterization of the water column and bottom sediment was performed. Density and biomass were determined and ecological and feeding guilds assigned to each fish species. Correspondence analysis (CA) was used to determine the spatio-temporal structure of the assemblage and its correlation to environmental variables. A total of 36 fish species were identified. The fish assemblage was dominated by few species, both in terms of density and biomass. The main fish species were Callionymus lyra, Arnoglossus laterna, Diplodus bellotti, Echiichthys vipera and Raja undulata. Seasonally Trachurus trachurus, Sardina pilchardus and Engraulis encrasicolus wer...
ABSTRACT Understanding whether fish move among estuarine areas and habitats or show high site fid... more ABSTRACT Understanding whether fish move among estuarine areas and habitats or show high site fidelity has major implications for habitat conservation and the safeguard of estuarine ecological integrity. Muscle stable isotopes (delta13C, delta15N) and otolith elemental composition (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca and Pb:Ca) were used to evaluate connectivity between two separate estuarine nursery areas in summer and autumn for juvenile age-0 Dicentrarchus labrax and Pomatoschistus microps. Distinct isotopic ratios and otolith elemental signatures were found between areas for D. labrax and P. microps, and in both sampling times. High classification accuracies to collection sites were achieved via otolith elemental signatures (80 – 94%), and a combined analysis using both muscle stable isotopes otolith chemistry resulted in increased accuracy with no classification errors. Overall, low site connectivity was found for both species. The use of two distinct natural tags provided corroborative and complementary information on fish movement and intra-estuarine habitat use at different temporal scales, whilst elucidating distinct ecological and environmental linkages. Ultimately, the combined use of distinct natural tags showed great promise to unravel intra-estuarine connectivity patterns.
1.Knowledge on global patterns of biodiversity and regulating variables is indispensable to devel... more 1.Knowledge on global patterns of biodiversity and regulating variables is indispensable to develop predictive models. 2.The present study used predictive modelling approaches to investigate hypotheses that explain the variation in fish species richness between estuaries over a worldwide spatial extent. Ultimately, such models will allow assessment of future changes in ecosystem structure and function as a result of environmental changes. 3.A comprehensive worldwide database was compiled on the fish assemblage composition and environmental characteristics of estuaries. Generalized Linear Models were used to quantify how variation in species richness among estuaries is related to historical events, energy dynamics, and ecosystem characteristics, whilst controlling for sampling effect. 4.At the global extent, species richness differed among marine biogeographic realms and continents, and increased with mean sea surface temperature, terrestrial net primary productivity, and the stability of connectivity with marine ecosystem (open versus temporarily open estuaries). At a smaller extent (within marine biogeographic realm or continent) other characteristics were also important in predicting variation in species richness, with species richness increasing with estuary area and continental shelf width. 5.The results suggest that species richness in an estuary is defined by predictors that are spatially hierarchical. Over the largest spatial extents species richness is influenced by the broader distributions and habitat use patterns of marine and freshwater species that can colonize estuaries, which are in turn governed by history contingency, energy dynamics and productivity variables. Species richness is also influenced by more regional and local parameters that can further affect the process of community colonization in an estuary including the connectivity of the estuarine with the adjacent marine habitat, and, over smaller spatial extents, the size of these habitats. In summary, patterns of species richness in estuaries across large spatial extents seem to reflect from global to local processes acting on community colonization. The importance of considering spatial extent, sampling effects and of combining history and contemporary environmental characteristics when exploring biodiversity is highlighted. This article is protected by copyright. All rights reserved.
