Living in the front: Neomysis americana (Mysidacea) in the Río de la Plata estuary, Argentina-Uruguay

The Río de la Plata is one of the main estuarine systems of South America. It is characterized by a salt wedge regime, a well-developed bottom salinity front, and a maximum turbidity zone associated with it. We described, for the first time, the spatial distributional patterns of Neomysis americana, the most abundant mysid and the main food item for juvenile fishes in this estuary. We analyzed the link between mysid distribution and abundance and the bottom salinity gradient. A total of 242 plankton samples were taken from the Río de la Plata estuary in spring and fall between 1991 and 2001. Bottom salinity gradient was quantified from grids created on the basis of 348 oceanographic stations. The N. americana population was characterized by high abundances (up to 2500 ind. m⁻³), with juveniles, males, gravid and non-gravid females present in both spring and fall of different years. N. americana distribution followed the position of the bottom salinity front in different years and seasons. Pearson’s correlation analysis between mysid abundance and bottom salinity gradient confirmed the association of mysids with the bottom salinity front (maximum salinity gradient). No correlation was detected between mysid abundance and salinity per se or temperature (neither in spring nor in fall). We speculate that mysids concentrated at the front could take advantage of the high concentration of detrital material for feeding. The results of our work highlight the importance of the magnitude of salinity gradient for the ecological processes of a salt-wedge estuary like the Río de la Plata. The analysis of the spatial distribution of gradient values presented in this work also constitutes a useful tool to locate key ecological areas such as fronts.     

Horizontal transport,mixing and retention in a large,shallow estuary: Río de la Plata

We use field data and a high-resolution three-dimensional (3D) hydrodynamic numerical model to investigate the horizontal transport and dispersion characteristics in the upper reaches of the shallow Río de la Plata estuary, located between the Argentinean and Uruguayan coasts, with the objective of relating the mixing characteristics to the likelihood of algal bloom formation. The 3D hydrodynamic model was validated with an extensive field experiment including both, synoptic profiling and in situ data, and then used to quantify the geographic variability of the local residence time and rate of dispersion. We show that during a high inflow regime, the aquatic environment near the Uruguayan coast, stretching almost to the middle of the estuary, had short residence time and horizontal dispersion coefficient of around 77 \(\mathrm {m}^{2}\,\mathrm {s}^{-1}\) , compared to the conditions along the Argentinean coastal regime where the residence time was much longer and the dispersion coefficient (40 \(\mathrm {m}^{2}\,\mathrm {s}^{-1}\) ) much smaller, making the Argentinian coastal margin more susceptible for algae blooms.     

Seasonal changes of benthic megafauna in the Ría de Muros e Noia (Galicia,North-West Spain)

A community of decapod crustaceans (Brachyura) was sampled seasonally (October 1978–July 1979) from three habitats (raft, middle and beach) in the Ría de Muros e Noia (North-West Spain), with the purpose of studying spatial and temporal changes in the community and comparing with communities in the neighbouring Ría de Arousa, which supports an intense mussel (Mytilus edulis)-raft culture. The Portunidae family dominated the decapod community. Polybius henslowi, a species with pelagic stages, which enters the rías periodically in large numbers, was the dominant species at all the stations throughout the sampling period, attaining densities of 1.6 individuals m^-2 (18.7 g wet wt m^-2) in summer. Macropipus depurator and M. puber were the next most important species at the raft station, M. depurator at middle stations, and M. vernalis and Carcinus maenas at beach stations. The highest population densities were recorded in summer, due to the great abundance of Polybius henslowi at this time. When the data were reconsidered omitting p. henslowi, highest densities were in autumn and winter in the inner ría. In general, the nature of the substratum, the presence of mussel rafts, depth and salinity were the main factors determining the structure of the community. Density and biomass in the Ría de Muros e Noia (P. henslowi omitted) were lower than in the Ría de Arousa (up to six times lower in some areas). The Ría de Muros lacks the extensive number of mussel rafts present in the Ría de Arousa which constitute an important food resource for decapods.     

