Travaux du Muséum National d’Histoire Naturelle © 30 décembre «Grigore Antipa» Vol. LVI (2) pp. 227–251 2013 DOI: 10.2478/travmu-2013-0017

THE ZOOPLANKTON OF THE - CANAL IN THE FIRST TWO DECADES OF THE ECOSYSTEM EXISTENCE VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Abstract. This paper reports the invasive subspecies Podonevadne trigona ovum (Zernov, 1901), as dominant in the Danube-Black Sea Canal. In the first two years of the existence of the anthropogenic ecosystem (1985-1986) the zooplankton summarizes only 72 species. Over two decades it recorded the presence of 127 species. As a result of nutrient accumulation, in 2005, the zooplankton abundance has significantly increased, reaching 330 ind L-1, followed by an evident growth of biomass (2285 μg wet weight L-1). In 2005, the productivity registered 731.8 μg wet weight L-1/24h.

Résumé. Le présent papier rapport l’existence de la sous-espèce envahissante Podonevadne trigona ovum (Zernov, 1901), dominante dans le canal Danube – Mer Noire. La sous-espèce appartient à l’ordre Onychopoda, et elle a une origine Caspienne. Dans les premières deux années qui suit l’apparition de cet écosystème anthropogénique (1985-1986), le zooplancton a été reprèsenté par 72 espèces; après deux décennies, le nombre d’espèces a augmenté à 127. A la suite d’accumulation de nutriments, en 2005 l’abondance du zooplancton a augmentée de manière significative, atteignant 330 ind L-1, suivie d’une augmentation marquée de la biomasse (2285 mg s.um. L-1). En 2005, la productivité du zooplancton a enregistré 731,8 mg mat.hum. L-1/24h.

Key words: Danube - Black Sea Canal, species richness, abundance, biomass, productivity, invasive species.

INTRODUCTION The need to develop continental shipping, shortening of waterways and ensuring water supply to urban, industrial or agricultural centers, caused the appearance of man-made basins in the last 4-5 centuries. Much larger navigable canals were built beginning with the 19th century. In this category the Caledonian Canal (Scotland, 97 km), Erie (584 km), Illinois (154 km) or Intracoastal Waterway (4800 km) (United States), the Volga-Don (101 km), Volga-White Sea, 227 km (Russia or Black Sea-Dnieper-Bug-Baltic Sea (Ukraine and Belarus) can be mentioned (www.waterwayguide.com; www.scottishcanals. co.uk.; www.european-waterways.eu). In the hierarchy of the major channels of Earth, the Danube-Black Sea Canal occupies the third position, after Suez and Panama. It represents a significant segment of the important European waterways which ensures, together with the Danube River and the Danube-Main-Rhine Canal (171 km) the link between the Black Sea and the North Sea (www.geografialumii.ro). Having a series of benefits to human society, the canals can generate, at the same time, important ecological disorders. By passing geographical barriers for millions of years old, they make possible the spread of some species into new ecosystems. In favourable environmental conditions, the alien species can get invasive characteristics by changing the structure and trophic relationships of the indigenous communities and ultimately, causing damage of an economic nature (Marlene, 1990; Rivier, 1998; Zinevici et al., 2011). 228 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU For example, the construction of the Volga-Don Canal allowed the expansion of invasive organisms of the Caspian Sea to the Sea of Azov and the Black Sea. A similar phenomenon has been found in the Central Europe after opening the Main – Danube Canal that connect the Danube basin and the Black Sea to the Rhine and the North Sea. Other Ponto-Caspian species arrived in the Baltic Sea basin and later in the American Great Lakes after building a complex system of channels that links Volga, the Don, Dnieper, Bug, Vistula, Oder, Elba, Ladoga, Onega, connecting the Baltic Sea with the Black Sea and the Caspian Sea (Reid & Orlova, 2002; Alexandrov et al., 2007; Grigorovich et al., 2002). Strong invasive phenomena generated by the building of some canals were produced also in the marine environment. The creation of the Suez Canal caused the migration from the Indian Ocean and Red Sea into the Eastern part of the Mediterranean Sea over 300 species (Galil, 2000; Goren & Aronov, 2002; Briggs, 2007). The phenomenon is known as “lessepsian migration” (after the name of Ferdinand de Lesseps, the designer of the channel). It is estimated that approx. 17% of invasive marine species were transported through the channels (Galil et al., 2007). In , 67 invasive species were reported (60% marine and 40% freshwater species) (Skolka & Preda, 2010). Among these, Mnemiopsis leidyi Agassiz, 1865 has produced a true collapse of the Black Sea (Faasse & Bayha, 2006). More invasive species (185) have penetrated in the last decades of the 20th century in the Great Lakes. Dreissena polymorpha (Pallas, 1771), Bythotrephes longimanus Leydig, 1860 and Cercopagis pengoi (Ostroumov, 1891) produced important ecological changes and economic damage (Johannsson et al., 1991; Cohen & Carlton, 1998; Therriault et. al., 2002). The intrusion of the immigrants in aquatic basins is achieved mainly on passive way (69%), through anthropogenic vectors (ballast water and biofuel), complementary through aquaculture (6%), fish keeping, birds and aquatic animals (10%) (Ruiz & Carlton, 2003; Molnar et al., 2008; Minchin et al., 2009). The vessel traffic in the Danube-Black Sea Canal, the contact with the Black Sea waters, its interaction with the Sea of Azov and the presence of seabirds, running extensive movements in the area of the two marine pools have created conditions for the appearance of the zooplankton species in channel originating in the Caspian basin (Zinevici et al., 2011). As a result of the extensive effects induced by some invasive species, most ecological research aimed, mainly, at their ecology and interaction with some native species and less at the diversity or the community production. These aspects bring a touch of originality of this article.

