2.4 Parameters of Introduction and Acclimatization of Exota . 



The actual possibility of introduction and acclimatization 

 (naturalization) of exota is determined by the physical-geographic, 

 autoecologicand synecologic, or biotic parameters. The possibility of 

 acclimatization is determined primarily by the agreement of the 

 physical -geographic (abiotic) conditions of the acceptor body of water 

 with the conditions in the donor body of water. The basis of this 

 agreement in naturally separated regions is the symmetry of the ocean 

 (Zenkevitch, 1948). Regions of the oceans which are located in areas of 

 similar climate but are separated by impassable continents, climatic or 

 water barriers, may be quite similar in terms of abiotic conditions. 

 The regions of the Boreal labitudes of the Atlantic and Pacific Oceans, 

 the western and eastern waters of these oceans, the Boreal and Notal 

 regions, the Arctic and Antarctic, as well as the tropical areas of the 

 Atlantic, Indian and Pacific Oceans are comparable in this aspect. The 

 capability for acclimatization and naturalization is determined by the 

 autoecologic parameters when the acceptor body of water has the 

 conditions necessary to the intruder species during the period of 

 reproduction for survival of the eggs and larvae, which are more 

 vulnerable than the species in other periods of life. The possibility 

 of introducing exota is determined by synecologic parameters, depending 

 on the local biota, the existence of an ecologic niche which is open, or 

 occupied by a less viable local species, the presence of sufficient food 

 resources, the resistence of the intruder in terms of parasitic invasion 

 and its susceptibility to local predators. These parameters basically 

 determine the nature of acclimatization, either interstitial or 

 replacement (Zinkevitch, 1963). 



The presence of an unoccupied niche in the biota of individual 

 regions of the ocean is determined by the geologic history of the fauna 

 and flora. Quite demonstrative in this respect, for example, are the 

 unoccupied or weakly occupied niches of the southern Boreal transitional 

 fish off the Pacific coast of North America (in comparison to the 

 Atlantic coast), the niche of silt-feeders in the Caspian (in comparison 

 to the Azov Sea), the niche of temperate and cold-water fish in the 

 Barents Sea (in comparison to the Bering Sea), the niches of a number of 

 tropical species in Hawaii and the eastern Mediterranean, of brackish- 

 water hydrobionts in the Caspian Sea, Boreal fish in the cool layer of 

 water at 50-100 m depth in the Black Sea (in comparison to the Baltic 

 Sea), the niche of the tropical phytoplanktophages in the Caribbean Sea 

 (in comparison to the South China Sea and, after acclimatization of the 

 chanos, to the Pacific waters of Mexico), the niche of large 

 benthophages in the Arctic (in comparison to the Antarctic), etc. These 

 niches are easily filled by immigrants from more life-saturated regions, 

 or may be filled by introduction of the corresponding species (Rass, 

 1965, 1975). 



Unoccupied niches in the seas are also created as a result of human 

 activity, which may change the environment and the composition of biota 

 by changing the mode of continental runoff, resulting in a decrease in 

 the population of transitional fish, or by extremely selective fishing 

 for certain fish, as well as development of their competitors. The 



404 



