Феномен появления крупной ставриды в Чёрном море: версии и доказательства

Abstract

The paper provides an overview of literature data and results of the authors’ own investigations on the phenomenon of a sudden mass appearance of a “large” (“giant”) form of the horse mackerel (Trachurus, Carangidae) (LM) in the Black Sea in the late 1940s and its unexpected disappearance in the mid-1960s. This phenomenon was of great interest and attracted attention of many researchers hypothesizing that it was a new source of information for understanding processes of the organisms’ adaptation and important issues of microevolution and speciation. Different approaches to the study of this fact are analyzed, including determination of the LM origin and clarification of its taxonomic status. On their basis, three mutually exclusive versions are proposed. According to the first one, the LM is a new species of the Mediterranean origin; according to the second one, it is an ecomorph of Trachurus mediterraneus ponticus; and according to the third one, it is a hybrid of T. mediterraneus mediterraneus and T. mediterraneus ponticus. Based on the investigation on thermal resistance of isolated muscles and serological analysis of tissue proteins, Yu. Altukhov and co-authors identified the LM as an independent species of the Mediterranean (and, possibly, Atlantic) origin which appeared in the Black Sea because of a sudden expansion of its range after a sharp increase (outburst) in abundance. The main evidence for the Black Sea origin of the LM is the fact as follows: all stages of its life cycle, i. e., reproduction, growth of juveniles, feeding, and wintering of adults, occur in the Black Sea; moreover, its large specimens were known earlier. Belonging of the Black Sea “small” horse mackerel and LM to the same species was confirmed by the electrophoretic studies on protein composition of their blood serum. The idea of the hybrid origin of the LM was first proposed by I. Dobrovolov based on an investigation of electrophoretic spectra of nonspecific muscle esterases in T. mediterraneus ponticus and T. mediterraneus mediterraneus. According to our data, the third version of the LM origin seems more probable than other ones. Occurrence of T. mediterraneus mediterraneus in the Black Sea and its hybridization with T. mediterraneus ponticus are manifestations of the mediterranization; this process has intensified due to increasing anthropogenic load on the ecosystem of Azov–Black Sea Basin and ongoing disruption of freshwater balance resulting from overregulation of river flows and sea salinization. None of three versions can be refuted or confirmed by molecular genetic methods, since there is currently no LM in the Black Sea. Thus, the phenomenon of the “large” horse mackerel appearance in the Black Sea is still unexplained.

Keywords: Black Sea “large” horse mackerel, versions, Mediterranean origin, Black Sea origin, hybrid origin