Phytoplankton Communities and Cyanotoxin Production in Some Bulgarian Lowland Lakes and Reservoirs

One of the most evident consequences of eutrophication of waters is the progressive spreading of persistent cyanobacterial blooms. They are often accompanied by the production of cyanotoxins in concentrations, which are hazardous for human health. In this research, we analysed phytoplankton communities in four lowland water bodies, for the presence of cyanobacterial blooms and toxin production. The cyanobacterial biovolumes we found, determine three of the lowland water bodies: Onogur Reservoir (OR), Asparuhov Val Reservoir (AVR), and Srebarna Lake (SL) as “Alert Level 1” of potentially hazardous levels of cyanotoxins. Cyanobacterial biovolume exceeds the threshold value of 8 mm3 L-1 (recreational waters) in AVR and SL at the end of the summer period. In OR, we registered sustainable bloom of Microcystis spp. during the whole summer season, and extremely high average seasonal value of the total biovolume (146.5 mm3 L-1). Micro-cystins were reported in all four analysed water bodies, with the highest concentration in OR (6 µg L-1). Cylindrospermopsin was detected in AVR and OR, while saxitoxins were in AVR and SL. The concentrations of cyanotoxins do not exceed the guideline values in recreational waters. However, the increased biovolumes of cyanobacteria are a signal that in three of the analysed water bodies, monitoring is recommended at the levels of cyanotoxins during the summer period.

Changes in Ciliate Communities Reveal Modification of Lake Functioning Over the Last Century

Ciliates are unicellular heterotrophic organisms that play a key role in the planktonic and benthic food webs of lakes, and represent a great potential as bioindicator. In this study, we used the top-bottom paleolimnological approach to compare the recent and past (i.e. prior to major anthropogenic impacts) ciliate communities of 48 lakes located along an elevation gradient using metabarcoding techniques applied on sedimentary DNA (sed-DNA). Our results show an overall decline in the β-diversity in recent time, especially in lowland lakes which are more strongly expose to local human pressure. Analyses of the functional groups indicate important restructuration of the trophic food web and changes that are consistent with several well documented environmental changes such as the widespread increase in deep water anoxia, changes in thermal stability and nutrient cycling. Our study demonstrates the potential offered by sed-DNA to uncover information about past ciliate communities on a wide variety of lakes and the potential of using ciliates as valuable indicators, integrating information from the pelagic to the benthic profundal (and littoral) zones. Through trait-based functional community approach, the ciliates provide additional valuable information on ecosystem functioning, thus offering more a holistic view on the long-term changes of aquatic ecosystems.

Expanding the knowledge of plankton diversity of tropical lakes from the Northeast Colombian Andes

Introduction: A large number of planktonic communities found in tropical lakes have not yet been recorded, limiting understanding of how these ecosystems function and of the role that organisms play within them. Objective: Add new records of previously described species and to contribute to the knowledge of the planktonic communities present in tropical mountain and lowland lakes of the northeast Colombian Andes. Methods: Planktonic samples were collected and physicochemical variables measured in nine tropical lakes. Organisms were identified and a bibliographic search was carried out in databases and research articles to the identification of the new records to Colombia. Results: We present the data corresponding to six physicochemical variables measured in tropical lakes of this region and expand the existing information on organisms present in tropical lakes with a list of 391 taxa (299 phytoplankton and 92 zooplankton). The proportion of planktonic species unique to tropical lakes and the low similarity between lake types found with a Jaccard analysis indicated high heterogeneity of ecological conditions in the studied lakes. Conclusions: The 391 taxa found and 15 new records contribute to the list of planktonic organisms present in tropical lakes located in high and low areas of the Colombian northeast Andes.

Bacterial Diversity in Aquatic Ecosystems over the Central Himalayas, Nepal: Progress and Future Perspectives

Nepal hosts a large area of freshwater aquatic ecosystem including glacier associated system like glacier-fed streams and lakes as well as stream fed lowland lakes. Bacteriological studies are very important in aquatic ecosystems as bacteria are the major participants in biogeochemical cycles and food web structures. This study reviewed available literature in bacteriological studies of aquatic ecosystems in the Central Himalayas, Nepal and revealed that such studies are very limited. Thus, we conclude that future research works need to proceed through the latest molecular methods with high throughput technique using multiple environmental factors in the aquatic ecosystem.

