Distribution of benthic macrofaunal communities in intertidal flat under hydrodynamic influence:a case study of Jiangsu coast,East China

To identify the distribution pattern of macrofaunal assemblages of the Dafeng intertidal flats in response to hydrodynamic and sediment dynamic processes in the northern Jiangsu coast,East China,macrofauna sampling and hydrodynamic observations were carried out simultaneously across the mud flat,mixed mud-sand flat,and silt-sand flat of the intertidal zone in June 2018.Results show that there was a clear zonal distribution pattern of the macrofaunal communities,as is controlled by local hydrological and sedimentary environments.Principal component analysis(PCA)revealed three types of intertidal area in terms of hydrological and surficial sediment parameters.Similarly,three distinct groups of the macrofaunal communities,i.e.,mud flat,mix mud-sand,and silt-sand groups,were recognized at similarity level of 24%based on the CLUSTER analysis in similarity profile(SIMPROF)test.Correlation analysis upon best variables stepwise search(BVSTEP)indicated the importance of the hydrodynamics(e.g.,water temperature and salinity,tidal duration,flow speed,suspended sediment concentration,and wave height)in the differentiation of macrofaunal communities with different taxonomic classes over the intertidal zone.Therefore,macrofaunal assemblages,similar to hydrology and surficial sediment,have a unique zonation pattern.Small-sized deposit feeders adapt better to low energy environments,thus dominated the upper part of the intertidal flat,whilst the heavy and large-sized filter feeders and deposit feeders were dominant over the middle and lower parts.The hydrodynamic and sediment processes cause biota-niche separation,which affected the biological processes across the intertidal flat.

Ecological functioning of free-living marine nematodes in coastal wetlands: an overview

Nematodes are small multicellular, thread-like organisms, inhabiting almost all conceivable environments;among these, some 25 % are free-living marine forms with a population density of(1–12) 9 106 inds m-2in seabed sediment, reaching maximum values in muddy estuaries and salt marshes. A large quantity of carbon from the salt marsh plants enters the ecosystem via the detritus pathway,in which nematodes play an important role through their feeding and bioturbation activities. Vegetation influences the sedimentary environment and modifies the distribution pattern of nematode communities in coastal wetlands.Nematodes are coupled closely with bacteria/detritus in microbial food webs, stimulating bacterial growth and subsequent nutrient remineralization; they provide food sources for higher trophic levels and serve as a linkagebetween micro- and macro-fauna. Furthermore, nematodes have a potential to provide proxies that can be used in diagnosing environmental quality. In China, only a limited number of nematode data sets are available for the coastal wetlands across several different climatic zones. It is necessary to carry out additional investigations into the biology and ecology of nematodes in order to delineate their ecological functioning in coastal wetlands. On such a basis,the contribution made by nematodes to material cycling and the ecological functioning in coastal wetlands can be quantified. The assessment of their biological diversity should be a focus, which is fundamental in the study of wetland ecosystem dynamic mechanisms. In addition to laboratory and mesocosm experiments, mathematical models should be established to predict the responses of ecosystem to the environmental disturbance. Finally, it is necessary to improve the techniques for nematode analysis,to enhance the efficiency of data acquisition.