The objectives of this study were to compare the sensitivity of three freshwater macroinvertebrate shredder species (Atyaephyra desmarestii, Echinogammarus meridionalis and Schizopelex festiva) to acute stress induced by eucalyptus leaf extracts and copper, independently and in mixtures, and the ability of temperature to influence the chemicals’ toxicity. Laboratory bioassays based on mortality with single substances and mixtures were carried out with the three species at 10 and 20°C. After 96 h of exposure, S. festiva, A. desmarestii and E. meridionalis were found to have differences of sensitivity to copper, eucalyptus leaf extracts and their mixtures, with S. festiva being the least sensitive species at both 10 and 20°C. The relative sensitivity of A. desmarestii and E. meridionalis to chemical exposure seems to be chemical and temperature dependent. Overall, these findings suggest that chemical stress may modulate the biodiversity of stream shredders communities due to differential sensitivity of individual species to environmental contaminants, and that temperature may influence the process. Thus, more knowledge on the combined effects of multi-stressors is needed, particularly on temperature and chemicals’ interactions and on the molecular mechanisms underlying the responses observed at individual level.

The rotifer Brachionus calyciflorus often occurs simultaneously with the cladoceran Moina macrocopa in tropical water bodies. We studied the effects of temperature (20, 25 and 30°C) and algal density (0.5, 1.0 and 3.0×106 cells.mL−1Scenedesmus obliquus) on the outcome of competition and duration of coexistence between B. calyciflorus and M. macrocopa using population growth experiments. The results showed that regardless of temperature, M. macrocopa outcompeted B. calyciflorus at the lowest algal density (0.5×106 cells.mL−1), whereas B. calyciflorus outcompeted M. macrocopa at the higher algal densities (1.0 and 3.0×106 cells.mL−1). The duration of coexistence shortened with increasing temperature when M. macrocopa outcompeted B. calyciflorus, and those with increasing temperature and algal density when B. calyciflorus outcompeted M. macrocopa. Our results suggested that the competitive outcome between the rotifer B. calyciflorus and the cladoceran M. macrocopa was dependent on algal density but not temperature, the duration of coexistence between them was dependent on algal density and temperature, and the exploitative competition of M. macrocopa over B. calyciflorus may be more important than the interference competition.

Diatoms and geochemical stratigraphy were studied in sediment core samples collected from a heavily polluted urban lake (SE China) in order to track the history of eutrophication and heavy metal contamination. The sediment profile covered ca. 60 years (from ca. 1951 to 2011) based on 137Cs and Spheroidal carbonaceous particles (SCP) dating, and encompassed a period of rapid industrial development in this region. Diatoms experienced two visible shifts, including the replacement of benthic and epiphytic taxa by planktonic species (e.g., Cyclotella meneghiniana Kützing) in 1972, and the dominance of Cyclotella atomus Hustedt and Nitzschia palea (Kützing) W. Smith after 1999. Metals (i.e., Cd, Pb and Zn), total phosphorus, total nitrogen and total organic carbon all increased in the past 60 years. Redundancy analysis was used to correlate diatom with chemical change and explained 50.3–60% of total variation in diatom data for three periods (from 1951 to 1999, between 1951 and 2011 and from 1972 to 2011). The combined effects of nutrients and metals were the predominant factor, capturing 29.6–42.8% of the total variance. Nutrients alone accounted for little more variance than did metals alone for the first flora shift about 1972. The further shift after 1999 was more influenced by the sole effect of metals than that of nutrients. Increases in species (e.g., N. Palea) able to tolerate both nutrient-related and metal-related stressors were related to persistent nutrient and metal inputs. In addition, climate warming might exacerbate eutrophication and metal contamination in this lake.

Investigating forces driving the structure of aquatic communities has long been an important issue in ecology. In the present study, we focused on the effects of changed water supply for aquaculture ponds on phytoplankton, zooplankton and macrozoobenthos communities during two seasons of rearing common carp. We compared these communities between two types of inflow water: surface sources of water – a reservoir pond, two open wells and a small stream and groundwater – deep tube well. Significant changes were observed in environmental variables after the introduction of the groundwater source: oxygen concentration and water hardness decreased, while conductivity, phosphorus and un-ionized ammonia increased. Results revealed that all investigated groups, except Mollusca (macrozoobenthos), decreased in species richness, abundance and biomass due to changed water chemistry, but differed in the level of susceptibility. Rotifera and Cladocera were the most affected showing a sharp decline in density and number of species since 66% of species disappeared from the ponds. The abundance of Copepoda was relatively high although significantly lower under new conditions, with adults being more tolerant to changed inflow water than nauplii larvae. Phytoplankton had the highest potential to replace previous species with newcomers more adapted to changed water chemistry, providing 36 immigrant species, whereas 49 became extinct. Although mainly influenced by fish predation, Chironomidae (macrozoobenthos) were undoubtedly affected by changed water chemistry. These results suggest profound changes in three key ecological groups produced by significant changes of important environmental variables and water quality after the shift from surface to groundwater supply.

