Maria Špoljar

Vegetation Cover and Substrate Type as Factors Influencing the Spatial Distribution of Trichopterans along a Karstic River

In the longitudinal continuum of the Kupa River the vegetation cover and substrate type were the important environmental factors influencing the spatial differences in the biomass and community composition. Of total macroinvertebrate biomass, a significantly greater percentage of trichopterans was found on boulder and cobble substrata covered with moss (54.3% on boulders, 55.8% on cobbles) than on substrata covered with periphyton (9.9% on boulders, 14.8% on cobbles). In the potamal, trichopterans were markedly reduced (<2.5% of total macroinvertebrate biomass) on gravel substrata. A comparison of the Shannon diversity index values suggested that for trichopteran species diversity the substrate type was a more influential factor than vegetation cover. On the other hand, multidimensional scaling analysis showed that trichopteran community composition was related more significantly to vegetation cover and river area than to substrate type. In the rhithral the vegetation cover was an important factor influencing the functional feeding group composition of trichopterans. The spatial distribution of scrapers and filtering collectors depended significantly on the vegetation cover associated with substrate type, and shredder trichopterans were related to vegetation cover only. Predatory trichopterans made up 17‐65% of total predator biomass, and in the rhithron area they were correlated significantly only with vegetation cover. On gravel substrata in the potamal, vegetation cover did not affect the spatial distribution of shredder and collector-filterer trichopterans significantly.

Structure of rotifer assemblages in shallow waterbodies of semi-arid northwest Iran differing in salinity and vegetation cover

Rotifers are important components of freshwater ecosystems and sensitive indicators of environmental changes. This study was carried out to test the hypothesis that, among environmental variables, salinity and aquatic vegetation have significant effects on rotifer diversity and abundance. We analyzed rotifer assemblages in the littoral zone of 22 hydromorphologically different shallow waterbodies in West Azarbaijan, Iran. Rotifer diversity and abundance were not significantly associated with basin morphology, but were positively correlated with the percentage of vegetation cover. Salinity and electroconductivity positively influenced rotifer abundance, while they had significantly negative effects on rotifer diversity. Halobiont species from the genera Brachionus, Hexarthra, Synchaeta, and Notholca reached their highest abundances in the waterbodies with pronouncedly higher salinities. Our findings are in agreement with recent records showing that distinct rotifer assemblages occur in saline and non-saline waterbodies. The role of salinity and aquatic vegetation as the most important environmental drivers in shaping rotifer communities is confirmed. The results of this study suggested that environmental changes could be significant on the micro-biogeographical level, and that the interaction of salinity and observed human impact, i.e., trophic level, promote rotifer abundance as sensitive indicators of environmental changes.

Transport of seston in the karstic hydrosystem of the Plitvice Lakes (Croatia)

Research into spatial and temporal variation in seston transport was carried out during the year 2000 on three reaches on the longitudinal profile of the karstic cascading system of the Plitvice Lakes in Croatia. The three investigated reaches were (i) a channel over a barrier with low gradient; (ii) flow through a deep lake; and (iii) a channel with cascades and a steep gradient. The aim of the study was to establish the influence of physiographical and hydrological differences of these reaches on the quality and quantity of seston transport and food resources in the seston. To calculate the seston transport, we measured: total suspended matter (TSM), particulate inorganic matter (PIM), particulate organic matter (POM), chlorophyll-a (chl-a), heterotrophic bacteria and discharge. The PIM contribution from TSM ranged between 60 and 90%, while the percentage of POM in TSM was the highest in summer and ranged from 33 to 46%. POM and discharge were significantly negatively correlated (r = −0.43, P < 0.05). For the transport of TSM, PIM, POM and chlorophyll-a statistically significant differences between the three reaches were established. In a principal component analysis, 86% of the variance was explained by the first two factors. The first factor corresponded well with net transport of TSM, PIM, POM and chl-a and distinguished investigated reaches in two groups: the 1st group with increasing (reaches with low gradient and with high gradient), and the 2nd group with decreasing net seston transport (reach with flow through a deep lake). The second factor corresponded strongly with discharge and distinguished investigated reaches according to their temporal variability.