MATERIAL AND METHODS The spatial analysis reveals the presence of two branches. The main (64 km) is located between the fluvial port of Cernavodă (Danube km 299) and the maritime port Agigea. Riverbed width varies within the limits of 120-140 m, and the average depth is 7 m. The secondary branch (31 km) is located between the Poarta Albă port (km 35 of main branch) and Midia seaport. The secondary channel width varies within the limits of 80-90 m and minimum depth is 5.5 m (Fig. 1). The water circulation and navigation are provided by 4 locks fitted with separate enclosures for every sense of movement. One of the locks is situated in the contact zone of the Danube waters with the main branch of the Canal, another is THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 229

11 Năvodari

Danube 1Cernavodă 2 9 10 Cernavodă lock 8 3 4 Ovidiu lock 5 7 Black Sea 6 Medgidia

Agigea 12 13

Agigea lock

Fig. 1 - The map of the Danube - Black Sea Canal with the indication of the sampling sites (1985 – 1986: 5, 12, 13; 2005: 1-11). located on the secondary branch, and the other two are located in the area of contact with the Black Sea. The water flows in the ranges of the two branches, between 0.3-0.9 mc/s and 0.13-0.23 mc/s, respectively. The water storage capacity is approximately 36 millions mc. Samples were collected in 1985, 1986 and 2005. Scientific data originated in two projects, one conducted during 1985-1986, the other in 2005. Most sampling points coincide, in 2005 (Fig. 1). Sampling was done seasonally in 13 sites (three in 1985 and 1986 and 11 in 2005) (Fig. 1, tab. 1). For this purpose a Patalas-Schindler device was used (5 l). For each sample 50 l throughout the water column were taken. The samples were concentrated by filtering through a gauze planktonic net with a mesh size of 65 µm. The sample preservation was made with 4% formaldehyde solution. Species were identified with an inverted Zeiss microscope using identification keys for ciliates (Foissner et al., 1991, 1992, 1994), testaceas (Bartoš, 1954; Grospietsch, 1972), rotifers (Ruttner-Kolisko, 1974; Rudescu, 1960), cladocerans (Negrea, 1983;

Table 1 Sampling sites of zooplankton. No st. Canal km Period Geographic landmark Canal section 1 64+000 2005 Cernavodă Danube – Black Sea 2 61+000 2005 Upstream Cernavodă lock Danube – Black Sea 3 47+600 2005 Mircea Vodă Danube – Black Sea 4 40+000 2005 Medgidia Danube – Black Sea 5 37+900 1985 - 1986, 2005 Medgidia Danube – Black Sea 6 28+700 2005 Poarta Albă Danube – Black Sea 7 23+000 2005 Basarabi Danube – Black Sea 8 20+700 2005 - Poarta Albă – Năvodari 9 15+100 2005 - Poarta Albă – Năvodari 10 10+000 2005 Downstream Ovidiu lock Poarta Albă – Navodari 11 2+000 2005 Năvodari Poarta Albă – Năvodari 12 0+000 1985 - 1986 Upstream Agigea lock Danube – Black Sea 13 - 1985 - 1986 Black Sea Agigea Zone 230 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU Rivier, 1998; Smirnov, 1996; Benzie, 2005), copepods (Damian-Georgescu, 1963, 1966, 1970; Dussart & Defaye, 2001). The analysis of abundance, biomass and productivity was assessed at species level. The results were presented by systematic groups, trophic levels (herbivorous zooplankton - c1 and predator zooplankton - c 2) and total zooplankton. The abundance was expressed in ind L-1, biomass in µg wet weight L-1and productivity in μg wet weight L-1/24h. In order to concentrate the great volume of data, the analysis of zooplankton was made, in most cases, for the whole ecosystem (mean values). In turn, for the evaluation of the spatial dynamics of the invasive Podonevadne trigona ovum, the data analysis was detailed on the 13 stations. For the biomass estimations the literature cited data in detail by species, sexes, stages of development and size classes were used (Nauwerck, 1963; Dussart & Defaye, 2001; Osmera, 1966; Odermatt, 1970; Dumont et al., 1975). The evaluation of productivity was achieved by methods of Galkowskaja (Rotatoria), Ilkowska-Stankzykowska (for planktonic larvae of Lamellibranchia); Winberg, Pečen and Shushkina (Copepoda and Cladocera) described in Edmondson & Winberg, 1971. Used formulas: -- for Rotatoria: P = Beggsx1/De+Badultx1/D2, where B = biomass, 1/De = daily rate of egg growth, 1/D2 = daily rate of adult growth; -- for Dreissena polymorpha larvae: P = 0.65xN/D, where N = ind L-1, D = the average time of larvae development, 0.65 = the average weight /ind. in D time; -1 -- for Cladocera: P = NexBe/De+NjxBj/Dj, where N = ind L , B = µg wet -1 -1 weight L , De = development time of eggs, Nj = ind L (juveniles), Bj = juvenile biomass, Dj = development time of juvenils; -- for Copepoda: P = NexBe/De+NnxBn/Dn+NcxBc/Dc, where e = eggs, n = naupli larvae, c = copepodits The values of development time are extracted from regression curves based on water temperature and plankton biomass (Edmondson & Winberg, 1971; Pourriot et al., 1982). In order to establish if statistically significant differences between the sampling stations and seasons exist, two factors without replication ANOVA test have been applied. The assessment of the role played by physical-chemical factors in determining the dynamics of zooplankton ecological parameters was revealed by means of Pearson simple correlations. For statistical processing, PAST software (Hammer et al., 2001), free version and XLSTAT (trial version) were used.

RESULTS The analysis of zooplankton community in the Danube-Black Sea Canal throughout the first two decades of the existence of anthropogenic ecosystem highlights the occurrence of a large species richness, illustrated by the presence of 191 species, organized in two trophic levels: primary consumers (herbivorous- detritivorous) (163 species) and secondary consumers (predators) (28 species) (Tab. 2, fig. 2). In terms of species richness of the primary consumers, the annual analysis revealed the dominance of rotifers (55.21%) followed, at long distance, by ciliates and THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 231

Table 2 The taxonomic list of the zooplankton in Danube – Black Sea Canal. Taxonomic structure 1985 1986 2005

