Long-term study shows cyanobacterial blooms reduce ciliate functional stability by altering network complexity

Ecological communities are normally composed of multiple interacting species. A fundamental interaction type is the trophic (feeding) interaction. As an example, blooming cyanobacteria may impact the assembly and diversity of ciliate communities in waters. However, it is unclear to what extent cyanobacterial blooms – in the short and long term – affect the functional stability of ciliates and the complexity of the ciliate-cyanobacterium interdomain network. In this study, we analyzed nine years of high throughput sequence data of amplicons targeting the V9 region of the 18S rRNA gene of ciliates and the V3–V4 region of the 16S rRNA gene of cyanobacteria in two subtropical reservoirs. Our results demonstrated cyanobacterial bloom succession in terms of biomass –with three distinct bloom and two non-bloom periods over nine years. Similarly, the functional trait distribution of ciliate communities showed significant bloom-related variations and differences in functional composition, accounting for 43% and 52% of the total variation in the Shidou and Bantou reservoirs, respectively. The variation in functional composition of ciliate communities in the different bloom periods ranged from 15% to 96% in Shidou Reservoir and from 16% to 84% in Bantou Reservoir. Using network analyses, we found that the ciliate-cyanobacterium interdomain network exhibited a bloom-related temporal trajectory with complex modular associations. Influential analyses showed that some cyanobacterial nodes played an important role in network structure and complexity, accounting for 21.4% and 22.2% cyanobacterial influential nodes between bloom and non-bloom periods in Shidou and Bantou reservoirs, respectively. The variation in cyanobacterial nodes in the different bloom periods ranged from 14.7 to 32.6% in Shidou Reservoir and from 19.5% to 35.6% in Bantou Reservoir. Furthermore, the functional stability of ciliates and the robustness of the ciliate-cyanobacterium interdomain network were comparatively lower during bloom than non-bloom periods, indicating that cyanobacterial blooms had a significant negative impact on ciliate functional stability and on ciliate-cyanobacterium interdomain network complexity. We also found a weaker influence of environmental factors during cyanobacterial blooms, and bloom-induced ecological changes were critical for microbial interactions and stability, highlighting the negative and strong impact of cyanobacterial blooms in freshwater ecosystems. • Ciliate functional traits changed with cyanobacterial biomass. • Ciliate-cyanobacterium network showed bloom-induced temporal trajectories. • Cyanobacterial influential played key role in maintaining network complexity. • Ciliate functional stability was associated with cyanobacterial bloom successions.