2. Introduction and Acclimatization of Marine Organisms 

 (T. S. Rass, 0. G. Reznichenko) 



The composition of the fauna and flora of the oceans and seas is 

 related to a great extent to the history of their formation. Many 

 regions of the World Ocean are exposed to similar climatic conditions, 

 but are separated by barriers which are impassable to hydrobionts. The 

 fauna and flora of these regions contain taxonomically different, but 

 ecologically similar components, based on vicarious species. 



Over the past centuries, and particularly the 20th century, stable 

 species compositions and relationships of components of biota in many 

 regions have been disrupted by the introduction (stocking) and 

 acclimatization of exotic (foreign) species; we shall refer to these 

 species as exota. The spreading of many species beyond the limits of 

 their ordinary area of distribution occurs constantly, in spite of the 

 impediments (in the words of L. A. Zenkevitch), i.e., impassable natural 

 barriers. The most important means by which hydrobionts are carried 

 from one body of water to another is man. Independently of the wishes 

 of man, many species expand their area of development, utilizing 

 anthropogenic changes in nature: the digging of canals, changes in 

 estuarine spaces of seas due to decreases and alterations of runoff 

 resulting from the diversion of water for irrigation, the construction 

 of dams, the descent of industrial and domestic wastes down rivers, the 

 dumping of heated water by shoreline power plants. To a still greater 

 extent, the spreading of exota has been facilitated by transportation. 

 This is clearly indicated by the fact that, due to the recent spreading 

 of certain invertebrates carried by ships (the crabs Eriocheir sinensis , 

 Rhithropnopeus harrisi tridentatus , carcinus maenas , the cirripedia 

 Elminius modestus , Balanus improvisus , B^. eburneus , the polychaeta 

 Mercierella enigmatica l, the total area of their potential distribution 

 has now reached 2.5 'lO*^ km^, equal to the total surface of the Barents 

 Sea, the Baltic Sea, the White Sea and all of the southern seas of the 

 USSR (Reznichenko, 1976). The naturalization of such autoimmi grants is 

 greatly facilitated by underwater substrates created by man. Their 

 total surface is now at least 2,000 km^ (Reznichenko, 1976). Finally, 

 man actively distributes organisms for their maintenance in aquariums 

 (from which they frequently enter natural bodies of water) and for 

 acclimatization, breeding and culturation in new regions. 



In connection with the improvement of transportation, the 

 possibilities of introduction and acclimatization of marine exota have 

 greatly increased and have become at the present time an important 

 problem for oceanography. Until quite recently, even the most complete 

 reviews of oceanography did not even touch on this problem; now, that 

 would be a clear omission. 



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