Chydorus Sphaericus Research Articles

Ratio-dependent functional response of two common Cladocera present in farmland ponds to Batrachochytrium dendrobatidis

Batrachochytrium dendrobatidis is responsible for amphibian declines worldwide. Decreasing the aquatic density of this chytrid through consumption of its infectious zoospores by Cladocera (water fleas) may mitigate the impact of chytridiomycosis. Understanding this predator-prey relationship requires insights in the zoospore ingestion rate of an average water flea, but such data are almost non-existent. We investigated the functional response of Simocephalus vetulus and Chydorus sphaericus feeding on B. dendrobatidis zoospores. These Cladocera commonly occur in farmland ponds, which may represent a major habitat for disease control. Both water fleas actively ingested zoospores and their per capita ingestion rate was best modelled in function of zoospore-to-Cladocera ratio, implying mutual interference among water fleas during zoospore feeding. The larger S. vetulus substantially consumed more zoospores, characterised by a maximum ingestion rate of 2.5 × 10 5 zoospores.Cladocera −1 .h −1 .mL −1 , which is about 12 times higher than for C. sphaericus . These findings are useful to support model-based management of chytridiomycosis. • Simocephalus vetulus and Chydorus sphaericus are common Cladocera in farmland ponds. • S. vetulus and C. sphaericus consume zoospores of B. dendrobatidis . • Zoospore ingestion rate for both Cladocera depends on zoospore-to-Cladocera ratio. • The larger S. vetulus has a significant larger per capita ingestion rate than C. sphaericus .

Changes in Antibiotic-Resistance Genes Induced by the Grazing Effect in Three Cladoceran Species.

The acquisition of Antibiotic-Resistance Genes (ARGs) by natural bacteria caused by antibiotic abuse is causing serious problems for human and animal welfare. Here, we evaluated the influence of three cladoceran species on Antibiotic-Resistant Bacteria (ARB) and tetracycline-resistance gene (tet(A)) copies, and discussed the effect of these biological interactions on the distribution and diffusion of ARGs in freshwater ecosystems. Bacterial community and tet(A) abundances in water samples collected from wetlands were strongly influenced by cladoceran presence. The presence of Daphnia obtusa dramatically decreased ARB and tet(A) abundance compared to that with other cladoceran species (Chydorus sphaericus and Simocephalus vetulus). Interestingly, we found a high abundance of Flavobacteriales in the microbiomes of cladoceran species. Considering that Flavobacteriales species are potential carriers of the tet(A) gene, their adsorption and assimilation with cladocerans could significantly impact the reduction of tet(A) in water. Field surveys also showed that tet(A) abundance could be low if the dominance of D. obtusa in each wetland was high. This study highlighted the need for ecological interactions and a broad range of niches in the food web when discussing the fate of ARGs in freshwater ecosystems.

Death‐feigning behaviours increase survival rate of littoral cladocerans under predation by odonate larvae

Abstract Because littoral cladocerans are common prey for odonate larvae, they are ideal organisms to examine prey and predator interactions in aquatic habitats. Although death‐feigning behaviour observed in littoral cladocerans is viewed as a trait to reduce predation risk, no study has examined the effectiveness of death‐feigning at reducing mortality. We studied the effectiveness of death‐feigning behaviour by two littoral cladocerans, Chydorus sphaericus and Oxyurella tenuicaudis, against the odonate larvae of Sympetrum frequens. We first examined how the odonate larvae detected the prey and found that the larvae consumed active cladocerans, even under dark conditions, but they did not consume anaesthetised cladocerans, indicating that the larvae detect the prey using mechanical cues such as vibrational currents created by the prey individuals. We then observed behavioural events of odonate larvae and prey cladocerans using a video‐recording system to count the number of cladocerans that showed death‐feigning behaviours when odonate larvae attacked and those that were not consumed when they showed death‐feigning behaviours. We observed a total of 1,099 behavioural events in prey–predator interactions. On average, the odonate larvae pursued 63% of the cladocerans encountered, attacked 89% of the cladocerans pursued, and successfully captured only 29% of the cladocerans with the first attack. Among the cladocerans that were not captured, 38% of the individuals continually swam, but 62% ceased to move and exhibited death‐feigning behaviours. The odonate larvae's capture rate for cladocerans exhibiting the death‐feigning behaviours fell significantly short of that for cladocerans that were continually swimming. The experiments clearly showed that the littoral cladocerans' death‐feigning behaviour effectively decreased predation rate by odonate larvae. The results suggest that the death feigning serves as an adaptive behaviour to reduce mortality risk in littoral cladocerans under predation by such predators that can detect prey using mechanical cues such as those of vibrational currents.

