Biogeological Distribution Of Dinoflagellate Cysts In Surface Sediments From Southern Chinese Coast And Their Roles As A Signal Of Environmental Changes

Cyst is the resting stage of many dinoflagellates,which loss their flagella and motility and become as a non-motile cell.Cysts thicken their walls and deposit into the bottom sediments,and then enter into the resting stage of their life circle.Dinoflagellate cysts(Dinocysts)are regarded as the seed bed of algal blooms,and also the carrier for the worldwide expansion of harmful dinoflagellates.The thick sporopollenin wall makes cyst well preserved in sediments and to be the important micro-fossils.Dinocyst assemblages are regarded as a feasible signal to reflect environmental changes due to anthropogenic activities.Ninety-four stations from the seventeen sea areas were set along Southern Chinese coast in this study,including Zhelin Bay,Shantou Port,Jieshi Bay,Honghai Bay,Daya Bay,Dapeng Bay,Guishan Island,Hailing Bay,Shuidong Port,Leizhou Bay and Liusha Bay in Guangdong coast;Fangcheng Port and Beihai Port in Guangxi coast;Haikou Port,Macun Port,Yangpu Port and Basuo Port in Hannan Northwest coast.Surface sediments were collected,and dinocysts were qualitatively and quantitatively analyzed.The purpose of this study is to understand geographical distribution of cysts in Southern Chinese coast,and to enrich the species diversity of dinocysts.Dinocyst mappings were drawn to summarize cyst distribution along Chinese coast based on literatures and results of this study.Correlations among dincysts,eutrophication,metal contamination and algal blooms were studied using multiple statistical analyses to understand the role of dinocyst as the environmental indicator.A 186 cm core was collected in Zhelin Bay.Vertical profiles of dinocysts,biogenic and metals were analyzed to understand the environmental changes in Zhelin Bay in recent fifty years,and to highlight the response of dinocyst assemblages to environmental changes.The results of this study reveal the response of dinocysts to marine environment and assess their potential as the environmental indicator.Our findings provide a basis acknowledge for the protection of biodiversity and sustainable utilization of marine resources in Southern Chinese coast.The key results are summarized as following:(1)Altogether thirty-four dinocyst taxa were identified in 94 surface sediments from 17 sea areas along Southern Chinese coast,including twelve of autotrophic dinoflagellates and twenty-two of heterotrophic dinoflagellates.Taxonomic studies were conducted based on morphological characteristics of dinocysts,and a cyst atlas was established.The results enriched species diversity of dinocysts in Southern Chinese coast,and provide basis information for the further studies.(2)Cyst mappings of thirty-four taxa were drawn based on the results of this study and literatures.This is the first cyst mapping in Chinese coast.The results show that Scrippsiella trochoidea is the most common cyst taxa in Chinese coast,and cysts of some harmful algal bloom(HAB)species such as Alexandrium tamarense and Gymnodimium catenatum are widely distributed.High concentrations of cysts of the HAB species,mostly living cysts,were recorded in the Pearl River Estuary and Baihai Port,indicating the high potential of HABs in these areas.(3)Cyst concentrations were generally low in this study due to the coarse sediments,disturbance of shipping and aquaculture activities.Cyst concentrations were between 14 and 250 cysts/g D Wt with an average of 69 cysts/g D Wt in Guangdong Coast,between 70 and 571 cysts/g D Wt with an average of 249 cysts/g D Wt in Guangxi Coast,and between 34 and 375 cysts/g D Wt with an average of 109 cysts/g D Wt in Northwest Hainan Coast.(4)The proportions of cysts of heterotrophic dinoflagellates were high,with the averages of 52.8%,43.9% and 71.2% in Guangdong Coast,Guangxi Coast,and Northwest Hainan Coast,respectively.The low cyst concentration and high percentage of heterotrophys were signals of combined effects of industry pollution,eutrophication and shipping disturbance.(5)Biogenic silica(BSi)and Cd were two important elements for dinocyst distribution in Guangdong Coast based on redundancy analysis(RDA),and the inflection points were 0.7% and 0.114 mg/kg for BSi and Cd,respectively.While total nitrogen(TN)significantly influenced cyst distribution in Guangxi Coast,with the inflection point of 0.15%.Salinity influenced cyst distribution in Northwest Hainan Coast,with the inflection point of 31.42.(6)The results from IndVal showed that Scrippsiella trochoidea,Gonyaulax spp.and Protoperidinium conicum were indicators of eutrophication in the Mid Guangdong Coast,and Protoperidinium conicum was the indicator of metal contamination in the East Guangdong Coast.Cyst of Diplopsalis lenticular indicated high TN concentration in Guangxi Coast.Furthermore cyst of S.trochoidea could be a feasible indicator of multiple environmental changes such as eutrophication and salinity.(7)The increasing proportions of cysts of heterotrophic dinoflagellates in core samples from Zhelin Bay reflexed the eutrophic process in the nearby areas.Furthermore,cysts of heterotrophys have high tolerance to metal pollution.The increasing eutrophication in Zhelin Bay resulted in low diatom productivity as well.Based on the vertical profiles of dinocysts,biogenic,and metals in this study,the environmental changes in Zhelin Bay in the past 50 years can be divided into three stages:(1)before the late 1980 s,during which biogenic and cyst flux were low,and metals belonged to the background value;(2)from the 1990 to the early 2000 s,characterized by an obvious increase of dinocysts,TOC,TN and most metals,meanwhile TOC/TN and BSi decreased;and(3)after 2000,the period of rapid increase of dinocysts,TOC and TN,however the decrease of some contamination metals.The vertical distribution of biogenic indexes and metals in this study corresponds well to the development of local economy and eutrophication history since the 1950 s.The results indicated that composition and distribution of dinocysts reflected the processes of eutrophication and other anthropogenic environmental changes in the Southern Chinese coast,and would be a feasible biological signal for marine environmental changes.