| Seventeen surface sediment samples were collected in the three different functional sea areas in the Qingdao Coast,including the Laoshan Coast,the Amphioxus Reserve area,and Jiaozhou Bay.Diversity and community structure of eukaryotic organisms especially those of microalgae were assessed by metabarcoding V4 region of the 18 S r DNA.And dinflalgellate cysts were analyzed under microscopic observation.Biogenic elements including total organic carbon(TOC),organic matter(OM),total nitrogen(TN),total phosphorus(TP),biogenic silicon(BSi),and moisture content(MC)were analyzed in the thirty-three sediment samples.The origin of organic matter was assessed based on the molar ratios of biogenic elements,and the pollution status of biogenic elements was evaluated.Furthermore,relationships between biogenic elements and community structure of eukaryotic algae and dinoflagellate cysts were estimated.The results of this study reveal the diversity and community structure of eukaryotic algae in the surface sediments of the Qingdao Coast,give a better understanding on the background of marine environments,and provide scientific basis for environmental protection and sustainable development of the Qingdao Coast.The main results of this study are as followings:(1)A total of 948,236 DNA reads of eukaryotic organisms were obtained through metabarcoding in this study,including 171,722 reads of eukaryotic algae which accounted for 18.12% of the total sequences.A total of 1,496 eukaryotic OTUs were measured,including 207 eukaryotic algae OTUs,which contributed to 13.84%of the total OTUs.Ninety-eight species in 8 phyla,24 classes of eukaryotic algae were detected.Within them,48 species have been reported to form resting stages,36 species are toxic and harmful algal bloom species,and 12 species are firstly recorded in the Chinese coastal waters.Dinophyta dominated in both DNA reads and OTU richness,which contributed to 73.02% and 61.35% of the eukaryotic algae sequences and OTUs,respectively.(2)DNA reads and OTU richness of eukaryotic algae were higher in Laoshan Coast,and lower in Jiaozhou Bay.The average DNA reads and OTU richness per sample were higher in the Amphioxus Reserve area,and lower in Jiaozhou Bay.Alpha diversity indexes were generally higher in the Laoshan Coast,and lower in Jiaozhou Bay.The predominant groups of eukaryotic algae in the three sea areas were different,which were dominated by chrysophytes in Jiaozhou Bay,and by dinoflagellates in the Laoshan Coast.However the eukaryotic algae were co-dominated by dinoflagellates and chrysophytes in the Amphioxus Reserve area.Results from the clustering analysis also showed that stations in the Laoshan Coast and the Amphioxus Reserve area were clustered together,while the stations in Jiaozhou Bay were clustered separately.(3)Twenty-three taxa of dinoflagellate cysts were found in the surface sediments of Qingdao Coast,of which 13 were identified to species level.Dinoflagellate cyst concentration ranged from 81.4 to 158.1 cysts/g D Wt,with the average of 121.3 cysts/g D Wt.Cyst concentrations were high in the Amphioxus Reserve area,and lower in Jiaozhou Bay.Protoperidinium dominated in the cyst assemblages in Jiaozhou Bay and the Laoshan Coast,while cysts of Scrippsiella dominated in the Amphioxus Reserve area.(4)A total of 17 autotrophic dinoflagellate cysts and 6 heterotrophic dinoflagellate cysts were found in the Qingdao Coast.Generally autotrophic dinoflagellate cysts dominated,with the average proportion of 65.42%.Both concentrations and proportions of autotrophic flagellate cysts were higher in the Amphioxus Reserve,while were lower in Jiaozhou Bay.The G:P ratios from the higher to lower were in the order of the Amphioxus Reserve area,the Laoshan Coast,and Jiaozhou Bay.The higher proportions of heterotrophic cysts and lower G:P ratios in sediments from Jiaozhou Bay indicated the high level of eutrophication.Meanwhile,the Shannon index and Pielou evenness index of dinoflagellate cysts were higher in Amphioxus Reserve area than those in the other two sea areas.Six taxa of cysts of toxic/harmful algal species were also found in the surface sediments in the Qingdao Coast,including Alexandrium minutum,Alexandrium tamarense,Gonyaulax spinifera,Protoceratium reticulatum,Scrippsiella trochoidea,and Gymnodinium impudicum.Cysts of Scrippsiella trochoidea distributed widely and abundantly.(5)Concentrations of TOC,TN,TP and BSi in the surface sediment of Qingdao Coast were in the range of 0.21%-1.43%,0.02%-0.13%,0.06%-0.15%,0.26%-0.60%,1.35%-9.34%,0.18%-0.44%,respectively.TOC,TN,OM and MC were high in Jiaozhou Bay and the Laoshan Coast.While,TP and BSi were high in the Amphioxus reserve area.The distribution of biogenic elements in Jiaozhou Bay generally shows a downward trend from the northeast to southwest of the bay,from the inner bay to the outer bay.Hot spot of biogenic elements in the Laoshan coast was Laoshantou,and showed a decreasing trend to both sides.Biogenic elements were higher in the northern part of the Amphioxus reserve area,which is close to the urban area.(6)Based on the molar ratios of TOC/TN,TOC in Jiaozhou Bay and Amphioxus reserve area was originated from mixture inputs of terrestrial and marine sources,while was mainly originated from marine sources in Laoshan coastal area.TOC/BSi ratios were generally lower than the Redfield ratio,indicating the higher decomposition rate of organic matter than the dissolution rate of BSi.Results from pollution assessment of biogenic elements indicated that TOC in the surface sediments from Qingdao Coast belonged to the uncontaminated level,however TN and TP reached moderate pollution level.Generally speaking,the Amphioxus reserve area is unpolluted or slightly polluted.Biogenic elements generally showed no significant effects on eukaryotic algae,however had some effects on the distribution of dinoflagellate cysts.Concentrations of overall and autotrophic dinoflagellate cysts showed significantly positive correlations with BSi,while concentration of heterotrophic dinoflagellate cysts positively correlated with TOC and TN. |
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