Changes in the structure and dominance of the zooplankton community of the Kremenchuk Reservoir under the effect of climate changes

Zooplankton plays an important role in aquatic food webs and changes in its abundance and diversity under changing climatic conditions can significantly affect the abundance and diversity of other aquatic organisms. The aim of the study was to assess quantitative and qualitative parameters of zooplankton development, dynamics of development of its dominant groups and the effect of water temperature. Species composition and abundance of zooplankton of the Kremenchuk Reservoir were studied in 2006, 2010–2012 and 2020 in relation to water temperature and pollution. Zooplankton species diversity fluctuated significantly over the years of the study. A total of 46 taxa were recorded in the reservoir during the study period. The number of recorded zooplankton taxa ranged 26 to 32 depending on the year. The most abundant zooplankters were Chydorus sphaericus, Copepoda nauplii, Brachionus diversicornis. The abundance of zooplankters in the reservoir during the study period ranged 23·103 to 256·103 ind./m3, and biomass 0.14 to 0.89 g/m3. A significant positive relationship was observed between the abundance of cladocerans, including some individual species (Ch. sphaericus and Ceriodaphnia sp.), and water temperature. Indicator species of water pollution in different years and in different parts of the Kremenchuk Reservoir differed significantly, which probably depended on the presence or absence (in a certain period of time) of polluting discharges. The total saprobity index in different years in different parts of the reservoir was in the range of 1.5–1.9. Structural indicators of zooplankton and its dominant complexes characterize the water in the Kremenchuk Reservoir as β-mesosaprobic. It is probably too early to assess the impact of climate change zooplankton as these changes are still unstable and short in time, but it is necessary to constantly monitor the biota of aquatic ecosystems to further study and summarize the data, which could later allow an identification of such changes.

Cladocera responses to climate changes and treeline shifts in an alpine lake-catchment since the Last Glacial Maximum

The study of alpine lake ecosystem ontogeny provides an understanding of how climate dynamics and the associated catchment changes impact on lake functioning. Here, a high-resolution subfossil Cladocera sedimentary record, together with geochemistry proxies, from an alpine, treeline lake (Cuoqia Lake) in SW China were analyzed to understand the lake ecosystem response to changes in the regional Indian summer monsoon (ISM) climate and the local mountain environment since the Last Glacial Maximum (LGM, ca. 19.5 cal kyr BP to present). The results show that the cladoceran record from Cuoqia Lake clearly responds to long-term climate change and significant climate events. The lake was depauperate in cladoceran species throughout the late glacial period (ca. 16–11 cal kyr BP) but Daphnia longispina-group and Chydorus sphaericus were the pioneer taxa when the lake was formed. The rapid proliferation of open-water and littoral cladoceran taxa began with increasing water temperature. The Younger Dryas (YD) cold event was recorded by high abundance of the cold-tolerant taxon C. sphaericus during ca. 12–11 cal kyr BP. At the onset of the Holocene (ca. 11 cal kyr BP), Alona spp. and macrophyte-associated taxa became dominant while numbers of C. sphaericus decreased dramatically. In the mid- to late-Holocene, the productivity of Cuoqia Lake seemed to have increased as reflected by higher Cladocera concentration and the appearance of Ceriodaphnia spp. and raptorial P. pediculus which are common in high nutrient waters. Partial Redundancy Analysis (partial-RDA) results highlight the strong effect of indirect climate change (mediated via catchment processes) on cladoceran assemblages during the Holocene. Abrupt shifts in sediment geochemical proxies and regional catchment vegetation at ca. 11 cal kyr BP indicate that substantial nutrient inputs, treeline advancement, and soil development in catchment resulted from the intensified ISM. Therefore, the cladoceran community changes suggest a long-term direct response of the alpine lake ecosystem to climate change since the LGM, but one that was strongly mediated by catchment-vegetation processes, such as the treeline shifts.