Herbivorous zooplankton (c1) CILIATA Carchesium polypinum (Linnaeus, 1758) Ehrenberg, 1831 + Codonella cratera (Leidy, 1877) Imhof, 1885 + + + Colpoda cucullus O. F. Müller, 1773 + Epistylis plicatilis Ehrenberg, 1831 + Holophrya discolor Ehrenberg, 1833 + Holophrya gracilis (Pénard, 1922) Kahl, 1930 + Holophrya nigricans Lauterborn, 1894 + Ophryoglena collini Lichtenstein, 1921 + Ophryoglena flavicans Ehrenberg, 1831 + Ophryoglena oblonga Gajevskaja, 1927 + Paramecium aurelia O. F. Müller, 1773 + + Paramecium bursaria (Ehrenberg, 1831) Focke, 1836 + Paramecium caudatum Ehrenberg, 1834 + Strombidium velox Beardsley, 1902 + Strombidium viride Stein, 1867 + Strombilidium gyrans (Stokes, 1887) + Tintinnidium fluviatile (Stein, 1863) Kent, 1881 + Tintinnopsis cylindrata Kofoid & Campbell, 1929 + Urotricha pusilla Pénard, 1922 + Vorticella campanula Ehrenberg, 1831 + + Vorticella convallaria (Linnaeus, 1758) + Vorticella microstoma Ehrenberg, 1830 + Zoothamnium kentii Grenfell, 1884 + TESTACEA Arcella arenaria Greef, 1866 + + + Arcella vulgaris Ehrenberg, 1830 + Centropyxis discoides Pénard, 1902 + + + Centropyxis kolkwitzi Van Oye, 1949 + Centropyxis marsupiformis Deflandre, 1929 + Centropyxis penardi Deflandre, 1929 + Cyphoderia ampulla (Ehrenberg, 1840) Leidy, 1878 + Difflugia acuminata Ehrenberg, 1838 + Difflugia corona Wallich, 1864 + Difflugia globulosa (Dujardin, 1837) Pénard, 1902 + + + Difflugia fallax Pénard, 1890 Difflugia lobostoma Leidy, 1879 + Difflugia mammillaris Pénard, 1893 + Difflugia oblonga Ehrenberg, 1838 + + Difflugia oblonga acuminata Ehrenberg, 1838 + Difflugia oblonga brevicola Cash, 1909 + Difflugia tuberculata (Wallich, 1864) + Nebela collaris (Ehrenberg, 1848) Leidy, 1879 + LAMELLIBRANCHIA Dreissena polymorpha (Pallas, 1771) + + + ROTATORIA Anuraeopsis fissa Gosse, 1851 + Bdelloidea g. spp. + + 232 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 2 (continued) Taxonomic structure 1985 1986 2005 Brachionus angularis Gosse, 1851 + + + Brachionus angularis bidens Plate, 1886 + Brachionus angularis aestivus Skorikov, 1914 + + Brachionus bennini Leissling, 1924 + Brachionus budapestinensis Daday, 1885 + + + Brachionus calyciflorus amphiceros Ehrenberg, 1838 + + + Brachionus calyciflorus aneuriformis Brehm, 1909 + + + Brachionus calyciflorus calyciflorusPallas, 1766 + + Brachionus calyciflorus dorcas Gosse, 1851 + + + Brachionus calyciflorus dorcas spinosa Wierzejski, 1891 + + Brachionus diversicornis (Daday, 1883) + + + Brachionus falcatus Zacharias, 1898 + Brachionus forficula Wierzejski, 1891 + Brachionus leydigi rotundus Rousselet, 1907 + + + Brachionus quadridentatus brevispinus (Ehrenberg, 1832) + Brachionus quadridentatus cluniorbicularis (Skorikov, 1884) + + Brachionus quadridentatus quadridentatus Hermann, 1783 + Brachionus urceolaris O. F. Müller, 1773 + + + Colurella adriatica Ehrenberg, 1831 + Conochilus deltaicus (Rudescu, 1960) + Conochilus unicornis Rousselet, 1892 + Epiphanes macrourus (Barois & Daday, 1894) + + Epiphanes senta (O. F. Müller, 1773) + Euchlanis dilatata Ehrenberg, 1832 + + Euchlanis dilatata macrura Ehrenberg, 1832 + + Euchlanis lyra Hudson, 1886 + Euchlanis oropha Gosse, 1887 + Filinia limnetica (Zacharias, 1893) + Filinia maior Colditz, 1914 + + Filinia passa (O. F. Müller, 1786) + Filinia terminalis (Plate, 1886) + + Filinia sp. + Gastropus stylifer (Imhof, 1891) + Habrotrocha constricta (Dujardin, 1841) + Habrotrocha crenata (Murray, 1905) + Habrotrocha solida Donner, 1949 + Habrotrocha tripus (Murray, 1907) + Hexarthra fennica (Levander, 1892) + Kellicottia longispina (Kellicott, 1879) + Keratella cochlearis (Gosse, 1851) + + + Keratella quadrata (O. F. Müller, 1786) + + + Keratella ticinensis (Callerio, 1920) + Keratella tropica (Apstein, 1907) + Keratella valga (Ehrenberg, 1834) + + Lecane arcuata (Bryce, 1891) + Lecane bulla (Gosse, 1851) + Lecane luna (Müller, 1776) + + Lepadella quadricarinata (Stenroos, 1898) + Lophocharis salpina (Ehrenberg, 1834) + Mytilina crassipes (Lucks, 1912) + THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 233

Table 2 (continued) Taxonomic structure 1985 1986 2005 Mytilina videns (Levander, 1894) + Notholca acuminata (Ehrenberg, 1832) + + Notholca squamula (O. F. Müller, 1786) + Notommata tripus Ehrenberg, 1838 + Ploesoma truncatum (Levander, 1894) + Polyarthra dolychoptera Idelson, 1925 + + + Polyarthra euryptera Wierzejski, 1891 + Polyarthra minor Voigt, 1904 + Polyarthra remata Skorikov, 1896 + + + Polyarthra sp. + Pompholyx complanata Gosse, 1851 + + + Pompholyx sulcata Hudson, 1885 + Rotaria neptunia (Ehrenberg, 1832) + Rotaria rotatoria (Pallas, 1766) + Rotaria socialis (Kellicott, 1888) + Synchaeta grandis Zacharias, 1893 + + Synchaeta monopus Plate, 1889 + Synchaeta oblonga Ehrenberg, 1832 + + + Synchaeta pectinata Ehrenberg, 1832 + + Synchaeta stylata Wierzejski, 1893 + Testudinella emarginula (Stenroos, 1898) + Testudinella patina (Hermann, 1783) + + Trichocerca capucina (Wierzejski & Zacharias, 1893) + Trichocerca cylindrica (Imhof, 1891) + + Trichocerca elongata (Gosse, 1886) + + Trichocerca gracilis (Tessin, 1890) + Trichocerca iernis (Gosse, 1887) + Trichocerca pussila (Jennings, 1903) + + Trichocerca rousseleti (Voigt, 1902) + Trichocerca rattus (O. F. Müller, 1776) + Trichocerca similis (Wierzejski, 1893) + Trichocerca stylata (Gosse, 1851) + + Trichotria pocillum (O. F. Müller, 1776) + Trichotria tetractis (Ehrenberg, 1830) + Trochosphaera solstitialis Thorpe, 1893 + CIRRIPEDIA Balanus improvisus Darwin, 1854 + + CLADOCERA Alona costata Sars, 1862 + Alona guttata Sars, 1862 + Alona protzi Hartwig, 1900 + Alona quadrangularis (O. F. Müller, 1776) + Alonella excisa (Fisher, 1854) + Alonella nana (Baird, 1843) + Bosmina longirostris (O. F. Müller,1776) + + + Ceriodaphnia pulchella Sars, 1862 + Chydorus sphaericus (O. F. Müller, 1776) + + + Daphnia cucullata kahlbergensis Schoedler, 1866 + + + Daphnia galeata Sars, 1864 + + + Diaphanosoma orghidani Negrea, 1982 + + + 234 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 2 (continued) Taxonomic structure 1985 1986 2005 Disparalona rostrata (Koch, 1841) + Graptoleberis testudinaria (Fischer, 1848) + Macrothrix laticornis (Jurine, 1820) + Moina brachyata (Jurine, 1820) + Moina micrura Kurz, 1874 + + + Moina sp. + Pleuroxus aduncus (Jurine, 1820) + Pleuroxus laevis Sars, 1862 + Sida crystallina (O. F. Müller, 1776) + + COPEPODA Acartia clausi Giesbrecht, 1889 + + Calanipeda aquaedulcis Kritschagin, 1873 + Eurytemora lacustris (Poppe, 1887) + + Eurytemora hirundoides (Nordquist, 1888) + Eurytemora velox ( Lilljeborg, 1853) + Heterocope caspia Sars, 1897 + + Nitocrella hibernica (Brady, 1880) + + Harpacticoida g. spp. + + +

