Abstract
Periphytic ciliate communities of riverine floodplains have hardly been studied, although they play an important role in aquatic food webs and contribute to the overall ecosystem functioning. In this study we analyzed the taxonomic and functional composition and diversity of these communities across all seasons and hydrological phases. The study was conducted in a floodplain lake, a part of the large natural Danube floodplain, from February 2015 to September 2016. We found that higher temperature and hydrologically stable conditions during the lake isolation phase, when a high amount of suspended food is available, result in the highest ciliate abundances and dominance of relatively large suspension-feeding ciliates, mainly peritrichs, which could serve as good bioindicators for detecting disturbances in river-floodplain ecosystems. During the flow pulse phase, associated with lower temperatures, and during the phase of extreme floods, when the availability of suspended food was largely reduced, small surface-feeding ciliates prevailed in the periphyton. Further, while the total ciliate abundance was the lowest, the highest taxonomic and functional diversity was found, especially during an intermediate level of hydrological connectivity (flow pulse). Our results confirm the importance of different levels of hydrological connectivity for maintaining biodiversity in riverine floodplains and add to a growing awareness of the need to preserve the natural hydrological regimes of large rivers.
Highlights
Periphytic or biofilm communities are complex microecosystems composed of both primary producers and various consumers living in a heterogenous matrix of extracellular polymeric substances, detrital material, and inorganic particles [1,2,3]
Motile ciliates that feed on surface-associated food items can affect the periphyton morphology through grazing on the periphyton matrix, thereby altering the periphyton spatial heterogeneity and affecting the population dynamics of other periphytic microorganisms, and they contribute to the carbon flux in the periphyton [20,26,27]
We suggest that the high abundances of planktonic algae combined with the lower water levels and highest values of water temperature led to the high abundances of ciliates in periphyton
Summary
Periphytic or biofilm communities are complex microecosystems composed of both primary producers and various consumers living in a heterogenous matrix of extracellular polymeric substances, detrital material, and inorganic particles [1,2,3]. Ciliates (Ciliophora), the group of phagotrophic protists, often dominate periphytic communities and are usually represented by high abundance and diversity [4,5,6] Because they utilize food particles of various sizes, ranging from bacteria to small metazoans, and provide food for organisms at higher trophic levels, ciliates serve as important mediators of carbon and energy flux within aquatic food webs [4,7,8]. Sessile filter feeders (suspension-feeding ciliates such as peritrichs) can consume considerable amounts of planktonic pico- and nano-sized food particles (bacteria and small algae) [5,6,23], and several studies pointed out that these ciliates, which often prevail in mature periphytic communities, play a major role in importing organic matter from planktonic to the periphytic food web, contributing to the coupling of pelagic and benthic habitats [6,24,25]. Motile ciliates that feed on surface-associated food items can affect the periphyton morphology through grazing on the periphyton matrix, thereby altering the periphyton spatial heterogeneity and affecting the population dynamics of other periphytic microorganisms, and they contribute to the carbon flux in the periphyton [20,26,27]
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