Yu. V. Bespalaya

Results of testing the comparatory method: The curvature of the shell valve frontal section is inappropriate as a systematic character for the freshwater pearl mussel of the genus Margaritifera

This paper continues a discussion on the number of pearl mussel species of the genus Margaritifera in northern Europe. A biometric study of 1711 pearl mussel Margaritifera margaritifera shells from 15 rivers in Russia and Latvia (basins of the White and Baltic seas) has been conducted. All the examined samples fall into two groups: the northern group (with the shells more flattened on average, f. margaritifera) and the southern one (with more convex shells, f. elongata); the boundary between these groups is at 63° N. Analysis of intrapopulation variation has shown that the samples contain individuals that correspond to f. margaritifera, f. elongata, and f. borealis. However, any hiatus between these forms is absent in all the samples, and individuals belonging to two intermediate forms are rather frequent. The hypothesis on the species specificity of the shell valve frontal section has not been confirmed based on examination of large shell samples. The pearl mussels inhabiting rivers of Northern Europe belong to a single species, M. margaritifera.

State of the population of the European pearl mussel Margaritifera margaritifera (L.) (Mollusca, Margaritiferidae) at the northeastern boundary of its range (Solza River, White Sea Basin)

Only two river basins in which the European pearl mussel has survived to date are known in Arkhangelsk oblast. These are the Solza and Kozha basins. The northeastern boundary of the European range of this species passes along the watershed between the basins of the Solza and the Shirshema (the Onega Peninsula) and then along the Onega-Northern Dvina watershed. The population density and the proportion of juveniles widely vary in different parts of the Solza Basin, and, therefore, the previously conclusion concerning the ageing of the population in the Kazanka River (Bolotov and Semushin, 2003) applies only to certain parts of this river. The highest density of the pearl mussel in the Solza Basin is 68 ind./m2. Fish cultivation contributes to the conservation of this pearl mussel population, as the release of Atlantic salmon juveniles ensures reproduction of the mollusk under conditions of regulated river flow.

Freshwater Pearl mussels of the genus Margaritifera (Mollusca: Bivalvia) described as M. elongata (Lamarck, 1819) and M. borealis (Westerlund, 1871) should be classified with M. margaritifera (Linnaeus, 1758)

The shells of Pearl mussels from the basins of the Solza, Keret’, and Umba rivers flowing into the White Sea have been measured to determine the ratio of shell convexity to its maximum height. This ratio is the main character that, according to Bogatov et al. (2003), allows one to distinguish between three species of the genus Margaritifera: M. margaritifera, M. elongata, and M. borealis. It has been found that the above ratio gradually increases as the shell grows. Therefore, this character is unsuitable for species diagnosis, the more so that no hiatus in it between the three forms of pearl mussels has been revealed in any of the samples studied. On this basis, it may be concluded that Northern Europe, including Russia, is inhabited by only one species of pearl mussels, M. margaritifera.

Ecology and evolution of hydrobionts in hot springs of the subarctic and arctic: Formation of similar assemblages, adaptation of species, and microevolutionary processes

In the Subarctic and Arctic, the fauna of hydrothermal systems is considered to be an allochthonous, migration-mediated system comprised of the representatives of different taxa, which are characterized by a set of preadaptations to life in hot springs. These adaptations evolved before species had colonized this thermal anomalous environment. Hot springs characterizing by a constant temperature and hydrochemical regime appear to be the favorable sites compared to the usual local environment. The short-term existence of thermal springs on the geological time scale and their evolutionary evanescence serve as preconditions for the low fauna endemism that make up the taxa on the intraspecific and species levels. The taxonomical status of many of these forms has not yet been defined with certainty, since populations of new species and intraspecific taxonomic categories of mollusks that inhabit thermal pools may evolve similar morphological, physiological, and biochemical features independently; i.e., they may exhibit convergent similarity.