Predator zooplankton (c2) CILIATA Acineta flava Kellicott, 1885 + Acineta sp. + Amphileptus carchesii Stein, 1867 + Didinium balbianii Butschli, 1874 + + Didinium nasutum (Müller, 1773) Stein, 1859 + Dileptus margaritifer (Ehrenberg, 1834) Dujardin, 1841 + Euplotes affinis (Dujardin, 1841) Perty, 1852 + Frontonia acuminata (Ehrenberg, 1834) Bütschli, 1889 + Frontonia leucas (Ehrenberg, 1834) Ehrenberg, 1838 + Litonotus sp. + Lohmanniella spiralis Leegaard, 1915 + Trachelius ovum (Ehrenberg, 1831) Ehrenberg, 1838 + ROTATORIA Asplanchna brightwellii Gosse, 1850 + Asplanchna herrikii de Guerne, 1888 + Asplanchna priodonta Gosse, 1850 + CLADOCERA Leptodora kindtii (Focke, 1844) + + + Podonevadne trigona ovum (Zernov, 1901) + + COPEPODA Acanthocyclops languidus (Sars, 1863) + Acanthocyclops vernalis (Fischer, 1853) + + + Cyclops insignis Claus, 1857 + Cyclops scutifer Sars, 1863 + Cyclops vicinus Ulyanin, 1875 + Eucyclops serrulatus (Fischer, 1851) + Mesocyclops crassus (Fischer, 1853) + + Mesocyclops sp. + Oithona nana Giesbrecht, 1892 + + Paracyclops fimbriatus (Fischer, 1853) + THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 235

250

200 r e b

m 150 u n

s

e 100 ec i p s 50

0 1985 1986 2005

herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 2 - The zooplankton species richness detailed on trophic level. cladocerans (each 14.12%). In the case of secundary consumers, ciliates (46.44%) and cyclopids (Copepoda) (35.71%) were the most numerous species (Tab. 3). The analysis of annual species richness dynamics reveals the increasing trend of the primary consumers species number in relation to the secondary ones. Under these circumstances, the zooplankton abundance was characterized, in the first two years of the ecosystem existence, by low values (89.35 ind L-1). The gradual accumulation of nutrients has improved, to some extent, in the period ahead, the environmental conditions of the ecosystem. As a result, in 2005, two decades of existence of the ecosystem, the zooplankton abundance has significantly increased, reaching 330 ind L-1(Fig. 3). However, the average value in the period 1985-2005

Table 3 The zooplankton species richness (c1 and c2) (species number). Taxonomic composition 1985 1986 2005 Σ

Herbivorous zooplankton (c1) Ciliata 9 6 13 23 Testacea 4 4 16 18 Rotifera 31 31 65 90 Lamellibranchia 1 1 1 1 Cladocera 13 11 14 23 Cirripedia 1 1 - 1 Copepoda 3 4 5 7

Predator zooplancton (c2) Ciliata 2 3 8 13 Rotifera 2 2 1 3 Cladocera 2 2 2 10 Copepoda 4 5 2 2 236 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

350 300 250

l 200 / nd .

i 150 100 50 0 1985 1986 2005 Xa herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 3 - The zooplankton abundance (ind L-1) detailed on trophic level.

(152 ind L-1) is far below the multiannual average characterizing the zooplankton from the channels (532 ind L-1) (Zinevici & Parpală, 2006, 2007). Also, in this case, the abundance dynamics of c1/c2 ratio presents an overall downward trend. The analysis of the herbivorous consumer abundance reveals the dominance of the diaptomids (Copepoda) (36.19%) and rotifers (32.69%). In the case of secondary consumers stand out the dominance of cyclopids (Copepoda) (63.48%) followed by the cladocerans (17.35%) (Tab. 4). The biomass presents a similar dynamics: low value in the first two years of the zooplankton community formation (1440 and 470 μg wet weight L-1) (Zinevici et al., 1987), followed by an evident growth (2285 μg wet weight L-1) two decades

Table 4 -1 The zooplankton abundance (c1 and c2) (ind L ). Taxonomic composition 1985 1986 2005 Xa

Herbivorous zooplankton (c1) Ciliata 1.7 1.6 13.8 5.7 Testacea 0.2 0.1 2.2 0.8 Rotatoria 5.7 12.4 170.8 63 Lamellibranchia 6 3 60.1 23.1 Cladocera 10 5.4 53.7 23 Cirripedia 0.4 0.3 - 0.2 Copepoda 63 10.2 17.4 30.2

Predator zooplankton (c2) Ciliata - 0.1 1.3 0.5 Rotatoria 0.02 - 4.7 1.6 Cladocera 0.28 - 4.8 1.7 Copepoda 1.7 1.9 1.2 1.6 THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 237 later (Fig. 4). Also, the multiannual mean of biomass of the Danube-Black Sea Canal is obviously lower than the average of zooplankton biomass in the channels of the Danube Delta (Zinevici & Parpală, 2006, 2007).

2500,00

2000,00

l

t 1500,00 / e h w g

i e g 1000,00 w

500,00

0,00 1985 1986 2005 Xa herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 4 - The zooplankton biomass (μg wet weight L-1) detailed on trophic level.

