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Carles Ibanez - One of the best experts on this subject based on the ideXlab platform.
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influence of salinity regime on the food web structure and feeding ecology of fish species from mediterranean coastal Lagoons
Estuarine Coastal and Shelf Science, 2014Co-Authors: Patricia Prado, Carolina Vergara, Nuno Caiola, Carles IbanezAbstract:Abstract Dual δ 15 N and δ 13 C analyses and estimates of biomass were used to characterize the food webs of valuable fish species in three coastal Lagoons of the Ebro Delta subjected to contrasting salinity regimes (polyhaline in the Tancada Lagoon, mesohaline in the Encanyissada and oligohaline in the Clot Lagoon). The δ 13 C signatures of the entire food-web including primary producers, sediment organic matter and consumers showed the most enriched values in the Tancada Lagoon (from approx. −4.8‰ in sediments to −19.7‰ in fish) and the most depleted ones in the Clot Lagoon (from approx. −11.4‰ in sediments to −25.4‰ in fish), consistent with dominant contributions from marine and continental sources, respectively. For δ 15 N, particularly high values were detected in the submersed vegetation (11.3 ± 0.3‰) together with more enriched sediment values at lower salinities (by approx. 2.5‰), suggesting that historical loadings of agricultural fertilizers are still retained by the systems and transmitted across trophic levels. Negative relationships between δ 15 N and salinity were also observed for the amphipod Gammarus aequicauda and the isopod Sphaeroma hookeri , suggesting some consumption of accumulated and resuspended detrital material. In contrast, δ 15 N signatures of fish showed lower values and inconsistent patterns, possibly because most species have a seasonal use of the Lagoons. The biomass of fish species did not show a clear effect of the salinity regime (except for the mosquitofish Gambusia holbrookii ), but results for mixing models suggest a diet shift from higher contribution of zooplankton size fractions in the Encanyissada (from 57 to 73%) to macrofauna at the other Lagoons (from 40 to 67%). We suggest that alterations in salinity might modify the trophic dynamics of the systems from benthic to planktonic pathways, without large-scale differences in δ 15 N of fish suggestive of similar trophic levels.
MH Ahmed - One of the best experts on this subject based on the ideXlab platform.
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Environmental influences on the qualitative and quantitative composition of phytoplankton and zooplankton in North African coastal Lagoons
HYDROBIOLOGIA, 2009Co-Authors: MH AhmedAbstract:Within the framework of the international research project MELMARINA, seasonal dynamics of plankton communities in three North African coastal Lagoons (Merja Zerga, Ghar El Melh, and Lake Manzala) were investigated. The sampling period extended from July 2003 to September 2004 with the aim of evaluating hydrological and other influences on the structure, composition and space-time development of these communities in each Lagoon. Phytoplankton in Merja Zerga showed a quasi-permanent predominance of marine diatoms in the open sea station and in the marine inlet channel. Dinoflagellates were abundant in summer and early autumn in the marine inlet and extended into the central Lagoon station. In Ghar El Melh, marine species (especially diatoms and dinoflagellates) dominated despite occasional winter inflows of freshwater. In Lake Manzala, freshwater species generally predominated and the planktonic communities were comparatively very diverse. Chlorophyceae contributed 39% of the total species recorded and diatoms and cyanophyceans were also common; the Dinophyceae, Euglenophyceae, Chrysophyceae and Cryptophyceae less so. Zooplankton communities in both Ghar El Melh and Merja Zerga were dominated by marine copepods. Rotifera, Copepoda, Ostracoda, and Cladocera were recorded in both Lagoons as were meroplanktonic larvae of Polychaeta, Cirripedia, Mysidacea and Gastropoda and free living nematodes. Ghar El Melh was the more productive of these two Lagoons with spring and early summer being the productive seasons. Zooplankton communities in Lake Manzala were generally dominated by rotifers and highest zooplankton abundances occurred in April (2003). Sampling stations near the marine inlets showed the highest diversity and the zooplankton communities showed considerable spatial variation within this large Lagoon. The three Lagoons represent very different water bodies contrasted strongly in terms of tidal effects and freshwater availability. Yet, there are some similarities in ecosystem structure. Space-time development of the plankton communities was similar especially in Merja Zerga and Ghar El Melh. Species abundances and specific diversities indicated that seasonal changes in salinity and nutrient concentrations were the main influential factors. Lake Manzala was the most productive Lagoon and all the three sites supported toxic algal species. Relatively low plankton biomass in Merja Zerga and Ghar El Melh probably resulted from a combination of factors including highly episodic nutrient inputs, light suppression (by turbidity) and nutrient competition with benthic algae. Water quality variables were largely driven by the hydrological regime specific to each Lagoon. Nutrient enrichment and, particularly for Lake Manzala, sea level rise threaten the sustainability of the planktonic ecosystems in all three Lagoons.
OS Petersen - One of the best experts on this subject based on the ideXlab platform.
