Monthly changes in the benthic macro-invertebrate community structure in the habitats of Phragmites australis marsh in the Dongtan wetland of the Yangtze River estuary, China

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Based on the data of the benthic macro-invertebrates community in the Phragmites australis marsh in the Dongtan Wetland of the Yangtze River estuary collected from May 2015 to April 2016, we evaluated the monthly variations in the species composition, biodiversity and community structure of the benthic macro-invertebrates. The results showed that the average height and degree of coverage for P. australis increased monthly from March to August, and then deceased from September. The density and aboveground biomass (dry mass, g) of P. australis peaked in July. A total of twenty species (including 2 species only identified to genus level and 2 species identified to family level) were found in the survey periods, including 11 Gastropoda, 5 Malacostraca, 2 Insecta and 2 Polychaeta. Three snail species (Assiminea latericea, Assiminea violacea and Cerithideopsis largillierti) dominated the benthic communities in terms of numerical abundance. The number of epifauna species was the most (11 species), followed by 5 burrowing species and 4 infauna species. There were significant monthly variations in the density and biomass of the macro-invertebrates. The density and biomass of benthic community reached the maximum in August. The Margalef's species richness index (D) and Shannon index (H) showed significant differences monthly, but Pielou's index (J) except in November. Three macro-zoobenthic assemblages were identified with the 42% similarity level. The non-Metric Multidimensional scaling plot indicates that the benthic community in May, October and November was distinct compared to that in the other months. The present study suggested the density of the benthic macro-invertebrates community in the P. australis marshes was somewhat correlated with water temperature, underground biomass and salinity. But those correlation were not significant (P>0.05). Because of the continuous impact of anthropogenic activities, the biodiversity of the benthic macro-invertebrate community has been decreasing for several years. More attention should be paid to the habitat value of the P. australis marshes in the future.