Fluxes and Transport of Organic Carbon and Trace Metals in the Tropical Tsengwen Estuary,Southwestern Taiwan

Distributions of organic carbon and trace metals were investigated in the tropical Tsengwen river end-member and in the estuary to better understand thoroughly the riverine fluxes and estuarine transports of constituents into the sea. Experimental results indicated that riverine fluxes of organic carbon and trace metals possessed a highly temporal variability, attributed primarily to temporal variation in river water discharge and suspended load. More than 70% of annual fluxes of dissolved constituents and >90% of particulate constituents arose from river floods caused by summer typhoons. the flushing time of fresh water in the estuary varied from a half month in the dry season to a half day in the flood period. Dissolved organic carbon (DOC) and nutrienttype metals (Cd, Cu, Zn) were conservatively transported through the estuary. Dissolved particle-reactive metals (Mn, Pb), however, were apparently transported non-conservatively through the estuary. Particulate organic carbon (POC) and trace metals (PTM) were transported non-conservatively by following the transport mode of total suspended matter (TSM) in the estuary. DOC slightly dominates the transport of organic carbon while particle-reactive PTM predominates the transport of trace metals through the estuary. Total organic carbon (TOC) in estuarine sediment was progressively enriched with ¹³C downstream, as derived by mixing the overlying TSM between terrestrial and marine end-members. Distributions of trace metals in sediment were subsequently controlled by sedimentary TOC and particle size. Based on results presented here, we believe that enrichments of trace metals in the estuary are attributed primarily to the natural processes of transport and sedimentation of fluvial TSM     

Evidence of in situ diel vertical migration of a red-tide microplankton species in Ría de Vigo (NW Spain)

The migration capacity of red-tide species in the natural environment was studied at a station in the Ría de Vigo (Rías Bajas, NW Spain) over a 24 h period in September 1991. The Ría de Vigo, where red tides are frequent, normally shows a positive estuarine circulation and is subjected to seasonal upwelling and downwelling phenomena. A marked diel pattern was observed for five species that are capable of causing red tides (Ceratium furca, Scrippsiella trochoidea, Dinophysis acuminata, Mesodinium rubrum, and Eutreptiella sp.). Such diel behaviour could be clearly advantageous in a stratified environment where light and nutrients are often in two separate layers. Active movement enables species such as dinoflagellates and some ciliates to exploit high levels of irradiance at the surface during the day and to take up nutrients in deeper layers at night. Patchy distribution of phytoplankton, shear-induced horizontal dispersion and density variations were considered, but none of them accounted for the vertical changes observed. Vertical migration is thought to be one of the mechanisms that could promote blooms in nutrient-depleted surface layers.     

Macrozoobenthic community structure in the Ría de Foz,an intertidal estuary (Galicia,Northwest Spain)

The community structure of the macrobenthic (>1 mm) fauna of an intertidal soft-bottom estuary, the Ría de Foz (Galicia, Northwest Spain) was investigated on 99 occasions during June, September and December 1984 and March 1985. The infaunal data were subjected to classification and ordination techniques. The analyses indicated that sediment characteristics (grain size, percentage silt-clay and organic-matter content) and tidal height are the most important factors governing the distribution and abundance of the intertidal communities. Three faunal assemblages were identified and examined in terms of species dominance, constancy and fidelity. In the clean sands of the outer estuary two main assemblages were distinguished; one, corresponding to the boreal LusitanianTellina community, inhabited the middle and lower tidal levels; the other, typical of a biocoenosis of sands and slightly muddy mediolittoral sands, inhabited the upper tidal level. The third benthic assemblage occupied the muddy sands and mud of the inner estuary and displayed some features in common with theCardium edule-Scrobicularia community described by Thorson.     

A novelty coastal susceptibility assessment method: application to Valdelagrana area (SW Spain)

The main aim of this paper is to present a new methodology to determine coastal susceptibility to erosion and flooding processes by means of an index-based method. The proposed indices take into account physical parameters, such as dune and beach geomorphologic characteristics, shoreline evolution, local significant wave height and relative run-up. The coastal susceptibility has been estimated by elaboration of spatial input data into a GIS environment. The method has been tested in Valdelagrana area, a sandy spit located in SW Spain. The spit includes several morpho-sedimentary environments: sandy beach, discontinuous embryo dunes and foredunes, mud flats and wide areas of vegetated salt marshes. The Northernmost sector is densely urbanized whilst the rest is part of a natural protected area belonging to the Bahía de Cádiz Natural Park. The results obtained showed how the Southern part of the spit presented a high susceptibility due to an elevated erosion rate and the presence of low and discontinuous dune ridges.     

