Meiofauna comprises small benthic metazoans that play a crucial role in aquatic ecosystems and reflect the ecological condition of marine, estuarine, and freshwater environments. In this study, intertidal meiobenthic communities were examined across three coastal environment types along the Uruguayan coast (freshwater, estuarine, and oceanic), and the influence of anthropogenic impact on biodiversity and community structure was evaluated. Three pairs of dissipative sandy beaches were sampled (one impacted and one less impacted per environment type), and the main meiobenthic taxa were quantified and richness, Shannon diversity, Pielou's evenness, total abundance, and nematode abundance were calculated. Physicochemical water variables (dissolved oxygen and pH) and sediment characteristics (mean grain size and organic matter content) were also measured. Generalized linear models showed that biodiversity indices were significantly associated with sediment properties and water parameters, with richness and abundance increasing in finer sediments and with higher organic matter content, and diversity and evenness decreasing under higher organic enrichment. Dissolved oxygen was positively related to richness, Shannon exponential diversity, and evenness. Nematodes, copepods, gastrotrichs, turbellarians, and nauplii dominated the assemblages, with nematodes being the most abundant group overall. Multivariate analyses (NMDS based on Bray-Curtis dissimilarities, PERMANOVA, and beta-dispersion) revealed a clear structuring of communities according to environmental type and the level of anthropogenic impact. In particular, less impacted beaches exhibited a more homogeneous community composition (lower dispersion), whereas impacted beaches showed greater heterogeneity (higher dispersion), reflecting increased variability in composition among their samples. Indicator value analysis identified taxa associated with specific environments and impact levels. Overall, these results highlight that meiobenthic disturbance, supporting the use of meiofauna as a sensitive tool for coastal ecosystem assessment.

This study examined meiofaunal communities inhabiting sandy beaches, one of the least explored components of marine ecosystems. These organisms occupy the interstitial environment, a habitat highly vulnerable to urban-driven changes and fundamental to multiple ecosystem functions and services in sandy beach systems. The main objective was to assess changes in community structure along the intertidal zones of beaches in the Río de la Plata estuary subjected to different degrees of urbanization. Specifically, the study aimed to characterize meiofaunal assemblages across an urbanization gradient, evaluate correlations with environmental variables, examine seasonal variation, and identify key anthropogenic drivers. Systematic sampling was conducted on six beaches in Montevideo, three located in the urbanized eastern sector and three in the non-urbanized western sector, across seasons and across both upper and lower intertidal zones. The results revealed differences in environmental conditions and community structure between urban and non-urban beaches, including shifts in richness, diversity, and the distribution of dominant and rare taxa. Multivariate analyses confirmed differences in community composition, primarily driven by beach slope, organic matter content, and the degree of urbanization. Urbanization influenced the distribution of meiofaunal taxa, with flatworms and nematodes becoming more dominant on impacted beaches, while tardigrades and crustaceans showed negative responses to urban disturbance. Acari and Cnidaria were exclusive to urban beaches. Overall, the study demonstrates that urbanization alters meiofaunal communities both directly and indirectly, modifying taxonomic composition and diversity in ways that can compromise the broader network of ecological functions and processes supported by meiofauna in estuarine sandy beaches.

We examined the taxonomical and functional traits of free-living nematodes, focusing on their density by genus, maturity index (MI), and trophic diversity index (ITD) to determine whether these indices are sensitive to changes in the organic content of the sediment. Samples were collected in autumn and spring from 12 subtidal sampling stations in Rocha Lagoon, distributed between the outer (near the mouth) and the inner sector. We identified 26 genera, with higher abundance in the inner sector, likely due to increased organic matter and biopolymers. In spring, both sectors had sediments rich in fresh organic matter, dominated by deposit-feeding nematodes and showing low trophic diversity (high ITD values). In autumn, the inner sector maintained similar characteristics to spring sampling, while the outer one was dominated by older organic matter, predatory nematodes and higher trophic diversity. The MI showed low variation between sectors, suggesting a disturbed environment. Our findings support the use of ITD to assess other aspects of communities such as the response of trophic groups to the freshness of organic matter, while the MI seems less effective for assessing the ecological status of Rocha Lagoon. Understanding nematode biodiversity and functional traits is crucial for effective ecological quality assessments.

