Andrey I. Azovsky

Cryptic diversity of the 'cosmopolitan' harpacticoid copepod Nannopus palustris: genetic and morphological evidence.

Nannopus palustris Brady, 1880 is a free‐living widely distributed harpacticoid copepod, which has been formerly assumed to be a single, cosmopolitan but highly variable species. We compared several geographically distant N. palustris populations in terms of their morphology and genetics. Populations from the White Sea (WS), the North Sea (NS), the Black Sea (BS) and two sympatric morphs from South Carolina, USA (SC notched and SC straight morphs), were considered. The NS, BS and to a lesser extent SC notched specimens were morphologically similar and partly coincided to the ‘canonical’ description of the species. By contrast, WS population showed remarkable anatomical and morphometric peculiarities that correspond to some earlier descriptions. Genetic analyses of mitochondrial (cytochrome b) and nuclear (28S rDNA) genes demonstrated the significant distinctness among WS, both SC and (NS+BS) populations, the latter two being genetically indistinguishable. Concordance between mitochondrial and nuclear gene trees and morphological data supports that N. palustris is in fact composed of several pseudo‐sibling species, which are genetically and morphologically divergent. Neither correlation between genetic divergence and geographical distance nor significant intrapopulation diversity was found for these species. Taxonomic status, distribution and phylogenetic relationships of the species within the Nannopus genus need to be reconsidered. A further subdivision of species complexes might have important implications for the analysis of biodiversity of benthic copepods and consequently for the interpretation of their (species‐specific) ecological function.

Large-scale patterns in marine harpacticoid (Crustacea, Copepoda) diversity and distribution

The zoogeographic distributions of 1,747 species of shallow-sea benthic Harpacticoida from 370 genera and 51 families reported in the Northern Hemisphere (Atlantic and Arctic Oceans and the European seas) were analyzed. Faunal diversity analysis revealed that the Northeast Atlantic and the North and Mediterranean Seas contain the richest faunas, while certain Arctic regions and internal seas (Caspian, Azov and Aral Seas) are the poorest ones. The distribution of families and genera was also briefly analyzed. Most families are widely distributed (probably cosmopolitan), though others are restricted to boreo-subtropical or even tropical zones, and no purely Arctic families were discovered. Many more genera are present in (or even restricted to) the tropics/subtropics compared with the Arctic/Subarctic zone. Over 15% of species and 55% of genera can be still considered either widespread or cosmopolitan. Cluster-analysis of the regions by species composition revealed six main clusters: Arctic (central Arctic basin, Kara, Laptev, East Siberian, Chukchi and Beaufort Seas), Boreal (North Atlantic Ocean, and North, Baltic, White and Barents Seas), Mediterranean, Ponto-Caspian (Black, Azov, Caspian and Aral Seas), Central East Atlantic, and Central West Atlantic. The distinction between the Mediterranean and Ponto-Caspian faunas is considered in particular, as the latter is not an exact derivative of the Mediterranean one but instead has more atlanto-boreal features. The percent of regional endemics, mean species occurrence and number of families correlate with total species richness, which primarily reflects the degree of exploration in a given region. After removing this effect, the abovementioned features show significant latitudinal trends, with a few endemics present in polar waters. The distribution patterns of different life-forms also vary according to their dispersal abilities. At both global and regional scales, bentho-pelagic forms are the most widely distributed, followed by phytal species, whereas benthic species, especially interstitial, have a more restricted distribution. Overall, our results confirm and statistically validate the main features of marine harpacticoid biogeography asserted a quarter of a century ago by Abele [In: Abele LG (ed) The biology of crustacea. Academic Press, New York, pp 242–304, 1982] and Wells (Syllogeus 58:126-135, 1986).

An Estimation of the Global Diversity and Distribution of the Smallest Eukaryotes: Biogeography of Marine Benthic Heterotrophic Flagellates

Protists are ubiquitous, but the factors influencing their diversity and biogeography remain unclear. We use a comprehensive database on the marine benthic heterotrophic flagellate (HF) morphospecies to explore the worldwide patterns in their diversity and distribution in comparison with predictions of the Ubiquity model (UM) and Moderate Endemicity model (MEM). The number of known HF morphospecies was limited (even when considering the rates of descriptions), and the local-to-global diversity ratio was relatively high (10-25%). Regional diversity was highly correlated with the investigative effort, indicating considerable under-exploration. Regional endemics were few (not over 19% of total richness), and many morphospecies were widespread or even cosmopolitan. No obvious latitudinal trend in HF diversity was detected. By species composition, the regions were distinctly arranged into three groups according to cold, temperate and warm waters, but not in accordance with geographical distances. This distribution pattern was most likely explained by contemporary climate (temperature) but did not suggest clear geographical barriers for dispersal. Therefore, the HF are less concordant with the MEM predictions but closer to the UM than other (larger) protists. Molecular studies reveal significantly higher HF diversity; the distributional patterns obtained from genetic- and morphology-based data, however, complement but not generally contradict each other.

Spatial variability of the structure of the Harpacticoida (Copepoda) crustacean assemblages in intertidal and shallow-water zones of European seas

On the basis of original and published data for 26 sites off Europe (the Barents, White, Black, Caspian, North, Baltic, Mediterranean, and Adriatic seas and the Atlantic Ocean) we assessed the variability of the near-shore benthic harpacticoid assemblages. A set of six life forms is recognized that retains its composition regardless of the geographical location and species composition of the assemblage. It is shown that the geographical variability of harpacticoid assemblages is low and intraregional and biotopical variations in the structure of these assemblages are often greater than their interregional (geographical) variability. It seems that the main factors that control the composition of species and life forms of harpacticoids are the characteristics of the sediments and the hydrodynamical processes that determine the structure of the sediments and the salinity.

