Страница №292

. ДВУСТВОРЧАТЫЕ МОЛЛЮСКИ БЕЛОГО МОРЯ. Опыт эколого-фаунистического анализа


A natural border should be found for any waterbody to define its fauna. Such a boundary is expected along the line of maximum gradients of environmental characteristics if the waterbasins are connected to another one. According to conducted analysis of water structure and water current peculiarities (Naumov, Fedyakov, 1991, a), a narrow area in the White Sea fits this condition. It lies in the northern open part of the sea where Barents Sea waters are mixed with White Sea waters in equal proportion between the mouths of Ponoy and Shoyna Rivers in the middle part of Voronka Strait (Fig. 18). It was also found out that a number of Barents Sea species do not spread southward behind this line (Naumov et al., 1987; Naumov, Fedyakov, 1991, a). It allows drawing the faunistic border of the White Sea within the area of oceanographic boundary mentioned above. Thus, Derjugin's (1928) opinion of the White Sea independency was confirmed once more. The White Sea is an individual waterbody with its own features of hydrological regime and its own fauna, different from fauna of other seas.

The revision of clam species composition was needed after the introduction of clarity into the faunistic boundary of the White Sea. Two species: Yoldiella intermedia (M. Sars) and Macoma torelli (Steenstrup) were excluded because they were encountered only in the northern part of Voronka Strait northward of the faunistic border. Furthermore, it was discovered that no living specimens were found in the White Sea among some species previously included by different authors in the list of the White Sea bivalve mollusks. This concerns Portlandia aestuariorum (Mossewitsch), Bathyarca glacialis (Gray) and Zirphaea crispata (Linnaeus). The majority of modern malacologists consider Mya pseudoarenaria (Schlesch) as a synonym of Mya (Mya) truncata (Linnaeus) and Lyonsia schimkewitschi Derjugin, Gurjanova as a synonym of Lyonsia arenosa (Moller), so they also should be excluded from the White Sea fauna. Some authors include the Pacific mussel Mytilus trossulus Gould in the White Sea clam list. They do this because in several specimens of the White Sea mussels colouration and shell structure near the ligament edge resemble those found in Pacific individuals. Such point of view cannot be accepted, since neither biochemical nor physiological data confirm it. Lastly, Yoldiella frigida (Torell) was added to the White Sea fauna due to mistaken perusal of the original label during writing down the data into the catalogue of the Zoological Institute basic collection. Yet, a new species for the White Sea bivalve fauna Yoldiella nana (M. Sars) was found during our investigations (Naumov et al., 1987). Besides, it has been ascertained that there are two species of genus Hiatella in the White Sea, not one, as it was considered before.

Seemingly, species composition of the White Sea bivalve mollusks is studied almost completely. At the moment, 39 species belonging to 30 genera, 20 families, 7 orders and 3 subclasses represent the White Sea fauna of this taxon. Theoretical calculations using the original method of the total species number in a regional fauna estimation (Naumov et al., 1986, a) show an opportunity to discover two or three extremely rare species in the future. Thus, it should be claimed, that inventory of the White Sea clams is almost finished; further investigations hardly can enlarge the species list within the framework of methods used.

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