1.2.3. Aquatic biota

The aquatic fauna of the Republic of Moldova includes about 2130 species and subspecies of 55 taxa 32. Algae are represented by over 2800 species and varieties. The dominant groups are Chlorophyta – 1566 species and varieties (44.2%), Euglenophyta – species and varieties (12.26%), Bacillariophyta – 556 species and varieties (24%), Cyanophyta – 291 species and varieties (12.56%). The number of algae species that can be found in the river courses is given in table 1.9.

Table 1.9

The average of algae species in the river courses of the Republic of Moldova

Water course / Algae groups
Cya
no-
phy
ta / Eu
gle
no-
phy
ta / Baci
llario
phy-
ta / Xan
to-
phy
ta / Dino
phy-
ta / Chri
so-
phy
ta / Chlorophyta / Cha-
ro-
phyta / Total
Vol
voci
neae /
Chlo-
rococ
cineae
/
Ulo-
trichi
neae
/
Con-
juga
teae

Dniester river

/ 82 / 234 / 215 / 9 / 26 / 17 / 12 / 278 / 17 / 22 / 7 / 919

Raut river

/ 124 / 112 / 218 / 6 / 10 / 10 / 16 / 174 / 10 / 18 / 2 / 700
Danube river(Giurgiuleşti) / 169 / 127 / 293 / 15 / 7 / 22 / 24 / 186 / 12 / 67 / 922

Small rivers

/ 47 / 130 / 73 / 9 / 4 / 11 / 17 / 212 / 6 / 20 / 1 / 530

According to the surveys conducted in 2002, the diversity of phytoplankton in the surface waters varies between 39 species (in the lower Dniester) and 79 species (in the Dubasari reservoir), mostlyrepresented by Cyanophyta, Bacillariophyta, Pyrrophyta and Chlorophyta. The average of phytoplankton density is in the range of 1.7-10.1 million cells/dm3 and biomass, between 2.6 and7.0 g/m3. In the Dniester river the phytoplankton comprises 330 species with 363 taxa. Diathoms (43.5%) and green algae (31%) prevail; blue-green algae account for 15.2% and the other components of phytoplankton, 11.2%. The development of phytoplankton in Dniester and Prut rivers hits two maxima: in spring, determined by the mass development of Stephanodiscus, Cyclotella, Synedra, Asterionella and Diatoma and in autumn (the highest one), conditioned by the intensive development of diatoms and Protococcophyceae. In different phases of the survey, the phytoplankton of the Dniester included between 29 and 67 species indicators of saprobity. An important role is played by -β-mezosaprobic (9.7-16.6%) and β-α-mezosaprobic forms (9.7-11.9% of total number).

The number of species of protozoa, zooplankton and zoobenthos does not differ much in different water streams of the republic. Protozoas include 26-34 species, with an average density of 258,800-545,600 ex/m3 and biomass of 0.2-0.4 g/m3. Zooplankton (30-38 species) includes Rotifera, Cladoceraand Copepoda, its density varies from 2,300 to 10,100 ex/m3 and biomass – from 0.01 to 0.06 g/m3. The zooplankton communities of Dniester river are very poor. The microzooplankton includes a large group of Infusoria(216 species and subspecies), and 105 taxa of rizopods. In total, there are about 570 taxa of organisms. The zoobenthos predominantly consists of mollusks, crustaceans, worms and Chironomidae, with a total average density between 2,620 organisms per m2 (middle Dniester) and 16,000 org./m2(lower Dniester), and a total biomass between 85.8 g/m2 in the Prut river and 400.4 g/m2 in the lake Cuciurgan. The middle reach of the Dniester is poorer than downstream reaches both in the biomass of protozoa, zooplankton and zoobenthos as well as in the average density of species.

The ichthyofauna of the middle Dniester is represented by 40 species and subspecies of fish belonging to 10 families. During the last 15 years, the populations ofcommercially valuable species (bream, sea-roach, zander, goldfish, etc.) are in decline and are increasingly replaced by species of less economic interest (chub, ruff, gudgeon, bleak, etc). This trend is due to changes in the hydrological and thermal regime of the river induced by the operation of the Novodnestrovsk hydropower station (Ukraine) which leaded to anomalies in water ecosystems and had a deleterious effect on the life cycle of certain species of fish. This has a negative impact on the natural reproduction of fish downstream, particularly strong in the middle Dniester. Between 1959-1984 about 30 valuable fish species reproduced in the middle and superior reaches of the river. Nowadays, the natural reproduction of thermophilic species, spawning at 15-22ºC (sterlet, barbel, coddling, bream, carp, sheat-fish, goldfish), is totally compromised or severely hampered. In the same time, even species spawning at 4-10ºC (rapacious carp, perch, zander, broad snout) were indirectly affected. At present fish resources of the Dniester river and Dubasari reservoir dropped by 96% compared to the period before the construction of the Dubasari barrage 32.

The specific diversity of the ichthyofauna of lower Dniester is richer including 46 species and subspecies of fish. About 18% of them are valuable species and 78%are species of lower economic value (rudd, gudgeon, rhodeus, bleak, etc.). In Dubasari reservoir there are 38 species and subspecies of fish, of which only 15 species (roach, sterlet, coddling, barbel, carp, goldfish, sheatfish, rapacious carp, zander, ictalurus, etc) are of economic importance. The numeric share of valuable populations constitutes only 20% with a downward trend. Similar diversity and trends are characteristic for the ichthyofauna of the Cuciurgan lake.

The Prutriver (lower part) is populated by 36 species and subspecies. The dominant species are bleak, gudgeon, roach, goldfish, Danube herring, zander, rapacious carp. The populations of the following species also reach significant numbers: bream (5,2%), sheatfish (4,7%), chub (2,9%).

The situation described above reveals the mesotrophic status of the large rivers and water bodies in Moldova, with a reduced biodiversity, poor fish productivity and many non-valuable fish populations.

The semi-aquatic terrestrial vertebrates are represented by 125 species: mammals – 4, birds – 109, reptiles – 3 and amphibians – 9.

As to the aquatic flora, its biodiversity is the highest in the Cuciurgan lake, 1280 species, the Dubasari reservoir, 996 species, the Dniester river, 930 species, and the Prut river, 710 species and 4,6,9,13,14. Phytobenthos and periphyton are particularly rich in algae. 90% of the 566 species of diatoms are typically benthic and the same ischaracteristic for green algae. Charophyts have almost totally disappeared from the surface waters and this is an alarm signal since they are indicators of clean waters. The number of Chrisophyta, Dinophyta and Desmidiaceae has being reduced as well. The intensive pollution of surface waters over the past decades has adversely influenced the water ecosystems; the total number of species in the main water courses decreased by 15-30%.

The aquatic angiosperm plants are represented by 175 species from 42 families. The taxonomic structure of plant communities in the majority of water bodies is continuously degrading. Only the plant communities of the wetland zones have relatively maintained their integrity.