Seasonal dynamics of the populations of intertidal harpacticoids (Harpacticoida: Copepoda) in the White Sea

In May to October 2001, seasonal variations in the population structure of four species of intertidal harpacticoids—Paraleptastacus kliei, Huntemannia jadensis, Heterolaophonte minuta, and Stenhelia palustris—were studied at three sites in the middle intertidal zone of Chernorechenskaya Bay (White Sea) with different sediment compositions. At different sites, the changes in the harpacticoid abundance, and the times and amplitudes of the peaks were different. The features of the local dynamics of the population are determined both by the intensity of its reproduction at the reproductive habitats and by the intensity of subsequent migrations. A comparison of the data available on the seasonal dynamics of the intertidal harpacticoids at various latitudes allows one to suggest that they are mainly determined by the temperature regime.

Structure of subtidal and intertidal communities of psammophilous ciliates of the Pechora Sea

A rich and diverse bottom ciliate fauna (168 species) was observed in the course of the studies of the subtidal and intertidal zones of the Pechora Sea; 81 of them were encountered for the first time in the Barents Sea region. As compared to the intertidal fauna, the sublittoral ciliofauna featured a higher species diversity but a lower total abundance (32.6 and 20.7 species per station and 10–100 and 2.4–443 ind./cm2 in the subtidal and intertidal zones, respectively). With respect to trophic strategies, raptorial feeders were most abundant in the sublittoral zone (up to 77% of the total biomass), while both raptorial feeders (45%) and upstream filter feeders (36%) dominated in the littoral sediments. In the subtidal zone, two different types of ciliate communities were distinguished according to their total abundance and species composition. The first type is represented by abundant and species-rich communities mainly dominated by large specific interstitial ciliates developed over fine-grained well-sorted sands. The second type of communities joins mainly nonspecific eurybiotic ciliates dwelling over heterogeneous silty sediments; they feature lower abundance and species richness values. The high species diversity, the low abundance or absolute absence of meso-and polysaprobic groups indicating organic pollution, and the high values of the ABC size structure index suggested a good condition of the sediments and biota in the region studied.

Modeling of the population density flow for periodically migrating organisms

The Patlak-Keller-Segel population density flow equation was derived based on the hypotheses concerning the way of movement of the benthic organisms with periodic appearance in the water mass differing from the commonly used assumptions [12, 14, 15]. On the basis of these hypotheses, a time-discrete and space-continuous individual-based model of the population distribution in the environment with the continuous stimulus distribution was built. Using this model, we have shown that the analyzed taxis mechanism (i.e., the decrease of the migration frequency of the individuals from the bottom to the water mass with the increase of the stimulus concentration) leads to the aggregation of the organisms in the places with a high concentration of the stimulus. The population dynamics is well approximated by the continuous model in which the obtained Patlak-Keller-Segel flow equation is used. The numerical modeling has shown that the form of the dependence of the individual migration frequency to the water mass on the stimulus concentration (hyperbolic, exponential, linear, and sigmoid) slightly influences the pattern of the individuals’ distribution.

Heterotrophic microbial communities on the water-sediment boundary in the Kara Sea

The qualitative and quantitative characteristics of the heterotrophic microbial communities (bacteria, flagellates, and ciliates) in the thin water-sediment layer in the Kara Sea are analyzed. The bacterial abundance correlated with the concentration of organic matter, whereas their size depended on the abundance of heterotrophic flagellates. The number of species of heterotrophic flagellates increased with the increase in the bacterial number. A positive relationship between the bacterial abundance and the ration of heterotrophic flagellates was observed at the offshore stations, probably due to the grazing pressure. The density of the ciliates on the soft silty and sandy-silty sediments was extremely low. The share of upstream filter feeding ciliate species increased with the increase in the abundance of the flagellates, probably due to the shift to less selective feeding strategies at higher values of the food concentrations. The classification of the heterotrophic microbial communities in the surface sediment layer has revealed two distinct types of the communities. The river communities are rich in species and are characterized by the high abundance of microorganisms. They are gradually replaced by marine communities at the salinity of 9%.

Diversity and Distribution of Free-living Ciliates from High-Arctic Kara Sea Sediments

For the first time, free-living ciliates were studied in sediments from a variety of habitats in the Kara Sea (the Arctic Ocean). Ciliates were found in a wide range of environmental conditions (from the intertidal zone up to depths of 554m, from salinities ranging from 0 to 34psu, and from coarse sands and gravel to muddy sediments), with total abundances varying from 1 to 127ind/cm3. Altogether, 114 species were identified, most of which were widely distributed and were previously reported from other Arctic regions. An unsaturated species accumulation curve and the presence of many rare species indicated that the Kara Sea is potentially as rich in ciliates as other regions. Fine- and medium-grained sands exhibited the richest and most abundant ciliate fauna, with many interstitial forms occurring up to depths of 200m; whereas both the coarse sands of the exposed intertidal beaches and the sublittoral muds were poorly inhabited by non-specific euryoecious species. The granulometric composition of sediments was suggested to be the main driver controlling the diversity and composition of ciliate communities, while the other factors, such as salinity, water productivity and depth, were of secondary importance.