Study On The Benthic Diatom Communities And Its Contributions To The Food Web In The Chongming Dongtan Mudflats

As a dominant composition of microphytobenthos and the important primary producer in the mudflats,diatoms could affect the quality and quantity of zoobenthos and waterbirds directly or indirectly.In this study,surface sediments,macrozoobenthos,waterbirds and salt marsh plant samples were collected in the Chongming Dongtan mudflats.The environmental factors and organic matter sources composition of surface sediments,together with the composition and spatial distribution of the benthic diatom assemblages were studied,and the contribution of benthic diatoms to sediment organic matter sources and to the food web material circulation and energy flow were discussed.The main results are as follows:Spatial distribution,sources of organic matter and its influencing factors in the Chongming Dongtan mudflats in summer:the content of organic matter was higher in the northern part of the Dongtan and lower in southern part in Chongming Dongtan mudflats in summer 2019.The organic matter mainly consisted of marine organic matter(35.2±9.2)%,terrestrial organic matter(34.4±4.9)%,and C₃ salt marsh(30.3±4.3)%.Marine organic matter was mainly derived from local benthic microalgae such as diatoms and phytoplanktons carried by the tide.The significant positive correlation between marine biomarkers,BSi and TOC indicated that diatom was an important contributor of sediment organic matter in the mudflats.The sediments grain size seemed to be the important factors affecting the spatial distribution of organic matter content in the mudflats,and the salinity might also be the influential factor.Spatial distribution of benthic diatom communities and influencing factors in the Chongming Dongtan mudflats in summer:a total of 103 species(including varieties)of diatoms were identified,belonging to 31 genera and 14 families in Chongming Dongtan mudflats in summer 2019.The dominant species included Paralia sulcata,Tryblioptychus cocconeiformis,Rhaphoneis amphiceros and etc.Spatially,the abundance and Shannon-Weaver diversity index of benthic diatoms were higher in the northern part and lower in southern part of Chongming Dongtan mudflats,with the abundance of salt water species such as Rhaphoneis amphiceros showing more obvious spatial difference.Correlation analysis showed that the difference between sediments grain size and interstidal seawater salinity might be the main factors influencing the abundance and composition of diatoms,respectively,while the impacts of nutrients were not obvious.The contributions of microphytobenthos to the food web of the Chongming Dongtan mudflats:the abundance of macrozoobenthos were higher in the northern part and lower in southern part in Chongming Dongtan mudflats,which was consistent with the spatial distribution of TOC,BSi content and diatoms abundance.?¹³C values and Iso Source model showed that microphytobenthos were the main direct food source of Bullacta exarate,Cerithidea largillierli and Helice tridens tientsinensis,and the main indirect food source of Scylla serrata,Nereididae sp.and Periophthalmus cantonensis.Salt marsh C₃ plant was the main food source of Chiromantes dehaani,and suspended particle was the main food source of Corbicula fluminea and Moerella iridescens.These macrozoobenthos might be the main food sources of Egretta sp.and Ardea cinerea,among which B.exarata,C.largillierli,Nereididae sp.and P.cantonensis might be the main food sources of Calidris alpine and Tringa nebularia.As the food base of macrozoobenthos such as B.exarate and Nereididae sp.in Dongtan,microphytobenthos transfered energy to higher-level waterbirds,and could impact the distribution and quantity of waterbirds in the Chongming Dongtan.This study illustrated the characteristics of benthic diatom communities and its influencing factors in the Chongming Dongtan mudflats,and inidcated that diatom was not only an important contributor of sediments organic matters,but also provided a direct or indirect food source for macrozoobenthos and waterbirds in the food web in mudflats.The benthic diatom affects the macrozoobenthos and waterbirds in their biomass and spatial distribution.This study could provid data and references in the understanding of the ecological role of benthic diatoms in mudflats and the protectionof waterbirds.However,the productivity and seasonal variations of benthic diatom communities in mudflats needed to be further supplemented and improved.