ОСОБЕННОСТИ СТРУКТУРЫ И ДИНАМИКИ ЗООПЛАНКТОНА ОЗЕРА НЕРО (ЯРОСЛАВСКАЯ ОБЛАСТЬ) В ПЕРИОД ПОТЕПЛЕНИЯ КЛИМАТА

Data on the abundance, biomass, and composition of the dominant complex of zooplankton in the shallow hypertrophic lake Nero (Yaroslavl region) from 2007 to 2017 are present. The spatiotemporal distribution of zooplankton is analyze. The high zooplankton species richness is characteristic of Lake Nero (>100 species in the general list and up to 22–27 species in the sample). 2007 to 2011, a low amount of zooplankton was noted (<37.9 thous. ind./m3 and 0.15 g/m3), with a relatively high proportion of copepods (up to 83%). Since 2012, the abundance of planktonic animals has increased (313 thous. ind./m3 and 1.20 g/m3). In 2007–2017 the composition of dominants remained close to that in previous years; small crustaceans (Bosmina longirostris, Chydorus sphaericus, Mesocyclops leuckarti), rotifers (genera Asplanchna, Brachionus, Keratella, Trichocerca and Anuraeopsis) dominated the zooplankton community. Rotifer-dominated communities (with a high abundance of thermophilic Brachionus diversicornis) formed during abnormally warm summers. Two species groups are determined: the first dominates in spring, early summer, and autumn, and the second in the second half of summer. The high abundance of zooplankton (>5 mil. ind./m3 and 10 g/m3) is in the thickets of macrophytes, which is 8–9 times higher than in the open littoral and pelagic zones. In the western littoral zone, the low abundance of zooplankton (<1 g/m3) may be associated with local pollution, high concentration of chlorophyll a, high phytoplankton biomass, represented by low food cyanobacteria. The center part and the adjacent open littoral zone differed in composition and abundance of dominant species from the southern bays occupied by macrophytes. The trophic status of the lake ecosystem in terms of zooplankton is hypertrophic since the 1980s. The abundance, composition and structure of the community in the long-term aspect are stable with interannual fluctuations common for a high-trophic shallow lake.

Impact of Fish Farming in floating cages on zooplankton Community in Euphrates River, Iraq

The Impact of floating cages Fish culture on zooplankton in Euphrates river of middle of Iraq was examined from cage and non-cage site at monthly intervals from January 2018 to December 2019. the physical and chemical properties of river water were measured including Water Temperature, Turbidity,Total Solid suspended ( TSS), pH, Electrical Conductivity(EC),Total Dissolved Solids(TDS),Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD5),phosphate (PO4) and Nitrate (NO3),The results indicated that: the, Turbidity,Total Solid suspended ( TSS), pH, Electrical Conductivity, Total Dissolved Solids(TDS), Biochemical Oxygen Demand (BOD5), (PO4) phosphate and (NO3) Nitrate values in cage site were significantly higher than non-cage site (p<0.05) This gives evidence of the effect of fish cages on this properties. In the current study about 48 Taxonomic units of zooplankton were identified, the rotifer was dominate group including 23 taxa to rotifera, 12 taxa belonging to cladocera and 13 taxa to copepod. The Zooplankton showed high density in river 9470 ind/m3 during April in non-cage site while lower1100 ind/m3 in December in cage site also the rotifer recorder density from (425 ind/m3 in cage site to 4925 ind/m3 non-cage site), cladocera density from225 ind/m3 in cage site to 1850 ind/m3 in non-cage site and copepod density from 450 ind/m3 in cage site to 2695 ind/m3 non-cage the high values were in spring and autumn while lowest values were recorded in summer and winter. The results of relative abundance index showed that the species rotifera: Keratella cochlearis,K.valga, Euchlanis delatata while the cladocera Alona rectangular, Bosmina longirostris, Chydorus sphaericus, Simocephalus vetulus and the copepods: nauplii were more abundant in the Euphrates river at cage site. The Shanon-Weiner index of total Zooplankton varied from 1.81 to 4.13 bit/ind while the Shanon index of Rotifer from 1.85 to 3.78 bit/Ind, Cladocera varied from 0.001 to 3.04 bit/Ind and Copeoda varied from 0.35 to 2.71 bit/Ind with greatest values were recorded at April and September in non-cage site while lower values at and June and November in cage site that give evident to effect of cage on zooplankton.