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Hydrological characteristics of three North African coastal Lagoons: insights from the MELMARINA project
HYDROBIOLOGIA, 2009Co-Authors: OS PetersenAbstract:Hydrological and hydrodynamic characteristics are important controls in all wetlands including coastal Lagoons. Enhanced understanding of Lagoon functioning can be obtained through the acquisition and interpretation of hydrological, meteorological and related data. The MELMARINA Project investigated links between hydrological and ecological conditions within North African coastal Lagoons. It employed three primary sites: Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. Hydrological, meteorological and related data were acquired for these Lagoons. Data included precipitation, evaporation, wind speed and direction, freshwater discharges into the Lagoons, tides beyond the Lagoons in the open sea, Lagoon bathymetry and time series of Lagoon water levels/depths. Data were acquired from secondary sources (including online archives) and targeted field survey and monitoring programmes. Interpretation of these data provides insights into the hydrological functioning of the Lagoons and contributed to the modelling requirements of MELMARINA. The functioning of Merja Zerga is dominated by the exchange of water between the Atlantic and the Lagoon. Large, tidally induced oscillations in water level are responsible for the inundation of extensive inter-tidal mudflats whilst the rapid replacement of water by exchanges with the sea diminishes the influence of freshwater inflows and winter rainfall. The smaller Mediterranean tides reduce the magnitude of Lagoon-sea exchanges and result in much smaller water level oscillations within Ghar El Melh. As a result, this Lagoon lacks the inter-tidal environments found within the Moroccan site and hydrodynamic conditions are more likely influenced by wind set up. Although freshwater inflows to Ghar El Melh are smaller than those in Merja Zerga, their effects, coupled with heavy winter rainfall, can persist due to longer residence times of water within the Lagoon. Freshwater inflows are central to the functioning of Lake Manzala. Large discharges of relatively freshwater are provided by major drains which cross the Nile Delta. These influence lake water levels and are responsible for the freshwater conditions within large parts of the lake. The small tidal range of the eastern Mediterranean, coupled with constricted connections with the sea, reduces the influence of lake-sea exchanges and tidally induced water level oscillations within Lake Manzala.
Patricia Prado - One of the best experts on this subject based on the ideXlab platform.
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influence of salinity regime on the food web structure and feeding ecology of fish species from mediterranean coastal Lagoons
Estuarine Coastal and Shelf Science, 2014Co-Authors: Patricia Prado, Carolina Vergara, Nuno Caiola, Carles IbanezAbstract:Abstract Dual δ 15 N and δ 13 C analyses and estimates of biomass were used to characterize the food webs of valuable fish species in three coastal Lagoons of the Ebro Delta subjected to contrasting salinity regimes (polyhaline in the Tancada Lagoon, mesohaline in the Encanyissada and oligohaline in the Clot Lagoon). The δ 13 C signatures of the entire food-web including primary producers, sediment organic matter and consumers showed the most enriched values in the Tancada Lagoon (from approx. −4.8‰ in sediments to −19.7‰ in fish) and the most depleted ones in the Clot Lagoon (from approx. −11.4‰ in sediments to −25.4‰ in fish), consistent with dominant contributions from marine and continental sources, respectively. For δ 15 N, particularly high values were detected in the submersed vegetation (11.3 ± 0.3‰) together with more enriched sediment values at lower salinities (by approx. 2.5‰), suggesting that historical loadings of agricultural fertilizers are still retained by the systems and transmitted across trophic levels. Negative relationships between δ 15 N and salinity were also observed for the amphipod Gammarus aequicauda and the isopod Sphaeroma hookeri , suggesting some consumption of accumulated and resuspended detrital material. In contrast, δ 15 N signatures of fish showed lower values and inconsistent patterns, possibly because most species have a seasonal use of the Lagoons. The biomass of fish species did not show a clear effect of the salinity regime (except for the mosquitofish Gambusia holbrookii ), but results for mixing models suggest a diet shift from higher contribution of zooplankton size fractions in the Encanyissada (from 57 to 73%) to macrofauna at the other Lagoons (from 40 to 67%). We suggest that alterations in salinity might modify the trophic dynamics of the systems from benthic to planktonic pathways, without large-scale differences in δ 15 N of fish suggestive of similar trophic levels.
B G Thom - One of the best experts on this subject based on the ideXlab platform.
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morphometric assessment of intermittently open closed coastal Lagoons in new south wales australia
Estuarine Coastal and Shelf Science, 2006Co-Authors: P E Haines, Rodger Benson Tomlinson, B G ThomAbstract:Abstract This paper provides a framework for the assessment of the natural sensitivity of coastal Lagoons to anthropogenic and other external inputs. The assessment framework is based on analysis and consideration of morphometric characteristics, and is demonstrated in this paper using eight example intermittently open coastal Lagoons from New South Wales, Australia. The framework presented extends to a rudimentary classification of the eight example coastal Lagoons, relative to the other 70 or so intermittently open coastal Lagoons in NSW, which can be used to provide an indication of the relative importance of these Lagoons with respect to future management, such as remediation or conservation. Morphometry describes the physical geographic characteristics of waterways such as coastal Lagoons. Morphometric parameters are relatively easy to determine, as they essentially describe the physical and topographic features of waterways. Morphometry therefore provides a simple means to define the natural sensitivity, or vulnerability, of individual systems to external loads and other artificial (primarily anthropogenic) modifications. Morphometric parameters, such as waterway area, waterway volume, waterway shape and the proportion of time that the entrance is either open or closed to the ocean, have been used to define three separate factors that each measures one aspect of the natural sensitivity, or vulnerability, of a coastal Lagoon to external loads and other inputs. The first factor (called the Evacuation Factor) is a measure of how efficiently a coastal Lagoon can remove pollutants and other inputs through tidal flushing (i.e. the tidal flushing efficiency). The second factor (called the Dilution Factor) is a measure of the relative difference between the input loads from the catchment and the resident volume of the coastal Lagoon. The third factor (called the Assimilation Factor) is a measure of the water level variability in a coastal Lagoon, which can subsequently influence the extent and diversity of biological processes and their capacity to assimilate or accommodate external inputs. The morphometric-based assessment and classification framework presented in this paper could be applied to any country that contains a series of similar coastal Lagoons that have intermittent connections to the ocean and which requires a relative assessment for prioritisation of future management and planning.
