Journal Article

Cascading effects in freshwater microbial food webs by predatory Cercozoa, Katablepharidacea and ciliates feeding on aplastidic bacterivorous cryptophytes

Mehrshad, Maliheh, Grujčić, Vesna, Mukherjee, Indranil, Nedoma, Jiří, Salcher, Michaela M, Posch, Thomas, Šimek, Karel, Kasalický, Vojtěch

2020

Overview

ABSTRACT Heterotrophic nanoflagellates (HNF) are considered as major planktonic bacterivores, however, larger HNF taxa can also be important predators of eukaryotes. To examine this trophic cascading, natural protistan communities from a freshwater reservoir were released from grazing pressure by zooplankton via filtration through 10- and 5-µm filters, yielding microbial food webs of different complexity. Protistan growth was stimulated by amendments of five Limnohabitans strains, thus yielding five prey-specific treatments distinctly modulating protistan communities in 10- versus 5-µm fractions. HNF dynamics was tracked by applying five eukaryotic fluorescence in situ hybridization probes covering 55–90% of total flagellates. During the first experimental part, mainly small bacterivorous Cryptophyceae prevailed, with significantly higher abundances in 5-µm treatments. Larger predatory flagellates affiliating with Katablepharidacea and one Cercozoan lineage (increasing to up to 28% of total HNF) proliferated towards the experimental endpoint, having obviously small phagocytized HNF in their food vacuoles. These predatory flagellates reached higher abundances in 10-µm treatments, where small ciliate predators and flagellate hunters also (Urotricha spp., Balanion planctonicum) dominated the ciliate assemblage. Overall, our study reports pronounced cascading effects from bacteria to bacterivorous HNF, predatory HNF and ciliates in highly treatment-specific fashions, defined by both prey-food characteristics and feeding modes of predominating protists. Presented are experimentally induced cascading effects from bacteria to bacterivorous flagellates, predatory flagellates and ciliates in different plankton size fractions, modulated by prey-food characteristics and feeding modes of predominating protists.

• Publisher: Oxford University Press
• Subject: Analysis / Animals / bacterivorous and predatory flagellates / Cercozoa / Ciliata / ciliates / Cryptophyceae / Cryptophyta / Flagellates / Fluorescence / Food Chain / Fresh Water / freshwater microbial food webs / Heterotrophs / Identification and classification / In Situ Hybridization, Fluorescence / Katablepharidacea / Methods / Physiological aspects / Rhizaria / Trophic cascades