Nematofauna of red piranha Pygocentrus nattereri (Kner, 1958) (Characiformes: Serrasalmidae) from Amazonia, Brazil

Between March and October 2008, 355 specimens of Pygocentrus nattereri were collected from the lowland lakes of Central Amazonia, Brazil, to study their nematode fauna. A total of 1.116 specimens of Nematoda were collected, belonging to six species. Procamallanus (Spirocamallanus) inopinatus was the species with the highest parasite indices. Larvae of Anisakis sp. have zoonotic potential and were found parasitizing the intestine and liver of Pygocentrus nattereri. Some of these nematode species were new records for the host P. nattereri. The diversity of nematodes that use P. nattereri as a host indicates the important role of this fish species in the maintenance of these six nematode species in the lowland lakes of Central Amazonia.

Zooplankton of mountain and lowland waterbodies of Northwestern India

In 2013–2015, 9 waterbodies situated in mountain and lowland regions of Northwestern India were studied. 46 species of zooplankton organisms were revealed, among them 18 Rotifera species, 20 Cladocera, 8 Copepoda, and 1 species of Anostraca. For this part of India, it was the first time detected 8 Rotifera species, 5 Cladocera, and 2 Copepoda. Cosmopolites and Paleotropic species were registered in all waterbodies studied in the Himalayans and lowland India. Palearctic and Holarctic species — in the Himalayans only. Tropic species were found in lowland India only. Species number and zooplankton species diversity index were low. Zooplankton density was relatively high in one from four mountain lakes and in all lowland waterbodies (99–487 thousands ind./m3). Zooplankton biomass was low (0.04–8.00 g/m3) in both mountain and lowland lakes, in exception two lowland lakes with wind onset and overwintering place for large birds. Rotifera dominated by biomass only in mountain region. Cladocera predominated in zooplankton density and biomass in majority of studied waterbodies. This group was represented by coastal and macrophyte forms which are usual for shallow waterbodies. Copepoda were abundant in five studied waterbodies and basically were represented by Cyclopoida. Calanoida group (Diaptomidae) was revealed in only one lowland lake located in a desert. Macrofiltrators represented the main part of zooplankton trophic structure. Microphages and predators subdominated in zooplankton communities.

Ecology of Cladocera species from Central America based on subfossil assemblages

<p>Cladocera species composition was analyzed in surface sediments of 29 lakes in Central America (Guatemala, El Salvador and Honduras). The material studied was collected with an Ekman grab in autumn 2013 from lakes located in lowland, highland and mountain regions. The study revealed high variability in qualitative and quantitative composition of subfossil Cladocera. A total of 31 Cladocera species (5 planktonic and 26 littoral) were identified, as well as 4 morphotypes that could not be identified (NRR<em> </em>1-4). Planktonic Bosminidae<em> </em>and<em> </em>Daphniidae were the most abundant families. Daphniidae were restricted to water bodies in mountain regions, whereas Bosminidae were widely distributed in lakes with different abiotic conditions. Moreover, Bosminidae species also occurred in highly mineralized waters (&gt; 900 µS cm^-1). The great majority of the identified Cladocera species belonged to the littoral family Chydoridae. <em>Chydorus </em>cf.<em> sphaericus</em> was the most common species (found in 20 lakes), which probably reflects its tolerance to a wide spectrum of habitat conditions. Cluster analysis discriminated 6 groups of Cladocera species with a high correlation level within groups (≥0.8), which showed different types of correlation with lake characteristics and environmental variables. Canonical correspondence analysis (CCA) showed that altitude and secondly water electrical conductivity were the most important drivers of Cladocera species composition in the region studied. Furthermore, CCA analysis indicated lowland lakes with low water transparency were also characterized by peculiar species assemblages. <strong></strong></p>