The biomass structure reflects the dominance of cladocerans (67%) and diaptomids (Copepoda) (23.18%) in the case of primary consumers, as well as rotifers (43.86%) and cyclopides (Copepoda) (21.03%), as secondary consumers (Tab. 5). In 2005, the zooplankton productivity of the Danube-Black Sea Canal highlights, surprisingly, a higher value (732 μg wet weight L-1/24 h) (Tab. 6) than in the deltaic channel system (422 μg wet weight L-1/24 h) (Zinevici & Parpală, 2006).

Table 5 -1 The zooplankton biomass (c1 and c2) (µg wet weight L ). Taxonomic composition 1985 1986 2005 Xa

Herbivorous zooplankton (c1) Ciliata 0.14 0.29 1.65 0.69 Testacea 0.14 0.04 1.46 0.55 Rotatoria 6.23 5.88 279.38 97.16 Lamellibranchia 8.30 3.11 47.08 19.5 Cladocera 823.68 224.94 1384.6 811.07 Cirripedia 0.97 0.58 - 0.52 Copepoda 544.64 179.41 117.8 280.62

Predator zooplankton (c2) Ciliata 0.29 1.26 5.57 2.37 Rotatoria 14.61 2.14 231.2 82.66 Cladocera 10.9 - 180.51 63.80 Copepoda 30.4 52.7 35.79 39.63 238 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 6 -1 The zooplankton productivity (c1 and c2) in 2005 (µg wet weight L /24h). Taxonomic composition

Herbivorous zooplankton (c1) Rotatoria 277.49 Lamellibranchia 5.72 Cladocera 208.2 Copepoda 10.39

Predator zooplankton (c2) Rotatoria 203.34 Cladocera 25.81 Copepoda 0.85

The dominant groups of both trophic levels are rotifers and cladocerans, which sums the 55.3%, 41.49 % respectively (c1), 88.41%, and 11.22%, respectively in the case of secondary consumers (Tab. 6). The analysis of the frequency index for the 127 identified species in 2005 is edifying in this respect. It is noted, first of all, the absence of euconstant species. Secondly, it highlights the presence of extremely low (3 rotifers) persistent species: Synchaeta oblonga Ehrenberg, 1832 (65.91%), Polyarthra remata Skorikov, 1896 (59.09%) and Keratella cochlearis (Gosse, 1851) (54.54%). They represent only 2.36% of the total identified species compared with the accessories and accidental species, which sums 11.81%, 85.83%, respectively. In 2005, in the zooplankton structure of the Danube-Black Sea Canal, only two species were dominant: Synchaeta oblonga (Rotifera, c1) and Podonevadne trigona ovum (Cladocera, c2). Note also that Synchaeta oblonga is the only component of the zooplankton structure of the Danube-Black Sea Canal which meets both the dominant status as numerical abundance, biomass and productivity, as well as the constancy. The seasonal dynamics of the zooplankton in the Danube-Black Sea Canal, considered in the period March-December 2005, highlights the lowest values of the four ecological parameters in early March (Figs 5-8). Close values to those recorded in early December, when ends the development cycle of most species. The annual maximum of species richness is recorded in September as a result of the persistence of the thermophilic species and occurrence of those which prefer colder waters (Fig. 5). Instead, the higher values of abundance, biomass and productivity (Figs 6-8), conditioned in a significant extent of high levels of temperature, occur in August. The lowest seasonal variations are recorded in case of specific richness. Much wider variations are noted in the case of abundance and especially in those of the biomass and productivity. The seasonal dynamics of the four ecological parameters of zooplankton reveals the dominance of rotifers c1 and cladocerans c2 (Tabs 7-10). By applying the Pearson correlation, there was a highly significant relationship between all assessed zooplankton parameters and temperature (P<0.0001) (Tabs 11- -l 2 14). Abundance was also related to CCO-Cr (mg O2 ) (P<0.0001, R =0.50) (Tab. 12) -l 2 -l 2 and biomass to NO2 (mg N ) (P<0.001, R =0.27) and TP (μg P ) (P<0.001, R =0.23) (Tab. 13). The zooplankton productivity in the studied period was significant, related -l 2 -l 2 -l to NO2 (mg N ) (P<0.01, R =0.19), PO4 (μg P ) (P<0.01, R =0.15), TP (μg P ) (P<0.01, 2 -l 2 R =0.23), and CCO-Cr (mg O2 ) (P<0.01, R =0.18) (Tab. 14). THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 239

80 70 60 r e

b 50 m u n

40 s e 30 ec i p s 20 10 0 III VIII IX XII herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 5 - The seasonal dynamics of zooplankton species richness detailed on trophic level in 2005.

DISCUSSIONS The establishment of planktonic zoocoenoses in anthropogenic ecosystems is the result of an evolutionary process of completing with new species of not occupied ecological niches starting from a low level of diversity. This characterization of the formation and evolution processes of species richness is also valid for the zooplankton of the Danube-Black Sea Canal. In the first two years of the existence of the ecosystem (1985-1986) the zooplankton summarizes

900,00 800,00 700,00 600,00 l / . 500,00 d n i 400,00 300,00 200,00 100,00 0,00 III VIII IX XII herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 6 - The seasonal dynamics of zooplankton abundance (ind L-1) detailed on trophic level in 2005. 240 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

8.000,00

6.000,00 l / h g i

e 4.000,00 w

t e w

g 2.000,00

0,00

III VIII IX XII

herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 7 - The seasonal dynamics of zooplankton biomass (c1 and c2) detailed on trophic level in 2005. only 72 species. Over two decades it recorded the presence of 127 species. A very similar evolution presents the zooplankton community of Lake Iron Gate I (Danube km 948-1072): 74 species, in the first two years of the existence of the ecosystem. Three decades later 125 species were recorded (Zinevici & Teodorescu, 1982). The water circulation in the lacustrian system of the Danube Delta is provided by a complex network of natural and man-made canals that make the link between the branches of the river and lakes. They sum up to 3000 km. The dimensions and

3000 2500 2000 h 4

t

e 1500 /l/ 2 w

h g g i u 1000 e w 500 0 III VIII IX XII herbivorous zooplankton (c1) predator zooplankton (c2) total zooplankton

Fig. 8 - The seasonal dynamics of zooplankton productivity (c1 and c2) detailed on trophic level in 2005. THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 241

Table 7 The seasonal dynamics of zooplankton species richness (c1 and c2) detalied on sistematic groups in 2005. Taxonomic composition III VIII IX XII

Herbivorous zooplankton (c1) Ciliata 3 8 6 7 Testacea 8 6 10 9 Rotatoria 22 32 36 25 Lamellibranchia 1 1 1 1 Cladocera 3 5 9 6 Copepoda 1 4 3 3

