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. ДВУСТВОРЧАТЫЕ МОЛЛЮСКИ БЕЛОГО МОРЯ. Опыт эколого-фаунистического анализа

The study of fauna of any region is closely connected with the investigation of taxo-nomic position of species within the taxa under consideration. Traditionally, the verbal shell description is mostly used in bivalve mollusks systematics. In spite of the numerous modern molecular researches, the conchological features make up the basics of our knowledge in this field up to now. That is why many malacologists try to formalize valve shape in order to make possible mathematical processing of data. Calculation of shell proportions became one of the first steps in this direction. This method primary used in the beginning of the 20-th century (Odhner, 1915; Mossewitsch, 1928; Mesiacev, 1931) seemed very promising and many authors suggested results of the shell shape analysis as crucial; but for all neither ecological plasticity nor age dynamics of the shell proportions were taken into account. A number of species and infraspecific forms were recognized (Derjugin, Gurja-nova, 1926; Mossewitsch, 1928; Mesiacev, 1931) unfoundedly as a result. The approach described was very important, no doubt, but it should be notified that regression analysis widely extends the possibilities of mathematical methods in bivalve mollusks systematics. On one hand, it allows distinguishing closely related species with similar shell proportions, and on the other it proves to be a convenient tool for exploration of an intraspecific variability (Naumov, Fedyakov, 1985, г). Moreover, it allows synonymizing mistakenly described species. Thus, the analysis of relationships between different dimensions of clam shells is very useful as a parallel approach to traditional investigation of their shape, because, in some cases, it becomes more informative and permits direct comparison of different aged samples. That is why in every case when available material allows, both proportions of the shell and regression equations are included in species diagnoses placed in this book.

The fauna inventory being an essential base of any faunistic investigation cannot be the end in itself nowadays. There are numerous important aspects concerning ecosystems functioning: Seasonal and long-term dynamics of species abundance in concrete biotopes is one of them. Investigation tradition considers such changes to be related with impact of abiotic factors. Meanwhile, the more data is accumulated, the more cases of dynamics that cannot be explained by direct influence of environmental characteristics we observe.

Previous observations of dense settlements of Mytilus edulis (Lukanin et al., 1986, а, б, 1989, 1990), Macoma balthica and Mya arenaria carried out by the author and his colleagues showed that long-term dynamics of abundance in species mentioned above cannot be totally explained by seawater temperature and salinity oscillations. Only elder, fully developed specimens can be often found in the colonies of some species, while juveniles rarely are encountered (Flyachinskaya, Naumov, 2003). Mathematical simulation of colony development created by the author demonstrates cyclic oscillations of biomass and population density, generating by recruitment conditions. This process can be regulated by adult mollusks. The possibility of such regulation is rather doubtless, however its mechanisms widely discussed in literature are not clear enough (Woodin, 1976; Moller, 1986; 'Olafsson,

1989 and others). The model is based on the demographic vector search in arbitrary time moment using Leslei transfer matrix depending on recruitment and differential mortality rate in individual generations. A new function for differential mortality rate was developed. The model obtained is rather flexible. Depending on initial parameters, it can describe both unchanging colonies and colonies, which possess different autocyclic oscillations of biomass and density. The generation of dynamics with relaxation oscillations of abundance is also possible.

Bivalve mollusks, being one of the most important benthic groups, play an essential role in many processes, which proceed in sea floor communities. In particular, cyclic oscillations of blue mussel abundance on a huge mussel bed was the main reason which provoked starfish Asterias rubens to be abnormally washed ashore on the Letny Shore (Dvina Bay) in

1990 (Buryakov, Naumov, 1991; Naumov, Buryakov, 1994). Obviously, the role of clams

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