Spatial Differentiation and Their Influencing Factors of Marine Nematode Community Structure and Functional Traits in Mangrove Sediments in Guangxi

To explore the spatial differentiation and causes of marine nematode communities in mangrove forests, this study investigated the community structure and functional traits of marine nematodes in sediments of three mangrove forests formed by the single tree species Avicennia marina in Beihai, Guangxi, in September, 2021. The results demonstrated that significant differences existed in the abundance, diversity, species composition, and functional traits of marine nematodes among the three Avicennia marina forests. A total of 132 species of marine nematodes were identified, belonging to 54 genera and 28 families. Among the three sites, the Zhulin Avicennia marina forests exhibited the highest average nematode abundance ((1 016.00±199.69) ind./10 cm²), which was significantly higher than that in Dongwei ((183.28±118.36) ind./10 cm²) and Golden Bay ((339.68±137.90) ind./10 cm²). The Zhulin Avicennia marina forests also showed the highest species number, Margalef′s richness index, Pielou′s evenness index, Shannon-Wiener diversity index, and Simpson diversity index, and its nematode community composition was significantly distinct from the other two sites; Maximum body width and esophageal length of marine nematodes were significantly larger, and the community was dominated by non-selective deposit feeders, but with a higher proportion of epistratum feeders and omnivores/predators compared with the other two sites. The nematode communities in Golden Bay and Dongwei Avicennia marina forests exhibited high similarity, with Diplolaimella and Terschellingia as co-dominant genera and deposit feeders accounting for ＞ 80% of the community; however, the body length, body width, and esophageal length of marine nematodes in Golden Bay Avicennia marina forests were significantly smaller than those in Dongwei. Correlation analysis with environmental factors revealed that the spatial differentiation of abundance, diversity, species composition, and functional traits of marine nematodes were significantly correlated with sediment hydrolysable tannin content, organic matter content, and grain size characteristics. This study clarifies the response patterns of marine nematodes to habitat heterogeneity in Avicennia marina forests of Guangxi, providing a theoretical basis for the conservation and scientific management of mangrove ecosystems.