The wetlands found in the Brazilian Cerrado are poorly studied environments regarding ecological aspects. Assessing the diversity of aquatic invertebrates in wetlands is a challenging task, since there are no standard sampling methods that minimize the spatial effects caused by macrophytes. The aim of this study was to evaluate the efficiency of a new sampling method for assessing Cladocera richness in macrophyte-rich wetlands of Brazilian Cerrado. In six wetlands, one transect was established which corresponded to a gradient of depth or change in aquatic vegetation. Samples containing cladocerans were collected using plankton net dragged among aquatic vegetation in the dry and rainy seasons. The species accumulation curves using non-parametric estimators and the overestimation of richness were used to determine the sampling efficiency. The species accumulation curves showed different asymptotic trends regarding the season and wetland studied. Especially in the rainy season, an asymptotic trend was not observed in two of the wetlands studied, which may reflect the influence of seasonality on Cladocera assemblage. Nevertheless, the overestimation of species richness showed that the method of sampling was able to find more than 60% of the estimated species richness, regardless of season or wetland studied. These results indicate that the method employed for sampling Cladocera in the Cerrado wetlands can be considered adequate.

Aquatic plants play a substantial role in almost all freshwater habitats throughout the world. Even though submerged aquatic plants dominantly spread by the dispersal of vegetative plant fragments, most aquatic plant species show a broad distribution range. Here we studied the differences in the regeneration capacity and the regeneration type of fragments (by root and/or shoot growth) of eight submerged plant species (Ceratophyllum demersum, Egeria najas, Elodea canadensis, Elodea nuttallii, Hydrilla verticillata, Myriophyllum aquaticum, Myriophyllum heterophyllum and Myriophyllum spicatum) under different water nutrients in sediment-free conditions. Overall, M. spicatum showed the highest regeneration (82±2%) in this study, followed by C. demersum (73±2%) and M. aquaticum (47±4%), whereas M. heterophyllum showed the lowest (1±1%). The shoot fragments of E. canadensis, H. verticillata, E. najas and E. nuttallii regenerated by 40±2, 23±2, 16±2 and 7±1%. The nitrate concentration affected the regeneration capacities of E. najas (P=0.05), M. spicatum (P=0.013) and C. demersum (P=0.001), whereas phosphate had no significant effect. Additionally, the different nutrient concentrations had a significant effect on the portion of the regeneration types within E. canadensis, E. nuttallii and H. verticillata. Summarizing, submerged plants differ significantly in their regeneration capacity, and water nutrients have a potential effect on the regeneration of submerged plant fragments. This might influence the further colonization and spread of the species under field conditions.

Reservoirs cause hydrological changes (i.e., water level stabilization) that favor the colonization of aquatic macrophytes. Knowing the ecological factors that determine the occurrence of these plants is critical for water management (e.g., plant control) and biodiversity conservation. In this sense, the present study investigated colonization patterns of Ludwigia sedoides in Lajeado reservoir (Tocantins River, Amazon Basin), in order to identify variables that influence colonization at habitat scale. We investigated the relationship between colonization (coverage area and occurrence) and morphometric (fetch, slope, depth and distance from shoreline) and biotic variables (local diversity of macrophytes and co-occurrence patterns). Stepwise regression selected fetch, depth and slope as the best variables to explain the variation in L. sedoides coverage, which together explained 46% of data variability. Fetch and slope were negatively correlated with coverage, whereas depth showed a positive correlation. No biotic variable was included in the model (P>0.05). However, the investigation of the geometric shape of bivariate correlations (null models) showed positive relationships with local species richness and richness of life forms (i.e., submerged, emergent, floating and epiphytic). In addition, an analysis of species co-occurrence (C-score) revealed that L. sedoides is negatively associated with some macrophyte species. We believe, however, that these results may be associated with species preferences for particular environmental conditions. In conclusion, the present study indicated that morphometric variables are potential predictors of the colonization of L. sedoides in Lajeado reservoir. Sheltered sites with low slope and moderate depths represent favorable environment for colonization and growth.

Body size strongly influences the type and strength of species interactions. Animals with complex life cycles, such as dragonflies, usually go through different stages that include a variation in body size and may involve shifts in their trophic position in the food web. This investigation analyzes the position of the dragonfly Rhionaeschna variegata, in the food web according to its body size, in Andean wetland communities of Northwestern Patagonia (Argentina). The phenology of R. variegata larvae and their potential intraguild predators were studied in wetlands with different hydroperiods. Under controlled experimental conditions, feeding trials were performed to assess the effect of R. variegata on the survivorship of different types of prey. The effects of cannibalism and intraguild predation (IGP) on the survivorship of the small larvae of R. variegata were investigated with and without alternative prey as well as different sympatric predators. The phenology of R. variegata and intraguild predators differed among wetlands. The feeding trials showed that R. variegata has a significant effect on the survivorship of invertebrate and vertebrate prey. Cannibalism increased with body size in odonate larvae. The survivorship of small- and medium-sized larvae was mainly affected by the presence of larger predators such as belosmatids. The field and experimental data show that the effect of IGP and cannibalism is affected by the cohort dynamics of R. variegata. Body size in R. variegata determines the strength of its interaction with other components of the community.