Ecological Distribution Of Dinoflagellate Cysts In The Sediments Of The East China Sea And Yellow Sea And Its Relationships With Marine Pollution

In the present study, surface sediment samples were collected at14stations（28°21′00″－34°00′00″N，121°17′24″－123°15′00″E）from the East China Sea and Yellow Sea in the spring of2010and29stations from the East China Sea（28°10′12″－30°30′00″N，121°57′00″－123°30′00″E） in2011, and one135cm sediment core from za3station （29°31′12″N，122°37′48″E）near the Changjiang Estuary were collected to investigate the species diversity,geographical distribution, as well as horizontal distributions and vertical variations ofdinoflagellate cysts in this area.According to the morphological characteristics of the cysts, thirty dinoflagellate cystspecies representing6groups were identified, including5species of Gonyaulacoids,1ofTuberculodinioid,4of Calcoidinellids,4of Gymnodinioids,1of Diplopsalid and15ofProtoperidinioids, while heterotrophic Protoperidinioids cysts dominated in the cyst assemblagesindicates severe water eutrophication. Twenty-six dinoflagellate cyst species were identified inthe surface sediments from samples in2010with the cell density ranged from5to362cysts g-1dry weight, and correspondly, to Shannon-Weaver species diversity index varied between0.97-4.11. Thirty dinoflagellate species were detected from samples in2011with cell densityranged from8to283cysts g-1dry weight and relevant Shannon-Weaver species diversity indexvaried from1.50to4.31. Scrippsiella trochoidea was the dominant cyst type in two years survey,and cysts of Alexandrium tamarense which produces paralytic shellfish poisoning toxins wasalso detected almost in all locations. In the East China Sea, species number of dinoflagellate cyst,total cyst density, cyst density of Scrippsiella trochoidea and Alexandrium spp. were higher inoffshore areas, and increased from the west to the east,and from the north to the south within thestudied area. The highest value of all these indexes were obtained at the station zb11, far fromestuary, indicating that precipitation velocity decreases with the augment of the distance from theestuary, which causes the rise of cysts density. Twenty-nine cysts species were observed in thesamples of sediment cores from za3stations, and cyst density ranged from1to305cysts g-1dryweight. It showed prominent vertical variation in the layers from0to25cm. Species number,total cyst density, cysts density of Scrippsiella trochoidea and Alexandrium spp. were relativelyhigher in0-25cm depth of sediment samples compared with deeper layers, and demonstratingindustial pollution and water eutrophication have deteriorated gradually in the last three decades.The Protoperidinioids cysts were observed in each layer, indicating that Protoperidinioids cystsnot only distributed widely in the global areas, but also have existed for a long time in this area.Cysts of an oligotabulate species belonging to Calcoidinellid group, Posoniella tricarinelloides,were observed in three stations surface sediment samples of2011. This cyst wasnot detected in the surface sediments sample but in the upper25cm depth sample of the sedimentcores at za3stations with cyst density ranging from2to34cysts g-1dry weight.The results may help to better understand the relationship between phytoplanktoncomposition and the HAB occurrence history in this area. Data analysis should contribute touncover the relationship between dinoflagellate cysts’ distribution and coastal eutrophicationresulting from industrial pollution and will help to predict the population dynamics of vegetativecells in the water column and the potential of HAB occurrence.