Tvrtko Dražina

Epiphytic metazoans on emergent macrophytes in oxbow lakes of the Krapina River, Croatia: differences related to plant species and limnological conditions

Epiphytic metazoans on emergent macrophytes in oxbow lakes of the Krapina River, Croatia: differences related to plant species and limnological conditions This study investigated the structure of the epiphytic metazoans on emerged macrophytes in the littoral zone of two oxbow lakes with different trophic levels. Differences in the diversity and density of the epiphytic metazoans were analyzed in relation to plant architecture (simple or complex stems), food resources (algae and detritus) and water characteristics (transparency and derived trophic state index). A significant negative correlation was found between detritus on plants as food resource, and diversity and density of epiphytic metazoans, indicating grazing of microphagous species. Rotifers dominated in diversity and density in the epiphyton on all habitats. Total density of metazoans, rotifers and copepods in epiphyton were significantly higher on Mentha in mesotrophic lake than on Iris in a eutrophic lake. We presume that macrophyte belt width and trophic state governed biotic interactions and consequently epiphytic assemblages more strongly than macrophyte architecture. However, a Mentha habitat showed a slightly higher density and diversity of epiphytic metazoans in relation to Iris at the same site, but these differences were not significant.

ZOOPLANKTON STRUCTURE IN TWO INTERCONNECTED PONDS: SIMILARITIES AND DIFFERENCES

Abstract The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilter-feeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure.

Insect fauna in nests of the Eurasian griffon vulture (Gyps fulvus) in Croatia

Qualitative, quantitative and trophic structure of insects found in Eurasian griffon vulture nests were analysed. A total of 249 insects belonging to six orders were found in 18 griffon vulture nests, collected in three colonies on the islands Cres and Plavnik (Adriatic Sea). Eudominant orders were beetles (64.26%) and ants (22.49%). Dermestid beetles were present in all examined nests and comprise the permanent nest fauna. Other groups of insects (cockroaches, web spinners, ants, flies, aphids) were found to occur occasionally in nests.

Meiofauna constitute a considerable portion of invertebrate drift among moss-rich patches within a karst hydrosystem

Aiming to establish the most frequent invertebrate taxa in drift at the small spatial scale within a moss-rich karst tufa-precipitating hydrosystem, we sampled drift among microhabitats differing in substratum type and flow conditions along a tufa barrier-cascading lotic reach. Additionally, we addressed the question of the contribution and the potential significance of meiofauna within the overall invertebrate drift at the small spatial scale. During the study period, a total of 60 invertebrate taxa were recorded in the drift. Six of these taxa belonged to the annelid/arthropod meiofauna and they represented 35% of total drift density. Macroinvertebrates found in drift were represented mainly by larval insects. The composition of the most abundant taxa in total drift was as follows: Alona spp. (Cladocera 26.7%), Riolus spp. (Coleoptera: Elmidae 13.2%), Simulium spp. (Diptera: Simuliidae 12.2%), Enchytraeidae (Oligochaeta 10.4%), Hydrachnidia (6.3%), Orthocladinae (Diptera: Chironomidae 3.9%) and Naididae (Oligochaeta 3.6%). Faunal drift densities and amounts of transported particulate matter (PM) were highest at the fast-flowing sites located at the barriers and lowest at the slow-flowing sites within pools. Similarly to the seasonal amounts of transported PM, faunal drift was lowest in winter, and peaked in autumn and in late spring/early summer. Correlation between flow velocity and PM-faunal drift densities suggested a significant effect of the dislodged PM, though a minor influence of discharge and flow velocity on faunal drift. We suggest that the small-scale habitat heterogeneity and the respective feeding and refugial strategies of the fauna, as well as faunal passive dislodgement initiated by the shear forces of the flow were the most important drivers of observed drift patterns.

Mesostigmatic mites (Acari: Mesostigmata) in nests of the Eurasian griffon vulture (Gyps fulvus) in Croatia

We examined the species composition and community structure of mites of the order Mesostigmata (Acari) in nests of the Eurasian griffon vulture (Gyps fulvus Hablizl, 1783) in Croatia. Material collected from 18 nests included 565 mites belonging to seven species. The most abundant species were Leiodinychus orbicularis (C.L. Koch, 1839) (Trematuridae) and Androlaelaps casalis (Berlese, 1887) (Laelapidae). The results were compared with the community structure and frequency of dominant species of Mesostigmata in nests of 32 other bird species. Leiodinychus orbicularis occurred in the nests of 13 species of birds. It is a typical nidicolous species which occurs most frequently in the perennial nests of birds of prey. In contrast, A. casalis rarely occurs in the nests of birds of prey.

