Uso del hábitat por una gran población superficial de Pinna nobilis

We investigated the habitat use and size structure of the fan mussel, Pinna nobilis L. in the Alfacs Bay (Ebro Delta, Spain, NW Mediterranean). Shore-parallel transects were conducted to assess the abundance, size, and orientation of individuals and to record habitat features along the Banya Sandspit, at depths of 20 to 130 cm. Results showed two distinctive areas in terms of population density, marked by the end of local salt pan dikes that we named Good Habitat (GH) and Bad Habitat (BH). To extrapolate these results to the full area of BH and GH, perpendicular transects were conducted to determine the local bathymetry. Then, the underestimation of individuals due to the effects of distance, depth and seagrass cover (Distance 6 computer package) was added to raw abundances to obtain a corrected population of 90303 individuals (12085 in the BH and 782018 in the GH), the largest so far reported at such low depths. Most recorded individuals were adults (40 to 60 cm shell length), with no occurrence of sizes < 20 cm, and with a strong association with Cymodocea nodosa seagrass beds. Given the shallow distribution of the population, the absence of small sizes during the study period, and the presence of human activities that may damage P. nobilis and its habitat, the development of a management plan appears imperative for the conservation of the species.El uso del hábitat y la estructura poblacional de la nacra, Pinna nobilis L. fue investigado en la bahía dels Alfacs (Delta del Ebro, Spain, Mediterráneo noroccidental). La abundancia, talla, y orientación de los individuos, así como las características del hábitat se evaluaron mediante transectos paralelos a la costa, a profundidades comprendidas entre los 20 y los 130 cm. Los resultados evidenciaron la presencia de dos áreas con densidades poblacionales diferenciadas, delimitadas por el final de los diques de las salinas locales, a las que se denominó Good Habitat (GH) y Bad Habitat (BH). Para extrapolar los resultados a toda el área del BH y el GH, se realizaron transectos perpendiculares para determinar la batimetría local. A continuación, las tasas de infravaloración de individuos debido al efecto de la distancia, la profundidad, y la cobertura de fanerógamas marinas obtenidas con el paquete informático Distance 6 se añadieron a los valores no corregidos, y resultaron en una estima de 90.303 individuos (12.085 en el BH y 78.2018 en el GH, la mayor hasta ahora registrada en aguas poco profundas. La mayoría de los individuos observados eran adultos (40 a 60 cm de longitud de valvas), sin ocurrencia de tallas < 20 cm, y con una fuerte asociación a la pradera de Cymodocea nodosa. Dada su distribución poco profunda, la ausencia de individuos juveniles durante el periodo de estudio, y la presencia de actividades humanas en la zona que potencialmente pueden perjudicar a P. nobilis y a su hábitat, la implantación de un plan de gestión es prioritario para la conservación de la población local

Environmental flows in the lower Ebro River and Delta: Current status and guidelines for a holistic approach

Deltas are a particular type of estuarine system in which the dependence on river flow (water, sediments and nutrients) is very strong, especially in river-dominated deltas such as the Mediterranean ones, but environmental flow (e-flow) proposals for deltaic systems are scarce. The Ebro Delta is one of the largest wetland areas in the western Mediterranean and one of the most important estuarine systems in Europe. The aim of this paper is to review the state of the art regarding e-flows and to carry out a critical analysis of the proposals for the lower Ebro River and Delta, in order to highlight the possible environmental and socioeconomic impacts arising from the e-flow regime currently approved. Additionally, based on existing scientific information, methods to establish an e-flow regime that allows the maintenance of the main socio-ecological functions and values are discussed; including those functions and values for which not enough information is available. The study concludes that the currently approved e-flows are not suitable for maintaining most functions and values, as they would not prevent the proliferation of alien fish species and macrophytes in the river, the intrusion of the salt wedge in the estuary, the deficit of sediment/nutrient transport and the degradation of riparian habitats or the decline of coastal fisheries. Socioeconomic consequences on coastal fisheries, river navigation, salt water intrusion, sediment deficit, biodiversity, water quality, aquaculture and hydropower are also considered. Other e-flow proposals such as the proposed by the Catalan government would be more suitable to maintain the main socioecological functions and values of the lower Ebro River and Delta. Nevertheless, additional studies are needed to validate e-flows in some relevant aspects such as the capacity of the river to transport sediments to the delta to avoid coastal regression and mitigate the effects of sea level rise and subsidence, as well as the capacity of floods to control the spread of macrophytes. The lower Ebro River and delta is among the case studies where more quantitative and qualitative criteria to set e-flows with a holistic approach have been established.info:eu-repo/semantics/publishedVersio

Environmental typology of rivers from the Brazilian semiarid as a first step for the application of the index of biotic integrity: The case of the Chapada Diamantina