Effects of humic substances on the aqueous stability of cerium dioxide nanoparticles and their toxicity to aquatic organisms

The impacts of humic substances (HS) on the aquatic stability and toxicity of nano‑cerium dioxide (nCeO2) to three organisms with different exposure characteristics were investigated. Addition of HS to suspensions of nCeO2 lowered the surface zeta potential of the particles, reduced their hydrodynamic size, and increased the energy barrier as indicated by the total potential energy profile. This resulted in a more stable suspension compared to suspensions without HS added. Moreover, a higher concentration of HS further stabilized nCeO2 in the suspension. Acute toxicity of the suspensions to the unicellular green alga Raphidocelis subcapitata and to the crustacean Chydorus sphaericus was lower as compared to exposure without HS added. The acute toxicity of nCeO2 suspensions to the zebrafish (Danio rerio) eleutheroembryo was on the other hand significantly enhanced (additive and synergistic) upon increasing HS concentration. Our findings emphasize that HS is important to stabilize the nano-suspensions and that its impact on nCeO2 toxicity differs across different aquatic organisms. Emphasizing the exposure characteristics of each of the organisms selected from the trophic levels can explain how particle stability impacts particle toxicity.

Spatiotemporal patterns and impact of a cyclone on the zooplankton community structure in a brackish coastal lagoon

Zooplankton communities in response to hydrological (salinity, turbidity, water temperature, nitrate, phosphate, silicate) and biological (phytoplankton density) variables were studied in the Asia’s largest brackish water lagoon, Chilika (India). Water samples were collected from 13 stations on a monthly frequency between July 2014–June 2015. A total of 141 species of holoplankton including Ciliophora, Foraminifera, Rotifera, Rhizopoda, Gastropoda, Cladocera, Copepoda, Ostracoda, Malacostraca, Chaetognatha, Chordata, Nematoda, and 18 types of planktonic larvae were identified. Copepods were the most dominant and diverse zooplankton in terms of their species richness, numerical abundance, and widespread distribution in the lagoon. The major holoplanktonic taxa were Acartia sp., Acrocalanus gibber, Acrocalanus gracilis, Acrocalanus longicornis, Euterpina acutifrons, Lecane sp., Oithona sp., Pseudodiaptomus serricaudatus, and Tintinnopsis tubulosa. The dominant planktonic larvae were bivalve veliger, copepod nauplii, cyphonautes larvae, gastropod veliger, and protozoea of lucifer. Canonical correspondence analysis showed that distribution of zooplankton assemblages was influenced by salinity, turbidity, and phytoplankton density. Indicator analysis demarcated 26 indicator zooplankton taxa. Of these, the most prominent indicator zooplankton such as Belzebub hanseni, Mesopodopsis orientalis, Chydorus sphaericus, and Corycaeus catus were characteristic to salinity gradient in southern sector, sediment resuspension in central sector, eutrophic conditions in northern sector, and tide-induced intrusion of marine forms in outer channel, respectively. Hudhud, a category 4 cyclone resulted decline in the abundances of zooplankton population. Copepod nauplii and copepodites were dominant during post-Hudhud and their succession was linked to the increased phytoplankton density due to an upsurge in the nutrient level in the northern sector of the lagoon. The present study provided a comprehensive detail on the zooplankton composition and their environmental drivers including the impact of a tropical cyclone from a tropical coastal lagoon system.

Kayalıköy Barajı’nın (Kırklareli/Türkiye) planktonik mikrokrustase (Copepoda, Cladocera) tür çeşitliliği, bolluğu ve mevsimsel dağılımı

This study was carried out to determine the diversity, abundance and seasonal distribution of planktonic microcrustaceans (Cladocera, Copepoda) in Kayalıköy Reservoir. Cladocera and Copepoda samples were collected from May 2018 to April 2019 at three stations in the reservoir and some environmental parameters were measured. The qualitative evaluation of the samples revealed presence of 40 species, 24 from Cladocera and 16 from Copepoda, in the reservoir. The quantitative evaluation of the samples showed that 52690 ind./m³ zooplankton on average was found in the reservoir. The most common species in the reservoir were Daphnia cucullata, D. longispina, D. pulex, Bosmina longirostris and Chydorus sphaericus from Cladocera, and Arctodiaptomus wierzejskii, Acanthocyclops robustus and Thermocyclops crassus from Copepoda. According to the water quality standards, the measured values of water temperature, dissolved oxygen, sulfate, salinity and chloride indicated the first quality of water, while the light permeability, nitrite-nitrogen, nitrate-nitrogen, ortho-phosphate and chlorophyll-a values indicated the second and third quality of water levels. According to these results, we conclude that Kayalıköy Reservoir has a mesotrophic character in terms of the microcrustacean fauna and the physicochemical parameters.