Review of the genus Typhloiulus Latzel, 1884 in the Dinaric region, with a description of four new species and the first description of the male of Typhloiulus insularis Strasser, 1938 (Diplopoda: Julida: Julidae)

A review of the genus Typhloiulus Latzel, 1884 (Julida: Julidae) in the Dinaric region is given. Previously published and new faunistic records are provided for each species, together with notes for some of them. Four new species are described: T. clavatus sp. nov., T. gracilis sp. nov., T. opisthonodus sp. nov., and T. parvulus sp. nov., all from caves in Dalmatia and Herzegovina. In addition, we provide the first description of the male of T. insularis Strasser, 1938. Some taxonomic relationships among Typhloiulus species and biogeographical aspects (with distribution maps) of the genus are discussed.

Review of the family Anthogonidae (Diplopoda, Chordeumatida), with descriptions of three new species from the Balkan Peninsula

Three new species of the family Anthogonidae are described from caves in Croatia and Montenegro, respectively: Egonpretneria vudutschajldi Antić & Dražina sp. n., Haasia jalzici Antić & Dražina sp. n., and Macrochaetosoma bertiscea Antić & Makarov sp. n. All three subfamilies within Anthogonidae are diagnosed, with brief discussion of relationships between genera and notes on their biogeography. A map of the global distribution of Anthogonidae is presented, as well as maps of the distribution of each species of Balkan anthogonids, including numerous new locality data. The first SEM images are provided for some representatives of this family. A key is given to all seven anthogonid genera. The subfamily Haasiinae Hoffman, 1980 is a new synonym of Anthogonidae, syn. n., while Macrochaetosoma bifurcatum Ćurčić & Makarov, 2001 becomes a new synonym for M. troglomontanum Absolon & Lang, 1933, syn. n..

Three new monotypic genera of Trichopolydesmidae from Croatia, Balkan Peninsula (Diplopoda, Polydesmida)

Three new monotypic genera are described from underground habitats in Croatia: Balkanodesmus biokovensis gen. n., sp. n., Solentanodesmus insularis gen. n., sp. n. and Velebitodesmus cavernicolus gen. n., sp. n. In all three new genera the prefemoral part of the gonopods is orientated transversely to the main body axis, and all three new genera possess numerous metatergal setae arranged in a few transverse irregular rows, a condition observed in several European trichopolydesmids. These three new genera are very close to the genus Verhoeffodesmus. A distribution map and a brief discussion about the relationship with congeners are provided.

Epifauna of native and alien freshwater crayfish species (Crustacea:Decapoda): a host-specific community?

Freshwater crayfishes serve as hosts to diverse epifaunal assemblages. We investigated epifauna on 3 native and 2 alien freshwater crayfish collected in Croatia (Europe). Our main goals were to compare epifauna with surrounding infauna and periphyton and to test whether epifauna differ among crayfish species. A total of 40 epibiont taxa were identified. Ciliophorans were the most abundant, whereas rotifers were the most diverse (17 taxa). Five species of branchiobdellidans were found as crayfish ectosymbionts. Two new biogeographical records of nonindigenous epibiont species, the branchiobdellidan Xironogiton victoriensis and ostracod Uncinocythere occidental, were identified on the alien North American crayfish Pacifastacus leniusculus. On native crayfishes, a few specific epibiont species were recorded: 1 copepod (Nitocra divaricata) and 4 rotifers (Lepadella astacicola, L. branchiola, L. parasitica, and Dicranophorus cambari). Results indicated a highly diverse and complex crayfish epifaunal community that differed significantly from surrounding infauna and periphyton. Our results indicated differences in the epifaunal assemblage between native and alien crayfishes that suggest the possibility of a specific connection between epifauna and hosts. We presume that future studies will reveal higher epifaunal diversity on freshwater crayfish, with some new insights in taxonomy and ecology.

Impact of water level fluctuation in shaping of zooplankton assemblage in shallow lake

Abstract Shallow lakes are strongly affected by global climate changes reflected in significant parameters of ecosystem deterioration, i.e. biodiversity decrease, and water turbidity. Zooplankton research in Škrčev kut oxbow lake (Krapina River watershed, NW Croatia, Europe) was conducted during the summer of 2012 and 2013 with the aim to determine the effect of inter-annual, short-timescale changes of hydrological regime on environmental conditions, macrophytes, zooplankton and fish assemblage within an oxbow lake in the temperate region. Within one-year period the water level increased by 2 meters. This caused a significant reduction of floating-leaved macrophytes (i.e. Nuphar lutea), while turbidity, ortho-phosphate and chlorophyll a concentrations increased. These altered ecological conditions were reflected in the shift from floating-leaved macrophytes at the lower water level to phytoplankton-dominated lake at the higher water level. Zooplankton underwent significant alteration in assemblage. The results suggest that fish preference suppressed cladocerans and enhanced the rotifer and copepod abundance. Our results indicate that even in a short-timescale zooplankton assemblage mediates in the modification of ecosystem functioning.