不同地貌类型区自然村落生态系统的比较分析

本文运用调查方法,定量分析不同地貌类型区(山区丘陵、山前平原、低平原和滨海平原)表征村落生态系统结构和功能的几个指标的变化。结果表明:1.平原地带的庭院面积大于丘陵山区,主要是由于地形及土地利用政策的影响;2.庭院经济收入取决于庭院面积与经营程度;3.村落规模、密度的变化与农田生产力变化一致;4.适当增加村落密度,控制村落规模,有利于缩短耕作半径,提高劳动生产率。     

Distribution of the soft-bottom macroinfauna in an estuary of Southern Chile

In April 1981, a quantitative survey (20 stations) of the soft-bottom macroinfauna of the littoral and sublittoral was conducted in a Southern Chilean estuary. A principal component analysis rendered three groups of stations with different substrate conditions. A total of 16 775 animals was collected (40 taxa), with Oligochaeta, Polychaeta and Ostracoda representing 83% of the individuals. Most of the biomass was attributed to Bivalvia (43.7%) and Polychaeta (33.6%). Factor analysis using abundance data of the 21 most abundant taxa rendered three groups of stations in the Q-mode (a cluster analysis rendered 4) and three groups of taxa in the R-mode. One group mainly inhabited the sandy outlet area of the estuary where salinity was highest. Another group of organisms was mainly found in the upper zone of the estuary where salinity was low and the substrate was muddy. The third group was principally distributed in the central part of the estuary and spread from there either to the outlet area or to the upper zone. Some ungrouped taxa were distributed relatively homogeneously within the estuary. It was found that besides substrate properties salinity and turbulence also played an important role in the distribution of organisms in the Río Lingue Estuary.     

Bioavailability and accumulation of trace elements in soils and plants of a highly contaminated estuary (Domingo Rubio tidal channel,SW Spain)

The Domingo Rubio tidal channel (Palos de la Frontera, Huelva, Spain) is an estuary located in the mouth of the Tinto River. The estuary is affected by different sources of pollution (waters of the Tinto River, contaminated with trace elements from the Iberian Pyrite belt, and effluent from the Huelva chemical industrial area). Soil and the most frequent plant species were collected in 2004 and 2006 at six different locations on the estuary. In general, N-Kjedahl, Total Organic Carbon values, salinity and contamination (total trace elements up to 1,000 mg kg⁻¹ As, 6 mg kg⁻¹ Cd, 2,500 mg kg⁻¹ Cu, 1,900 mg kg⁻¹ Pb and 1,300 mg kg⁻¹ Zn) tended to increase downstream of the tidal channel. Soil biochemical properties were not negatively affected either by the high salinity or by trace element contamination. Despite the high values of the trace elements, analysed plant samples showed that Cu was the only metal that could be a serious risk for the food chain.     

Spatial distribution of the infaunal benthic communities of the Ría de Muros,north-west Spain

Benthic samples were collected at 13 stations in the Ría de Muros, north-west Spain. There are three major communities: (1) in the southern and outer part of the ría, an Amphiura filiformis—Thyone fusus community, inhabiting sandy sediments with low organic content; (2) in the middle part of the ría, and Amphiura chiajei—Maldane glebifex community, inhabiting muddy sediments that are not anoxic (sulphide not detected); (3) in Muros Bay and the inner part of the ría, a Spiochaetopterus costarum community, inhabiting anoxic sediments with high organic content. Biomass is very high (up to 46.2 g ash-free dry wt) in the first two communities. In the Spiochaetopterus costarum community, biomass and diversity are much lower, probably because of oxygen deficiency.     

