[Niche and interspecific association of major nekton in the sea area to the east of the Nanji Islands].

According to the fishery resources investigation data in the east of the Nanji Islands during autumn in 2017 and spring in 2018, the inter-specific relationships and ecological relationships between major nekton were analyzed via the index of relative importance, niche breadth, cluster analysis, niche overlap, χ-test, variance ratio test, association coefficient, percentage of co-occurrence, and point correlation coefficients. The results showed that there were 30 major nekton species in this area. The dominant species were Harpadon nehereus, Portunus trituberculatus, and Oratosquilla oratoria. The niche width of these dominant species was relatively wide. Based on the cluster analysis of niche breadth, the 30 major nekton species could be divided into three categories, wide niche breadth species, moderate niche breath species, and narrow niche breath species. The distribution range of niche overlap value was [0, 0.98], indicating that there were differences in the similarity of species to resource utilization and that the niche was differentiated and accompanied by inter-specific competition. The values of VR and W showed that there was a significant positive correlation among the major nekton species. The χ-test results indicated significantly interspecific association for 76 species pair (χ≥3.841), which was related to community stability and species coexistence. Results of association coefficient, percentage of co-occurrence and point correlation coefficients test suggested that the interspecific association was strong and tended to be positive.