[Monthly changes and related affecting factors in community structure and diversity of the crab assemblages in central Jiaozhou Bay, China].

Based on the monthly bottom trawl surveys in the central area of Jiaozhou Bay from September 2008 to August 2009, monthly changes and related affecting factors in community structure and diversity of the crab assemblages were examined using index of relative importance, ecological diversity indices, multivariate statistical analysis. In total, 18 crab species were caught and they belonged to 11 families, 17 genera. The relative abundance of crab varied dramatically among months, which was high in June, July and August. The dominant species composition of crab assemblage was observed to vary over months dramatically. The dominant species for the whole year was Charybdis bimaculata, and the dominant species in different specific months were C. bimaculata, C. japonica, Portunus trituberculatus, Raphidopus ciliatus and Eucrate crenata. The ranges across months of the Margalef' s species richness index (D), Shannon diversity index (H) and Pielou's evenness index (J) of the crab community structure were 0.54-2.86, 0.06-2.59 and 0.03-0.97, respectively. The diversity indices in winter months were the highest, and the diversity indices in autumn months were higher than in the spring and autumn months. MDS and CLUSTER analyses revealed that three groups/clusters, which were Group I (from May to October), Group, II (April, November and December) and Group III (January, February and March), were identi- fied for crab community during all the year in the central area of Jiaozhou Bay. ANOSIM analysis in community structure indicated that there were extremely significant differences among the groups, significant differences between Group I and Group II or between Group I and Group III, and no significant differences between Group II and Group III. Typifying species in the within-group included C. bimaculata, P. trituberculatus, C. japonica, E. crenata and R. ciliatus, and discriminating species between groups included C. bimaculata, C. japonica and P. trituberculatus. These typifying and discriminating species influenced the crab community structure significantly. BIOENV analysis indicated that bottom water temperature was the most important environmental factor affecting monthly variations of the crab community structure in the central area of Jiaozhou Bay.