Predator zooplankton (c2) Ciliata - 3 5 2 Rotatoria - 1 1 - Cladocera 1 2 1 - Copepoda - 1 3 -

Table 8 -1 The dynamics of zooplankton abundance (c1 and c2) detalied on sistematic groups (ind L ) in 2005. Taxonomic composition III VIII IX XII

Herbivorous zooplankton (c1) Ciliata 0.66 40.22 12.86 1.52 Testacea 0.60 5.03 2.04 0.93 Rotatoria 78.83 346.82 173.15 84.1 Lamellibranchia 0.02 153.61 86.41 0.08 Cladocera 0.04 181.97 32.37 0.4 Copepoda 3.85 47.35 17.17 0.97

Predator zooplankton (c2) Ciliata - 2.33 2.58 - Rotatoria - 18.04 0.44 - Cladocera 0.02 16.14 2.43 - Copepoda - 3.49 1.05 0.3

Table 9 The seasonal dynamics of zooplankton biomass (c1 and c2) detalied on sistematic groups (µg wet weight L-1) in 2005. Taxonomic composition III VIII IX XII

Herbivorous zooplankton (c1) Ciliata 0.59 5.41 0.83 0.14 Testacea 0.39 3.61 1.19 1.13 Rotatoria 40.6 778.73 251.97 46.09 Lamellibranchia 0.01 132.19 56.11 0.02 Cladocera 0.36 4829.84 701.12 6.42 Copepoda 22.56 258.98 177.33 12.27

Predator zooplankton (c2) Ciliata - 11.65 10.47 0.09 Rotatoria - 918.1 6.68 - Cladocera 0.59 661.52 59.95 - Copepoda - 96.72 45.65 0.86 242 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 10 The seasonal dynamics of zooplankton productivity (c1 and c2) detalied on sistematic groups (µg wet weight L-1/24h) in 2005. Taxonomic composition III VIII IX XII Herbivorous zooplankton (c1) Rotatoria 4.93 998.08 103.26 3.91 Lamellibranchia 0.001 699.18 7.02 0.004 Cladocera 0.01 31.51 117.58 0.08 Copepoda 0.61 31.51 9.34 0.09 Predator zooplankton (c2) Rotatoria - 809.89 3.59 - Cladocera 0.002 93.26 9.99 - Copepoda - 3.17 0.26 0.02 water flow of deltaic channels are more reduced in relation to those of the Danube- Black Sea Canal. Instead, the reversibility of the water circulation, conditioned by the dynamics of the annual hydrological regime, provides significant changes in lotic and lentic species ratio. Under these circumstances, the species richness of these ecosystems is maintained within comparable limits to those highlighted in the Danube-Black Sea Canal (34-121 species) (Zinevici & Parpală, 2007). The evolution of the productivity of the zooplankton in anthropogenic ecosystems is characterized usually by high values in the initial period of their existence, as a result of inclusion in the structure of the pools of terrestrial areas, rich in organic substance. The partial reduction of the nutrient concentrations in the coming years determine the downward trend of the parameter values leading to a relative environmental stability. Such a situation characterized the dynamics of zooplankton in Lake Iron Gates in the first decade of the ecosystem existence (Brezeanu & Petcu, 1973; Zinevici & Teodorescu, 1982; Zinevici & Parpală, 2004; Brezeanu & Zinevici, 1984).

Table 11 The correlation parameters between zooplankton species richness and environmental factors in the Danube-Black Sea Canal. Y Label R² P Significance level depth (m) 0.0060 0.6160 transparency(m) 0.1863 0.0034 ** T/D 0.1503 0.0093 ** temperature 0.7212 6.14228E-13 **** pH 0.0801 0.0627 conductivity 0.0097 0.5242

NH4(mgN/l) 0.0810 0.0612

NO2(mgN/l) 0.0416 0.1841

NO3(mgN/l) 0.0125 0.4700

PO4(µg/l) 6.00347E-05 0.9602 Org P(µg/l) 0.1214 0.0204 * TP(µg/l) 0.0170 0.3985 CCO-Cr(mgO/l) 0.2575 0.0004 *** DIN(mgN/l) 0.0296 0.2643 DIN/TRP 0.0051 0.8663 THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 243

Table 12 The correlation parameters between zooplankton abundance and environmental factors in the Danube-Black Sea Canal. Y Label R² P Significance level depth (m) 0.0881 0.0504 transparency(m) 0.0384 0.2021 T/D 0.0210 0.3479 temperature 0.3866 8.57E-06 **** pH 0.1489 0.0097 ** conductivity 0.0529 0.1330

NH4(mgN/l) 0.0064 0.6069

NO2(mgN/l) 0.0146 0.4347

NO3(mgN/l) 0.0067 0.5968

PO4(µg/l) 0.0221 0.3360 Org P(µg/l) 0.2790 0.0002 *** TP(µg/l) 0.1203 0.0211 * CCO-Cr(mgO/l) 0.5007 7.83E-08 **** DIN(mgN/l) 0.0823 0.0590 DIN/TRP 0.0014 0.9309

Two – way ANOVA with single observations showed that, in terms of the species richness and abundance, there are statistically significant differences (p=0.03, p=7.52 E-12, p=0.01, and p=1.88E-06) between stations and seasons. This canal passes over different areas, industrial, agricultural, with rich vegetation areas or completely devoid of vegetation, and has large size, large volume of water that suggests important ambient heterogeneity reflected on the zooplankton community structure. From the functional point of view (biomass and productivity), ANOVA test has found differences only in terms of season (p=9.77 E-07, p=1.78 E-06), probably due to the temporal succession of the dominant groups in the community. This test also

Table 13 The correlation parameters between zooplankton biomass and environmental factors in the Danube- Black Sea Canal. Y Label R² P Significance level depth 0.0471 0.1570 transparency 0.0303 0.2585 T/D 0.0183 0.3817 temperature 0.3964 6.1E-06 **** pH 5.22E-06 0.988261 conductivity 0.0103 0.512733

NH4(mgN/l) 0.0006 0.870218

NO2(mgN/l) 0.2683 0.000316 ***

NO3(mgN/l) 0.0207 0.350907

PO4(µg/l) 0.1927 0.002871 ** Org P(µg/l) 0.0698 0.083009 TP(µg/l) 0.2303 0.000979 *** CCO-Cr(mgO/l) 0.0962 0.040438 * DIN(mgN/l) 0.0212 0.345259 DIN/TRP 0.0366 0.650159 244 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 14 The correlation parameters between zooplankton productivity and environmental factors in the Danube-Black Sea Canal. Y Label R² P Significance level depth (m) 0.0235 0.3203 transparency(m) 0.0229 0.3264 T/D 0.0165 0.4060 temperature 0.3734 1.35E-05 **** pH 0.0185 0.3791 conductivity 0.0038 0.6929

