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To investigate the potential long-term consequences of environmental warming in subtropical systems, we compare the trophic structure of shallow lakes in tropical and subtropical regions. In total, 25 meso-eutrophic lakes with piscivorous fish were sampled during summer along a latitudinal gradient in South America. The fish catch per unit of effort and the omnivorous fish to zooplankton biomass ratios were significantly lower in the tropical lakes. Despite the lower fish biomass, no significant difference was found in zooplankton or phytoplankton communities or in the zooplankton to phytoplankton biomass ratio between the two sets of lakes. Nevertheless, regression models based on the combined dataset show higher cyanobacteria and total phytoplankton biomass at lower zooplankton to phytoplankton biomass ratio and higher omnivorous fish to zooplankton biomass ratio. Cyanobacteria biomass was dominated by non bloom-forming taxa and was inversely related to the biomass of calanoid copepods suggesting that these herbivores may play an important role in controlling edible cyanobacteria in warm shallow lakes. Overall, our results, however, suggest that warming will have relatively minor impacts on the pelagic trophic structure of shallow subtropical lakes supporting the idea of weaker trophic cascades in warm (sub)tropical lakes in comparison to temperate ones.

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Lacerot, G., Lozoya, J.P., Teixeira de Mello, F. 2020. Plasticos en ecosistemas acuaticos: presencia, transporte y efectos. Ecosistemas 29(3):2122. https://doi.org/10.7818/ECOS.2122

Plastics have been found in marine water and sediments, sea ice, marine invertebrates, and penguins in Antarctica; however, there is no evidence of their presence in Antarctic glaciers. Our pilot study investigated plastic occurrence on two ice surfaces that constitute part of the ablation zone of Collins Glacier (King George Island, Antarctica). Our results showed concentrations of expanded polystyrene (EPS) in the 0.17–0.33 items m−2 range. We registered an atmospheric dry deposition between 0.08 and 0.17 items m−2 day−1 (February 2019). This is the first report of plastic presence in an Antarctic glacier, which was probably transported by wind.

Global warming may intensify eutrophication of shallow lakes by affecting nutrient loading, evaporation rates, and water level and thus produce major changes in food webs. We investigated to what degree food webs in tropical humid lakes differed from those in more eutrophic semi-arid lakes of the same latitude. Our results indicate that the catchment area-to-lake area ratio, nutrients, chlorophyll a, suspended solids, abundances of phytoplankton, zooplankton, and omnivorous fish as well as total fish catch per unit effort were all higher in the semi-arid lakes, whereas inlet water-to-evaporation ratio (proxy for water balance), water transparency, percentage macrophytes cover, and the piscivores:omnivores ratio were higher in the humid lakes. Our results suggest that reduced inlet water-to-evaporation ratio will increase lake eutrophication, which, in turn, as in temperate regions, will alter trophic structure of the freshwater community.

Este artículo contiene 16 páginas, 6 figuras, 3 tablas., 1. Pigments in lake surface sediments integrate both benthic and pelagic primary producer composition at the whole‐lake ecosystem level. 2. We gathered a comprehensive set of water chemistry, morphometric, physical and biological lake variables, catchment and climate characteristics, and geographical descriptors. We used multiple regressions to relate whole‐lake algal pigment concentration to environmental conditions and multivariate statistical analyses to assess the factors most associated with photoautotrophic algal and bacterial community composition. The relative influence of environmental factors and spatial distribution was assessed by variance partitioning analysis among three groups of variables: (1) in‐lake factors, (2) external factors, and (3) geographic descriptors. 3. Pigment concentration and community composition were most sensitive to in‐lake factors. Pigment‐inferred abundance of algae, including cyanobacteria, tended to be highest in shallower systems with high nutrient concentrations, independent of the latitudinal temperature or irradiance gradients. Pigment‐inferred community composition was best explained by nutrients and biotic composition (zooplankton and fish communities). Only in maritime temperate lakes did a link with regional location occur due to their low dissolved inorganic nitrogen to soluble reactive phosphorus ratios (1.5 atomic ratio), suggesting nitrogen limitation of phytoplankton growth; accordingly, the sediment pigments revealed cyanobacteria to be the dominant group, although this may also be a consequence of the overall high nutrient levels in these 4. Despite the large climate gradient covered, in‐lake rather than external factors were associated with the patterns observed in pigment concentration (from benthic and pelagic microorganisms) and inferred composition and abundance in these shallow lakes. Our results suggest that pigment assemblages in sediments, which integrate both benthic and pelagic microbial photoautotrophic community and processes, are valuable indicators of changes in shallow (0.75–12 m depth) lake ecosystems., This research was funded by a post‐doctoral Beatriu de Pinós grant from the Departament d'Universitats, Recerca i Societat de la Informació, Generalitat de Catalunya (T.B.). Further support came from The Netherlands Organization for Scientific Research (NWO) grant W84‐549 and WB84‐586, The National Geographic Society grant 7864‐5; in Brazil by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) grants 480122, 490409, 311427; in Uruguay by PEDECIBA, Maestría en Ciencias Ambientales, Donación Aguas de la Costa S.A., and Banco de Seguros del Estado. N.M. was supported by Sistema Nacional de Investigadores. E.J. was supported by the MARS project (Managing Aquatic ecosystems and water Resources under multiple Stress) funded under the 7th EU Framework Programme, Theme 6 (Environment including Climate Change) and AU Centre for Water Technology (watec.au.dk).