Influence of mussel rafts on spatial and seasonal abundance of crabs in the Ría de Arousa,North-West Spain

The crab community in the Ría de Arousa, North-West Spain, was studied for 2 yr (1974–1975; 1975–1976), firstly to detect any differences due to mussel (Mytilus edulis) raft aquaculture; secondly to study temporal changes in spatial distributions in beach, raft and non-raft areas throughout the ría. Portunid crabs dominated the fauna, the dominant species being Macropipus puber and M. depurator in the raft areas, M. depurator in non-raft subtidal areas, and M. arcuatus in beach stations. No substantial seasonal changes were observed in species composition throughout the ría. In general, the highest densities occurred in fall and winter. Raft stations showed the highest values of abundance, up to 0.47 individual per m², and 8.20 g wet wt m^-2. The food resource provided by the rich epifauna associated with the mussel rafts, and changes in the sediment due to shell deposits could account for the high density values in raft areas. Raft areas (polygons) cover about 10% of the surface of the Ría de Arousa and, thus, the raft aquaculture of mussels significantly increases crab production.     

Ultrastructural changes in the gill epithelium of the crab Chasmagnathus granulatus (Decapoda: Grapsidae) in diluted and concentrated seawater

Chasmagnathus granulatus Dana, 1851 is an intertidal estuarine crab that experiences acute salinity changes ranging from <1‰ to full-strength seawater and even hypersaline waters in tide pools concentrated by evaporation. Ultrastructural changes induced by salinity in the posterior gills were examined in crabs collected from the Rio de la Plata estuary Argentina during March 1999. The posterior gills of C. granulatus are involved both in ion uptake and ion secretion depending on the acclimation medium. These organs are mostly lined with a thick tissue, which presents the characteristics of a typical salt-transporting epithelium. Electron microscopy analysis of gill tissue from crabs acclimated to dilute, full, and concentrated seawater (12‰, 34‰, and 45‰ salinity) showed significant development of basolateral membrane interdigitations, with numerous mitochondria and conspicuous apical membrane infoldings. Morphometrical analysis indicated that the subcuticular space delimited by the infolding of the apical membrane was significantly increased in the gills of high-salinity acclimated crabs. Septate junctions, which are thought to define the paracellular permeability, were significantly shorter in high-salinity acclimated crabs, suggesting a possible role of the paracellular pathway in salt secretion.     

Global Effects of Local Human Population Density and Distance to Markets on the Condition of Coral Reef Fisheries

Coral reef fisheries support the livelihoods of millions of people but have been severely and negatively affected by anthropogenic activities. We conducted a systematic review of published data on the biomass of coral reef fishes to explore how the condition of reef fisheries is related to the density of local human populations, proximity of the reef to markets, and key environmental variables (including broad geomorphologic reef type, reef area, and net productivity). When only population density and environmental covariates were considered, high variability in fisheries conditions at low human population densities resulted in relatively weak explanatory models. The presence or absence of human settlements, habitat type, and distance to fish markets provided a much stronger explanatory model for the condition of reef fisheries. Fish biomass remained relatively low within 14 km of markets, then biomass increased exponentially as distance from reefs to markets increased. Our results suggest the need for an increased science and policy focus on markets as both a key driver of the condition of reef fisheries and a potential source of solutions. Efectos Globales de la Densidad de Población Humana Local y la Distancia a los Mercados sobre la Condición de Pesquerías en Arrecifes de Coral     

Phylogeography of the Southwestern Atlantic menhaden genus <Emphasis Type="Italic">Brevoortia</Emphasis> (Clupeidae,Alosinae)