Defining environmental river types is an essential step in the development of accurate fish‐based methods (IBI, Index of Biotic Integrity) to assess the environmental quality of aquatic ecosystems. In this study, the environmental typology of the rivers and streams in the region of Chapada Diamantina was developed. Thirty‐five sampling sites representative of the upper Paraguaçu River and its main tributaries were characterized to characterize the fish assemblages and abiotic environmental descriptors. A cluster analysis based on fish species CPUE was performed to define a first biological typology. Then, a discriminant analysis model was developed to select the environmental descriptors that explained the fish‐based river types. The model selected 11 environmental variables and classified 91% of the cases. The river typology defined in this study will be used for the development of an IBI to assess the ecological status of the Chapada Diamantina rivers. It is expected that both the typology developed here and the future IBI will provide important and useful tools to develop and apply nature conservation‐oriented management schemes in the Chapada Diamantina aquatic ecosystems.info:eu-repo/semantics/acceptedVersio

Estructura de la comunidad de macroinvertebrados bentónicos en un estuario mediterráneo altamente estratificado

The community composition and spatial distribution of benthic macroinvertebrates were studied along the Ebro estuary, a highly stratified estuary located in the NE Iberian Peninsula. During the last decade the oligotrophication process occurring in the lower Ebro River and its estuary has allowed a complex benthic macroinvertebrate community to become established; these results contrast with the poor community found there in the early nineties. A total of 214 taxa were identified, and polychaetes dominated the community both in abundance and species richness. The results showed spatial differences in the structure and composition of macroinvertebrates, which suggests that there are two distinct communities along the estuary. Each community was found in a specific stretch (upper and lower estuary) in function of the presence of the salt wedge. The macrobenthos of the upper estuary was dominated by freshwater taxa, but some euryhaline species were also found. The lower estuary showed a marine community typical of shallow Mediterranean environments. The transition between these two communities fits an ecotone model. The highest abundances, richness and diversities were recorded at the lower estuarine stations, especially those closer to the river mouth, whereas the lowest values corresponded to the stations adjacent to the tip of the salt wedge.La composición de la comunidad y la distribución espacial de los macroinvertebrados bentónicos ha sido estudiada a lo largo del estuario del Río Ebro, un estuario altamente estratificado localizado al NE de la Península Ibérica. El proceso de oligotrofización ocurrido durante la última década en el tramo bajo del río Ebro y su estuario, ha permitido el establecimiento de una compleja comunidad de macroinvertebrados, contrastando con la comunidad encontrada a principios de los noventa. Un total de 214 taxones fueron identificados; los poliquetos constituyeron el grupo dominante en términos de riqueza y abundancia. Los resultados mostraron diferencias espaciales en la estructura y composición de macroinvertebrados, sugiriendo la existencia de dos comunidades diferentes a lo largo del estuario. Cada una de estas comunidades fue encontrada en un tramo específico (alto y bajo estuario) en función de la presencia de la cuña salina. El macrobentos del tramo alto del estuario estaba integrado mayoritariamente por taxones de agua dulce y algunos taxones eurihalinos. Por el contario, el tramo bajo presentó una comunidad marina típica de ambientes mediterráneos someros. La transición entre estas dos comunidades encajó con un modelo ecotonal. Las abundancias, riquezas y diversidades más elevadas fueron registradas en las estaciones del tramo bajo, especialmente en aquellas cercanas a la desembocadura; en cambio, los valores más bajos correspondieron a las estaciones adyacentes al extremo de la cuña salina

La salinidad como el principal factor en la estructuración de comunidades de peces de pequeño tamaño en lagunas costeras mediterráneas hidrológicamente alteradas