The effects and interactions of three invasive fish species introduced to the aquatic ecosystem of a Turkish Lake (Eğirdir Lake)

We studied feeding behavior and prey selection of topmouth gudgeon (Pseudorasbora parva), big-scale sand smelt (Atherina boyeri) and pike-perch (Sander lucioperca) in Lake Egirdir, the second largest freshwater lake in Turkey. Fish specimens were collected between January and August in 2010 and 2011 using gill-nets and purse seines. A total of 941 specimens were analyzed for stomach contents analysis. We expressed the importance of the food items present in their guts with the relative importance index (IRI) and estimated their diet selectivity indices with Pearre’s index. Pseudorasbora parva had a diverse diet comprising mainly Nitokra hibernica (copepod), Chydorus sphaericus, and Bosmina longirostris (cladoceran) (each, at p 0.05). Big-scale sand smelt often preferred B. longirostris, N. hibernica, and Alona quadrangularis (each at p 0.05), Carassius gibelio was not preferred by pike-perch as food item (p > 0.05). Our results indicate that invasive species altered the food chain in Lake Egirdir. Thus, because these fish species constitute a major threat for native fish species for food and breeding grounds, extensive care should be taken to prevent invasive fish species entering lakes in Turkey.

Demographic consequences of mitigating strategies in planktonic invertebrates facing global browning of freshwater ecosystem

Recently, it has been reported that freshwater browning has less effect on planktonic invertebrate abundances than would be expected from current knowledge regarding of the biochemical activity of dissolved organic matter. It may be that the weak responses of whole communities to browning are masked because the individual mitigating strategies of community components have disparate demographic consequences. To examine the above hypothesis, individual-, population- and community-level responses of freshwater invertebrates to varying concentrations of terrestrial dissolved organic matter (tDOM) were investigated. Common cladocerans of the Chydoridae family, Chydorus sphaericus and Acroperus harpae, were used in the experiment which revealed that species employed different strategies to cope with tDOM. C. sphaericus maintained high production of asexual offspring at the cost of individual body growth, so any decreases in the population sizes were not observed. A. harpae, conversely, invested mainly in the production of resting eggs and increased survivability, which resulted in smaller populations. Invertebrate communities showed similar resilience and temporal stability across tDOM concentrations. Therefore, the influence of tDOM was apparently negligible at community level, since the effects of the mitigating strategies of the two species complemented one another. This experiment showed that symptoms of freshwater browning might be difficult to observe at population and community level due to effective mitigating strategies performed at the level of individuals. The effects of browning on freshwater invertebrates might be better considered in the context of alterations in the demographic rates together constituting life-cycle strategies to maintain species survival.

Role of sediment in determining the vulnerability of three littoral cladoceran species to odonate larvae predation

ABSTRACT Small cladocerans, found abundantly on surfaces of macrophytes and sediments in the littoral zone, are important prey not only for small fish but also for various invertebrates such as larvae of odonates in freshwater habitats. However, no study has documented how habitat substrates affect their behavior and vulnerability to predators and predation. We conducted laboratory experiments to examine the movement of 3 littoral cladoceran species, Chydorus sphaericus, Alona sp., and Ilyocryptus spinifer, to determine if their vulnerabilities to predation by odonate larvae changed depending on the presence or absence of bottom sediment. We observed that when sediment was present, Ilyocryptus crawled in and ceased movement. However, in the containers without sediment, they continuously swam or crawled. Similarly, Chydorus also reduced frequency of movement in a container with sediment, but Alona movement did not change regardless of the presence or absence of sediment. In the predation experiments with 2 or 3 prey species, Ilyocryptus was the most vulnerable to predation by odonate larvae in the containers without sediment but least vulnerable in those with sediment. The vulnerability of Chydorus to the odonate larvae was as low as that of Ilyocryptus in the containers with sediment. Alona was less preyed upon by odonates in containers with sediment but highly vulnerable to predation when containers had sediment with Chydorus and Ilyocryptus. These results indicate that behavior and vulnerability to predation of littoral cladocerans are species-specific and change depending on the presence of sediment and the existence of other species.