Understand the origin, transport, and character of organic matter entering Antarctic fjords is essential as they are major components of the global carbon cycle and budget. Macromolecular pools of particulate organic matter, bulk organic geochemistry, major and trace elements in surface sediments from Collins Bay were analysed as source indicators. Oceanographic conditions, bathymetry (multibeam) and grain size were considered as environmental controlling factors. Sediment samples were taken with a van Veen grab, during the ANTAR XXV Peruvian expedition (February 2018), onboard the R/V "BAP Carrasco" from the Peruvian Navy. Biopolymeric composition revealed the predominance of fresh marine protein-rich organic matter in the seafloor of Collins Bay, denoting high quality food resource for marine benthic heterotrophs. Based on Igeo values (between 0 and 1) Collins Bay can be considered unpolluted with natural levels of As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Distribution of most of these elements with a gradient of decrease from the shallow inner fjord towards the outer deepest fjord, suggest their association with the deposition of detrital material and lithogenic particles supplied by Collins Glacier frontal ablation and runoff. This first comprehensive baseline information would assist in interpreting downcore sedimentary reconstructions and future climate-induce changes.

The functional structure of the macrobenthos present in two morphologically different estuarine systems (coastal lagoons and estuaries) was studied. The objective was to determine differences between the predominant functional traits of both systems. Macrobenthos were classified into functional traits through the use of the Biological Trait Analysis (BTA). Given the scale-dependence of the macrobenthos, it was sampled in winter and spring at three spatial scales: habitat (streams, lagoons), habitat sectors (internal, external), and replicate sites (three in each sector). Two hypotheses were tested: (1) the geomorphology of the water body would determine the presence of functional traits and (2) the trophic state of the environment would condition the functional traits. Both hypotheses were true for most of the sites. As a result, it was observed that higher temperatures and finer sediments conditioned the presence of more degraded organic matter and with lower nutritional value in April, lagoons, and internal sectors. This conditioned the presence of surface depositivorous, epifaunal and first and second order opportunistic, typical characteristic of sites disturbed by nutrients. On the contrary, in October, estuaries and external sectors were characterized by filter feeders, infaunal, and organism's sensitive to organic enrichment, typical of undisturbed sites.

Chromadoridae is a widespread family of mostly free-living marine nematodes. This systematic review provides for each genus: a historical background, an updated diagnosis and a list of species. Our review recognizes 37 valid genera, 395 valid species, 57 descriptions without enough morphological information for accurate identification (species inquirenda) and 10 species incerta sedis. We also recognize 21 species as nomena nuda. Additionally, polytomous keys were constructed for the subfamilies and for the genera of the three major subfamilies (Chromadorinae, Euchromadorinae and Hypodontolaiminae) using the most important diagnostic characters. A phylogenetic analysis based on rDNA sequences of species available in the GenBank was also conducted. Phylogenetic trees based on the 18S and 28S rDNA confirmed the classification into three subfamilies (Spilipherinae, Hypodontolaiminae and Chromadorinae), despite the absence of defined synapomorphies. Phylogenetic relationships at lower taxonomic level are problematic given the large number of sequences not identified to species level.

The concentration and pollution level of heavy metals and As in surface sediments from Montevideo coastal zone (Río de la Plata estuary) were measured in 18 sites in March 2015, ranging from the western portion at the mouth of Santa Lucía river to the east at the mouth of Carrasco stream. The study area receives a continuous discharge of untreated domestic and industrial effluents through two streams and one submarine sewage pipe. Sediments were analysed for sediment fractions, organic matter content and heavy metal and As concentrations (As, Cd, Cr, Cu, Ni, Pb, Zn, Sc, Al, Fe and Mn). Results showed that in the study area the contribution of sand was low, with exception of the innermost region of Montevideo Bay at the mouth of Miguelete and Pantanoso streams. Total organic matter contents were in general high (ranged between 3.82 and 15.72%), and values are typical for estuarine, low energy and anthropized ecosystems. Concentrations in a descending order was Zn>Cr>Cu>Pb>Ni>As>Sc>Cd and highest concentrations were found in the innermost stations of the bay, while lower in the western portion of the study area. Pearson correlation and principal component analysis suggest the similar distinctiveness of Cr, Cu, Pb and Zn. The different indices applied suggest that the study area can be considered from low to mildly polluted by metals in general, and compared with previous results all the studied metals showed marked reductions, highlighting the importance of management measures. In this sense, efforts made by the government and industries some years ago apparently had positive results in terms of reclamation/reduction of particular metallic elements.

