574 BIOLOGY OF THE SEAS OF THE U.S.S.R. 



of some six species through the Kuma-Manych depression (Zostera nana, 

 Cardium edule, Fabricia sabella, Atherina mochon pontica caspia, Syngnathus 

 nigrolineatus caspius, Pomatoschistus caucasicus). 



The second period, which started in the twenties of this century, is linked 

 with the accidental or purposeful bringing in of species by man ; nine Mediter- 

 ranean species have penetrated into the Caspian Sea during this period (Rhizo- 

 solenia calcar-avis, Mytilaster lineatus, Syndesmya ovata, Nereis diversicolor, 

 Leander squilla, L. rectirostris, Mugil auratus, M. saliens, Pleuronectes flesus) ; 

 the fish Gambusia affinis was also imported about this time. 



The third period was the time of the establishment of a direct water route 

 between the Caspian and Azov Seas by the Volga-Don canal and the auto- 

 immigration into the Caspian Sea of nine new Mediterranean forms (Black- 

 fordia virginica, Membranipora {Electro) crustulenta, Balanus improvisus, B. 

 eburneus and Rlrithropanopues harrisii spp. tridentata, the polychaete Mercier- 

 ella enigmatica, Monodaena colorata, Corbulomya maeotica and Podon poly- 

 phemoides). This third period, which began a few years ago, will prob- 

 ably turn later on into a long, complex and extremely curious process of 

 the reconstruction of the Caspian Sea fauna, as a result of the free influx 

 of the most euryhaline members of the Mediterranean flora and fauna. 



Apart from the above-mentioned 23 animal species, ten new sea-weed 

 species have been discovered in the Caspian Sea : first, Ceramium diaphanum 

 and C. tenuissimum (M. Kireeva and T. Shchapova, 1957); secondly, Ecto- 

 carpus confervoides f.fluviatilis and Polysiphonia variegata (G. Zevina, 1958). 

 Apparently none of these four forms was present in the Caspian in the 

 'thirties (Kireeva and Shchapova). A number of sea-weed forms, hitherto 

 unknown in the Caspian Sea (Acrochaeta parasitica, Ectochaete leptochete, 

 Enteromorpha tubulosa, E. salina, Entoneme salina, Acrochaetium daviesii) 

 were found by Zevina in the growths fouling hydrotechnical constructions. 



Thus the 'Mediterranean' group in the Caspian Sea comprises only 28 

 species, including one diatom, ten bottom-living algae, one marine flowering 

 plant, one medusa, one bryozoan, two barnacles, two shrimps, one crab, two 

 polychaetes, three molluscs, one cladocer and three species of fish. 



The process of the colonization of the Caspian Sea by new members of 

 flora and fauna and an exceptional mass development of some of them in 

 their new habitat (Mytilaster, Mugil, Rhizosolenia, Leander, Nereis, Syn- 

 desmya and Balanus) is linked with a number of curious ecological (syne- 

 cological) phenomena. First of all, with some of them an extremely intensive 

 development, similar to a kind of 'biological explosion', has been observed. 

 Thus Rhizosolenia calcar-avis, which penetrated into the Caspian Sea early 

 in the 'thirties, probably in small numbers, had by 1934 multiplied into several 

 million tons, forming two-thirds of the whole mass of plankton. The first 

 wave of exceptional mass development was followed by a drop in its numbers 

 and the biocoenosis, into which the new form entered and adapted itself, 

 limited its development. Immigrants from distant seas are of particular inter- 

 est among the new forms of the Caspian fauna. There are two of these in the 

 composition of the Caspian Sea fauna: the medusa Blackfordia virginica 

 (B. Logvinenko, 1959) and the crab Rhithropanopeus harrisii sp. tridentata 