STUDY ON ZOOPLANKTON DIVERSITY DURING SPRING SEASON IN CHASHMA LAKE, PAKISTAN

The present study was conducted to know the zooplankton species diversity in Chashma Lake during spring (March 2016 to May 2016). Various physico-chemical parameters like Temperature, PH, Salinity, conductivity, Total dissolved solids (TDS), Turbidity, Dissolved Oxygen, Alkalinity, Chloride and Carbon dioxide which effect the distribution of zooplankton were also analyzed during this study. Zooplankton community was dominated by different species of rotifers. Those rotifers were Asplanchna herricki, Asplanchna brightwelli, Polyarthra remata, Brachionus angularis, Keratella cochlearis, Keratella tecta and Keratella valga tropica. Among these Keratella valga tropica was most common. Some species of copepods were recorded such as, Diacyclops thomasi, Acanthocyclops robustus, Mesocyclops edax, Tropocyclops prasinus mexicanus and Orthocyclops modestus. Among these Diacyclops thomasi was most abundant. Among copepods some nauplii and copepodid stages were also observed. Different species of cladocerans such as, Bosmina longirostris, Daphnia pulex, Chydorus sphaericus, Alona bicolor, Alonella exigua and Simocephalus serrulatus were also recorded.

First freshwater microcrustacean record in the bottom sediments of arctic ponds in Bellsund area (SW Spitsbergen)

First finds of small freshwater Crustacea in southern Bellsund (SW Spitsbergen) are presented. The remains of seven species of ostracods and three species of cladocerans were recovered from the bottom sediments of seven ponds in the region. The most abundant Arctocypris fuhrmanni Petkovski, Scharf and Keyser, 2016 was accompanied by the most widespread Candona rectangulata Alm, 1914, Limnocythere liporeticulata Delorme, 1968 and Tonnacypris glacialis (Sars, 1890) which are endemic to Arctic regions. New to the area Tonnacypris cf. mazepovae (Van der Meeren, Khand and Martens, 2009) was also encountered, being the first record of this species outside Northern Mongolia. Cladocerans were represented by the remains of Chydorus sphaericus (Müller, 1776), Daphnia pulex group Leydig, 1860 and Bosmina longirostris (Müller, 1785) for the first time noted in the bottom sediments in Spitsbergen.Significant differences in crustacean distribution occurred both between and within studied ponds presumably connected with the duration of active vegetation period and/or melt water delivery. The physical and chemical properties of the hostwater and/or some post-depositional processes could also affect the microcrustacean faunal distribution.

Biogeographic patterns of planktonic and meiobenthic fauna diversity in inland waters of the Russian Arctic

