Reproduction and fecundity of invader of internal insemination Trachelyopterus galeatus in a Neotropical floodplain

After the formation of Itaipu Reservoir, the invader Trachelyopterus galeatus colonized the upper Paraná River. Light microscopy was used to describe gametogenesis and the reproductive phases of females and males. The following data were verified: diameter of the oocytes, spawning type, batch fecundity by ovary weight, standard length, and total weight of the fish, along with the regions where this species reproduced in the upper Paraná River floodplain. A total of 470 specimens were collected quarterly in 2016, 2018 and 2019, and bimonthly in 2017. The gonads were fixed in a Karnovsky solution, dehydrated, infiltrated, and embedded in historesin. The histological slides were stained using PAS + iron hematoxylin + metanil yellow, analyzed and photographed under an image-capturing microscope. As regards diameter of the oocytes and fecundity estimates, ovaries whose oocytes were measured under a stereomicroscope were sampled. In the oogenesis, undifferentiated and differentiated oogonia, early primary growth oocytes, secondary growth oocytes, full-grown oocytes and maturing oocytes were recorded. In the spermatogenesis, primary and secondary spermatogonia, primary and secondary spermatocytes, spermatids and spermatozoa were recorded. The reproductive phases found for females and males were: immature, early development, late development, spawning/sperm-releasing capable, regression, and regeneration. Trachelyopterus galeatus prefers to occupy and reproduce in the Ventura, Patos, Guaraná, Fechada, Garças, and Pau Véio lagoons. The diameter of the oocytes varied from 0.4 to 2.9 mm. Females spawn, on average, 113 oocytes per batch. Batch fecundity variation shows that the larger the ovary, standard length, and total weight, the larger the number of oocytes to be spawned. This invader possesses reproductive success in the upper Paraná River floodplain, especially in lagoons.

MONITORING ACTIVE FIRES IN THE LOWER PARANÁ RIVER FLOODPLAIN: ANALYSIS AND REPRODUCIBLE REPORTS ON SATELLITE THERMAL HOTSPOTS

Floodplain wetlands play a key role in hydrological and biogeochemical cycles and comprise a large part of the world's biodiversity and resources. The exploitation of remote sensing data can substantially contribute to monitoring procedures at broad ecological scales. In 2020, the Lower Paraná River floodplain (also known as Paraná River Delta, Argentina) suffered from a severe drought, and extended areas were burned. To monitor the wildfire situation, satellite products provided by FIRMS-NASA were used. These thermal hotspots – associated with active fires – can be downloaded as zipped spatial objects (point shapefiles) and include recent and archive records from VIRRS and MODIS thermal infrared sensors. The main aim was to handle these data, analyze the number of hotspots during 2020, and compare the disaster with previous years' situation. Using a reproducible workflow was crucial to ingest the zip files and repeat the same series of plots and analyses when necessary. Obtaining updated reports allowed me to quickly respond to peers, technicians, and journalists about the evolving fire situation. A total of 39,821 VIIRS S-NPP thermal hotspots were detected, with August (winter) accounting for 39.8% of the whole year’s hotspots. MODIS hotspots have lower spatial resolution than VIIRS, so the cumulative MODIS hotspots recorded during 2020 were 8,673, the highest number of hotspots of the last 11 years. Scripts were written in R language and are shared under a CC BY 4.0 license. QGIS was also used to generate a high-quality animation. The workflow can be used in other study areas.

Response of Multi-Incidence Angle Polarimetric RADARSAT-2 Data to Herbaceous Vegetation Features in the Lower Paraná River Floodplain, Argentina

Wetland ecosystems play a key role in hydrological and biogeochemical cycles. In emergent vegetation targets, the occurrence of double-bounce scatter is indicative of the presence of water and can be valuable for hydrological monitoring. Double-bounce scatter would lead to an increase of σ0HH over σ0VV and a non-zero co-polarized phase difference (CPD). In the Lower Paraná River floodplain, a total of 11 full polarimetric RADARSAT-2 scenes from a wide range of incidence angles were acquired during a month. Flooded targets dominated by two herbaceous species were sampled: Schoenoplectus californicus (four sites, Bulrush marshes) and Ludwigia peruviana (three sites, Broadleaf marshes). As a general trend, σ0HH was higher than σ0VV, especially at the steeper incidence angles. By modeling CPD with maximum likelihood estimations, we found results consistent with double-bounce scatter in two Ludwigia plots, at certain scene incidence angles. Incidence angle accounted for most of the variation on σ0HH, whereas emergent green biomass was the main feature influencing σ0HV. Multivariate models explaining backscattering variation included the incidence angle and at least two of these variables: emergent plant height, stem diameter, number of green stems, and emergent green biomass. This study provides an example of using CPD to decide on the contribution of double-bounce scatter and highlights the influence of vegetation biomass on radar response. Even with the presence of water below vegetation, the contribution of double-bounce scatter to C-band backscattering depends on scene incidence angles and may be negligible in dense herbaceous targets.

Nutrient Concentrations in Macrophytes from Lotic and Lentic Environments of the Middle Parana River, Argentina

Objectives: The purpose of this work was to compare nutrient concentrations in water, sediment, and in plant tissues of Eichhornia crassipes and Panicum elephantipes from lotic and lentic environments of the Middle Parana River floodplain (Argentina). Materials and Methods: The study was carried out over an 18-month period. Plants, water, and sediment were collected in a lake (lentic environment) and in a river (lotic environment) from the Middle Parana River floodplain. Water and sediment were sampled in sites where P. elephantipes or E. crassipes were predominant and in sites without vegetation. Results and Discussion: The lentic and lotic environments dominated by E. crassipes showed the highest ammonium concentrations. The sediment from the lotic environment showed total phosphorus (TP) and total Kjeldahl nitrogen (TKN) concentrations significantly lower than those found in the sediment from the lentic environment. In the lentic environment, the sediment from the lake with the dominance of E. crassipes showed the highest TKN concentration, while the sediment from the lake dominated by P. elephantipes showed the highest TP concentration. For both plant species and for both environments, TKN and TP tissue concentrations were significantly higher in leaves in comparison with roots. Conclusions: Our results could be used to optimize the efficiency of treatment wetlands. Additionally, the use of locally available macrophytes as contaminant bioaccumulators in the Middle Parana River floodplain is completely feasible.

Long-term colonisation and propagule pressure of fish assemblages in a Neotropical floodplain

Biological invasions are a major threat to biodiversity in the Neotropical region. However, few studies have evaluated the mechanisms underlying the long-term establishment of fish propagules in aquatic environments. Here, we associated fish biomass, species richness, and proportion of non-native species (contamination index) to quantify propagule and colonisation pressures, and fish biodiversity (measured by the Kempton’s index) in lakes and rivers of the Parana River floodplain. We organised species into native and non-native assemblages sampled by gillnetting and beach seining in spatio-temporal gradients, seasonally, from 2000 to 2017. Native and non-native Kempton’s indices were inversely correlated, native extinctions occurred locally with non-native biotic differentiation in lakes, rivers, and ecosystem contamination. A constant propagule pressure resulted in an overwhelming biodiversity of non-natives at the end of the evaluated time series. Biotic resistance to introduction was not evidenced in our deterministic trends. The observed patterns agreed with previous studies highlighting native biotic homogenisation and species extinctions, depending on biological invasions, landscape connectivity, and riverine impoundments. Long-term propagule pressure and non-native fish colonisation were the drivers of biodiversity that led to the predominance of non-native over native assemblages in the Parana River floodplain.