Toxic effects of freshwater cyanobacteria on mesozooplankton partially depend on the feeding strategies, generalist (cladocera) or selective filter-feeders (copepod) and on the type of toxin. Blooms of Cylindrospermopsis raciborskii (Nostocales) are increasingly more common in freshwaters. It can produce neurotoxins (paralytic shellfish poison, PSP), particularly in warm regions of the Americas. The knowledge about the effects of these neurotoxins on the clearance rate of zooplankton from warm regions still lags behind that of other world regions. We compared the toxin profile (using HPLC), morphology and growth rates of two PSP-producing C. raciborskii strains from South America. We evaluated the effect of these two strains on the clearance rate of two medium-sized grazers typical from subtropical and tropical environments, the copepod Notodiaptomus iheringi (~1.1 mm) and the cladoceran Daphnia pulex (~0.8 mm) in 2.5 h experiments. We found differences in the PSP profile, toxicity and morphology of the two C. raciborskii strains. Medium-sized predators were able to remove filaments of both strains in a similar amount despite their morphological and toxin differences. However, cladocera were significantly more affected than copepods in their clearance rates, suggesting differential consequences for their survival and success in warm freshwaters.

We combined the use of polyclonal antibodies against saxitoxin with catalyzed reporter deposition to detect production of saxitoxin by the cyanobacterium Cylindrospermopsis raciborskii. The procedure is simple, allows detection of intracellular saxitoxin in cyanobacteria filaments by confocal laser microscopy and is a promising tool to study toxin production and metabolism.

Metacommunity studies on lake bacterioplankton indicate the importance of environmental factors in structuring communities. Yet most of these studies cover relatively small spatial scales. We assessed the relative importance of environmental and spatial factors in shaping bacterioplankton communities across a >6000km latitudinal range, studying 48 shallow lowland lakes in the tropical, tropicali (isothermal subzone of the tropics) and tundra climate regions of South America using denaturing gradient gel electrophoresis. Bacterioplankton community composition (BCC) differed significantly across regions. Although a large fraction of the variation in BCC remained unexplained, the results supported a consistent significant contribution of local environmental variables and to a lesser extent spatial variables, irrespective of spatial scale. Upon correction for space, mainly biotic environmental factors significantly explained the variation in BCC. The abundance of pelagic cladocerans remained particularly significant, suggesting grazer effects on bacterioplankton communities in the studied lakes. These results confirm that bacterioplankton communities are predominantly structured by environmental factors, even over a large-scale latitudinal gradient (6026km), and stress the importance of including biotic variables in studies that aim to understand patterns in BCC.

It has been suggested that the overwhelming number of species in tropical ecosystems consist largely of "neutral" and functionally equivalent species. In phytoplankton, differences in functionality have been shown to be clearly distinguishable from morphological traits. Here we examine whether the increase in species towards the tropics goes together with an increase in functional richness or not. We analyse the latitudinal distribution of phytoplankton morphology-based functional groups (MBFG), the within-group richness and community morphological traits in 83 shallow lakes across South America (5-55°S). We further looked into explaining environmental variables. Despite the increment in species richness towards the (sub)tropics, the average number of MBFG remained constant. Furthermore, size average and variance decreased towards warmer regions. In warm lakes, phytoplankton communities were species rich but redundant in terms of belonging to a MBFG. Increasing species richness only translated into increasing number of rare species in some of the MBFG. In contrast, cold lakes were species poor but less redundant (i.e. essential to maintain the number of MBFG) and had a higher morphological variability. Our results support the hypothesis of higher functional redundancy in warmer areas and the relevance of increasing herbivory in colder regions as a main driving process of latitudinal patterns.

