Diversity Of Dinoflagellate Cysts In The Intertidal Zone Of China And Environmental Implication

Dinoflagellate cysts are immobile cells when planktonic dinoflagellates lose flagellums and swimming ability.It is a dormant stage for planktonic dinoflagellate to survive under unfortunate circumstances.When the environmental conditions are suitable,dinoflagellate cysts can germinate to form planktonic cells in large quantities and colonize the upper water column.When the number of cysts is large enough,they may become the "seed source" of harmful algal blooms,triggering red tide disasters.Therefore,understanding the diversity and quantity distribution of dinoflagellate cysts in marine sediments is one of the important items for monitoring harmful algal blooms.In addition,the species composition and distribution of dinoflagellate cysts in sediments are closely related to the physical and chemical environment of water column and sediments.Therefore,the species composition and abundance distribution of cysts can not only reflect the geographical distribution characteristics of the dinoflagellate in the water column,but also reflect the environmental quality of the relevant waters to a certain extent,indicating its important ecological indications.The intertidal zone is located at the junction of land and sea.And it is affected by various dynamic factors such as tides and waves.It is difficult to preserve dinoflagellate cysts from the ocean.In addition,the intertidal zone is often exposed to the air due to the dynamic tides,and considering the time taking in the formation of cysts,the intertidal zone is not suitable for the formation of in situ encystment.Therefore,dinoflagellate cysts in the intertidal zone have relatively rarely been reported.However,recent domestic studies have shown that due to human activities such as aquaculture,a large number of toxic dinoflagellates may be preserved in the intertidal zone,and variations in species composition and abundance of these toxic dinoflagellates are worth considering.Based on above background,we carried out a study on the quantity and diversity of dinoflagellate cysts in 11 intertidal zones from north to south along the coast in China.Surface sediments and water samples were collected from 11 intertidal zones including Daliao River Estuary of Liaoning,Jian River Estuary of Tianjin,Yellow River Estuary and Dagu River Estuary of Shandong,Yancheng shoal of Jiangsu,Chongming Dongtan of Shanghai,South bank of Hangzhou Bay,Zhejiang,Min River Estuary and Jiulong River Estuary of Fujian,Pearl River Estuary of Guangdong and Dongzhai port of Hainan for four seasons from 2014 to 2016.In this study,the seasonal variations of species diversity and quantity and the correlation with relative environmental factors were analyzed.The main results were as follows:1.Species composition of dinoflagellate cystsA large number of dinoflagellate cysts with a total of 47 dinoflagellate cyst species(belonging to 18 genera,including 19 autotrophic species and 28 heterotrophic species)and 12 undetermined species were identified in the surface sediments of the intertidal zones,with the main species belonging to Gonyaulacoid group and Protoperidinioid group.Among these species,Protoperidinium mendiolae,Echinidinium delicatum and E.transparantum were firstly reported in coastal areas of China,and four toxic species including paralytic shellfish poisoning(PSP)-producing Alexandrium tamarense complex and three yessotoxin(YTX)-producing species(Protoceratium reticulatum,Lingulodinium polyedrum,Gonyaulax spinifera)were also detected.2.Community structure of dinoflagellate cysts(1)The seasonal and spatial characteristics of dinoflagellate cysts abundance:The annual average abundance of dinoflagellate cysts in the study areas varied from 1 to 69 cysts/g DW,and the average was 17 cysts/g DW.There were significant spatial differences in the average abundance of the study areas: the average abundance of dinoflagellate cysts in the Daliao River Estuary of Liaoning(69 cysts/g DW),Jian River Estuary of Tianjin(49 cysts/g DW),Min River Estuary of Fujian(27 cysts/g DW)and Jiulong River Estuary of Fujian(23 cysts/g DW)were significantly higher than other stations.The abundance of heterotrophic dinoflagellate cysts was higher than that of autotrophic dinoflagellate cysts at most stations.There were seasonal differences in cyst abundance,ranging from 1 to 75 cysts/g DW in spring,with an average of 17cysts/g DW;In summer,the variation range was 1 to 94 cysts/g DW,with an average of 21 cysts/g DW;In autumn,the variation range was 1 to 50 cysts/g DW,with an average of 14 cysts/g DW;In winter,the variation range was 2 to 72 cysts/g DW,with an average of 17 cysts/g DW.There were significant seasonal differences in Daliao River Estuary of Liaoning,Jian River Estuary of Tianjin,Min River Estuary and Jiulong River Estuary of Fujian,but the seasonal variations were inconsistent at these four stations.