Cold seeps provide high environmental heterogeneity for marine benthos. Site F is one of the active cold seeps in the South China Sea. In this study, free-living marine nematode communities were investigated at Site F and the adjacent deep-sea area. A total of 67 genera and 32 families were identified. The mean density at cold seep sites ranged from 13.6 to 181.8 ind./10 cm2, and that at the adjacent deep-sea sites ranged from 36.9 to 301.4 ind./10 cm2. At cold seep sites, the most dominant nematode genera were Desmoscolex, Pierrickia, Sabatieria, Halalaimus, and Dorylaimopsis while at deep-sea sites, the most dominant genera were Retrotheristus, Thalassomonhystera, Desmoscolex, Cobbia, and Halalaimus. Deposit feeders of nematodes were dominant at all sites. Results of biological trait analysis showed that there was high environmental heterogeneity for nematodes at Site F. Water depth, sediment organic matter content, and sand proportion had important influences on nematode communities.

Free-living marine nematodes are valuable biological indicators for different environmental disturbances. Their taxonomic composition and functional traits often respond to environmental changes. In this study, marine nematodes, collected from the Bohai sea on the northeastern coast of China in 2014, were investigated in terms of their taxonomic composition and functional traits. Furthermore, the environmental quality of the investigated area was assessed based on nematode metrics. The studied nematode community showed spatial variation in taxonomic and functional composition, in response to changes in environmental variables such as sediment chlorophyll-a, phaeophytin-a, organic matter content, silt-clay content etc. Overall, high percentage of tolerant marine nematodes species or colonizers predominated, suggesting a disturbed environmental condition of the study area. Further results from the environmental quality assessment based on nematode metrics indicated a moderate quality status at the most investigated stations.

The exotic mangrove species Sonneratia apetala has been planted widely in China since 1985. As an exotic mangrove species, it is important to understand the influence of Sonneratia plantations on marine nematode assemblages. We studied the Zhanjiang and Xiatanwei mangrove wetlands on the South China Coast during the four seasons of 2010 and 2019. The results showed that S. apetala plantations increased the number of genera, Shannon-Wiener diversity, richness, evenness, maturity index (MI) and decreased the index of trophic diversity (ITD) values for nematodes compared to those in mudflats, but did not change significantly compared to those of native mangrove forests. In addition, Sonneratia plantations did not significantly change nematode assemblages compared to those of native mangroves, though they did change significantly compared to those in mudflats. Thus, interplanting S. apetala into native mangrove forests may be an effective substitute for using native mangroves in mangrove plantation.