Abstract Broad‐scale assessment of biodiversity is needed for detection of future changes across substantial regions of the Arctic. Presently, there are large data and information gaps in species composition and richness of the freshwater planktonic and meiobenthos communities of the Russian Arctic. Analysis of these data is very important for identifying the spatial distribution and temporal changes in species richness and diversity of rotifers, cladocerans, and copepods in the continental Russian Arctic. We investigated biogeographic patterns of freshwater plankton and meiobenthos from c. 67° to 73°N by analysing data over the period 1960–2017. These data include information on the composition of rotifers, cladocerans, and copepods obtained from planktonic and meiobenthic samples, as well as from subfossil remains in bottom sediments of seven regions from the Kola Peninsula in the west, to the Indigirka River Basin (east Siberia) in the east. Total richness included 175 species comprised of 49 rotifer genera, 81 species from 40 cladoceran genera, and 101 species from 42 genera of calanoid, cyclopoid, and harpacticoid copepods. Longitudinal trends in rotifer and micro‐crustacean diversity were revealed by change in species composition from Europe to eastern Siberia. The most common and widespread species were 19 ubiquitous taxa that included Kellicottia longispina (Rotifera), Chydorus sphaericus s. lat. (Cladocera), Heterocope borealis, Acanthocyclops vernalis, and Moraria duthiei (Copepoda). The highest number of rare species was recorded in the well‐studied region of the Bolshezemelskaya tundra and in the Putorana Plateau. The total number of copepod and rotifer species in both Arctic lakes and ponds tended to increase with latitude. Relative species richness of copepods was positively associated with waterbody area, elevation, and precipitation, while relative species richness of cladocerans was positively related to temperature. This result is consistent with known thermophilic characteristics of cladocerans and the cold tolerance properties of copepods, with the former being dominant in shallow, warmer waterbodies of some western regions, and the latter being dominant in large cold lakes and waterbodies of eastern regions. Rotifers showed a negative association with these factors. Alpha‐ and β‐diversity of zooplankton in the Russian Arctic were strongly related to waterbody type. Lake zooplankton communities were more diverse than those in pond and pool systems. Moreover, the highest β‐diversity values were observed in regions that showed a greater breadth in latitude and highly heterogeneous environmental conditions and waterbody types (Bolshezemelskaya tundra and Putorana Plateau). Redistribution of freshwater micro‐fauna caused by human activities occurred in the 1990s and 2000s. As a result of climate warming, a few cladoceran species appear to have extended their range northward. Nevertheless, the rotifer and micro‐crustacean fauna composition and diversity of the majority of Arctic regions generally remain temporally conservative, and spatial differences in composition and species richness are chiefly associated with the differences between the warmer European and colder east Siberian climates.

Lineage diversity and gene introgression in freshwater cladoceran crustaceans of the Chydorus sphaericus species complex

AbstractThere is increasing interest in the genetic diversity and phylogeography of aquatic invertebrate zooplankton in the Eastern Palearctic, yet these topics remain largely unexplored in China. Here, we investigated the lineage diversity and phylogeography of an important cladoceran taxon, the Chydorus sphaericus (Crustacea: Cladocera) species complex, which is common in various aquatic habitats. We found populations of this species complex in 30 of 154 waterbodies across China. Analysis of DNA sequences from a portion of the mitochondrial cytochrome c oxidase subunit I gene placed these populations in three lineages, one of them not previously recognized. There was a clear geographical separation of C. sphaericus lineages: lineage A2‐1 was the only lineage detected on the Qinghai‐Tibetan Plateau, whereas lineages A3‐1 and A3‐2 were present elsewhere in China. Several lineages (and even individual haplotypes) were widespread in Eurasia, suggesting an ability to disperse over long distances. Phylogenies based on nuclear ribosomal internal transcribed spacer fragments (both ITS‐1 and ITS‐2) recognized two distinct C. sphaericus clades in China. Interestingly, one specimen possessing mtDNA of lineage A3‐2 was found unexpectedly to have an ITS‐1 allele normally associated with mitochondrial lineage A2‐1, and ITS‐2 alleles consistent with this. This discordance between mtDNA and nuclear phylogenies is indicative of interspecific hybridization and gene introgression between different members of the species complex. This study contributes to an understanding of the genetic diversity of the C. sphaericus species complex in a Eurasian context.

Diversity, abundance, and life histories of littoral chydorids (Cladocera: Chydoridae) in a subarctic European lake

Abstract Littoral chydorids were sampled with a bottom sledge in Takvatn, a 15 km2 north Norwegian oligotrophic lake with poor vegetation. Three out of eight recorded species of chydorids were common, with abundance minima in late summer and maxima in autumn. Eurycercus lamellatus (O.F. Müller, 1776) and Acroperus harpae (Baird, 1835) were monocyclic, whereas Chydorus sphaericus (O.F. Müller, 1776) was seemingly acyclic. Females of E. lamellatus appeared in early June and grew to maximum sizes of 2–2.5 mm in early August. Parthenogenesis started in late July and two summer generations could be distinguished by size distributions. Gamogenesis took place in September. Acroperus harpae females appeared in early June and grew to maximum sizes of around 0.7 mm in early August. Parthenogenesis started in early July and gamogenesis took place in September and October. Parthenogenetic females of C. sphaericus appeared already at ice-break and had constant sizes of around 0.4 mm through the entire season. Males or ephippial females were not observed. The acyclic life history may be an adaptation to the challenging environment of this subarctic lake. Summer generations could not be distinguished in the two small-sized species, but both populations reached high abundances in autumn. The abundance of E. lamellatus increased from August, but then decreased, possibly as a result of fish predation. We argue that the present results are typical for large oligotrophic lakes in subarctic Europe.