ABSTRACT The main ecological patterns and the functioning of estuarine ecosystems are difficult t... more ABSTRACT The main ecological patterns and the functioning of estuarine ecosystems are difficult to evaluate due to natural and human induced complexity and variability. Broad geographical approaches appear particularly useful. This study tested, at a worldwide scale, the influence of global and local variables in fish species richness in estuaries, aiming to determine the latitudinal pattern of species richness, and patterns which could be driven by local features such as estuary area, estuary mouth width, river flow and intertidal area. Seventy one estuarine systems were considered with data obtained from the literature and geographical information system. Correlation tests and generalized linear models (GLM) were used in data analyses. Species richness varied from 23 to 153 fish species. GLM results showed that estuary area was the most important factor explaining species richness, followed by latitude and mouth width. Species richness increased towards the equator, and higher values were found in larger estuaries and with a wide mouth. All these trends showed a high variability. A larger estuary area probably reflects a higher diversity of habitats and/or productivity, which are key features for estuarine ecosystem functioning and biota. The mouth width effect is particularly notorious for marine and diadromous fish species, enhancing connectivity between marine and freshwater realms. The effects of river flow and intertidal area on the fish species richness appear to be less evident. These two factors may have a marked influence in the trophic structure of fish assemblages.
Short-term variability in biomarker responses and the effects of temperature and salinity variati... more Short-term variability in biomarker responses and the effects of temperature and salinity variation were explored in three fish species (Dicentrarchus labrax, Solea senegalensis and Pomatoschistus microps) occurring in the Tejo estuary. Short-term variability in biomarkers was observed in all species although no pattern was discerned over time (days to weeks). Antioxidant enzymes activity (superoxide dismutase (SOD) and catalase (CAT)) showed low temporal variability, indicating some constancy or baseline level in antioxidant responses. Only CAT activity in S. senegalensis was correlated with temperature, suggesting that exposure to contaminants triggered antioxidant acclimation. Higher short-term variability was observed in xenobiotic biotransformation enzymes activity (phase I ethoxyresorufin O-deethylase (EROD) and phase II glutathione S-transferase (GST)). Yet a significant correlation between EROD and GST in D. labrax and S. senegalensis suggests a concomitant response to contaminants. Moreover the lack of correlation between xenobiotic biotransformation enzymes and abiotic variables on concordant time scales, suggest a high specificity of these biomarkers to chemical exposure, rather than high variability due to environmental dynamics.
Understanding the factors that influence biological responses to contaminants has long been a maj... more Understanding the factors that influence biological responses to contaminants has long been a major goal in marine environmental research. Seven estuarine sites along the Portuguese coast were sampled over a year, and different biological responses of Pomatoschistus microps and Atherina presbyter were determined: superoxide dismutase, catalase, ethoxyresorufin O-deethylase, glutathione S-transferase, metallothioneins, lipid peroxidation, RNA:DNA ratio and condition factor K. Generalized linear models (GLM) were developed for each biological variable per species in relation to sediment chemical characterization (metals and polycyclic aromatic hydrocarbons concentration) and environmental conditions (month, site, water temperature, salinity, depth and mud percentage in the sediment). GLM varied in explanatory power and in the set of predictor variables included in the models. Environmental factors were frequently selected as predictor variables. Individual metals concentration and sediment quality guidelines (integrating all metals) were the major contaminants explaining biological variability. Accordingly, models for metallothioneins and lipid peroxidation had highest explanatory power. Species-specific responses and dataset size were the basis of observed differences between GLM for the two species.
ABSTRACT A better understanding of connectivity patterns between estuarine and coastal areas is f... more ABSTRACT A better understanding of connectivity patterns between estuarine and coastal areas is fundamental towards sustainable management of estuarine associated fish and identification of ecologically important habitats. Otolith geochemistry (Li:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca, Pb:Ca) determined in juveniles of Solea solea and Solea senegalensis in two year classes was used to determine the estuaries of origin of age 3+ and age 2+ fish sampled off the Portuguese coast. The contributions of estuarine nursery areas to coastal adult populations obtained using maximum likelihood estimation varied significantly over the two years. However, one estuary (Ria Aveiro) consistently contributed a large proportion (30%–87%) to the adult populations of both sole species while a second estuary (Mira) contributed almost no adults (0%–3%). Comparison of otolith geochemistry between juveniles from characterized estuarine nurseries and adults indicated that unknown nursery areas may have contributed to the coastal adult populations, particularly in one year class. Nevertheless, the estimated relative contributions, based on otolith geochemistry, successfully identified the estuarine systems that accounted for most of the recruitment to adult stocks in the two years. Ultimately, this information should promote the development of effective conservation strategies and integrated fisheries management plans for these two commercially important species.