Among pelagic fish, the Southwestern Atlantic menhaden genus Brevoortia (Clupeidae, Alosinae) constitutes an important species model to investigate the patterns of genetic differentiation. It is abundant in the Río de la Plata estuary and in the Atlantic coastal lagoons system from Uruguay and Southern Brazil. To access in the taxa discrimination and population structure in Brevoortia we perform a phylogeographic approach based on mitochondrial cytochrome b (cyt-b) sequences including 240 individuals from 16 collecting sites. Among the 720 bp cyt-b sequenced, 199 correspond to variables and 88 to phylogenetically informative sites. High values of haplotype diversity (h = 1.000) and nucleotide diversity (π = 0.061), as well as an average of 0.084 polymorphic segregating sites and 46 different haplotypes were found. Maximum likelihood analysis based on the GTR + I + G model and Bayesian inference strongly support the idea that B. aurea is the only species of the genus inhabiting the Southwestern Atlantic region. Our analyses revealed a complex population pattern characterized by the existence of long-term highly structured genetic assemblages of mixed stocks. Each monophyletic entity included individuals from different collecting sites, different age groups and collected in different years. Our data also suggest that the recruitment of unrelated mtDNA haplotypes carried out by individuals within schools could be occurring in the same nursery areas revealing the existence of many different maternal lineages. A scenario where different simultaneously and successively mixed mtDNA lineages remain historically connected through basal haplotypes among different clades could explains more accurately the complex and ordered metapopulation dynamic found in this pelagic fish.     

太湖典型入湖河道中氨氮去除研究

入湖河流是湖泊营养物质的一个重要来源,因此入湖河道水质的改善是控制湖泊富营养化的关键。文章采用自行研制的新型仿生填料直接布设在河道内的生物接触氧化法,在不影响河流生态结构和原有使用功能的前提下,对河流微污染水体进行氨氮的去除研究。研究结果显示,氨氮的净去除率在5.35%~39.91%,其中最高为7月的39.91%,最低月为12月的5.35%。试验期间生物膜的平均厚度为0.8~1.1mm(雨后略厚),生物膜内的微生物主要是一些贫营养微生物,数量少,因此形成的生物膜较薄,生物膜由表及里几乎全是好气层。同时,根据氨氮去除率与硝化菌的数量关系也可以看出试验河段内氨氮的去除主要是靠硝化菌的硝化作用来完成的。     

Trace metals in the coastal soils developed from estuarine floodplain sediments in the Croatian Mediterranean region

Fertile soils in the River Neretva estuary were developed by fluvial sedimentation and deposition of the eroded soil material from the karst hills within the catchment. After extensive reclamation, two reclaimed land zones (fluvial terraces and lower-laying terraces) have been delineated, both used for agriculture. The main objectives of this study were to evaluate soil chemical and geochemical properties in reclaimed zones that differ mainly in topography, soil types and agricultural land use. The origin of the trace metals in the arable soils was studied using multivariate statistics, and interpolation maps of trace metals were produced using GIS and geostatistics. Soil trace metal concentrations do not exceed a threshold value established by the Croatian Government regulation, with exception of copper. Comparative analysis of the main soil properties and trace metal concentrations in the study area showed a pronounced spatial variation and differences between two reclaimed zones in soil organic matter content, bioavailable P and total concentrations of Cd and Cu. Factor analysis in the area of the lower-laying terraces showed grouping of bioavailable P and K, organic matter content and pH (negative loading) in the component associated mostly with the land use. In the area of the fluvial terraces, bioavailable P and total Cd were grouped in the same component that may be explained by the traditional small farm agriculture and overuse of mineral fertilizers. In the whole study area, processes of secondary salinization were determined, accompanied by the raised chloride and sodium concentration measured in the saturation soil extract.     

Assessing stream restoration effectiveness at reducing nitrogen export to downstream waters

The degradation of headwater streams is common in urbanized coastal areas, and the role these streams play in contributing to downstream pollution is a concern among natural resource managers and policy makers. Thus, many urban stream restoration efforts are increasingly focused on reducing the downstream flux of pollutants. In regions that suffer from coastal eutrophication, it is unclear whether stream restoration does in fact reduce nitrogen (N) flux to downstream waters and, if so, by how much and at what cost. In this paper, we evaluate whether stream restoration implemented to improve water quality of urban and suburban streams in the Chesapeake Bay region, USA, is effective at reducing the export of N in stream flow to downstream waters. We assessed the effectiveness of restored streams positioned in the upland vs. lowland regions of Coastal Plain watershed during both average and stormflow conditions. We found that, during periods of low discharge, lowland streams that receive minor N inputs from groundwater or bank seepage reduced in-stream N fluxes. Furthermore, lowland streams with the highest N concentrations and lowest discharge were the most effective. During periods of high flow, only those restoration projects that converted lowland streams to stream-wetland complexes seemed to be effective at reducing N fluxes, presumably because the design promoted the spillover of stream flow onto adjacent floodplains and wetlands. The observed N-removal rates were relatively high for stream ecosystems, and on the order of 5% of the inputs to the watershed. The dominant forms of N entering restored reaches varied during low and high flows, indicating that N uptake and retention were controlled by distinctive processes during different hydrological conditions. Therefore, in order for stream restoration to effectively reduce N fluxes exported to downstream waters, restoration design should include features that enhance the processing and retention of different forms of N, and for a wide range of flow conditions. The use of strategic designs that match the dominant attributes of a stream such as position in the watershed, influence of groundwater, dominant flow conditions, and N concentrations is crucial to assure the success of restoration.     

