Limnocharis flava, a species native to tropical America, is naturalized as a noxious weed in Sri Lanka, India and some other Southeast Asian countries. It is widespread in flood plains, wetlands and agricultural wetlands resulting in poor drainage. In the current study, the influence of different water conditions on growth, development and morphology of L. flava was investigated. Plants were grown on experimental pots filled with wetland soil, simulating flood, standing water and dry conditions. The highest biomass and relative growth rate was observed in the plants grown at flood conditions, while the lowest total biomass content was observed in the plants grown at dry conditions. L. flava showed morphological adaptations in different water conditions, including significant differences in the relative biomass allocation for root, petioles and leaves. Root biomass significantly increased in flooded conditions. Observed decrease in leaf area and increase in leaf total chlorophyll content may facilitate the survival in dry conditions. Plant mortality and no production of inflorescence may indicate the difficulty in surviving at dry conditions. No significant difference was observed between the plants grown under ‘high flood’ conditions and ‘low flood’ conditions. Overall, L. flava showed difficulties to grow under dry conditions, but performed well under other conditions.

The genus Nanocladius Kieffer, 1913 (Diptera: Chironomidae: Orthocladiinae) has been frequently found in aquatic habitats of the Neotropical region. However, until now only one species was described living symphoretically on Ephemeroptera and no free-living species has been cited or formally described from the region. In the present study, two new species of Nanocladius are described and figured as male, pupa and larva: N. communis and N. longispicula. The specimens were collected from different streams in Brazil and are the first recorded species of the genus to the country.

Spaniophlebia male genitalia is described for the first time and the diagnosis of the genus is improved in order to encompass this new set of characteristics. Spaniophlebia kayapo sp. nov. is described based on male and female imagos from Pará and Mato Grosso states, Brazil, Spaniophlebia trailiae is redescribed based on newly collected material and comparison with the types, and Spaniophlebia escomeli is transferred to the genus Lachlania based on wing features and distributional data. A key to male imagos of the genus is provided as well as considerations regarding type-localities of Spaniophlebia species.

We investigated the diel vertical distribution patterns of microcrustacean zooplankton (Cladocera, Copepoda) in a shallow pond (max. depth: 70 cm) of the Öreg-turján peatland (Ócsa, Central Hungary) during three 24-h periods in July (19–20th), August (17–18th) and September (11–12th) 2011. Environmental variables showed remarkable vertical stratification. Oxygen concentration was close to zero in the entire water column from night until sunrise, while the lower strata (from 20 cm below the surface) were close to anoxic during all three diel cycles. It proved to be the main determinant of the vertical distribution of microcrustaceans. Accordingly, the highest proportion of individuals was present in the surface layer. Chlorophyll-a concentration and phytoplankton biomass were inversely distributed compared to zooplankton. Microcrustaceans (mainly Daphnia curvirostris) migrated to the middle layer only in August, which could be explained by a trade-off between food resources, dissolved oxygen (DO) and competition with littoral zooplankters. The diurnal density patterns of microcrustaceans suggested horizontal migration into the aquatic macrophytes during night, which could be a strategy to avoid Chaoborus predation. Our results show that strong vertical gradients of abiotic and biotic factors occur even in such shallow waterbodies. Among them, DO can maintain constant vertical aggregation of zooplankters by limiting their occurrence to the surface layers.

The present study focus on some aspects of zooplankton structure in the Alcantara River (Sicily, Italy), in relation to environmental factors. Zooplankton samplings were performed in spring in four sites, located from up- to downstream along the river course. Four low-flow velocity station points were chosen along a transversal river section in each site. Samples were taken from all station points in the four sites by two different mesh sizes (55 and 100 μm) rectangular nets. Rotifer abundances were an order of magnitude higher in 55 μm mesh size samples than in 100 μm mesh size ones. The two communities also resulted significantly different (ANOSIM test, ρ=0.212; P=0.1%). Generally, low abundances (from 3470±5133 to 422±474 ind.m−3) were explained by low chlorophyll a concentration and the high-flow regime of this river. Rotifer dominated the zooplankton community. Cladocerans, copepods and nauplii occurred with considerably lower abundances than rotifers. However, the relative contributions of these taxa to total abundances depended on the mesh sizes used. Euchlanis and Adineta genera exhibited the highest abundances in the rotifer assemblage. Conductivity alone or in association with temperature and dissolved oxygen was the most important environmental factor affecting rotifer community distribution. Cephalodella sp., Lepadella sp. and Trichotria pocillum showed a high positive relation to pico-plankton, showing this fraction as a possible rotifer food item. This paper demonstrated a higher efficiency of the finest net to characterize riverine zooplankton community that increases from up to downstream in terms of abundances and diversity.

Using data from nine lakes, sampled between 2002 and 2010, as well as literature we have analysed blooms of Gonyostomum semen (Ehr.) Diesing in a new spreading area (Polesie region, Central–Eastern Poland). We tried to determine habitat suitability for high biomass of the species, including both physicochemical and morphometric features. High biomass of Gonyostomum (>1.4 mg.L−1) was found in three groups of coloured water bodies: (a) very small (<0.002 km2) peat pits with low pH values and mineral content; (b) larger ponds with neutral pH values and intermediate conductivity; (c) natural lakes with intermediate parameters in terms of area, pH and mineral content. There were no statistical differences regarding the values of the species biomass among the groups of lakes. Gonyostomum biomass was closely positively correlated with water colour, whereas it was weakly negatively correlated with lake area and depth. The results show that G. semen in a new spreading area bloomed in a broad spectrum of freshwater habitats.

Cyanobacteria and their principal cyanotoxins were studied in the largest Italian lake (Lake Garda, 65 m a.s.l.) and in a near smaller reservoir (Lake Ledro, 652 m a.s.l.). The two lakes share a fraction of water due to a pipe pumping water from and into the lakes and the same dominant cyanobacterial species (Planktothrix rubescens). Despite the differences in the concentrations of cyanotoxins (mostly microcystins, MCs) and biovolumes of P. rubescens (BVPr) (over one order of magnitude), the Bayesian analyses linking these two variables showed striking similarities, suggesting the existence of similar toxic genotypes colonizing the two water bodies and a constitutive MC production. It was stressed that a greater sensitivity and reliability in the management strategies aimed at minimizing the risks due to cyanobacteria should also contemplate the use of specific lake-tailored models linking MCs and BVPr.

The “whitefin” gudgeon Romanogobio cf. belingi was recorded in the Nida River, a large lowland tributary of the upper Vistula (Southeastern Poland), for the first time in 2009. Since then, it has been caught during the periodical (three times per year) monitoring only sporadically. Conversely, in October and November 2012 R. cf. belingi was recorded frequently along an ∼60-km lowermost stretch of the Nida River. The abundance of this fish gradually increased downstream. This paper provides details of that phenomenon and discusses it in the context of the currently known distribution of this species.