The relative importance of nursery areas and their relationships with several environmental varia... more The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but ...
Journal of Experimental Marine Biology and Ecology, 2013
ABSTRACT The use of otolith geochemistry to track fish migration patterns and establish past habi... more ABSTRACT The use of otolith geochemistry to track fish migration patterns and establish past habitat use in estuarine environments relies on the presence of significant correlations between the physicochemical properties of ambient water and otolith composition. To test this assumption, juvenile Solea solea and ambient waters were sampled at fortnightly and monthly intervals in six sites within the Tejo estuary (Portugal) from May to October 2009. A number of element:Ca ratios (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca) along with δ13C and δ18O values were measured in otoliths and water samples. The distributions of some element:Ca ratios (Mg:Ca, Cu:Ca and Ba:Ca) and both δ13C of dissolved inorganic carbon (DIC) and δ18Owater values were correlated with salinity in the estuarine waters. Otolith Ba:Ca, δ13C and δ18O ratios were significantly correlated with their respective ambient water values. Each of these variables showed distinctive mixing patterns along the salinity gradient of the estuary and therefore may be valuable tracers of habitat use in euryhaline environments. Surprisingly, only the partition coefficient of Li (DLi) was significantly negatively correlated with ambient temperature. While more work is obviously needed, Li:Ca may be a useful, but currently overlooked, temperature proxy in fish otoliths. Our results highlight the difficulties of linking measurements of otolith geochemistry to individual water masses or habitats in estuarine systems with large physicochemical gradients over relatively small spatial and temporal scales.
ABSTRACT 1. Conservation science increasingly focuses on how ecosystem functioning is affected by... more ABSTRACT 1. Conservation science increasingly focuses on how ecosystem functioning is affected by anthropogenic pressures, which implies an understanding of the structural and functional changes in biological assemblages and requires indicators to detect such changes within a suitable time frame. 2. A novel approach that combines the spatial analysis of fishing gradients (based on vessel monitoring system records) with distance-based linear models was used to assess the response of several functional and structural metrics of fish assemblages to gradients of trawling, within four distinct habitat types. In addition, critical thresholds of trawling intensity were identified for the most sensitive metrics through piecewise regression models. 3. Overall, total biomass and dominance (i.e. number of species that make up 90% of the total biomass) metrics as well as metrics representing vulnerable features (such as chondrichthyes, species with very low resilience, and sedentary species) were shown to be sensitive to fishing. Our results suggest that decreasing trends in these indicators are likely to be associated with direct and indirect fishing effects acting synergistically on specific features of fish assemblages leading to its homogenization, with likely impacts on ecosystems resilience. 4. Critical thresholds at high, medium and low fishing intensity levels were identified depending on the metric used to assess fishing impacts, suggesting that it is difficult to define a single global target for fishing management as it ultimately will depend on management and conservation objectives (e.g. maintenance of biomass vs. maintenance of structure and function). 5. Synthesis and Applications. A key goal of the applied approach was to provide short-term indicators that are sensitive to gradients of trawling intensity and can be extrapolated to a broader geographic region. The identification of thresholds of fishing pressure that fish assemblages can withstand before ecosystem functioning is altered is key for the development of indicators as warning mechanisms, as well as to assess performance measures for management. Understanding responses to other pressure sources (e.g. pollution, dredging) requires further research and combining an integrative functional traits approach with a wider range of pressures may help make this achievable.
Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for ide... more Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for identifying important sites for juveniles as well as the basic environmental features that characterize these sites for different species. This is a key aspect towards understanding nursery function. Various estuarine systems along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria
ABSTRACT Statistical models predicting species distributions are essential not only to increase k... more ABSTRACT Statistical models predicting species distributions are essential not only to increase knowledge on species but for their application in conservation and ecologically-based management. The variation of fish species richness and abundance in the most representative habitats (saltmarsh, mudflat and subtidal) in five estuaries along the Portuguese coast was analysed through seasonal sampling surveys in 2009. Generalized additive models (GAM) were developed to describe the variation of species richness and abundances with a set of geomorphologic, hydrologic and environmental characteristics from the sampled estuaries and habitats. GAM were chosen as the complex interactions dominating these ecosystems and species distribution are non-linear. Final models built for each estuary and for all estuaries together performed well during the calibration phase and also during the validation phase, where an unused data sub-set from each estuary was used. There was not a similar combination of variables retained by the models for the studied estuaries but factors such as the area of the habitat, the distance to estuary mouth, percentage of mud in the sediment and depth were commonly retained. The partial effect of these predictor variables on the variation of species richness and abundance in the estuaries varied markedly and the importance of preserving the heterogeneity of habitats within estuaries was highlighted. Models for each individual estuary performed better than models for estuaries combined. Predictive models could be useful as a preliminary tool to prepare long-term conservation plans at different scales.
Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by varia... more Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by variations in juvenile growth and survival. Condition indices are renowned proxies of juvenile nutritional status and growth rates and are valuable tools to assess habitat quality. Biochemical (RNA:DNA ratio) and morphometric (Fulton's condition factor K) condition indices were determined in juveniles of Solea solea, Solea senegalensis, Platichthys
Due to their nature as transition systems, fishes in estuaries have affinities with both marine a... more Due to their nature as transition systems, fishes in estuaries have affinities with both marine and freshwater faunas. Estuarine fish assemblages face physicochemical dynamics and instability, as well as human-induced changes. These systems represent
a fundamental link in the life cycle of numerous species, which use them in specific life stages (in an obligatory or opportunistic manner). Many of these species represent important coastal fisheries and it is paramount to address the importance of estuaries as nurseries and their connectivity with the marine environment. Integrative approaches, as ecohydrology, may provide tools toward sustainability and restoration of estuarine ecological functions.
The relative importance of nursery areas and their relationships with several environmental varia... more The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but ...
The subtidal fish assemblage of Tagus estuary coastal area was sampled in order to infer about it... more The subtidal fish assemblage of Tagus estuary coastal area was sampled in order to infer about its relationship to environmental conditions and its possible nursery function for marine species. Fish sampling took place between May 2001 and February 2002 with an otter trawl. In addition to fish sampling, a physical, chemical and biological characterization of the water column and bottom sediment was performed. Density and biomass were determined and ecological and feeding guilds assigned to each fish species. Correspondence analysis (CA) was used to determine the spatio-temporal structure of the assemblage and its correlation to environmental variables. A total of 36 fish species were identified. The fish assemblage was dominated by few species, both in terms of density and biomass. The main fish species were Callionymus lyra, Arnoglossus laterna, Diplodus bellotti, Echiichthys vipera and Raja undulata. Seasonally Trachurus trachurus, Sardina pilchardus and Engraulis encrasicolus wer...
