Checklist and Distribution of Calanoida (Crustacea: Copepoda) in Kazakhstan (Central Asia)

This work aims to analyze the zoogeographic distribution of Calanoida in Kazakhstan. Kazakhstan belongs to the Palaearctic region, and its territory is ascribed to the European–Siberian and Nagorno–Asian biogeographical subregions. The European–Siberian subregion includes the Volga–Ural, Irtysh, and Turkestan–Aral provinces. The Balkhash province belongs to the Nagorno–Asian subregion. Studies of the Calanoida fauna were carried out between 1997 and 2019. For this purpose, 7250 zooplankton samples were taken in 130 different water bodies. Findings of 26 species of Calanoida have been documented. The richest in species composition (20) is the Calanoida fauna of the Irtysh province. Ten Calanoida species have been recorded in the Volga–Ural province, 8 in the Turkestan–Aral province, 7 in the Balkhash province, and 5 in the Ponto–Caspian region. The distribution of the species richness of the order is determined by a complex of climatic factors, including the density of the hydrographic network, a variety of hydrochemical conditions, and accidental acclimatization of species. Far Eastern species (Sinodiaptomus sarsi, Neutrodiaptomus incongruens, Neodiaptomus schmackeri) entered the inland water bodies of Kazakhstan, most likely through the introduction of non-native fish species. The Black Sea species Acartia tonsa and Calanipeda aquaedulcis were introduced into the Caspian Sea with ballast waters. Three autochthonous species (Limnocalanus macrurus, Eurytemora grimmi, Eurytemora minor), formerly inhabiting the Caspian Sea, can now be considered extinct. Acanthodiaptomus denticornis, Arctodiaptomus (R.) salinus, Phyllodiaptomus blanci, and Eudiaptomus graciloides are widespread in the region. Endemic species (Gigantodiaptomus irtyshensis, Arctodiaptomus naurzumensis) and species are new for Kazakhstan (Diaptomus (Chaetodiaptomus) mirus, Eudiaptomus transylvanicus, Arctodiaptomus dentifer, A. (Rh.) ulomskyi were found in small waterbodies; they are known only from single occurrence sites as well as Eurytemora caspica. The last one was described from the northern part of the Caspian Sea, in the coastal zone. Further research into small water bodies that are poorly studied may expand our knowledge of the diversity of Calanoida in Kazakhstan. Calanoida fauna of Kazakhstan was closest to the fauna of countries with a continental climate and most strongly differed from countries with subtropical and Mediterranean types of climates.

Genetic diversity of copepod, Limnocalanus macrurus, from Russian Arctic seas

The diversity, phylogenetic relationship and demographic history in glacial relict copepod, Limnocalanus macrurus from estuaries of large Siberian Arctic rivers Ob, Khatanga, Lena, Indigirka and Kolyma were studied using of mitochondrial cytochrome-oxidase c gene (CO I mtDNA). It was shown, that Siberian populations of Limnocalanus macrurus together with ones from Canadian Arctic and the Baltic Sea belong to the single Palearctic phylogenetic lineage, which probably survived in one refugium during the Last Glacial Maximum and then rapidly expand within the Arctic about 21 0007500 years ago. The presence of common haplotypes in L. macrurus from three Arctic seas and lack of differences in haplotypic frequencies may be caused recent origin of populations or present day genetic exchange between them.

