Towards environmental DNA-based bioassessment of freshwater reservoirs with small volumes of water: robust molecular protocols

Bioassessment of freshwater quality via eDNA is rapidly developing into a powerful alternative to traditional methods involving collecting, sorting, and identifying macroinvertebrates based on morphology. Particularly attractive would be methods that can use remote-controlled boats for sampling because it would allow for cost-effective, and frequent monitoring at multiple sites. The latter will be particularly important for tropical reservoirs that require year-around surveillance. We here optimize molecular protocols for capturing reservoir-specific differences in metazoan communities based on small water volumes (15 mL). The optimization is based on samples from two freshwater reservoirs with very different water qualities ("reservoir signal"). Each reservoir was sampled at three sites ("biological replicates"). For each water sample, the DNA was extracted twice ("technical replicates"). We then tested how much DNA template (0.1 ng to 15 ng) and how many PCR cycles (25 or 35) minimized variance between technical replicates. We find that 15 mL is sufficient for capturing the reservoir signal regardless of sampling time, template amounts, or PCR cycle numbers. Indeed, extrapolation from our results suggests that <1 mL would be sufficient because only 17 of 59 metazoan mOTUs (mainly planktonic crustaceans and rotifers) detected with a 313bp COI minibarcode were shared. We find that the use of 35 PCR cycles significantly lowered the number of detected species and that template amounts <0.5 ng yielded somewhat higher variance between technical replicates. Despite extensive trials, the variance between technical replicates remained high (Bray-Curtis: 5-20%; Jaccard: 10-40%) and we predict that it will be difficult to reduce this variance further. However, the overall reservoir differences are so strong that all biological and technical replicates can be correctly assigned.

Short-term heat shock perturbation affects populations of Daphnia magna and Eurytemora carolleeae: a warning to the water thermal pollution

Thermal pollution leads to short-term heat shock in aquatic invertebrates; however, the modulation of tolerance and life history of these invertebrates by thermal stress varies among regions, phenology, species, and their acclimation. To assess the effect of thermal shock, we conducted experiments on Daphnia magna and Eurytemora carolleeae at 25 °C, 30 °C, 35 °C, and 40 °C (in relation to 20 °C) in a different exposure time of the stressor (10, 30, and 60 min). The results showed that short-term heat shock leads to increased mortality and reduced fertility of the studied planktonic crustaceans. D. magna was more resistant to thermal shock than E. carolleeae according to all variants of exposure based on the calculated LT50 values for 24, 48, and 72 h. Thermal shock decreased the potential of the Daphnia population in terms of the total number of births, however, with regard to individual reproductive abilities, the non-lethal heat shock did not reduce the birth rate. Although Eurytemora is more sensitive to thermal shock than Daphnia, the type of parental care in Eurytemora might be more favorable for offspring survival following thermal shock than in Daphnia. In Eurytemora, despite maternal deaths, a relatively high number of newborns who survived high temperatures were observed. The obtained results can help to understand the ecological processes occurring due to anthropogenic thermal pollution.

Modern characteristics of mass fish species and their parasites in polar reservoirs of the Yenisei basin (on the example of Kureyskoye)

The results of ichthyological and parasitological studies of the Kureiskoye reservoir are presented. The features of the formation of ichthyofauna during the formation of a reservoir and its industrial use are shown. The ichthyofauna of the Kureiskoye reservoir was formed on the basis of the indigenous fauna of the river. Kureyki. The modern composition of fish includes 22 species. Grayling fish are represented only by the Siberian grayling — Thymallus arcticus (Pallas, 1776). This species has a relatively small number of scales in the lateral line (no more than 95). Grayling is found in Lake Munduyskoye, which on average has about 100 scales. Since Munduyskoye Lake belongs to the river basin Kureyka, we believe that the second species, the black Baikal grayling Th. baicalensis (Dybowski, 1874) is also present. The main processes of its formation took place as in the Khantaskoye reservoir. Currently, the number of salmon and whitefish is decreasing. These groups of fish previously formed the basis of the composition of the original ichthyofauna. Today salmon and whitefish are found in the zone of backwater and flooded tributaries of river channels. The composition and number of whitefishes has changed especially. Tugun practically disappeared, others (peled, wild boil, vendace, and whitefish) began to be found singularly. The dominant role is played by pike, which uses peat islands for its spawning, as well as perch and roach. The transformation of the reservoir led to radical changes in the composition and structure of communities of all groups of organisms in the aquatic biota. This influenced the composition and abundance of fish parasites. The parasite fauna of the fish of the Kureyskoye reservoir is represented by widespread species of helminths. Infection with helminths mainly occurs when fish feed on planktonic crustaceans.