In the Ebro Delta coastal lagoons, one of the main anthropogenic pressures is the artificial freshwater input. Each coastal lagoon has different water management schemes causing profound changes in its physicochemical characteristics. The main objective of this water management is to favour some bird species with interest either for conservation or hunting activities. The present study assesses the influence of hydrological alteration on the fish assemblages of three coastal lagoons in the Ebro Delta. The small-bodied fish fauna was mainly composed of five families: Gobiidae, Poecilidae, Cyprinodontidae, Atherinidae and Mugilidae. Salinity was found to be the main factor structuring fish community in the lagoons. The dominant species was the common goby (Pomatochistus microps) when the lagoons reached higher salinity values, whereas the invasive eastern mosquitofish (Gambusia holbrooki) dominated during the period of higher freshwater inputs. The juveniles of the family Mugilidae showed low catch per unit effort, especially during the period of lower salinity. This same pattern was found for the endangered Spanish toothcarp (Aphanius iberus). Overall, introduced species were favoured by low salinity, which highlights the importance of changing the present water management by reducing the freshwater inputs in order to maintain suitable levels of salinity to favour native species that are important for both commercial and conservation purposes.Una de las mayores presiones antropogénicas sobre las lagunas costeras del Delta del Ebro es la entrada artificial de agua dulce. Cada laguna costera presenta medidas de gestión distintas que alteran profundamente sus propiedades fisicoquímicas. Esta gestión del agua tiene como objetivo favorecer algunas especies de aves con interés para la caza y/o conservación. El presente estudio evalúa la influencia de la alteración hidrológica en la comunidad de peces de tres lagunas costeras del Delta del Ebro. La fracción de la ictiofauna integrada por individuos de pequeño tamaño estaba mayormente compuesta por cinco familias: Gobiidae, Poecilidae, Cyprinodontidae, Atherinidae y Mugilidae. La salinidad fue el factor que más contribuyó a la estructuración de la comunidad de peces de las lagunas. Con valores máximos de salinidad, la especie dominante en las lagunas fue el Gobito (Pomatoschistus microps), mientras que la Gambusia (Gambusia holbrooki), una especie invasora, fue dominante durante el período con mayores aportes de agua dulce. Los juveniles de la familia Mugilidae presentaron valores bajos de Capturas por Unidad de Esfuerzo (CPUE), especialmente durante el período de menor salinidad. El mismo patrón fue encontrado para el Fartet (Aphanius iberus), especie en peligro de extinción. En general, las especies introducidas fueron favorecidas por una baja salinidad, hecho que subraya la importancia de modificar la presente gestión del agua reduciendo los aportes de agua dulce con el fin de mantener niveles adecuados de salinidad que favorezcan a las especies nativas, importantes tanto desde el punto de vista comercial cómo conservacionista

Feeding Habits and Short-Term Mobility Patterns of Blue Crab, Callinectes sapidus, Across Invaded Habitats of the Ebro Delta Subjected to Contrasting Salinity

The blue crab Callinectes sapidus was first observed in the Ebro Delta in 2012 and since then captures have increased exponentially up to over 2 t per day, while its presence remains low in other Catalonian estuarine areas. Here, we use a stable isotope approach (δ15N and δ13C) to explore the dietary habits of adult blue crab in four different invaded habitats—bays, coastal lagoons, rice field drainage channels, and the Ebro River—in order to assess the strength of bottom-up forces and identify risks for native and aquaculture species, as well as patterns of site fidelity (male individuals). Mixing models showed average contributions of 35.89% from organic matter in sediments, 34.25% from animal resources (fish, crustaceans, gastropods, and bivalves), and 23.84% from vegetal resources (aquatic plants and algae), although there were important differences across habitat sites. In sites where bivalves were available, they can represent up to ca. 75% of the diet, thus threatening natural banks and local oyster and mussel farms. The average estimated trophic position of blue crabs in those sites was only 2.8, which confirms an omnivorous behavior but also can be attributed to the fact that mollusks were rare in the majority of the areas sampled in the Ebro Delta. Crabs from the same habitat site exhibited very little isotopic variability, suggesting that they remain in those environments long enough to reflect local salinity conditions. Overall, our results suggest that blue crabs are likely using all locally available resources and remain in certain sites, even when preferred animal preys are scarce and low-quality items are the main dietary option.info:eu-repo/semantics/acceptedVersio

Pristine vs. human-altered Ebro Delta habitats display contrasting resilience to RSLR

River deltas are ecologically and economically valuable coastal ecosystems but low elevations make them extremely sensitive to relative sea level rise (RSLR), i.e. the combined effects of sea level rise and subsidence. Most deltas are subjected to extensive human exploitation, which has altered the habitat composition, connectivity and geomorphology of deltaic landscapes. In the Ebro Delta, extensive wetland reclamation for rice cultivation over the last 150 years has resulted in the loss of 65% of the natural habitats. Here, we compare the dynamics of habitat shifts under two departure conditions (a simulated pristine delta vs. the human-altered delta) using the Sea Level Affecting Marshes Model (SLAMM) under the 4.5 and 8.5 RCP (Representative Concentration Pathways) scenarios for evaluating their resilience to RSLR (i.e. resistance to inundation). Results showed lower inundation rates in the human delta (~10 to 22% by the end of the century, depending on RCP conditions), mostly due to ~4.5 times lower initial extension of coastal lagoons compared to the pristine delta. Yet, inundation rates from ~15 to 30% of the total surface represent the worst possible human scenario, assuming no flooding protection measures. Besides, accretion rates within rice fields are disregarded since this option is not available in SLAMM for developed dry land. In the human delta, rice fields were largely shifted to other wetland habitats and experienced the highest reductions, mostly because of their larger surface. In contrast, in the pristine delta most of the habitats showed significant decreases by 2100 (~2 to 32% of the surface). Coastal infrastructures (dykes or flood protection dunes) and reintroduction of riverine sediments through irrigation channels are proposed to minimize impacts of RSLR. In the worst RCP scenarios, promoting preservation of natural habitats by transforming unproductive rice fields into wetlands could be the most sustainable option.info:eu-repo/semantics/acceptedVersio

