Zooplankton diversity in Acre state, Amazon, Brazil: an overview of previous studies

This work assesses current knowledge of zooplankton biodiversity in aquatic ecosystems of the state of Acre (Brazil). A bibliographic survey was undertaken, showing that most of the reported studies have focused on zooplankton diversity and composition. Fifteen locations have been studied. There is still a scarcity of information concerning zooplankton populations in the Amazon region. To date, 170 species of planktonic rotifers have been recorded, distributed in 26 families and 38 genera, together with 18 species of cladocerans, distributed in 8 families and 18 genera, and 4 species of copepods in 2 families and 6 genera. The results indicate the need for further research concerning the biodiversity of this group of organisms at locations in the basins of the Purus and Juruá Rivers, especially in lotic ecosystems and littoral zones, given the present lack of information and the socioeconomic importance they play in the region.

Variable Fitness Response of Two Rotifer Species Exposed to Microplastics Particles: The Role of Food Quantity and Quality

Plastic pollution is an increasing environmental problem, but a comprehensive understanding of its effect in the environment is still missing. The wide variety of size, shape, and polymer composition of plastics impedes an adequate risk assessment. We investigated the effect of differently sized polystyrene beads (1-, 3-, 6-µm; PS) and polyamide fragments (5–25 µm, PA) and non-plastics items such as silica beads (3-µm, SiO2) on the population growth, reproduction (egg ratio), and survival of two common aquatic micro invertebrates: the rotifer species Brachionus calyciflorus and Brachionus fernandoi. The MPs were combined with food quantity, limiting and saturating food concentration, and with food of different quality. We found variable fitness responses with a significant effect of 3-µm PS on the population growth rate in both rotifer species with respect to food quantity. An interaction between the food quality and the MPs treatments was found in the reproduction of B. calyciflorus. PA and SiO2 beads had no effect on fitness response. This study provides further evidence of the indirect effect of MPs in planktonic rotifers and the importance of testing different environmental conditions that could influence the effect of MPs.

Effect of salinity and food concentration on competition between Brachionus plicatilis Müller, 1786 and Brachionus calyciflorus Pallas, 1776 (Rotifera)

Natural populations of planktonic rotifers are affected by salinity and food density, among other stressors. Moreover, competition among congeneric species limits the abundance of certain rotifers in ecosystems without spatial heterogeneity and environmental fluctuations. We isolated Brachionus plicatilis and Brachionus calyciflorus from Salado River basin waterbodies and studied the demographic characteristics and competition between them at three salinity levels (0.75, 1.75 and 2.75gL–1 NaCl) and at two food concentrations (0.1×106 and 0.5×106 cells mL–1 Chlorella vulgaris). The lowest salinity level proved to be unfavourable for the population growth of B. plicatilis, but at higher salinity levels the growth was similar to that of controls (without competition), even in the presence of the competitor and at either food concentration. By contrast, the competitor almost always decreased the density of B. calyciflorus. Salinity greatly affected the peak density of B. plicatilis, whereas the effects of salinity and competition on B. calyciflorus were similar. Biomass was inversely related to salinity for both species, and was significantly affected by competition in B. plicatilis. These results show that B. calyciflorus is more adversely affected than B. plicatilis by competition and high salinity, and explain why both species can coexist in eutrophic saline lowland rivers and pampean shallow lakes.

Effects of beaver dams on the zooplankton assemblages in four temperate lowland streams (NW Poland)

Beaver ponds favour lentic species over the original lotic animals. The typical lentic animals are zooplankton, which can be good predictors of hydrological changes in streams caused by beaver activity. We analysed the effects of beaver dams on the zooplankton communities in small lowland streams in stream-beaver pond-stream systems. All spatial changes in the composition of zooplankton reflected the effects of physical changes introduced by the beaver dams. The rapid increase in the density of the aforementioned taxa was possible because the features typical of stagnant water reservoirs are present in beaver ponds. The number of taxa and the abundance and biodiversity of zooplankton, especially planktonic rotifers, were higher in the dam and downstream sites than in the upstream sites. Therefore, the impact of beaver ponds on the composition of zooplankton in streams below the dams is considerable, and there is an increase in the organic matter downstream, which leads to trophic changes in the stream.

Zooplankton of Mokraya Sura River

Structural and functional characteristics of zooplankton as well as the results of biotesting were researched to indicate the ecological status of Mokraya Sura river sites. Zooplankton sampling was performed at the sites of Mokraya Sura river in autumn 2014 and in spring 2015. Species composition and abundance of zooplankton showed that zooplankton is most depressed at the upper sites of the river due to joint effect of slime accumulation eutrophication and industrial sewage. Biotesting results estimated water quality of the site near aeration plant sewage emergency discharge as most polluted of the river sites where large abundance and biomass of zooplankton were created mostly by planktonic rotifers. Large figures of filter-seeding crustaceans as well as low saprobity index indicate improvement in water quality at the sites 3 km and 2 km upstream from the river mouth.