Dr. Bettina Sonntag is Senior Scientist at the Research Department for Limnology, Mondsee of the Leopold-Franzens-University of Innsbruck (LFUI) and head of the working group ‘Ciliate ecology and taxonomy’.

Abstract:
Planktonic ciliates are key organisms in lakes and oceans. Although species identification is standard in any phytoplankton or zooplankton investigation, ciliates are commonly neglected in any lake survey despite their importance in the trophic transfer in aquatic food webs and their good indicator value. In lake plankton, around 150 ciliate species can be found during the course of a year and each one has different demands on its environment. In this respect, ciliates need to be identified to the species level because ecologically different, i.e., mixotrophic and heterotrophic species can be found even within one genus. In our studies, we generally follow a ‘bottom-up process’ starting with the morphological identification of a species followed by single-cell sequence analyses and feeding of public databases which in turn form the basis for high-throughput-sequencing approaches. I will present a case study of a potentially new model ciliate species and show why ciliate plankton analyses needed to be based on a combination of morphology, molecular sequences and environmental data. Moreover, an interdisciplinary approach studying these freshwater planktonic protists is necessary to also investigate the nature of symbiotic relationships among ciliates and their algal symbionts. By frequently involving citizens and pupils into our research, we consequently transfer recent findings into classrooms and living rooms to initiate discussions and deposit knowledge on understanding aquatic food webs that form the basis for lake ecosystem functioning.

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