Normalized abundance spectra of fish community reflect hydro-peaking on a Mediterranean large river

The European Water Framework Directive requires the integration of body size characters as an important part of fish-based bioassessment tools for freshwaters ecological status determination. The study of the entire fish community size-structure provides valuable information about food web capacity, food web stability and ecological efficiency of aquatic ecosystems. One of the most used representations of community size structure is the Normalized Abundance Spectra (NAS) that provides an approximation of the total fish abundance and food web capacity (through the parameter y-intercept) and an estimation of food web efficiency (through the slope of the linear regression). In this study we explored NAS of the lower Ebro River fish community by integrating data from monthly electrofishing samplings during a whole year (November 2014- October 2015). We found that the percentage of total alien and alien-prey individuals were directly related with y-intercept and inversely related with slope of NAS. This is because the bulk of the community consists of introduced species of small body length. Furthermore, we detected significant relationships between NAS-related parameters and the hydrological variables describing diel flow oscillations and daily flow variability. Based on this, we suggest that high flow variability conditions and, above all, high hydro-peaking conditions, caused a diminution of the total abundance of fish and a decrease of the proportion of small sized fish (i.e. lower y-intercept and flatter slopes of NAS, respectively). Finally, a significant interaction between hydro-peaking and the percentage of alien-predators suggests that high hydro-peaking conditions benefit predation by facilitating predator-prey encounters. This is reflected by strong linear relationship between NAS parameters and percentage of piscivorous at high hydropeaking conditions that disappears at low hydro-peaking fluctuations. We concluded that the high proportion of alien fishes and the presence of a hydropower generation plant that operates by hydro-peaking are important factors determining fish size structure in the lower Ebro River.info:eu-repo/semantics/acceptedVersio

Community structure of benthic macroinvertebrates inhabiting a highly stratified Mediterranean estuary

The community composition and spatial distribution of benthic macroinvertebrates were studied along the Ebro estuary, a highly stratified estuary located in the NE Iberian Peninsula. During the last decade the oligotrophication process occurring in the lower Ebro River and its estuary has allowed a complex benthic macroinvertebrate community to become established; these results contrast with the poor community found there in the early nineties. A total of 214 taxa were identified, and polychaetes dominated the community both in abundance and species richness. The results showed spatial differences in the structure and composition of macroinvertebrates, which suggests that there are two distinct communities along the estuary. Each community was found in a specific stretch (upper and lower estuary) in function of the presence of the salt wedge. The macrobenthos of the upper estuary was dominated by freshwater taxa, but some euryhaline species were also found. The lower estuary showed a marine community typical of shallow Mediterranean environments. The transition between these two communities fits an ecotone model. The highest abundances, richness and diversities were recorded at the lower estuarine stations, especially those closer to the river mouth, whereas the lowest values corresponded to the stations adjacent to the tip of the salt wedge

The combined use of chemical and biochemical markers in Rutilus rutilus to assess the effect of dredging in the lower course of the Ebro River

The lower course of the Ebro River is polluted with high concentrations of organochlorine compounds dumped by a chloro-alkali plant during the last century. A remediation plan, including building of a protective wall, removal and disposal of polluted sediments started in 2012. With the aim of assessing the effects of dredging of contaminated sediments and potential alterations of water quality, areas located upstream (RR) and downstream (BE, A) the chemical plant (FL) were monitored prior (October 2012) and during dredging (June 2013) using roach (Rutilus rutilus) as sentinel organisms. Concentrations of organochlorine compounds (OCs) in fish muscle and biliary levels of polycyclic aromatic hydrocarbons (PAHs), galaxolide (HHCB) and alkyphenols (APEs) were determined together with selected enzymatic activities (7-ethoxyresorufin-O-deethylase (EROD), 7-benzyloxy-4-trifluoromethyl-coumarin O-debenzyloxylase (BFCOD) and UDP-glucuronyltransferase (UGT)) in the liver. The obtained results proved the effectiveness of the wall retaining suspended particles and avoiding further contamination of downstream sites as fish sampled at downstream sites showed up to 9-fold higher concentrations of OCs in muscle during wall construction than during dredging. EROD and UGT activities were induced in fish from downstream sites; however, no clear response to the observed pollution gradient was detected.info:eu-repo/semantics/acceptedVersio