An evaluation of the concentration of metals in terrestrial and aquatic environments near Artigas Antarctic Scientific Base was assessed. Granulometric characteristics, total organic matter content, concentration of metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) and metalloid (As) in soil, marine and freshwater sediments were determined. The geoaccumulation index (Igeo) was used in order to analyse the contamination magnitude. Samples were collected in summer 2015–2016 covering 31 sampling stations; 15 terrestrial/soil stations (T0–T14) were placed considering the distribution of Artigas Base buildings and the septic tanks’ location. Eleven freshwater stations were placed along the three meltwater streams near Artigas Base (S0–S10), and two in Uruguay Lake (L1 and L2). Finally, three marine stations in Maxwell Bay were placed one near the Artigas Base (AB) and two far from it in North Cove (NC1, NC2). Some of the terrestrial stations (T2, T10, T11 and T13) presented the highest concentration of metals and Igeo values, which was associated to anthropic activities. Highest metal levels were related to fuel storage and handling, but also, with sewage release and the presence of old leaded paint residues. These polluted sites were limited to a restricted area of Artigas Base, not affecting surrounding environments. Concentrations of the analysed metals in unpolluted sites had the same order of magnitude recorded in other unpolluted areas of the Fildes Peninsula and other Antarctic regions.

Organic enrichment, especially from anthropogenic sources, is one of the current threats to coastal marine biodiversity. Organic enrichment occurs mainly in sheltered soft bottoms, characterized by fine sediments, and results in multiple changes in the benthic habitat, including hypoxia and an increased concentration of compounds that are toxic to marine invertebrates. We report on the results of a microcosm-based experiment (duration = 30 d), quantifying the effects of organic enrichment on taxonomic and functional diversity of nematode assemblages from an open/closed coastal lagoon of South America (Rocha Lagoon, Uruguay). In open/closed lagoons, the input of organic matter becomes a major disturbance due the limitation in water renewal. In our experiment, enrichment led to reductions in abundance, richness and trophic diversity of the nematode assemblage. Rapid reductions in total abundance (after 4 d) were registered, while richness decreased only towards the end of the experiment (similar to 30 d). Trophic changes were characterized by loss of predators/omnivores and dominance of selective deposit-feeders and epigrowth-feeders. By contrast, we did not find any selective effect of enrichment associated with life history traits (e.g. maturity index). Overall, these findings have 2 important implications for the conservation and monitoring of the health of coastal lagoons: first, monitoring of nematode assemblages at the genus level is sufficient to detect enrichment effects; second, an index of trophic diversity would be a good indicator of the effects of enrichment on natural communities.

AbstractAliphatic and polycyclic aromatic hydrocarbons (AHs and PAHs) were investigated in soil and meltwater stream sediments near the Uruguayan Artigas Research Station (BCAA). Gas chromatography with flame ionization detection and gas chromatography mass spectrometry were used to determine the composition of AHs and PAHs, respectively. Total AH concentrations were in the range 0.57–2333 µg g-1, while total PAH concentrations were in the range 1.36–51 650 ng g-1. Based on AH and PAH concentrations, sites in the service area and next to the boat storeroom are highly contaminated, while the other sites sampled have moderate to low contamination levels or are not impacted. High unresolved complex mixture concentrations indicate the occurrence of previous petrogenic contamination, but the dominance of low molecular weight and alkyl PAHs indicate recent oil introductions. Anthropogenic hydrocarbons dominate and are related to diesel fuel and organic residue combustion, fuel storage and boat traffic. Petrogenic contamination is relatively high, as at other Antarctic stations, but is restricted to the boat storeroom and the service area where the incinerator, the generator room and fuel tanks are located. Improvements made in fuel management procedures and the dismantling of the old fuel tanks will reduce the risk of diesel leaks and their impact on the environment near the BCAA. This study provides reference information for future environmental monitoring.

