Seasonal changes in water assemblages in a temporary pond of Lonjsko polje nature Park Martina Temunović 1,2, Lucija Šerić Jelaska 3

1 Faculty of Forestry, University of Zagreb, Svetosimunska 25, 10 000 Zagreb, 2 Association for Biological Research - BIOM, Sestinski dol 12, 10 000 Zagreb, Croatia; [email protected] 3Group for Systematic Zoology and Entomology, Department of Biology, Faculty of Science, Rooseveltov trg 6, 10 000 Zagreb, Croatia; [email protected]

Date (2004) 4/6 16/6 2/7 15/7 22/10 Σ D % 225 Hydrophilidae Family 200 Hydraenidae of 1. Dytiscidae 107 75 77 18 6 283 19,46 175 Introduction Helophoridae 150 2. Haliplidae 2 3 0 0 1 6 0,41 Hydrochidae 125 3. Helophoridae 9 77 75 34 40 235 16,1 100

4. Hydrophilidae 195 72 37 19 75 398 27,28 abundance Water (Coleoptera, Insecta) constitute one of the main groups of 75 5. Hydraenidae 19 44 98 66 125 352 24,12 aquatic macroinvertebrates in temporary and permanent standing waters 50 6. Hydrochidae 8 26 39 14 63 150 10,28 25 which represent the most important habitats for this group of . 7. Dryopidae 5 3 1 0 2 11 0,75 0 4.6. 16.6. 2.7. 15.7. 22.10. Lonjsko polje is one of the largest naturally flooded plains in Europe with a 8. Spercheidae 1 1 0 0 0 2 0,14 date 9. Chrysomelidae 7 3 3 0 3 16 1,09 variety of aquatic habitats, included in Ramsar List of Wetlands of Interna- Figure 3: Seasonal dynamics of eudominant water beetle families 10. Curculionidae 1 2 1 0 1 5 0,34 tional Importance. Σ 354 306 331 151 316 1458 40 Hydroglyphus geminus • Hydroporus palustris Table 1: Abundance and dominance (D%) of water beetle families 35 • Coelambus impressopunctatus 30 The main objective of this study was to determine in details the seasonal dy- Variable 1 Variable 2 r p • Laccophilus minutus 25 • Hyphydrus anatolicus namics of water beetles in a single semipermanent pond in the area of Lon- Hydradephagan richness pond surface (lenght x width) Liopterus haemorrhoidalis 0,96 0,008 20 Hydradephagan richness conductivity jsko polje Nature Park (Figure 1) over one year period. - 0,93 0,019 abundance 15

Hydradephagan abundance pond surface (lenght x width) 0,87 0,05 10

Hydradephagan abundance pond depth 0,90 0,033 5

Furthermore, we wanted to investigate the relation between the changes in Hydradephagan abundance conductivity - 0,87 0,055 0 4.6. 16.6. 2.7. 15.7. 22.10. Hydradephagan abundance CaCO3 assemblage composition with respect to fluctuations of pond dimensions and - 0,97 0,005 date physico-chemical properties of the pond and finally to test if the two micro- Table 2: Correlation Coefficients (r) and their p-values between variables Figure 4: Seasonal dynamics of six most abundant Hydradephagan species habitats within the pond (deepwater vs. shoreline) significantly differ. Results

Altogether, 1458 specimens belonging to 10 families of water beetles were collected (Table 1). Seasonal dynamics of eudominant water beetle families is presented in Figure 3. Although abundance of individual families vary strong- ly, the overall number of water beetles in the pond is more or less constant through the season (Table 1). The pond was dried out during August and Sep- tember. Among 289 Hydradephagan specimens, 22 species were identified (Table 3). Seasonal fluctuation of six most abundant species is presented in Figure 4, showing that most species reach the peak of their abundance in June. Results show a significant positive correlation of Hydradephagan abundance Figure 1: Location of Lonjsko polje in Croatia Figure 2: Pond Trebez and species richness with pond dimensions (Figure 6) and negative correla- tion with conductivity and dissolved CaCO3 in water (Table 2), as previously demonstrated by some authors. We found no significant correlations between Polyphagan water beetle fauna and examined parameters. T-test showed that Hydradephagan abundance is significantly different in the Materials and Methods two microhabitat types (p = 0.0097), being significantly higher at the shore- line (Figure 5) as proposed in literature. Field survey was conducted from May to December 2004. in an open tempo- rary pond “Trebez” situated near the forest edge (Figure 2). Date (2004) 4/6 16/6 2/7 15/7 22/10 Σ S Σ W Σ D% Species • Hydroporus angustatus 1 1 0 1 0.35 Aquatic coleoptera were collected using semiquantitative method of sweep- • Hydroporus planus 3 2 1 3 1.03 • Hydroporus palustris 23 20 16 2 22 39 61 21.03 ing D-frame pond net. Sampling was performed through the entire water • Suphrodytes dorsalis 2 4 0 6 6 2.07 column for deepwater samples and close to the shore through the vegetation • Porhydrus lineatus 1 0 1 1 0.35 • Bidessus nasutus 2 2 1 3 4 1.38 against the banks for shoreline samples. • Guignotus pusillus 28 27 12 9 29 56 76 26.2 • Hyphydrus sp. 15 4 3 16 19 6.55 • Hygrotus decoratus 2 3 1 1 1 6 7 2.41 Water temperature, dissolved oxygen concentration, pH and conductivity • Hygrotus inaequalis 1 1 0 2 2 0.69 • Coelambus impressopunctatus 36 6 8 18 32 50 17.24 were measured at each sampling date, along with pond dimensions (lenght, Figure 5: T-test between water and shoreline Hydradephgan • Rhantus latitans 2 3 1 2 4 6 2.07 width and max. depth). abundance (SE - standard error) • Rhantus bistriatus 1 0 1 1 0.35 • sp. 1 0 1 1 0.35 Polyphaga abundance 350 200 Hydradephaga abundance • Agabus undulatus 2 2 0 4 4 1.38 Hydradephaga richness 300 175 pond surface • Copelatus haemorrhoidalis 1 1 8 2 1 4 9 13 4.48 pond depth 150 Fluctuations of water beetle fauna during the season has been recorded in re- 250 • Laccophilus minutus 9 6 7 3 7 18 25 8.62 125 lation with measured physical−chemical parameters using Pearson’s Corre- 200 • Hydaticus transversalis 1 1 1 1 2 0.69 100 • Acilius sulcatus 1 1 0 1 0.35 150 lation Coefficient in Excel. Differences between the two pond microhabitats 75 • Dytiscus marginalis 1 1 0 1 0.35 abundance/richness 100 50 pond surface (m2)/depth (cm) • Haliplinus ruficollis 1 1 1 1 2 0.69 were tested with standard t-test. 50 25 • Haliplinus heydeni 1 1 1 1 1 3 1.03 0 0 • Peltodytes caesus 1 0 1 1 0.35 4.6. 16.6. 2.7. 15.7. 22.10.

date Σ 110 78 77 18 7 203 87 290

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