Increased geographical distribution and richness of non-native freshwater fish species in Argentina: evidence from a literature review

The present study is a full review of the non-native freshwater fish species introduced into Argentina and their relationship to the main environmental features and introduction vectors of each freshwater ecoregion. The total number of non-native freshwater fish species was compiled through a literature survey; information on spatial–temporal patterns of species records and invasion vectors was retrieved for all ten freshwater ecoregions of Argentina. Our survey revealed that 18–22 non-native fish species had been recorded up to 1999, and a total of 40 introduced fish species, of which 18 are invasive and five potentially invasive, had been registered in seven Argentinean ecoregions as of May 2020. According to georeferenced records, the rainbow trout Oncorhynchus mykiss and common carp Cyprinus carpio were the non-native fish species with the greatest number of records and largest invaded areas, probably due to their species-specific ecological traits. Invasive fish species differed clearly between the Patagonia, Lower Paraná, and Lower Uruguay ecoregions, probably because of a combination of the environmental conditions, structure of native assemblages, and invasion pathways in each ecoregion. Except for the recognized impact of non-native salmonids, the adverse effects of introduced fish species have been little studied, indicating the need for further research to clarify the role of ecological shifts triggered by the introduction and establishment of non-native fish species in Argentina. In contrast to the high diversity of aquatic species and freshwater environments, the spread and impact of invasive fish species in Argentina is little known, particularly compared with other South American countries.Fil: Espínola, Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Rabuffetti, Ana Pia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Carrara, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Abrial, Elie. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Ferlay, Elise Mathilde Charlotte. Polytechnic School Of The University Of Tours; FranciaFil: Yoya, Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; ArgentinaFil: Baigún, Claudio Rafael M.. Universidad Nacional de San Martín. Instituto de Investigación e Ingeniería Ambiental. - Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigación e Ingeniería Ambiental; ArgentinaFil: Wantzen, Karl Matthias. Centre National de la Recherche Scientifique; FranciaFil: Neves dos Santos, Luciano. Universidade Federal do Estado do Rio de Janeiro; Brasi

Analysis and decomposition of condensed tannins in tree leaves

The decomposition of leaf litter is controlled by several factors. One factor that may play an important role is the content of condensed tannins (proanthocyanidins). Here we designed a combined method to isolate proanthocyanidins from leaf extracts, to convert them to anthocyanidins, and to quantify individual anthocyanidins exactly with a new simple, but sensitive high-performance liquid chromatography method. We used this method to show composition of proanthocyanidins and to monitor degradation of proanthocyanidins and individual constituents in leaf litter in an aquatic environment over time. Despite the rapid decrease in the initial concentrations, a fraction of the proanthocyanidins remained detectable for several weeks

Soil Erosion from Agriculture and Mining: A Threat to Tropical Stream Ecosystems

In tropical countries soil erosion is often increased due to high erodibility of geologically old and weathered soils; intensive rainfall; inappropriate soil management; removal of forest vegetation cover; and mining activities. Stream ecosystems draining agricultural or mining areas are often severely impacted by the high loads of eroded material entering the stream channel; increasing turbidity; covering instream habitat and affecting the riparian zone; and thereby modifying habitat and food web structures. The biodiversity is severely threatened by these negative effects as the aquatic and riparian fauna and flora are not adapted to cope with excessive rates of erosion and sedimentation. Eroded material may also be polluted by pesticides or heavy metals that have an aggravating effect on functions and ecosystem services. Loss of superficial material and deepening of erosion gullies impoverish the nutrient and carbon contents of the soils; and lower the water tables; causing a “lose-lose” situation for agricultural productivity and environmental integrity. Several examples show how to interrupt this vicious cycle by integrated catchment management and by combining “green” and “hard” engineering for habitat restoration. In this review; we summarize current findings on this issue from tropical countries with a focus on case studies from Suriname and Brazil

Soil Erosion from Agriculture and Mining: A Threat to Tropical Stream Ecosystems

In tropical countries soil erosion is often increased due to high erodibility of geologically old and weathered soils; intensive rainfall; inappropriate soil management; removal of forest vegetation cover; and mining activities. Stream ecosystems draining agricultural or mining areas are often severely impacted by the high loads of eroded material entering the stream channel; increasing turbidity; covering instream habitat and affecting the riparian zone; and thereby modifying habitat and food web structures. The biodiversity is severely threatened by these negative effects as the aquatic and riparian fauna and flora are not adapted to cope with excessive rates of erosion and sedimentation. Eroded material may also be polluted by pesticides or heavy metals that have an aggravating effect on functions and ecosystem services. Loss of superficial material and deepening of erosion gullies impoverish the nutrient and carbon contents of the soils; and lower the water tables; causing a “lose-lose” situation for agricultural productivity and environmental integrity. Several examples show how to interrupt this vicious cycle by integrated catchment management and by combining “green” and “hard” engineering for habitat restoration. In this review; we summarize current findings on this issue from tropical countries with a focus on case studies from Suriname and Brazil

Flood pulse effects on benthic invertebrate assemblages in the hypolacustric interstitial zone of Lake Constance