Human activities in the Antarctica including tourism and scientific research have been raised substantially in the last century with the concomitant impact on the Antarctic ecosystems through the release of wastewater mainly from different scientific stations activities. The aim of this study was to assess the wastewater contamination of surface waters and sediments of three melt-water streams (11 sites) by leaking septic tanks located in the vicinity of the Uruguayan Scientific Station in the Fildes Peninsula, King George Island, Antarctica, during summer 2015. For this purpose, we combined the analysis of fecal steroids in sediments by using gas chromatography and six enteric viruses in surface waters by quantitative and qualitative PCR. Coprostanol concentrations (from 0.03 to 3.31μgg-1) and fecal steroids diagnostic ratios indicated that stations C7 and C8 located in the kitchen stream presented sewage contamination. Rotavirus was the only enteric virus detected in five sites with concentration ranging from 1.2×105gcL-1 to 5.1×105gcL-1 being three of them located downstream from the leaking AINA and Kitchen septic tanks. This study shows for the first time the presence of both virological and molecular biomarkers of wastewater pollution in surface waters and sediments of three melt-water streams in the vicinity of a scientific station in the Antarctica. These results highlight the importance of the complementation of these biomarkers in two different matrices (surface waters and sediments) to assess wastewater pollution in an Antarctic environment related to anthropogenic activities in the area.

The benthic trophic status of Uruguayan coastal estuarine habitats (permanently open estuaries and open or closed coastal lagoons) was evaluated, twice in 1 year and at different spatial scales, using the amount and biochemical composition of the sedimentary organic matter. Nested hierarchical ANOVAs were applied to evaluate differences at the habitat level, among sites for each type of estuarine habitat (three estuaries and three lagoons) and between sectors located at different distances from the sea (inner v. outer sectors). Morphological and hydrodynamic differences between the two types of habitats explained site-to-site variations in eutrophic conditions in the open or closed coastal lagoons and meso-oligotrophic conditions in permanently open estuaries. These differences followed the patterns found for sediment grain size, with inner sectors (lower-energy areas) favouring the accumulation of finer sediments and higher amounts of degraded–detrital organic matter. In autumn, biochemical parameters indicated the dominance of aged and more degraded organic matter, with both types of habitats having a low nutritional value no matter which sector was considered. By contrast, in spring, biochemical composition showed the prevalence of fresh and more labile sedimentary organic matter with a high food value, especially in the outer sectors.

The knowledge of the extent of DNA damage in aquatic organisms in polluted areas is an important issue because contamination may alter their health at sublethal levels. Although molluscs have been widely used to monitor water pollution, there are no records of in vivo genotoxicity studies. Heleobia cf. australis, is distributed in almost all Uruguayan coastal ecosystems, including highly polluted sites. The comet assay is a damage genetic biomarker based on the migration of negatively charged DNA fragments produced by mutagenic agents in individual cells. Live individuals were collected in the Montevideo Bay (impacted area) and Laguna Garzon (control) to analyze the presence of mutagenic agents in the former site through comet assay. Cells from organisms of the impacted area showed significantly higher levels of genetic damage than those obtained in the control population, measured by percentage of DNA in the tail. Although preliminary, this approach supports the idea that H. cf. australis could be used as a sentinel to evaluate the presence of mutagenic agents in estuarine environments, alerting to the impact of contamination in its early stages.