Structural-functional characteristics оf zooplankton in the ob estuary and adjacent Kara sea shelf in summer

The study was carried out in the Ob estuary and the adjacent shelf of the Kara Sea in July 2016. For the first time data on the species composition, abundance and distribution as well as on feeding of zooplankton were obtained during the period of intensive river runoff. The biomass of zooplankton in terms of wet weight (without jelly animals and chaetognaths) varied over a wide range from 40 to 1880 mg/m3. The biomass was dominared by the Limnocalanus macrurus population, represented by all age stages, and Pseudocalanus spp. (an average of 60% and 17% of biomass, respectively. Maxima of zooplankton biomass were associated with the boundary of the distribution of river waters and with the southern periphery of the estuary frontal zone (EFZ). The short-term temporal variation of the abundance of zooplankton was observed when the transect was repeated after 2 days: the biomass at the southern periphery of the EFZ decreased from 1900 to 250 mg/m3). The observed changes is supposed to be caused by the shift of the southern boundary of the EFZ under the change in the wind regime. At high phytoplankton biomass in the estuary (>7 μg Chl-a/l), the daily ingestion of autotrophic phytoplankton of different copepodite stages of Limnocalanus macrurus was 5.77, 4.46, 2.59 and 1.4 μg C/ind/day in CVI, CV, CIV and CIII, respectively. Energy intake by younger copepodite stages not only covered the metabolic requirements, but also enabled the copepods to growth. At a relatively low Chl-a concentration (<2 μg/l) on the shelf, the mean values for older stages were lower (1.56 μg C/ind/day and 1.17 μg C/ind/day in CVI and CV, respectively) and hardly met the metabolic demands. The zooplankton grazing impact estimated with the gut fluorescence method varied from 0.2 to 7.3% of phytoplankton standing stock and from 2.2 to 30% of primary production. The results are discussed in relation to the specific hydrophysical conditions in the summer period and in comparison with the data obtained earlier for the autumn season.

Multidecadal dynamics of the Arctic copepod Limnocalanus macrurus in relation to environmental variability in the Baltic Sea

The Arctic Limnocalanus macrurus is a prominent representative of large copepods which performs several essential functions in freshwater and marine ecosystems. Being a cold stenotherm species, its distribution is primarily confined to deeper water layers. Based on the long-term observations from one of the largest spatially confined natural populations of this species in the Baltic Sea, we detected profound long-term variability of L. macrurus during 1958–2016: high abundances before the 1980s, then nearly disappearance in the 1990s and recovery in the 2000s. The main environmental parameters explaining the interannual variability of L. macrurus in spring were herring spawning stock biomass in preceding year, winter severity, and bottom water temperature in preceding summer. The effect of winter severity and water temperature was also non-linear. The sliding window correlation analysis pointed to a non-stationary relationship between the abundance of L. macrurus and the key variables. Given the observed pronounced seasonality in the population structure of L. macrurus (young stages dominated in the beginning of the year and only adults were left in the population in summer and autumn) we identified the dynamics of key environmental variables to understand this species under different ecosystem configurations and different combinations of drivers of change.

Mercury-methylating bacteria are associated with zooplankton: a proof-of-principle survey in the Baltic Sea

Methylmercury (MeHg) is a potent neurotoxin that biomagnifies in marine food-webs. Inorganic mercury (Hg) methylation is generally considered to be conducted by bacteria associated with sediment or detritus, but endogenous methylation by the gut microbiome of animals in the lower food webs is another possible source. We examined the occurrence of the bacterial gene (hgcA), required for Hg methylation, in the guts of dominant Baltic zooplankters. A qPCR assay targeting thehgcAsequence in three main clades (Deltaproteobacteria, FirmicutesandArchaea) was used in the field-collected specimens of copepods (Acartia bifilosa, Eurytemora affinis, Pseudocalanus acuspesandLimnocalanus macrurus) and cladocerans (Bosmina coregoni maritimaandCercopagis pengoi). All copepods were found to carryhgcAgenes in their gut microbiome, whereas no positive amplification was recorded in the cladocerans. In the copepods,hgcAgenes belonging to onlyDeltaproteobacteriaandFirmicuteswere detected. These findings suggest that endogenous Hg methylation can occur in zooplankton and may contribute to seasonal, spatial and vertical MeHg variability in water column and food webs. Additional molecular and metagenomics studies are needed to identify bacteria carryinghgcAgenes and improve their quantification in microbiota.