Distribution patterns and driving mechanisms of ciliate communities from continental shelf to deep basin of the Northeastern South China Sea

Ciliates are common components of microplankton and play crucial roles in the marine microbial food web, but little is known regarding how community assembly and species association vary from shelf to basin. A survey of ciliate diversity was conducted in the northeastern South China Sea during the winter of 2013, and the spatial distribution, driving mechanisms and network relationships of ciliate community were revealed. Our results showed that ciliate community compositions were similar between continental shelf and basin areas but significantly different between photic and aphotic waters. Higher ciliate abundances were found in shelf and photic waters than in basin and aphotic waters, primarily due to differences in light, nutrients and food resources. Across the entire sea area, environmental factors had a more significant influence on communities than spatial factors, suggesting that deterministic processes played a significant role in ciliate distribution. Co-occurrence network analysis revealed that ciliate networks were more stable in basin and photic waters than in shelf and aphotic waters, which was probably related to more complex relationships in the former two waters. Combined with the broader niche breadth, our study suggested that the ciliate community in basin and photic waters would show a stronger defense capability against environmental changes.