Bottom-up versus top-down effects on ciliate community composition in four eutrophic lakes (China)

Previous studies have shown that ciliate plankton is generally controlled by food resources (e.g., algae) and predators (e.g., metazooplankton). Among lakes with similar trophic levels but different distributions of phyto- and metazooplankton, the main forces acting on ciliate assemblages may be different. We investigated the relationship between ciliate communities and bottom-up versus top-down variables based on a survey of four subtropical eutrophic lakes (China). Two of the lakes (Chaohu, Taihu) are located on the Mid-lower Yangtze Plain near sea level, and the other two (Dianchi, Xingyunhu) on the Yunnan-Kweichow Plateau at 1700 m above sea level. Blooms of cyanobacteria developed during summer in Lakes Chaohu and Taihu and throughout the year in Lakes Dianchi and Xingyunhu. Ciliate functional feeding groups differed significantly between lakes. The results of canonical correspondence analysis (CCA) and variation partitioning showed that cyanobacteria significantly influence ciliate species, whereas 'edible' algae (cryptophytes, diatoms) and cladocerans were the important variables in explaining the ciliate community structure of Lakes Dianchi and Xingyunhu compared with Lakes Taihu and Chaohu. Our results highlight the importance of consistent cyanobacterial blooms in shaping the ciliate community in subtropical eutrophic shallow lakes by interacting with top-down and bottom-up factors.