| Understanding shrimp and crab community structure in regional scales is vital in the study of its ecological roles to predators, especially when studied area are happened to be idea feeding and spawning grounds for commercial fishes. Based on samples collected by shrimp trawls from summer(July) and autumn(October) in 2013 to winter(March) and spring(May) in 2014 in the protected Ma′an Archipelago area, we analyzed the seasonal variations in species composition, dominance, resource density including the horizontal distribution and diversity indices of shrimp and crab, and further discussed the contribution of dominant species to the total resource density in the meantime. In all, 20 species of shrimp were collected. From summer to spring, the number of shrimp species turned out to be 12, 16, 13 and 14. Palaemon gravie, Parapenaeopsis tenella and Oratosquilla oratoria were dominant species in all year, the main species influencing the variation in shrimp resource density with Solenocera crassicornis and Latreutes mucronatus. The biomass and abundance of shrimp were greatest in summer(230.0 kg/km2; 115.8×103 ind/km2), followed by spring(80.4 kg/km2; 113.3×103 ind/km2), and then winter(53.2 kg/km2; 55.7×103 ind/km2), whereas least in autumn(45.4 kg/km2; 28.7×103 ind/km2). As well as the biomass, the shrimp abundance was well-distributed in summer, but greater in central and eastern area in next season and aslo spring, yet in central and western area in winter. The Margalef richness index(D) of shrimp was 1.12~1.55, the Shannon-Wiener index(H′) was 0.84~1.55, and the Pielou evenness index(J′) was 0.41~0.76. Diversity indinces tend to be highest in autumn, and then was in winter and summer, but lowest in spring. One-way ANOVA declared that diversity indinces had notable difference between seasons(P<0.05).We identified 22 species of crab in total, with the most in summer(20 species), the next in autumn(16 species), then in spring(9 species) and the least in winter(8 species). Charybdis japonica and Charybdis bimaculata were absolute dominant species in all year, Portunus trituberculatus was second dominant species both in summer and autumn. The biomass of crab turned out to be the most in autumn(135.4 kg/km2), followed by summer(126.0 kg/km2), and then winter(23.2 kg/km2), while least in the spring(12.9 kg/km2). However,the rank of abundance was summer(34.6×103 ind/km2), autumn(11.6×103 ind/km2), spring(1.7×103 ind/km2), and winter(1.6×103 ind/km2). The stepwise regression analysis indicated that the crab biomass increased distinctively with bottom water temperature(P=0.045<0.05).The resource of crab was equally distributed in winter, while greater in central and eastern area than in western area in other seasons. The main species Charybdis japonica, Charybdis bimaculata and Portunus trituberculatus with high dominance influenced the seasonal change of crab resource density with the same horizontal distribution. The Margalef richness index(D) of crab was 0.48~1.50, the Shannon-Wiener diversity index(H′) was 0.15~1.20, and the Pielou evenness index(J′) was 0.09~1.00. Species diversity and richness indinces tended to have the consistant seasonal variation like that autumn was first, and then ware summer and spring, whereas winter was last. Nevertheless,the evenness index(J′) increased since summer. The analysis result by Cluster and n MDS in shrimp community structure demonstrated that significant differences existed among seasons, while not in crab community structure. The community structure of shrimp and crab were relatively stable. The bottom temperature was the single factor with the highest influence on community structure of shrimp and crab. |
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