(2)The seasonal and spatial variatioins of dinoflagellate cysts diversity:The annual average of the Shannon-Wiener index(H?)of dinoflagellate cysts in the study area varied from 0.18 to 2.81,indicating that there were significant spatial differences in species diversity.Daliao River Estuary of Liaoning(2.61),Jian River Estuary of Tianjin(2.81),Dagu River Estuary of Shandong(1.99),South Bank of Hangzhou Bay,Zhejiang(1.78)and Jiulong River Estuary of Fujian(1.80)have higher species diversity.Seasonal differences were found in species diversity.The ShannonWiener Index(H?)varied from 0 to 3.10 in spring,with an average of 1.30.In summer,the range was 0 to 2.84,with an average of 1.24.In autumn,the range was from 0 to2.88,with an average of 1.26.In winter,the range was from 0.44 to 3.50,with an average of 1.59.At most stations,the species diversity in winter is slightly higher than that in other seasons.3.Analysis of the relationship between dinoflagellate cyst community and environmental factors: four high-abundance estuary intertidal zones including Daliao River Estuary of Liaoning,Jian River Estuary of Tianjin,Min River Estuary and Jiulong River Estuary of Fujian were selected as representatives to analyze the relationship between cyst abundance,species diversity and environmental factors.(1)Pearson correlation analysis showed that the total abundance of cysts had a significant positive correlation with dissolved inorganic nitrogen(DIN)and a significant negative correlation with tidal range and Pb concentration.The abundance of autotrophic cysts had a significant positive correlation with Cr and As concentrations,and a significant negative correlation with precipitation,tidal range,Pb concentration,Cd concentration and Hg concentration.The abundance of heterotrophic cysts was not significantly correlated with environmental factors,indicating that heterotrophic cysts were less sensitive to environment than autotrophic cysts.The Shannon-Wiener index(H?)was significantly positively correlated with sediment grain size(<63 ?m)and As concentration,and was significantly negatively correlated with precipitation,tidal range,Pb concentration,Cd concentration and Hg concentration.(2)The Redundancy Analysis of dominant species abundance and environmental factors showed that the species distribution was mainly affected by the concentration of Pb,DIN,As and Cd.All dominant species were negatively correlated with Pb concentration.Among them,A.leei,Fragilidium mexicanum,P.reticulatum,G.spinifera,P.expansum and P.leonis had a significant positive correlation with DIN concentration and As concentration,a significant negative correlation with Cd concentration.G.spinifera,P.denticulatum,P.oblongum and P.conicum had a significant positive correlation with Cd concentration,and negative correlation with DIN and As concentrations.The comprehensive analysis of environmental factors,human activities and the distribution characteristics of dinoflagellate cysts in the adjacent waters of the intertidal zone shows that a variety of environmental factors affected the distribution of dinoflagellate cysts.The dominant species,P.reticulatum,could be considered as an indicator of eutrophication in the Daliao River Estuary of Liaoning and Jian River Estuary of Tianjin.Although the species richness and the number of dinoflagellate cysts in the intertidal zone of the estuary were lower than those in the adjacent seas,their existence could not be ignored,especially the number of toxic dinoflagellate cysts.The monitoring of toxic dinoflagellate cysts should be strengthened.The source of cysts in the intertidal zone was closely related to the cysts in the adjacent seas in space.It was possible that cysts had transported over long distances along the ocean current.Whether the three newly reported cysts formed in situ remained to be further investigated.The group and mechanism of cyst formation in the intertidal zone were worthy of further study.