Abstract: Seasonal variations of crab assemblage, composition of dominant species, species diversity and richness in Ma’an Archipelago area were studied, based on sampling data collected by shrimp trawls from July (summer) and October (autumn) in 2013 to March (winter) and May (spring) in 2014. The relationship between crab community structure and environmental factors were analyzed. The results showed that 22 crab species were collected belonging to 15 genera and 11 families. The numbers of crab species in different seasons were in order of summer (20 species) > autumn (16 species) > spring (9 species) > winter (8 species). Charybdis japonica and Charybdis bimaculata were the most dominant species in the all seasons, Portunus trituberculatus was the subdominant species both in summer and autumn. The Margalef richness index (D) of crab community ranged from 0.43 to 1.01, and the Shannon diversity index (H) ranged from 0.34 to 0.94. These two indices were the highest in autumn and lowest in winter. The Pielou evenness (J) reached the maximum value in spring (0.70), followed by winter and autumn, and the lowest in summer (0.35). Bottom temperature was the most important factor affecting crab community structure. Cluster and nMDS analysis showed that there were no significant differences in crab community structure among seasons, which suggested that the crab community structure in Ma’an Archipelago area was relatively stable.

Key words: watershed, ‘source-sink’ theory, landscape pattern, regulation, key ‘source’ landscape, non-point source pollution