Jasna Vidaković

The colonization and succession patterns of the periphytic ciliate community in a temperate floodplain lake

Abstract An in situ experiment to investigate periphytic community development was conducted on an artificial substrate (glass slides) in a Danube floodplain lake in Croatia. The main aim of the research was to analyze the structure of the ciliate community (Ciliophora, Protozoa) in the periphyton. We wanted to investigate how biotic and abiotic factors change and influence the ciliate community, reflecting not only the temporal community dynamics, but also the complex interactions within the periphyton. The experiment lasted from April to December 2009. To monitor the colonization process, the samples were collected on the 1st, 3rd, 5th, 7th and 14th day of exposure. After that, sampling was conducted biweekly, with the aim of studying the successional patterns of the periphytic ciliate community. 116 ciliate taxa were recorded. Non-metric multidimensional scaling indicated that development of the periphytic ciliate community occurred in three phases: initial, intermediate and mature. Water temperature and transparency were the most important parameters influencing the initial and intermediate phases of community development when mainly vagile bacterivorous and algivorous ciliates were present. The mature phase was characterized by higher organic content in the periphyton and an increased concentration of chlorophyll in the water column, indicating the potential food source as the primary factor influencing ciliates. The complex three-dimensional structure of the periphyton also affected the ciliate assemblage throughout the later successional stages. The trophic structure of the ciliates became more diverse during the mature phase, with sessile suspension-feeding and predatory ciliates as dominant groups. The present study shows that the early stages of the periphytic ciliate community are influenced mainly by external abiotic factors, whilst the mature community is characterized by biotic factors.

The importance of microphytic composition on coarse woody debris for nematode colonization: a case study in a fluvial floodplain environment

Abstract Coarse woody debris (CWD) are an important structural feature of many aquatic ecosystems. This study focused on the relationships between nematode colonization and microphytic community structure on CWD. In situ investigations were performed using white willow branches introduced into the floodplain lake, a part of the large natural floodplain in the middle section of the Danube River (Europe) impacted by strong sandy and silt accumulations. Our results showed that CWD support rapid colonization and high species richness of microphytes, regardless of seasonality and flood-induced environmental changes. Successional stages during the accrual of microphytic communities were expressed. Nematode functional feeding group compositions closely followed microphytic composition. The epistrate feeder Chromadorina bioculata over-dominated in diatom-dominated communities with adnate/prostrate and stalk-forming species in spring and autumn. The complex structure of cyanobacterial mats associated with green algae and diatom assemblages in summer attracted suction feeders, represented by the Dorylaimidae family. The obtained results indicated that nematodes are involved in strong trophic coupling with a microbial habitat on CWD. The retention of CWD in aquatic environments or addition of CWD to systems with little or no wood may have important implications for the primary and secondary production in these ecosystems.