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With 6 main basins, and being the second smallest country in South America, Uruguay has a high freshwater ecosystem diversity. The study of zooplankton communities dates back to 1949, but remained marginal until the end of the 20th century when the number of publications increased notably. Here, we revise the history and accumulated knowledge on the zooplankton community in Uruguayan continental ecosystems, highlighting the main approaches and milestones. So far, ca. 100 academic papers with 219 authors have been published in international, regional, and local journals, accumulating more than 2150 citations. Most of the published studies come from shallow lakes, followed by reservoirs and estuaries, and were concentrated in the southern part of Uruguay. Most taxonomic records correspond to the Río de la Plata basin, followed by the Atlantic Ocean basin, and the Río Uruguay basin. The number of records in the rest of the country is comparatively low, with minima occurring in the basins of the rivers Negro and Santa Lucía. A total of 170 species belonging to 117 genera have been recorded, mainly for Copepoda, Cladocera and Rotifera. Limnological studies in Uruguay have historically followed an ecosystemic approach, thus, most of the literature referring to zooplankton has such a perspective. The most relevant ecological aspects analyzed so far include trophic interactions, species survival and dispersion, biological invasions, the relationship with eutrophication and climatic variability, and have applied traditional as well as functional and trait-based approaches. Our analysis allowed us to detect important knowledge gaps, that warrant attention for future studies which can help elucidate local and regional processes in freshwater zooplankton in Uruguay. [ABSTRACT FROM AUTHOR]

The 2009–2010 "El Niño"-Southern Oscillation (ENSO) event was characterized by a warm-phase leading to a five-fold increase in the Río de la Plata river flow and an associated change in trophic state because of organic enrichment. We analyzed the biotic response of benthic communities to such an increased trophic state during this ENSO event using community and biotic indices (diversity indices and AMBI). Polychaeta exhibited the highest richness and second the most abundant values while the small gastropod Heleobia australis was the most abundant and frequent species. An increase in richness and diversity of Polychaeta was associated to a concomitant increase of RdlP flow and the organic enrichment of the macrobenthic species. Community indices (richness and diversity) showed variability at both temporal and spatial scale but only AMBI exhibited spatial variability without significant differences between contrasting environmental conditions (ENOS phases). [Display omitted] • An ENSO event promoted changes in chemical and biotic sediment variables. • Variability in salinity and protein sediment content were reflected in macrobenthic community indices. • AMBI was useful to infer spatial differences between zones with different environmental quality. • Richness, diversity and AMBI are recommended for the Montevideo Coastal zone environmental monitoring programs. [ABSTRACT FROM AUTHOR]

We evaluated, in two consecutive austral summers, the biochemical composition, sources, distribution and degradation state of particulate organic matter (POM) in surface coastal waters of Collins Bay, King George Island, Antarctica. Bulk elemental and stable isotope analyses were combined with molecular-level proxies (fatty acids and amino acids) to obtain more comprehensive evidence about POM characteristics. Two different settings were recognized. In February 2016, there was a reduced glacier melting condition and meltwater runoff due to cold weather. Marine fresh phytoplankton and ice-associated POM with the dominance of diatoms, bacteria, zooplankton and ice-associated fauna were the major components of POM. In contrast, in January 2017 under increased glacier melting and meltwater runoff due to warm weather conditions, suspended POM was constituted by marine phytoplankton, Rhodophyta macroalgae detritus and an increased terrestrial contribution. The lower degradation state of suspended POM in February 2016 than in January 2017 and the early bacterial response to the input of fresh protein-rich organic matter derived from marine phytoplankton, mainly diatoms, was supported. Our results provide evidence of the negative impact of glacier retreat and increased meltwater runoff on POM features in Collins Bay, which can be relevant to other Antarctic coastal marine ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: Proxies of terrigenous versus marine input (Al and Ti, Fe/Ca and Ti/Ca ratios), origin of organic matter (δ13C, δ15N and C/N ratio), productivity (Corg; Nt; CaCO3, P, Ca, and Ba content; and Ba/Al and Ba/Ti ratios), hydrodynamics (grain size, mean diameter and sorting) and biological records of the main features of the environment (benthic foraminifera assemblage distribution) were used to assess the sediment footprint of river vs. marine influence along the salinity gradient between the Rio de la Plata (RdlP) estuary and the adjacent South Western Atlantic Shelf. These criteria permitted characterisation and interpretation of the sedimentary processes influencing transition between three known environments: tidal river, estuarine and marine zones. Increases in sand and clay content at the transition between tidal river and proper estuarine zones indicate resuspension/deposition processes associated with the maximum turbidity zone (MTZ). The MTZ was also characterised by an increase in mixed organic matter content indicated by stable carbon and nitrogen isotope values, an increment in productivity proxies (Corg, Nt and CaCO3) and the substitution of the Miliammina fusca assemblage (brackish environments) for the Ammonia tepida assemblage (estuarine environments). The transition between estuarine and marine environments was characterised by a sharp (up to 99%) increase in sand content, reflecting the progradation of modern RdlP sediments toward relict continental shelf sediment. C/N values typical of the marine environment, decreased trace element concentrations and the distribution of the Buliminella elegantissima assemblage (a more marine assemblage) also highlight the marine environment. This paper is particularly important as a tool both to better understand sedimentological dynamics in salinity fronts (along the shelf sediment of large estuaries) and to elaborate more precise palaeoenvironmental and palaeoceanographic reconstructions. [Copyright &y& Elsevier]

Abstract: Biotic indices based on benthic communities have become an important tool in the assessment and monitoring of marine pollution. These communities vary at several spatial and temporal scales giving rise to scale-dependent patterns of distribution, being of particular importance because results from the application of ecological indices, and the subsequent classification of communities, could reflect these variations at several scales. We test some of the most widely applied indices for the evaluation of coastal benthic communities, using a hierarchical spatio-temporal sampling design, within two sets of estuarine habitats in the Atlantic coastal zone of Uruguay. Results showed that ecological indices can vary at different spatial scales, with important variation at small scales. So, independently from the used index, an appropriate sampling design should be taken into account considering different scales (both spatial and temporal). At some of the scales studied, indices appear to reflect natural variations in disturbance through currents rather than variation in anthropogenic effects. At the large scale, variation is low consistent with a preliminary classification of sites according to the putative levels of human activity. The low level of similarity between all indices could be denoting some degree of inconsistency in the assignment of the categories to an ecological status. [Copyright &y& Elsevier]