In contrast to rivers, the effects of water level fluctuations on the biota are severely understudied in lakes. Lake Constance has a naturally pulsing hydrograph with average amplitudes of 1.4 m between winter drought and summer flood seasons (annual flood pulse (AFP)). Additionally, heavy rainstorms in summer have the potential to create short-term summer flood pulses (SFP). The flood pulse concept for lakes predicts that littoral organisms should be adapted to the regularly occurring AFP, i.e. taking advantage of benefits such as an influx of food sources and low predator pressure, though these organisms will not possess adaptations for the SFP. To test this hypothesis, we studied the aquatic invertebrate assemblages colonizing the gravel sediments of Lake Constance, the AFP in spring and a dramatic SFP event consisting of a one meter rise of water level in 24 h. Here, we introduce the term ‘hypolacustric interstitial’ for lakes analog to the hyporheic zone of running water ecosystems. Our results confirm the hypothesis of contrasting effects of a regular AFP and a random SFP indicating that the AFP enhances the productivity and biodiversity of the littoral zone with benthic invertebrates displaying an array of adaptations enabling them to survive. The littoral zones of lakes deliver important ecosystem services by regulating flood effects, producing biomass and supporting biodiversity. To maintain and foster these services, the maintenance or reintroduction of natural water level fluctuations and the conservation of the habitat structures of the hypolacustric interstitial are urgently needed

Gammarids in Lake Constance : habitat segregation between the invasive Dikerogammarus villosus and the indigenous Gammarus roeselii

Over the past decades the invasive Ponto-Caspian gammarid Dikerogammarus villosus spread throughout large rivers of central Europe, thereby rapidly displacing most of the native gammarid species. In 2003, D. villosus was first observed in Lake Constance and was predicted to out-compete the native Gammarus roeselii. However, today the two species coexist at several sites. We hypothesized that a higher variability of substrates in the littoral zone of Lake Constance, compared to that found in most European waterways, allows coexistence of these two species. To analyze substrate choice of these two gammarid species we exposed them individually and together in enclosures to the littoral zone in the lake. These enclosures contained a combination of the following substrates: bare stones, stones covered with Dreissena polymorpha, Chara sp., shells of Corbicula fl uminea, leaves, and sand. D. villosus strongly preferred structure-rich hard substrates like stones while avoiding sand and leaf litter. G. roeselii barely differentiated among substrates occupying even sandy habitats. To compare these results with natural gammarid habitat choice we measured gammarid densities on the substrates mentioned above in the littoral zone of Lake Constance. In contrast to enclosures, G. roeselii was virtually displaced by D. villosus on stones covered with D. polymorpha in the lake. Even four years after the invasion of D. villosus, high densities of G. roeselii could still be found in Chara and leaf litter. From these data we hypothesize that G. roeselii takes refuge from D. villosus by colonizing substrates not occupied by the invader. These substrate types only exist in natural waterbodies and are lacking in regulated rivers which generally have poor substrate richness

Leaf litter degradation in the wave impact zone of a pre-alpine lake

Contrary to streams, decomposition processes of terrestrial leaf litter are still poorly understood in lakes. Here, we examined the decomposition of two leaf species, beech (Fagus sylvatica) and poplar (Populus nigra italica ) in the littoral zone of a large pre-alpine lake at a wave exposed site. We focussed on the shredding impact of benthic invertebrates in a field experiment and on the effects of wave-induced disturbances under field and mesocosm conditions. In contrast to our expectations, benthic shredders did not reveal an important role in leaf processing under the conditions of the field experiment (early spring time, wave impact zone). Strong wave turbulence during storm events significantly reduced leaf mass, FPOM and invertebrate densities at field conditions. Several reasons can explain the low importance of shredders in our field study: (a) phenology of the shredder species, (b) feeding preferences and alternative food sources for gammarids, (c) generally low abundance of the native gammarid species due to the recent occurrence of an invasive predator, (d) disturbance of shredder activity due to high wave impact and (e) relatively low food value of the offered leaves. We suggest that leaf litter decomposition in lakes occurs in specific process domains, which largely depend on the hydraulic characteristics and on water-level fluctuations

The Lower Paraguay river-floodplain habitats in the context of the Fluvial Hydrosystem Approach

We report herein the first description of the physical structure of the aquatic habitats of the Lower Paraguay River along 390 km from Asunción city (Paraguay) to the confluence with the Paraná River. The hierarchical ordination of the Fluvial Hydrosystem Approach (FHA) allowed us to classify the Lower Paraguay as a meandering functional sector where five functional sets were identified: (a) main channel, (b) floodplain channel, (c) floodplain lentic environment, (d) tributary, and (f) aquatic-terrestrial transition zone. These functional sets encompassed twenty one functional units and sixty one major mesohabitats. We attribute the riverine habitat diversity to the changes in the channel-floodplain morphology and in the strength, duration and frequency of their hydrological connectivity. The variable river-floodplain- tributary complex developed several types of fluvial-lacustrine boundaries and riverine ecotones