Co-occurrence patterns and community assembly mechanisms of benthic foraminiferal communities in South Chinese bays

Benthic foraminifera are among the most important components of marine benthic communities and can provide valuable information about the structure and activity of those communities. The distribution and diversity of benthic foraminifera have been well documented, but their co-occurrence patterns and community assembly processes have rarely been elucidated. To fill this gap, we used network analysis and null/neutral model approaches to benthic foraminiferal communities in five bays in South China to evaluate the influences of environmental factors and interspecies interactions on species co-occurrence and the relative importance of deterministic and stochastic processes in shaping community structure, respectively. The spatial heterogeneity of foraminiferal communities across bays was characterized by nonmetric multidimensional scaling analysis. Variation partitioning analysis showed that heavy metals (Cr, Co, Cu, As, Sb, and Hg) were the most important factor influencing community structure, while less importance was attributed to organic matter and grain sizes, which was likely due to the low TOC contents and small variations in TOC and grain size across sites. Network analysis showed that closely related species tended to co-occur with each other, which may be mediated by environmental filtering. The network was divided into three distinct clusters: one cluster consisted of miliolid, and two were dominated by rotaliids, each of which represented a special niche according to the habitat preference of the dominant taxa. The structure of the network was highly informative, as illustrated by the fact that the observed structure was denser than that of randomly constructed networks with the same size or the same degree sequence. The frequency of occurrence of most species (70%) met neutral model expectations, indicating that neutral processes were important for the assembly of benthic foraminiferal communities. However, PER-SIMPER analysis revealed that niche-assembly processes were more important than dispersal-assembly processes in shaping species abundance. Overall, this study provides the first insight into the mechanisms maintaining the community structure and diversity of benthic foraminifera.