NH4(mgN/l) 0.0133 0.4568

NO2(mgN/l) 0.1913 0.0030 **

NO3(mgN/l) 0.0348 0.2256

PO4(µg/l) 0.1557 0.0080 ** Org P(µg/l) 0.1212 0.0206 * TP(µg/l) 0.2293 0.0010 ** CCO-Cr(mgO/l) 0.1792 0.0042 ** DIN(mgN/l) 0.0353 0.2219 DIN/TRP 0.0293 0.6854 suggests the ecosystem carrying capacity because different structures have reached a homogeneous functional unit and stable ecological parameters, demonstrating that artificial created ecosystem tends to reach its own status of functioning. The short generation times correlated with species sensitivity to ecological fluctuations leads to frequent changes in time and space of the zooplankton species richness in inland waters. The large dimensions of the Danube-Black Sea Canal enhance the possibility of significant spatial variations of water quality and its trophic resources. These, in turn, create additional conditions for the manifestation of these dynamic traits of zooplankton species. The low occurrence of persistent species and the absence of euconstant species that provides continuity in time and space significantly influence the dynamics of ecological balance of the zooplankton community in the whole ecosystem. The dynamics of ecological balance, the configuration of trophic relationships or the value of quantitative ecological parameters also depend on a significant extent, by dominant species. Due to the fact that zooplankton organisms have short lifetime, most dominant species exercise this function over limited periods. This fact was highlighted in the case of zooplankton in the Danube-Black Sea Canal (Tabs 15-17). Fewer species maintain this function during the whole period of vegetation. But in the latter case, most species retain a dominant role only for a single ecological parameter. Zooplankton communities respond to a wide variety of disturbances including nutrient loading (Dodson, 1992) and other physical – chemical factors. Although zooplankton exists under a wide range of environmental condition, yet many species are limited by dissolved oxygen, pH, salinity, alkalinity, temperature, light and grazing affecting zooplankton population (George, 1962; Hutchinson, 1967). The main physical-chemical factor influencing the zooplankton dynamics in the Danube – Black Sea Canal in 2005 was the temperature (P<0.0001). Also, NO2 -l -l -l -l (mg N ), PO4 (μg P ), TP (μg P ) and CCO-Cr (mg O2 ) determined the variation of zooplankton productivity. THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 245

Table 15 The dominant species based on abundance in 2005. Dominant species III VIII IX XII

Herbivorous zooplankton (c1) TESTACEA Arcella arenaria Greef, 1866 5.07 6.69 ROTATORIA Polyarthra remata Skorikov, 1896 13.04 Synchaeta oblonga Ehrenberg, 1831 52.90 32.53 Synchaeta stylata Wierzejski, 1893 5.70 LAMELLIBRANCHIA Dreissena polymorpha (Pallas, 1771) 22.24 CLADOCERA Diaphanosoma orghidani Negrea, 1982 12.21

Predator zooplankton (c2) CILIATA Didinium nasutum (Müller, 1773) Stein, 1859 9.09 Frontonia acuminata (Ehrenberg, 1833) 16.67 18.18 ROTATORIA Asplanchna priodonta Gosse, 1850 23.81 CLADOCERA Podonevadne trigona ovum (Zernov, 1901) 9.09 33.43 29.93

Table 16 The dominant species based on biomass in 2005. Dominant species III VIII IX XII

Herbivorous zooplankton (c1) ROTATORIA Brachionus calyciflorus anuraeiformis Brehm, 1909 8.46 Synchaeta oblonga Ehrenberg, 1831 31.97 22.13 CLADOCERA Alona quadrangularis (O. F. Müller, 1776) 11.40 Bosmina longirostris (O. F. Müller, 1776) 13.97 24.22 Diaphanosoma orghidani Negrea, 1982 16.46 COPEPODA Heterocope caspia Sars, 1897 7.38

Predator zooplankton (c2) CILIATA Didinium nasutum (Müller, 1773) Stein, 1859 9.09 Frontonia acuminata (Ehrenberg, 1833) 18.18 ROTATORIA Asplanchna priodonta Gosse, 1850 42.07 CLADOCERA Podonevadne trigona ovum (Zernov, 1901) 9.09 21.35 34.89 COPEPODA Mesocyclops crassus (Fischer, 1853) 19.19 246 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 17 The dominant species based on productivity in 2005. Dominant species III VIII IX XII

Herbivorous zooplankton (c1) ROTATORIA Brachionus calyciflorus anuraeiformis Brehm, 1909 10.23 8.47 Brachionus calyciflorus dorcas Gosse, 1851 Synchaeta oblonga Ehrenberg, 1831 53.04 25.43 CLADOCERA Alona quadrangularis (O. F. Müller, 1776) 9.17 Bosmina longirostris (O. F. Müller, 1776) 21.16 20.55 Diaphanosoma orghidani Negrea, 1982 14.76

Predator zooplankton (c2) ROTATORIA Asplanchna priodonta Gosse, 1850 51.35 9.09 CLADOCERA Leptodora kindtii (Focke, 1844) 11.77 Podonevadne trigona ovum (Zernov, 1901) 9.09 54.54