Synthetic plastics have become an indispensable component of modern life, and the amount of plastics disposal has increased dramatically as a result. With human population increasing, it is expected that the prevalence of plastic debris in the environment will also increase, unless sustainable daily habits are incorporated, waste management improved, and new alternative materials are discovered and popularized. To date, several reports show negative effects of plastic debris on marine and freshwater fauna (e.g. invertebrates, birds, turtles, marine mammals). Plastic are ubiquitous in the water column, deposited in fine sediments and enter the guts, respiratory structures and tissues of different aquatic species, and are incorporated into food webs via ingestion. This global problem also affects beach and near-shore activities (e.g. tourism, fisheries, and aquaculture) with negative social and economic consequences. The research of plastics effect on aquatic environments in Uruguay is only incipient. With the aim of contributing to scientific knowledge, decision-making and the management of plastic debris, here we reviewed the available information on plastic debris sources, their impacts on biodiversity, and policy issues in Uruguayan aquatic systems. Moreover, we reviewed and systematized community outreach initiatives, and examined national policies and management initiatives. We found that Uruguayan aquatic systems (freshwater, coastal marine and benthic) are affected by plastic pollution, both from land-based and sea-based activities, although national-level policies are modern and well suited for minimizing the impacts of plastic pollution. We reviewed biota-plastic debris interactions, and found evidence for impacts on a number of aquatic taxa, including the poorly reported ingestion of microplastics in freshwaters fishes and the association with plastic benthic debris. Global and regional hydrographic settings (Río de la Plata Estuary), as well as idiosyn-cratic ecological, socio-economic and cultural issues, make Uruguay a valuable test-site for this topic. Our ultimate goal is to minimize the effects of this widespread environmental, economic, health and aesthetic problem. Produtos plásticos tem se tornado um componente indispensável na vida moderna, como conseqüência disso a quantidade de plásticos descartados tem dramaticamente aumentado. É esperado que com o aumento da população de seres humanos a prevalência de descartes plásticos também aumente, a menos que hábitos cotidianos sustentáveis sejam incorporados, e novos materiais alternativos sejam descobertos e popularizados. Até o momento, diversas pesquisas têm mostrado os efeitos negativos de descartes plásticos sobre a fauna marinha e dulcícola (p. ex.: invertebrados, aves, tartarugas e mamíferos marinhos). Em ambientes aquáticos, plásticos estão em toda parte: na coluna de água, depositados em sedimento fino e dentro de estômago, estruturas respiratórias e tecidos de diversas espécies aquáticas, e são incorporadas nas teias alimentares através da ingestão. Este problema global também afeta atividades realizadas na praia e próximas à costa (p. ex.: turismo, pesca, e aqüicultura) com conseqüências sociais e econômicas negativas. Pesquisas que abordem os efeitos de plásticos sobre ambientes aquáticos no Uruguai é ainda incipiente. Com o objetivo de contribuir para o conhecimento científico, a tomada de decisões e o manejo de descartes plásticos, revisou-se a informação disponível acerca de fontes de descartes plásticos, observando os impactos delas sobre a biodiversidade e sobre questões políticas em sistemas aquáticos uruguaios. Além disso, revisou-se e sistematizou-se o alcance de iniciativas da comunidade, e examinou-se a política nacional de iniciativas de manejo. Descobrimos que os sistemas aquáticos uruguaios (de água doce, costeiros e marinhos bentônicos) são afetados pela poluição de plástico, pelas atividades terrestres e pelas atividades ligadas ao mar, embora as políticas a nível nacional sejam modernas e bem adaptadas para minimizar os impactos dessa poluição. Revisamos as interações biota-detritos plásticos, e encontramos evidência de impactos sobre diversos taxa aquáticos, incluindo a ingestão de microplástico per peixes de água doce, e da associação que existe entre biota e os detritos plásticos bentônica, geralmente pouco relatados. As configurações hidrográficas globais e regionais (Estuário Rio de la Plata), bem como questões ecológicas idiossincráticas, sócio-econômico e culturais fazem do Uruguai um valioso lugar-teste para este tópico. O objetivo final dessa pesquisa é minimizar os efeitos deste amplamente difundido problema de saúde, ambiental, econômico e estético.