Subfossil cladocerans as quantitative indicators of past ecological conditions in Yangtze River Basin lakes, China

Cladocerans (Crustacea: Branchiopoda) are an essential component of the food webs of shallow lakes. However, their potential significance as sentinels of environmental change in subtropical regions of South-East Asia, is not well elucidated. In this study, we examined the distribution pattern of cladoceran subfossils in the surface sediments of 64 shallow lakes located in the middle and lower reaches of the Yangtze River Basin (MLYB). Using constrained ordination and multivariate regression trees (MRT), we explored the relationships between the distribution of cladocerans and contemporary environmental variables. The results indicated that macrophyte abundance is the most important regulator, followed by chlorophyll a and total phosphorus that all were important drivers of cladoceran community dynamics. Despite intensive aquaculture in the MLYB lakes over the past decades, fish predation did not have a significant influence on the cladoceran community, likely because the fish predation pressure was generally high. The MRT analysis showed distinct variations in the composition of cladoceran communities and was able to identify the key indicator species of various stressors, including Bosmina coregoni, small Alona (A. intermedia, A. rectangula) and Leydigia acanthocercoides, Leydigia leydigi and Chydorus sphaericus. Boosted Regression Tree (BRT), a novel numerical model, was employed to establish the quantitative relationship between cladoceran composition and environmental variables. The model was used to reconstruct historical macrophyte coverage over the past 60 years in a typical Yangtze lake, Liangzi Lake, based on sedimentary cladoceran records. The BRT-inferred macrophyte coverage was validated well by the macrofossil records in the same lake. Using subfossil cladocerans as indicator of the past environmental change in MLYB lakes is potentially useful given their key ecological roles. However, caution should be taken due to species-specific differences in preservation in the sediment and confounding environmental processes that to some extent may bias the conclusions.

Biological and geochemical indicators of climatic oscillations during the Last Glacial Termination, the Kaniewo palaeolake (Central Poland)

• Bølling-Allerød complex shows climatic heterogeneity and includes cold events. • Deglaciation passed 3 cold (GS-2a, GI-1d, GS-1) and 2 warm periods (GI-1e, GI-1a-c) • Traces of cold oscillation (GI-1b) within the Allerød were found. This study presents the results and interpretations of biological (floral and faunal) and geochemical (isotopic and chemical element composition) investigations of the Late Glacial and Holocene sediment accumulated in the Kaniewo palaeolake. These data allowed us to determine the indicators of environmental changes in this lake ecosystem, such as zooplankton and vegetation development, trophic state, water temperature, and water level. We documented the three cold periods (Oldest, Older, and Younger Dryas) separated by two warm periods (Bølling, Allerød). Additionally, we found traces of cold oscillations within the Allerød, lasting approximately 150 years, probably the Intra-Allerød-Gerzensee oscillation, recorded in western and southern Europe. Our data show that sediment accumulation began at the end of the Oldest Dryas period before ca. 13,900 yr cal BP. The top of the studied sediments represented the transition from the Late Glacial to the early Holocene (Preboreal period, ca.10,500 yr cal BP). The lithology of the sediments changed from silty sands at the bottom, then calcareous detritus gyttja partially interbedded by lake marl to peat at the top. Organic matter occurring in the deposits reflects algae and terrestrial sources. In the cold periods, small number of both Cladocera individuals and species (e.g. Bosmina (E.) longispina , Chydorus sphaericus , Alona affinis ), corroborate the unfavourable conditions for the development of zooplankton. Cladocera species indicated the initial oligotrophic status of the lake and the subsequent increase in trophic status. Plant and animal macrofossils indicate initial shallow lake ecosystem. Chara meadow developed at the bottom of the lake with a belt of vascular plants ( Carex sp., Hippuris vulgaris , Scirpus sp . ) in the littoral zone of the lake. Rich shallow vegetation was accompanied by animals, such as Mollusca (e.g. Valvata piscinalis, Pisidium obtusale, Bithynia tentaculata ) and Oribatidae sp., Cristatella mucedo , and Plumatella type.