ABSTRACT Understanding whether fish move among estuarine areas and habitats or show high site fid... more ABSTRACT Understanding whether fish move among estuarine areas and habitats or show high site fidelity has major implications for habitat conservation and the safeguard of estuarine ecological integrity. Muscle stable isotopes (delta13C, delta15N) and otolith elemental composition (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca and Pb:Ca) were used to evaluate connectivity between two separate estuarine nursery areas in summer and autumn for juvenile age-0 Dicentrarchus labrax and Pomatoschistus microps. Distinct isotopic ratios and otolith elemental signatures were found between areas for D. labrax and P. microps, and in both sampling times. High classification accuracies to collection sites were achieved via otolith elemental signatures (80 – 94%), and a combined analysis using both muscle stable isotopes otolith chemistry resulted in increased accuracy with no classification errors. Overall, low site connectivity was found for both species. The use of two distinct natural tags provided corroborative and complementary information on fish movement and intra-estuarine habitat use at different temporal scales, whilst elucidating distinct ecological and environmental linkages. Ultimately, the combined use of distinct natural tags showed great promise to unravel intra-estuarine connectivity patterns.
1.Knowledge on global patterns of biodiversity and regulating variables is indispensable to devel... more 1.Knowledge on global patterns of biodiversity and regulating variables is indispensable to develop predictive models. 2.The present study used predictive modelling approaches to investigate hypotheses that explain the variation in fish species richness between estuaries over a worldwide spatial extent. Ultimately, such models will allow assessment of future changes in ecosystem structure and function as a result of environmental changes. 3.A comprehensive worldwide database was compiled on the fish assemblage composition and environmental characteristics of estuaries. Generalized Linear Models were used to quantify how variation in species richness among estuaries is related to historical events, energy dynamics, and ecosystem characteristics, whilst controlling for sampling effect. 4.At the global extent, species richness differed among marine biogeographic realms and continents, and increased with mean sea surface temperature, terrestrial net primary productivity, and the stability of connectivity with marine ecosystem (open versus temporarily open estuaries). At a smaller extent (within marine biogeographic realm or continent) other characteristics were also important in predicting variation in species richness, with species richness increasing with estuary area and continental shelf width. 5.The results suggest that species richness in an estuary is defined by predictors that are spatially hierarchical. Over the largest spatial extents species richness is influenced by the broader distributions and habitat use patterns of marine and freshwater species that can colonize estuaries, which are in turn governed by history contingency, energy dynamics and productivity variables. Species richness is also influenced by more regional and local parameters that can further affect the process of community colonization in an estuary including the connectivity of the estuarine with the adjacent marine habitat, and, over smaller spatial extents, the size of these habitats. In summary, patterns of species richness in estuaries across large spatial extents seem to reflect from global to local processes acting on community colonization. The importance of considering spatial extent, sampling effects and of combining history and contemporary environmental characteristics when exploring biodiversity is highlighted. This article is protected by copyright. All rights reserved.
ABSTRACT The main ecological patterns and the functioning of estuarine ecosystems are difficult t... more ABSTRACT The main ecological patterns and the functioning of estuarine ecosystems are difficult to evaluate due to natural and human induced complexity and variability. Broad geographical approaches appear particularly useful. This study tested, at a worldwide scale, the influence of global and local variables in fish species richness in estuaries, aiming to determine the latitudinal pattern of species richness, and patterns which could be driven by local features such as estuary area, estuary mouth width, river flow and intertidal area. Seventy one estuarine systems were considered with data obtained from the literature and geographical information system. Correlation tests and generalized linear models (GLM) were used in data analyses. Species richness varied from 23 to 153 fish species. GLM results showed that estuary area was the most important factor explaining species richness, followed by latitude and mouth width. Species richness increased towards the equator, and higher values were found in larger estuaries and with a wide mouth. All these trends showed a high variability. A larger estuary area probably reflects a higher diversity of habitats and/or productivity, which are key features for estuarine ecosystem functioning and biota. The mouth width effect is particularly notorious for marine and diadromous fish species, enhancing connectivity between marine and freshwater realms. The effects of river flow and intertidal area on the fish species richness appear to be less evident. These two factors may have a marked influence in the trophic structure of fish assemblages.
