| Meiofaunal and environmental samples were collected during cruises carried out in September and December 2016,at the boundary and its adjacent area of the Yellow Sea and the East China Sea.Meiofaunal community composition,abundance,biomass,distribution patterns and their relationship with environmental variables,as well as species composition and taxonomy of benthic harpacticoids,were studied.The results were as follows:1)a total of 16 taxa were identified in the study area,with nematodes being the most dominant groups,followed by copepods,kinorhynchs,polychaetes,bivalves etc.The average abundance of meiofauna in September was(1758±759)ind./10 cm~2,with nematodes accounting for 95.6%;the average biomass was(1216.4±464.7)?g·dwt./10cm~2,with nematodes accounting for 55.26%.The average abundance of meiofauna in December was(2011±1471)ind./10 cm~2,with nematodes accounting for 95.6%;average biomass was(1143.0±755.0)?g·dwt./10 cm~2,with nematodes accounting for 67.28%.2)Meiofaunal communities can be divided into two groups,one near-shore community and one offshore community.Results of ANOSIM showed that there were no significant differences between September and December in terms of meiofaunal communities.Results of CLUSTER analysis showed that meiofaunal community in the study area can be divided into two main groups.One group is composed of sites in the nearshore area with high abundance but low diversity,while the other group is mainly composed of site in the offshore area with relative low abundance.BIOENV analysis showed that sediment organic matter content,water depth,sand content and heavy metal content can best explain the differences of meiofaunal groups?3)Upwelling and hypxia outside the Changjiang estuary may lead to the increase of meiofaunal abundance but decrease of diversity in this area.In September the highest abundance occurred in the overlap of upwelling and hypoxia area,with high percentage of nematodes and low percentage of other taxa.This may be explained by the increase of primary productivity in water column,which benefits from the upwellings and provides sufficient food for meiofauna,and the inhibition of hypoxia on the existence of macrofauna and other sensitive meiofaunal groups,which reduces the pressure of predation and benifit the colonization of nematodes.4)The intrusion of Kuroshio may lead to the increase of meiofaunal abundance in its route.Meiofauna communities showed high abundance near the 60 m isobath,which well matches with the route of Kuroshio intrusion.The intrusion of Kuroshio may lead to increase of primary productivity in water column and brings waters with dissolved oxygen.In addition,the stability of Kuroshio water may reduce the damage caused by seanonal changes,and benefits the reproduction of meifauna.5)Two new species Haloschizopera cheni sp.nov.and Haloschizopera sheni sp.nov.,and two new records Heteropsyllus coreanus Nam&Lee,2006 and Zosime destituta Kim,Jung&Yoon,2016 were identified.About 80 species and 6 kinds of juveniles of benthic harpacticoid were identified in the study area,belonging to 36genera,17 families.The most dominant family of harpacticoids was Miraciidae,including 18 species belonging to 10 genera.A review of the genus Haloschizopera was made with a key to species.6)Harpacticoids communities can be devided into two near-shore community and offshore community.Results of CLUSTER shows that harpacticoids communities can be classified into three main groups.Group III was composed of sites in the near-shore area with lower abundance and diversity index,compared with Group I and II,both of which were composed of sites in the off shore area.Environmental stresses such as anthropogenic activites,pollution and hypoxia may be the main causes of lower abundance and diversity of harpacticoids in the near-shore area.BIOENV results showed that water depth and bottom salinity may best explain the differences of harpacticoids communities. |
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