The importance of aquatic plants in maintaining zooplankton diversity and abundance: An experimental approach

The influence of different species and ecological forms of higher aquatic plants on the abundance, biomass and species diversity of zooplankton was investigated in experimental ecosystems (microcosms). It was shown that in the absence of fish and macroinvertebrate predators, the abundance and diversity of zooplankton in the plants beds increased. Not only phytophilous, littoral, and small planktonic crustaceans, but also some large obligate planktonic crustaceans, reached a high abundance among the plants. Plants belonging to different ecological groups stimulated an increase in the abundance of different groups of zooplankton. In the beds of submerged plants, the number of Cladocera increased to a greater extent than Copepoda or Rotifera. The abundance of Copepoda, both Cyclopoida and Calanoida, grew in the beds of helophytes. The relative number of predators in the community increased among the plants. The species structure and quantitative parameters of zooplankton had their own characteristics in monospecies and mixed phytocenoses of the same plant species. The index of species diversity of zooplankton acquired the highest values in the mixed phytocenosis. Higher aquatic plants increase spatial heterogeneity, which stimulates the development of facultative planktonic and benthic species. The formation of phytogenic detritus and the lifetime release of organic substances by plants into the water causes the development of bacteria and protozoa, which expands the quality and size range of food organisms for zooplankton. Therefore, zooplankton becomes more diverse in terms of the set of trophic groups.

Feeding of young-of-the-year fishes of the Curonian lagoon of the Baltic sea in 2016

Results of studies on nutrition of juvenile fishes of the Curonian Lagoon of the Baltic Sea are presented. Material on young-of-the-years nutrition was collected in October 2016 during the expeditions of «AtlantNIRO» at 14 standard stations in the Curonian Lagoon. A total of 418 specimens of young-of-the-years were collected and processed. Juveniles of fishes of the Curonian Lagoon were represented by 10 species: pikeperch, bream, roach, perch, smelt, ruffe, three-spined stickleback, ninespine stickleback, bleak and sabrefish. Planktonic and benthic invertebrates formed a basis of the young-of-the-years diet. In most species of juvenile fishes, the nutritional spectra did not differ from the nutritional spectra in the range. An exception was juveniles of the ruff and ninespine stickleback, in which planktonic crustaceans predominated in the diet, while in other reservoirs they consumed bottom organisms. Only Cladocera and Copepoda were found in the diet of roach of juveniles; bottom organisms were absent. In the range of roach juveniles, bottom organisms and mollusks prevailed. The food similarity indices for juvenile fish in the Curonian Lagoon are quite high, which may indicate a tension in food relations between juveniles and (or) partial or complete overlap of their food niches. The weakening of food competition is ensured by the divergence of daily dietary peaks. Three-spined and nine-spined sticklebacks as well as a sabrefish and sticklebacks have the closest food spectrum. On the contrary, sabrefish and bream have a different food spectrum. The peculiarity of feeding of pikeperch juveniles in 2016 was the lack of transition to predatory nutrition.

Planktonic Crustacean Culture—Live Planktonic Crustaceans as Live Feed for Finfish and Shrimps in Aquaculture

The cultivation of planktonic crustaceans as live feed is of paramount importance for the aquaculture and aquarium industries. The use of live cladocerans as feed for freshwater fish is limited to the aquarium industry, whereas Artemia and copepods are used to feed edible marine fish larvae with small mouth gape. Live feed production is expensive and time consuming; therefore, it is only used for fish that cannot be fed an inert diet directly, and only until they are ready for weaning to an inert diet. High-quality planktonic crustacean cultures are furthermore used to conduct environmental risk assessments for hazardous chemicals. Cladocerans are widely used for ecotoxicology testing, but Artemia and copepods are emerging as new model species. The present chapter reviews the culturing procedures of these important planktonic crustaceans: Artemia, cladocerans, and copepods. It discusses their use as live feed and as test organisms for environmental risk assessments. The culturing procedures are categorized into three complexity levels: Extensive, semi-extensive, and intensive. In general, the pros for Artemia and cladocerans are that they are easier to culture than copepods. Copepods are often more difficult in term of culture requirements and feeding. Nevertheless, copepods have the advantage of being in either freshwater or saline water, whereas cladocerans are limited to freshwater and Artemia to seawater. Artemia cysts and copepod eggs have a well-defined protocol for storage and distribution to aquaculture end users. Cladocerans, however, have the potential for the ephippia stage, although this is not well developed. For toxicological testing, three species are used: Artemia franciscana, Daphnia magna, and Acartia tonsa, with Artemia and A. tonsa in seawater testing, D. magna in freshwater testing. The chapter concludes with a comparative analysis of these organisms from use and culturing capability and demonstrates that there are strong similarities and challenges across these taxa.