Short-term variability in biomarker responses and the effects of temperature and salinity variati... more Short-term variability in biomarker responses and the effects of temperature and salinity variation were explored in three fish species (Dicentrarchus labrax, Solea senegalensis and Pomatoschistus microps) occurring in the Tejo estuary. Short-term variability in biomarkers was observed in all species although no pattern was discerned over time (days to weeks). Antioxidant enzymes activity (superoxide dismutase (SOD) and catalase (CAT)) showed low temporal variability, indicating some constancy or baseline level in antioxidant responses. Only CAT activity in S. senegalensis was correlated with temperature, suggesting that exposure to contaminants triggered antioxidant acclimation. Higher short-term variability was observed in xenobiotic biotransformation enzymes activity (phase I ethoxyresorufin O-deethylase (EROD) and phase II glutathione S-transferase (GST)). Yet a significant correlation between EROD and GST in D. labrax and S. senegalensis suggests a concomitant response to contaminants. Moreover the lack of correlation between xenobiotic biotransformation enzymes and abiotic variables on concordant time scales, suggest a high specificity of these biomarkers to chemical exposure, rather than high variability due to environmental dynamics.
Understanding the factors that influence biological responses to contaminants has long been a maj... more Understanding the factors that influence biological responses to contaminants has long been a major goal in marine environmental research. Seven estuarine sites along the Portuguese coast were sampled over a year, and different biological responses of Pomatoschistus microps and Atherina presbyter were determined: superoxide dismutase, catalase, ethoxyresorufin O-deethylase, glutathione S-transferase, metallothioneins, lipid peroxidation, RNA:DNA ratio and condition factor K. Generalized linear models (GLM) were developed for each biological variable per species in relation to sediment chemical characterization (metals and polycyclic aromatic hydrocarbons concentration) and environmental conditions (month, site, water temperature, salinity, depth and mud percentage in the sediment). GLM varied in explanatory power and in the set of predictor variables included in the models. Environmental factors were frequently selected as predictor variables. Individual metals concentration and sediment quality guidelines (integrating all metals) were the major contaminants explaining biological variability. Accordingly, models for metallothioneins and lipid peroxidation had highest explanatory power. Species-specific responses and dataset size were the basis of observed differences between GLM for the two species.
ABSTRACT A better understanding of connectivity patterns between estuarine and coastal areas is f... more ABSTRACT A better understanding of connectivity patterns between estuarine and coastal areas is fundamental towards sustainable management of estuarine associated fish and identification of ecologically important habitats. Otolith geochemistry (Li:Ca, Mg:Ca, Mn:Ca, Sr:Ca, Ba:Ca, Pb:Ca) determined in juveniles of Solea solea and Solea senegalensis in two year classes was used to determine the estuaries of origin of age 3+ and age 2+ fish sampled off the Portuguese coast. The contributions of estuarine nursery areas to coastal adult populations obtained using maximum likelihood estimation varied significantly over the two years. However, one estuary (Ria Aveiro) consistently contributed a large proportion (30%–87%) to the adult populations of both sole species while a second estuary (Mira) contributed almost no adults (0%–3%). Comparison of otolith geochemistry between juveniles from characterized estuarine nurseries and adults indicated that unknown nursery areas may have contributed to the coastal adult populations, particularly in one year class. Nevertheless, the estimated relative contributions, based on otolith geochemistry, successfully identified the estuarine systems that accounted for most of the recruitment to adult stocks in the two years. Ultimately, this information should promote the development of effective conservation strategies and integrated fisheries management plans for these two commercially important species.
The relative importance of nursery areas and their relationships with several environmental varia... more The relative importance of nursery areas and their relationships with several environmental variables were evaluated in nine estuarine systems along the Portuguese coast based on trawl surveys. Historical data were used to outline changes and trends in the nursery function of some of these estuaries over the past decades. The dominant flatfish species in Portuguese estuaries were Platichthys flesus (Linnaeus, 1758), Solea solea (Linnaeus, 1758), Solea senegalensis Kaup, 1858 and Monochirus hispidus Rafinesque, 1814, but ...
