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

Abstract

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.

Keywords: co-occurrence network; community assembly; diversity; microzooplankton; protozoa.

Fig. 1

Comparison of ciliate communities in different spatial groups. NMDS analysis showing the distribution of ciliate samples in continental shelf and basin areas (A) and in photic and aphotic (D); Proportions of shared and endemic ciliate species in continental shelf and basin areas (B) and in photic and aphotic zones (E); Comparison of ciliate abundance in continental shelf and basin areas (C) and in photic and aphotic zones (F). Samples number: 59 in Shelf and 112 in Basin area, 136 in Photic and 35 in Aphotic zone.

Fig. 2

Comparison of ciliate species composition in different spatial groups. Taxonomic composition at class/subclass level to show their relative abundance in continental shelf and basin areas (A) and in photic and aphotic (D); Feeding type composition in continental shelf and basin areas (B) and in photic and aphotic (E); Biohabit type compositions in continental shelf and basin areas (C) and in photic and aphotic zones (F). A (Algivore), B (Bacterivore), D (Detritivore), N (Non-selective), R (Raptor), P (Planktonic), S (Sessile) and V (Vagile).

Fig. 3

The driving factors of ciliate community. (A) CCA ordination showing the ciliate communities across the entire sea area in relation to the various factors; (B, C, D, E, F) VPA analysis revealing the contributions of environmental and spatial variables to ciliate community structure in the entire sea area (B), continental shelf (C), basin (D), photic zone (E) and aphotic zone (F), respectively.

Fig. 4

Co-occurrence networks of ciliate community species in different spatial groups. (A) networks in the continental shelf area; (B) networks in the basin area; (C) networks in the photic zone; (D) networks in the aphotic zone. Nodes are colored according to their modular groupings within the network.

Fig. 5

Comparisons of ciliate network stability and community niche breadth in different areas. (A, C) Robustness measured as the natural connectivity with the taxa randomly removed from communities in continental shelf and basin areas (A), photic and aphotic zones (C). The higher natural connectivity indicates higher stability of community; (B, D) Comparison of average niche breadth of ciliate species between the continental shelf and basinnetworks (B), and between photic and aphotic zones networks (D). The group with wider niche breadth were expected to be more flexible to adapt environment change.