This study aimed to determine if estuarine meiofaunal communities of Uruguay (South America) vary between permanently open estuaries and open/closed coastal lagoons, or if they respond to the sediment composition. In Uruguay, estuaries and coastal lagoons vary in the degree of connectivity to the sea and in the sediment composition; sediments in estuaries are characterized by fine-medium sands but sediments vary from lagoon to lagoon (either fine-medium or coarse sand). Taxa richness (total = 16) showed less temporal variability in lagoons than in estuaries, due to patterns of presence/absence of the less abundant taxa. However, no major response to habitat was found in the most abundant groups: polychaetes (6% of total fauna) were on average 5% more abundant in lagoons than in estuaries. Some level of zonation, within estuaries and lagoons, was found in the most abundant groups, nematodes (63% of total fauna) and copepods (15%) in response to medium and fine sands. In addition, sediment type modulated seasonal patterns in the frequency of presence/absence in ostracods, polychaetes and oligochaetes. For instance, in polychaetes and ostracods the increase in the frequency of absences, occurring from summer to winter, was stronger in lagoons and estuaries dominated by fine sands. The lagoon habitat appears to ameliorate the effects of unfavourable (winter) conditions in less abundant meiofaunal taxa. In summary, sediment fractions explain spatial patterns in the average abundance of organisms (e.g. nematodes) as well as the seasonal changes in frequency of presence/absence (e.g. polychaetes). (c) 2015 Elsevier Ltd. All rights reserved.

In the current study we provide a reviewed list of valid genera and species of Xyalidae, a widespread family of mostly marine free-living nematodes. Comments are added about the historic background and taxonomic situation of the family, all valid genera and, when necessary, diagnostic characters are given. Additionally, information about distribution and geographical location of species recorded along the Brazilian coast is provided. Our review recognized 46 valid genera, 450 valid species and 73 descriptions without enough morphological information for identification (species inquerendae). Nearly 80 % of the species inquerendae belong to Daptonema and Theristus. To avoid homonymies, two Daptonema species were renamed, Daptonema biwaensis (Tsalolikhin, 2002) new name (former Mongolotheristus timoshkini) and Daptonema vietnamensis (Gagarin and Thu, 2008) new name (former D. curvatum sensu Gagarin and Thu, 2008). Cenolaimus sapeloensis is transferred to Xyala sapeloensis comb. nov. Along the Brazilian coast 28 genera and 41 species have been recorded. The species Elzalia floresi, Metadesmolaimus tersus, Paramonohystera stricta, Pseudosteineria scopae, Rhynchonema cemae, R. veronicae, Steineria ericia, S. marcorum, S. pavo, S. tripartita, Theristus acribus, T. flevensis, T. macroflevensis, T. pertenuis, T. stranus, Trichotheristus heterus, T. setosus and Zygonemella striata have the Brazilian coast as the type locality. Among all species, three occurred across three geographic regions, while the large majority was restricted to one. Xyalidae is typically encountered in oceanic sandy beaches, with only the species belonging to Daptonema, Theristus, Trichotheristus and Zygonemella being recorded in estuarine sediments. This observation suggests that the colonization of inland waters occurred multiple times along the evolutionary history.

The majority of studies have advocated that diversity of marine nematodes increases with increasing sediment grain size, although the opposite trend has also been suggested. The controversy is partially caused by not taking into account the effect of density on patterns of diversity and by analyzing datasets from different environments. The present study investigated nematode assemblages from sediments varying from very fine sand (mean grain size of 0.12 mm) to very coarse sand (1 mm) in shallow sublittoral marine environments. Contrary to previous studies, species richness was constant along the granulometric spectrum, despite significant changes in composition. The dominant genera were separated into five groups according to their optimum distribution and there was little overlap between these groups. Concepts from the niche theory explain to some extent the observed patterns. For instance, some of the coexisting genera were from different feeding types.

We studied the changes in geochemical variables in the middle section of Rio de la Plata estuary during the 2009-2010 El Nino-Southern Oscillation (ENSO) event. Protein, organic matter, chlorophyll-a and phaeopigment content of surface sediments were significantly correlated with the increased continental freshwater input associated with high total monthly rainfall. During the warm-phase ENSO event, river flow was 5-fold larger than average historical levels, which led to a steady decrease in salinity values and the highest levels of geochemical variables. The evidence presented herein suggests that warm-phase ENSO events increase the trophic state of the sediments because of the increased freshwater input. Thus, our findings may be useful to anticipate potential eutrophication episodes in the study area.