Development of ciliate community on artificial substrates associated with vertical gradients of environmental conditions in a karstic lake

The composition of ciliate communities, their abundance and biomass were studied on glass slides exposed in the epilimnion (1 m), metalimnion (9 m) and hypolimnion (18 m) in the karstic barrage Visovac Lake (SW Dinarid, Croatia). After one-month exposure periods from May 1995 to February 1996, mean ciliate biomass decreased with depth (at 1 m 54 μ g cm-2, at 9 m 37 μ g cm-2 and at 18 m 28 μ g cm-2), whereas the mean population density was relatively uniform (675 Ind. cm-2 at 1 m, 592 Ind. cm-2 at 9 m, and 678 Ind. cm-2 at 18 m). Sessile forms (peritrichs and suctorians) were dominant during all exposure periods and at all three depth layers. Omnivorous ciliates were dominant in the epilimnion, whereas in the metalimnion and hypolimnion bacterivores and carnivores were most abundant. Ciliates inhabiting artificial substrates in the epilimnion had two temporal peaks of density and biomass: in June and in October. In the deeper layers these maxima appeared one or two months later. Seasonal changes in ciliate biomass and community and trophic composition were associated with changes in thermal stratification and vertical oxygen gradients as important abiotic parameters, periphyton biomass as food source, and the tufa deposit determining the properties of substrate.

Trophic structure of ciliate associations in periphytic communities in karstic waters

Current speed, temperature, and the amount of dissolved and suspended organic matter as food source are the factors most responsible for the dynamics of ciliated protozoans living in different types of periphyton communities. In lotic and lentic habitats in the Plitvice cascade lake system located in the karstic Dinaric area we observed that the community and the trophic structure of ciliate associations depend upon the physical structure of the vegetation cover. These differences in trophic ciliate composition were explained by the degree of the retention and accumulation of organic detritus in periphytic habitats.

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.

Overflow effect on the dynamics of the rotifer community in cascade lake systems

Many recent studies have been concerned with rotifer life cycles in relation to changes of abiotic environmental conditions (PAULI 1990), predatory pressure (CHRISTOFFERSEN et al. 1993, DuMONT et al. 1994), competition (GILBERT 1985, SARMA et al. 1996) and availability of food (HESSEN 1992, RoTHHAUPT 1995). In karstic standing waters, especially in cascade hydrosystems, these ecological interactions are very complex and insufficiently understood.

Hydrology driven changes in the rotifer trophic structure and implications for food web interactions

Ecohydrology. 2018;11:e1917. https://doi.org/10.1002/eco.1917 Abstract Rotifers display r‐strategy life‐histories and are adaptable to environmental disturbances. Although rotifers constitute a large proportion of zooplankton in river‐floodplain systems, the influence of hydrology on their assemblage has been poorly studied. We postulated that rotifer assemblage and grazing activities were controlled by mechanisms associated with hydrological conditions. We conducted a 5‐year study (Kopački Rit Nature Park, NE Croatia) to assess the influence of hydrology on (a) rotifer assemblage during different hydrological phases, (b) the vertical distribution of rotifer abundance, functional feeding guilds, and grazing intensity, and (c) the main drivers affecting rotifer assemblage in the floodplain lake. The results indicated that (a) during isolation, longer residence time and high phytoplankton biomass microfilter‐feeders (mIff) and macrofilter‐feeders (mAff) grazing rates were similar whereas predators (Pr) were the most efficient consumers, (b) during high flow pulses, high conductivity and variable water level governed rotifer grazing rates of mIff and mAff at a retion of 1:2 and a decline of Pr grazing activity, and (c) during the flood pulse, reduced phytoplankton biomasss still resulted in mAff and Pr domination of the community whereas mIff grazing activity remained at the same level. Under stable hydrological conditions algivorous species codominated with bacterivores and predators, suggesting an increased biodiversity and food web interactions. In contrast, throughout the inundation period, algivorous species predominated. However, differences in rotifer assemblage between normal flow and flood pulses indicated the importance of hydrology in shaping rotifer trophic structure through modifying lower trophic levels and the availability of food sources.

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.