The subspecies Podonevadne trigona ovum, dominant in the Danube-Black Sea Canal belongs to the Caspian Onychopoda order that includes 33 species and subspecies. Only 46% of them maintain the endemic character, 21% inhabit both the native and other pools, and 33% have disappeared from the fauna of cladocerans of originating basin. Among them there are the mentioned subspecies (Rivier, 1998). After the specialists’ opinion, this species appeared 77,000 years ago, during a large transgression (to a maximum level of +50 m), early Khvalin time (7x104 – 4x104 y) of Pleistocene phase (Dumont, 1998; Rivier, 1998). The melting of glaciers caused the considerable rise in the water level of the Caspian basin. This has resulted in the flooding of huge areas, the emergence of communication ways with neighbouring basins and the significant decreasing of water salinity in the northern half of the basin. As the effect of the regression process, the cladoceran populations were isolated in the Azov basin and the middle sector of the River Ural. The further increasing of the water salinity of the Caspian Sea caused the disappearance of populations remaining in its interior. It was maintained, instead, localized populations in the Azov basin and Lake Chalchar in the middle sector of the Ural River. The construction of the Volga-Don Canal and dam lakes in the basins of the rivers Volga, Don, Dnieper, Bug and Dniester in the period 1930-1975 offered to the Onichopod cladoceran the opportunity to populate new ecosystems, including the Black Sea lagoons of the rivers Dnieper, Burg and Dniester (Gusynskaya, 1989; Mordukhai-Boltovskoi & Negrea, 1965). The analysis of the zooplankton in the main branch of the Danube-Black Sea Canal at the end of the first year of the ecosystem existence (October 1985) revealed the occurrence of the invasive species in the terminal area (upstream from the Agigea gateway), as well as in the mixture of fresh and marine water at the mouth of the Canal (Tabs 18, 19). It is the first finding of its penetration in the Romanian waters (Zinevici et al., 2011). The possible vectors of the cladoceran disseminations in the new ecosystem are seabirds and the ballast water of ships, which could carry the resistant eggs. THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 247 The adaptation of the immigrant at the new ecosystem conditions has encountered major difficulties, beginning what could not be overcome. As a result of this, his presence has not been confirmed in the following year. The resuming of the investigations after two decades revealed its recurrence in the zooplankton structure of the channel. Its occurrence in 10 of the 11 research stations examined during 2005 reflected the advanced stage of integration in the structure and trophic relationships of the ecosystem. The absence of the immigrant in the contact zone of river waters with those of the channel highlights the tendency to avoid the lotic environment. A similar situation was observed in the rivers Volga, Don, Dnieper, Dniester and Bug: set in the dam Lakes on their route, in the structure of the river, zooplankton is missing (Grigorovich et al., 2002). The evolution of the integration process of the invasive species in the zooplankton structure of the Danube-Black Sea Canal is reflected in the frequency index dynamics. In the initial phase of contact with the new ecosystem (October 1985), its frequency was accidental (25%) (Tab. 18). The occurrence of the immigrant was reported two decades later, during the whole cycle of vegetation in most analyzed areas of canal reflects the existence of an advanced process of integration into the structure of the predator zooplankton c2. The seasonal dynamics of frequency index highlights low values in spring, corresponding to the accessories status of the analysed species. At the end of the summer and the first half of autumn it becomes constant and euconstant component. At the end of autumn it disappears from the structure of the zooplankton, after laying of resistant eggs. The mentioned dynamics reflects the thermophile character of the Onychopod cladoceran, inherited, perhaps from the original species (Podoevadne trigona), from which it was detached during the evolutionary process, with 77,000 years ago. The analysis of abundance percentages of predator zooplankton highlights also the increased tendency of its integration into the structure of zooplankton communities. As a result of this process, carried out during the two decades, the Caspian cladoceran becomes the dominant component of the numerical abundance of predator zooplankton (Tab. 19). Throughout the seasonal cycle, the highest values of the caspian cladoceran abundance were recorded in summer. The highest abundance values recorded in the middle sector of the canal are due to the preference for the lentic fresh water environment. Taking into account the strong immigration trend of the Podonevadne

Tabel 18 The dynamics of frequency of Podonevadne trigona ovum. Year Month % Ecological status 1985 V - - VI - - X 25.00 accidental XI - - Xa V-XI 6.25 accidental 2005 III 9.09 accidental VIII 81.82 euconstant IX 54.54 constant XII - constant Xa III-XII 36.36 accessory 248 VICTOR ZINEVICI, LAURA PARPALĂ, LARISA FLORESCU, MIRELA MOLDOVEANU

Table 19 The dynamics of Podonevadne trigona ovum percentages in the predator zooplankton abundance. Month Year Stations V VI X XI 1995 2 - - - - 5 - - - - 12 - - 23.40 - 13 - - 0.86 - 2005 III VIII IX XII 1 - - - - 2 100 - - - 3 - 8.86 - - 4 - 59.04 - - 5 - 64.45 77.42 - 6 - 30.62 12.50 - 7 - 50.00 54.20 - 8 - 32.71 50.91 - 9 - 82.12 100 - 10 - 6.51 - 11 - 2.05 16.67 - Xa 1-11 9.09 30.58 26.82 trigona ovum it can be forecast that in the next stage, this species will populate a number of littoral lakes of the Romanian Black Sea coast. The invasive behaviour of some species belonging to Onychopoda, resulting in significant changes in the structure of ecosystems, suggests the need of monitoring of Podonevadne trigona ovum in the Danube-Black Sea Canal.

ACKNOWLEDGEMENTS Thanks to Dr. Ştefan Negrea, renowned scientist in the cladoceran systematics, for his support in determining the subspecies Podonevadne trigona ovum. Also, thanks to Dr. Cristina Sandu for providing the necessary physical - chemical data in statistical analysis. The authors thank Stela Fofa for the laboratory technical support and to Lucian Apetre for the map of the Danube -Black Sea Canal. Thanks are due to the Institute for Auto, Naval and Air Transport Design and the Administration of the Navigable Canals, Agigea S.A., related to the processes of formation and evolution of the Danube-Black Sea Canal. The study was funded by project no. RO1567-IBB02/2011 from the Institute of Biology Bucharest of .

ZOOPLANCTONUL DIN CANALUL DUNĂRE-MAREA NEAGRĂ ÎN PRIMELE DOUĂ DECENII DE EXISTENŢĂ A ECOSISTEMULUI REZUMAT Necesitatea dezvoltării transportului naval continental, a scurtării unor căi de navigaţie şi a asigurării cu apă a unor centre urbane, industriale sau agricole a determinat, în ultimele 4-5 secole, apariţia unor bazine hidrografice antropogene. Realizând o serie de beneficii pentru societatea umană, canalele pot genera totodată producerea unor importante dereglări ecologice. De remarcat este prezenţa subspeciei invazive Podonevadne trigona ovum, dominantă în Canalul Dunăre-Marea Neagră. Subspecia aparţine ordinului Onychopoda şi este de origine caspiană. În primii doi ani de existenţă ai ecosistemului antropizat (1985-1986), zooplanctonul era reprezentat prin 72 specii. După două decade, este raportat un număr de 127 specii. Ca rezultat al acumulării nutrienţilor, la nivelul anului 2005, abundenţa zooplanctonului creşte semnificativ, atingând 330 ind L-1, urmată fiind de THE ZOOPLANKTON OF THE DANUBE-BLACK SEA CANAL 249 o evidentă creştere a biomasei (2285 μg s.um. L-1). În anul 2005 productivitatea zooplanctonului înregistrează 731,8 μg s.um. L-1/24h.

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Received: January 22, 2013 Biological Institute of the Romanian Academy of Sciences, Accepted: December 23, 2013 Splaiul Independenţei no. 296, C.P.56-53, sector 6, 59651, Bucharest, Romania e-mails: [email protected] [email protected] [email protected] [email protected]