Oligochaeta community of the main Serbian waterways - Atanackovic et al. page 02

Material and Methods

The study is based on the results of investigations of Oligochaeta fauna in large potamon-type rivers in Serbia during the period from 2001 to 2005. The material was collected at 25 sampling sites on the Danube River, 6 on the Sava River, and 5 on the Tisa River (Figure 1), using a Hydraulic Polyp Grab, FBA hand net (mesh size 500 µm), benthological dredge (mesh size 250 µm), and Van Veen grab (270 cm2), mostly in the riverbank region. In the case of samples collected with Polyp and Van Veen grabs, animals were separated from the sediment by sieving (mesh size 200 µm).
The samples were preserved with a 4% formaldehyde solution. Sorting and identification were carried out using a binocular magnifier (5-50) and a stereomicroscope (10x10 and 10x40).
Characterization of the species with regard to saprobic condition, substrate and current preference was performed using AQEM software (AQEM, 2002).
A correspondence analysis (CA, Statistica 6.0) was performed on a matrix of 52 (taxa) x 3 (presence/absence of taxa in material from three river stretches). A correlation analysis was also carried out in order to quantify the relations between the rivers based on Oligochaeta compositions (presence/absence data).
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Results

A total of 52 taxa of aquatic worms from 32 genera, belonging to 9 families, were identified (Table 1).
For the duration of the investigation, a total of 37 taxa of Oligochaeta were found in the Danube River. The families Naididae and Tubificidae (16 species each), were found to be the principal members of the community in terms of species richness. The families Enchytraeidae (Enchytraeus albidus) and Propappidae (Propappus volki), were detected only in the Danube River.
In the Sava River, 21 Oligochaeta taxa were identified. Out of these taxa, 10 belong to the Tubificidae and 8 to the Naididae family, while other families were found to be less diverse. Criodrilus lacuum and Haplotaxis gordioides were detected only in the Sava River.
During investigation of the Tisa River, 27 taxa of aquatic worms were recorded. The family Tubificidae, with 17 identified species, was found to be the most diversified group of aquatic worms. Other families were less diverse – Naididae 6, Lumbriculidae 2, and Lumbricidae and Pristinidae 1 taxon each. The Tisa River is characterized by the presence of 11 taxa that were not recorded in the other investigated rivers (Table 1).
The species that were recorded only in one out of the three investigated river stretches comprise rare taxa (Aulophorus furcatus, Aulodrilsu limnobius, Dero nivea, Specaria josinae, Potamothrix moldaviensis, C. lacuum), according to previous investigations (JDS-ITR National Report, 2002; JDS-ITR National Tisa Report, 2002; Jurca and Miljanović, 2006; Paunovic et al,, 2008; Paunovic et al., 2007; Paunovic et al., 2005; Vojinović-Miloradov et al., 2003), or those not previously recorded (Tubifex montanus, Isochaeta baicalensis, Stylodrilus lemani, Pepsidrilus pusillus, H. gordioides) in the investigated area.


Taking into consideration all the species recorded in the investigated area, the majority could be considered as tolerant to high organic load. Thus, according to AQEM classification (AQEM, 2002) of the taxa, in terms of saprobic conditions (saprobic valence), 27.11% of the identified species belong to the beta-mesosaprobic group (adapted to or tolerant of medium-level organic pollution), while 27.50% of the taxa could be characterized as alpha-mesosaprobic (adapted to or tolerant of considerable organic pollution). Species adapted to high organic load (poly-saprobic) contributed 6.73% to the total number of taxa. Only 7.88% of the recorded taxa were classified as sensitive to organic pollution (xeno-saprobic and oligo-saprobic taxa). The remaining species (30.77%) could not be classified in terms of saprobic tolerance due to a lack of data.Further, according to the AQEM classification (AQEM, 2002) with regard to the preferred zone within the river continuum (longitudinal zonation), a major portion (43.65%) of the recorded species are characteristic of lower river courses (barbell and carp region), while 22.31% of the taxa recorded are typical of standing waters. A minor proportion of the taxa belong to those of the rhithral type (14.61%).
With regard to salinity preference, 36.15% of the recorded taxa are typical freshwater organisms. Out of the identified species, 11.92% were characterized as oligohaline and 1.92% belong to mesohaline taxa, while half of the taxa could not be classified into salinity preference groups due to insufficient data.
In terms of current preference, the recorded community is dominated by limnophylous (36.54% of the total number of recorded species) and limno to rheophilous (15.38%) taxa. A minor proportion of the species (11.54%) was characterized as indifferent to current conditions, while 23.08% of the taxa could not be classified in terms of current preference due to a lack of relevant data.
The majority of the identified species are adapted to the bottom substrate which is typical of large lowland rivers in the region (37): 43.35% of the taxa belong to pelophylous (19.42%), argillophylous (4.23%), and taxa that prefer sandy substrates (psammophylous, 17.69%). The taxa that could be characterized as phytophylous contributed 15.19% to the total number of the species, while for the remainder there was not enough information about microhabitat preference (AQEM, 2002).
The positions of the river stretches (squares) and species groups (circles), obtained by CA, are shown on Figure 2. The CA procedure yielded the positions of the species and the river stretches in the form of an ordination diagram. According to the CA, the species are grouped at seven positions. The species from the same position on the ordination diagram (Figure 2) are considered to be species groups (SG) and the SG qualification of each species is shown in Table 1.
According to correlation analyses, a significant negative correlation exists between the Tisa and the Danube based on the presence/absence of the Oligochaeta taxa. This difference between the two stretches revealed by CA is mostly due to the taxa belonging to SG 1, which comprises taxa that were found only at the Tisa River, and SG 4 (species recorded only in the Danube River). Two species belonging to SG 7 were found only in the Sava River. Other SGs are either represented in all the investigated rivers (SG 2), or present in two of the investigated rivers (SGs 3, 5, 6).

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