Distribution of selected elements and PAH in freshly deposited sediments of waste water streams from Lubin district, Southwest Poland

Nine selected elements (Cu, Pb, As, Zn, Co, Ni, Cr, Cd and Fe) were determined by inductively coupled plasma atomic emission spectroscopy in 15 samples from the tailings pond (Zelazny Most) and waste water streams (Moskorzynke and Rudna) in the Kupferschiefer mining district in Southwest Poland. Waste water from mining and industry enter the Zelazny Most pond. The water then flows through Moskorzynke and Rudna streams, and discharges into the River Odra. The analytic results indicate that the contamination with Cu, Pb, Zn, As, Co, Cd and Fe extend about 6km along the streams in contrast to the nonpolluted samples close the River Odra. Their concentrations reach a level, which could be toxic for plants, animals and humans. The contamination with Ni and Cr continued at least 20km along Rudna stream. Besides mechanical transport, redox conditions and C_org contents also played an important role for trace element and Fe contamination in Rudna stream. The samples with high C_org contents have also high contents of trace metals. In Moskorzynke stream the element contamination was mainly caused by mechanical transport of particles. Polyaromatic hydrocarbon (PAH), which is abundant in Kupferschiefer, is toxic for animals and humans. The PAH concentration in the stream sediments was determined by GC and GC/MS. The results indicate that the contamination of PAH reaches 6 and 17mgkg_–1 in samples TP1 and RS6, respectively. In the other samples, the PAH contents are lower than 3mgkg_–1. Some PAH could be solved by waste water in the tailings pond and migrated to the stream sediments. Some PAH might be contained in particles which were transported mechanically from the tailings pond into stream sediments.     

Diet of intertidal bivalves in the Ría de Arosa (NW Spain): evidence from stable C and N isotope analysis

We used natural abundance measurements of stable carbon and nitrogen isotopes and a short-term ¹⁵N-enrichment experiment to explore the importance of river-derived and autochthonous sources to the diet of intertidal suspension-feeding bivalves in the Ría de Arosa, an oceanic-dominated system in northwest Spain. Highly seasonal and intense phytoplankton "bloom" events occur in this estuary. However, relatively low phytoplankton standing crop and productivity are present during much of the year, suggesting that food sources other than phytoplankton must support bivalves during these periods. Bivalves (Cerastoderma edule, Tapes decussatus, Mytilus galloprovincialis) were sampled quarterly at four intertidal stations along the length of the estuary with increasing distance from the Ulla River. Muscle tissue was consistently enriched in ¹³C and ¹⁵N relative to stomach contents. The stable C isotope values of bivalves indicated that river-derived inputs were, at most, a minor component of diet. These values suggested the potential importance of benthic microalgae to bivalve diet much of the year and the incorporation of ¹⁵N label applied to the sediment surface into stomach contents and muscle tissue in a field experiment supported this conclusion. Other labeled components of the microbenthos such as bacteria could also have been ingested. ¹³C-depleted values of bivalves in May coincided with elevated offshore chlorophyll a concentrations, suggesting the increased use of a phytoplankton source during the spring. We propose that intertidal suspension-feeding bivalves in this estuary use primarily resuspended microbenthos during periods of low phytoplankton concentration, but that phytoplankton increases in relative dietary importance during bloom events.Communicated by P.W. Sammarco, Chauvin