Journal of Experimental Marine Biology and Ecology, 2013
ABSTRACT The use of otolith geochemistry to track fish migration patterns and establish past habi... more ABSTRACT The use of otolith geochemistry to track fish migration patterns and establish past habitat use in estuarine environments relies on the presence of significant correlations between the physicochemical properties of ambient water and otolith composition. To test this assumption, juvenile Solea solea and ambient waters were sampled at fortnightly and monthly intervals in six sites within the Tejo estuary (Portugal) from May to October 2009. A number of element:Ca ratios (Li:Ca, Mg:Ca, Mn:Ca, Cu:Ca, Sr:Ca, Ba:Ca) along with δ13C and δ18O values were measured in otoliths and water samples. The distributions of some element:Ca ratios (Mg:Ca, Cu:Ca and Ba:Ca) and both δ13C of dissolved inorganic carbon (DIC) and δ18Owater values were correlated with salinity in the estuarine waters. Otolith Ba:Ca, δ13C and δ18O ratios were significantly correlated with their respective ambient water values. Each of these variables showed distinctive mixing patterns along the salinity gradient of the estuary and therefore may be valuable tracers of habitat use in euryhaline environments. Surprisingly, only the partition coefficient of Li (DLi) was significantly negatively correlated with ambient temperature. While more work is obviously needed, Li:Ca may be a useful, but currently overlooked, temperature proxy in fish otoliths. Our results highlight the difficulties of linking measurements of otolith geochemistry to individual water masses or habitats in estuarine systems with large physicochemical gradients over relatively small spatial and temporal scales.
ABSTRACT 1. Conservation science increasingly focuses on how ecosystem functioning is affected by... more ABSTRACT 1. Conservation science increasingly focuses on how ecosystem functioning is affected by anthropogenic pressures, which implies an understanding of the structural and functional changes in biological assemblages and requires indicators to detect such changes within a suitable time frame. 2. A novel approach that combines the spatial analysis of fishing gradients (based on vessel monitoring system records) with distance-based linear models was used to assess the response of several functional and structural metrics of fish assemblages to gradients of trawling, within four distinct habitat types. In addition, critical thresholds of trawling intensity were identified for the most sensitive metrics through piecewise regression models. 3. Overall, total biomass and dominance (i.e. number of species that make up 90% of the total biomass) metrics as well as metrics representing vulnerable features (such as chondrichthyes, species with very low resilience, and sedentary species) were shown to be sensitive to fishing. Our results suggest that decreasing trends in these indicators are likely to be associated with direct and indirect fishing effects acting synergistically on specific features of fish assemblages leading to its homogenization, with likely impacts on ecosystems resilience. 4. Critical thresholds at high, medium and low fishing intensity levels were identified depending on the metric used to assess fishing impacts, suggesting that it is difficult to define a single global target for fishing management as it ultimately will depend on management and conservation objectives (e.g. maintenance of biomass vs. maintenance of structure and function). 5. Synthesis and Applications. A key goal of the applied approach was to provide short-term indicators that are sensitive to gradients of trawling intensity and can be extrapolated to a broader geographic region. The identification of thresholds of fishing pressure that fish assemblages can withstand before ecosystem functioning is altered is key for the development of indicators as warning mechanisms, as well as to assess performance measures for management. Understanding responses to other pressure sources (e.g. pollution, dredging) requires further research and combining an integrative functional traits approach with a wider range of pressures may help make this achievable.
Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for ide... more Analysing the estuarine use patterns of juveniles of marine migrant fish species is vital for identifying important sites for juveniles as well as the basic environmental features that characterize these sites for different species. This is a key aspect towards understanding nursery function. Various estuarine systems along the Portuguese coast (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria
ABSTRACT Statistical models predicting species distributions are essential not only to increase k... more ABSTRACT Statistical models predicting species distributions are essential not only to increase knowledge on species but for their application in conservation and ecologically-based management. The variation of fish species richness and abundance in the most representative habitats (saltmarsh, mudflat and subtidal) in five estuaries along the Portuguese coast was analysed through seasonal sampling surveys in 2009. Generalized additive models (GAM) were developed to describe the variation of species richness and abundances with a set of geomorphologic, hydrologic and environmental characteristics from the sampled estuaries and habitats. GAM were chosen as the complex interactions dominating these ecosystems and species distribution are non-linear. Final models built for each estuary and for all estuaries together performed well during the calibration phase and also during the validation phase, where an unused data sub-set from each estuary was used. There was not a similar combination of variables retained by the models for the studied estuaries but factors such as the area of the habitat, the distance to estuary mouth, percentage of mud in the sediment and depth were commonly retained. The partial effect of these predictor variables on the variation of species richness and abundance in the estuaries varied markedly and the importance of preserving the heterogeneity of habitats within estuaries was highlighted. Models for each individual estuary performed better than models for estuaries combined. Predictive models could be useful as a preliminary tool to prepare long-term conservation plans at different scales.
Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by varia... more Connectivity between estuarine fish nurseries and coastal adult habitats can be affected by variations in juvenile growth and survival. Condition indices are renowned proxies of juvenile nutritional status and growth rates and are valuable tools to assess habitat quality. Biochemical (RNA:DNA ratio) and morphometric (Fulton's condition factor K) condition indices were determined in juveniles of Solea solea, Solea senegalensis, Platichthys
Identifying the relative importance of estuaries as effective nurseries for marine fish juveniles... more Identifying the relative importance of estuaries as effective nurseries for marine fish juveniles is essential to understand the processes defining the life cycle and structure of these species’ meta-populations and raises scientific interest due to the ecological and economical importance of directly associated functions and resources. In the present work, some of the main Portuguese estuaries (Minho, Douro, Ria de Aveiro, Mondego, Tejo, Sado, Mira, Ria Formosa and Guadiana) and commercially important fish species acknowledged for their use of these estuaries as putative nurseries (Solea solea, Solea senegalensis, Platichthys flesus, Diplodus vulgaris and Dicentrarchus labrax) were analysed following an integrative, multi-metric and multi-species approach. Estuaries were ranked by natural vulnerability and anthropogenic pressures through the development of a multi-metric index; with ecological impacts and end-points of pressure sources conceptually identified. Sites identified in different estuaries as important for juveniles, for one or several species, varied in fish density and habitat quantity, which together defined the potential export of juveniles. The variability in environmental characteristics of these sites highlighted species’ resilience to potential changes in estuaries. Habitat quality, measured with RNA:DNA and Fulton (K) condition indices, showed species-specific patterns of variation amongst estuaries. Juvenile contamination by trace elements was reduced and, in general, similar amongst estuaries. Otolith elemental fingerprints were validated as natural tags to discriminate estuaries individually; with specific patterns requiring fingerprint application to be made independently. These tags allowed the retrospective identification of the estuaries where marine adults spent their juvenile period and revealed the differential effective contribution of estuaries to adult subpopulations, which also differed amongst species. Combined results of all metrics identified differences in the relative importance of estuaries as nurseries and effective juvenile habitats for the analysed species and revealed some agreement between potential and effective export estimates from individual estuaries.
Uploads
a fundamental link in the life cycle of numerous species, which use them in specific life stages (in an obligatory or opportunistic manner). Many of these species represent important coastal fisheries and it is paramount to address the importance of estuaries as nurseries and their connectivity with the marine environment. Integrative approaches, as ecohydrology, may provide tools toward sustainability and restoration of estuarine ecological functions.
a fundamental link in the life cycle of numerous species, which use them in specific life stages (in an obligatory or opportunistic manner). Many of these species represent important coastal fisheries and it is paramount to address the importance of estuaries as nurseries and their connectivity with the marine environment. Integrative approaches, as ecohydrology, may provide tools toward sustainability and restoration of estuarine ecological functions.