Influence of Historical Exploitation and Recovery of Biological Resources on Contemporary Status of Margaritifera margaritifera L. and Salmo salar L. Populations in Northwestern Russia

The influence of the historical exploitiation and recovery of biological resources on populations of freshwater pearl mussel and salmon was studied in the Kozha river (Onega River Basin). The freshwater pearl mussel was characterized by a low population density (0.09 ind./m2, on the average) and number of recruits. The role of the anthropogenic factor in the population is negligible; the effect of the pearl fishing is not observed. The dramatic decrease in the number of Atlantic salmon in the Onega River Basin in the late 20th century is a major reason for the slowed down reproduction of the freshwater pearl mussel. The second factor is the reconstruction of the Onega salmon hatchery in 1984, which led to a decrease in the juvenile salmon population density below the critical level on spawning and nursery grounds. As a result, mollusc reproduction has stopped. An artificial increase in the number of recruits must be developed in order to preserve the salmon population in the Onega River Basin. It is also necessary to forbid salmon fishing, including fishing migratory paths (with the exception of trapping for hatchery needs and traditional harvesting performed by locals in historical settlements).

Topical groups of mollusks in the lakes of Bol’shoy Solovetskiy Island (Solovetskiy Archipelago, White Sea, Northwestern Russian)

Topical groups of mollusks were studied in 13 lakes of Bol’shoy Solovetsky Island. A total of 20 species and 14 genera of mollusks were found. Five classes of mollusk topical groups may be defined with a higher probability. These groups include 12 to 19 species. All these species inhabit the littoral zone at depths of up to 3.2 m. No mollusks were found within the lakes’ deepwater zone (maximal depths of 10–30 m and silty grounds). A specific set of one to three dominant species is a characteristic of each class of topical groups. This may be treated as an effect of compensating for island communities: low species diversity is compensated for by increasing the density of colonies of some species. Ten mollusk species are significantly confined to a specific type of habitat.

Historical geography of pearl fishing in rivers of the Southern White Sea Region (Arkhangelsk Oblast)

The article provides an overview of literary and archival materials on the historical geography of pearl fishing, as well as a list of rivers of the Southern White Sea Region, where in the 17th–20th centuries pearls were mined. The most significant resources of pearls have been concentrated in the rivers Solza (with the tributary Kazanka) and Kozha (with the tributary Syvtuga) where there was regular and profitable trade of pearls for a long time. At present, pearl mussel populations have been preserved in these rivers, sometimes with a fairly high density. The volumes and frequency of pearl fishing can be indicators of shellfish abundance.

Mollusks in the Zoobenthos of Relict Lakes with Abnormally High Biological Production in the Eastern European Subarctic

Species diversity and density of mollusks have been studied in Vashutkiny Lakes (Bol’shezemel’skaya Tundra, northeastern Europe). These lakes are comparable to northern boreal lakes in mollusk species diversity and density levels. Two hypotheses proposed by Zvereva are analyzed: on the relict origin of the ecosystem of these lakes and on the leading role of intrazonal factors in the formation of their abnormally high level of production. Both hypotheses are confirmed by recent data. The production of these lakes is mainly determined by their flowing regime, which offers intense convective heat exchange between water masses and suprapermafrost taliks under the lakes and leads to the accumulation of summer heat in friable Quaternary sediments, which are widespread in lake depressions. Intense water exchange together with strong wind-induced mixing hinders the stratification of water masses.

Structure and species diversity of topical groups of mollusks in lakes of the Solovetsky Islands and Onega Peninsula, northwestern Russia

The main differences in the structure and species diversity of topical groups of mollusks between lakes on Solovetsky Island and continental lakes have been revealed. Insular groups are characterized by higher indices of species richness (the average number of species per sample) and density, with the level of dominance being decreased. In general, specific features of the insular territory impose limitations not only on the total species richness but also on the number of structural variants of topical mollusk groups, with the range of parameters of their species diversity being reduced against the background of sharp increase in the density of mollusk colonies. Insular topical groups of mollusks are characterized a certain set of species dominating in abundance.

Feeding of European Grayling Thymallus thymallus (Salmoniformes: Thymallidae) in the Early Winter Period in the Pymvashor Stream (Subarctic Hydrothermal System)

Water bodies of the North are characterized by a comparatively poor and at the same time rather vari� able food resources. Because of the instability of envi� ronmental factors and limitedness of the vegetative season, aquatic ecosystems cannot provide food requirements of fish by a single species or a group of feeds during a year. As a rule, this leads to euryphagy of fish inhabiting water bodies of high latitudes (Reshet� nikov, 1980).