Species Composition And Distribution Of Diatoms In Marine Aquaculture Waters Of China

Diatom is a main component of phytoplankton and benthic algae in marine aquaculture areas,which plays an important ecological role in element cycle and energy flow,and it is essential for understanding the primary production,increasing aquaculture capacity and improving the aquaculture environment.Taxonomy of diatom species in different kinds of marine aquaculture and non-aquaculture areas were studied,and the biodiversity,character of community structure,ecological distribution and seasonal change of diatom assemblages were investigated,which lead to our understanding of the ecological role of diatoms in marine aquaculture area.Planktonic and benthic diatoms were sampled during May,2003 to February, 2005 from several marine aquaculture areas along the coast of China including the Island of Zhangzi in Dalian city of Liaoning Province;Sangou bay,Jiaozhou bay, Rusan bay and Tandao bay in Shandong Province;Sanmen bay in Zhoushan city of Zhejiang Province;Tongan bay and Quanzhou bay in Fujian Province;and Daya bay in Guangdong Province,respectively.Totally,170 samples were collected.Sampling area included prawn culture,scallop culture,oyster culture,cage culture and laminaria culture。Diatoms in Xike aquaculture area of Tongan Bay were sampled monthly or bimonthly and that in Quanzhou bay were sampled seasonally.Samples were acidized before being oberserved and identified under light microscopy(LM),scanning electronic microscopy(SEM) and transmission electronic microscopy(TEM).The results were showed as following:1.Totally,200 species(including variety) belonging to 51 genera were identified, including one newly recorded species.138 species and variety belonging to 33 genera were found in prawn culture area,followed by 101 species and variety belonging to 42 genera in cage culture area,42 species and variety belonging to21 genera in laminaria culture area,54 species and variety belonging to 31 genera in scallop culture area, respectively.The common genera of diatom in marine aquaculture areas were Navicula, Synedra,Chaetoceros and Skeletonema,The genera with most species numbers were Nitzschia(25 species,12.5%),followed by the following genera:Nitzschia (15species,7.6%) and Diploneis(13species,6.5%),Pleurosigma(13species,6.5 %).2.Chaetoceros debilis was dominant at scallop culture area in Zhangzi Island of Dalian city at November,2004,and the average cell density of diatom assemblages was 6.8×10~3 cells/L.Cell density,richness and dominance index of diatom assemblages near seaside were more than that far from seaside,while biodiversity and evenness index of assemblages near seaside were less than that far from seaside. Dinoflagellates occurred in all sampled sites,and percentage of average cell density of that in phytoplankton was 5.7 percent.3.Water temperature of prawn culture area in Quanzhou bay during Nov.2003 to May 2004 ranged significantly from 12.8 to 27.5 seasonally,while salinity of that ranged from 16 to 20 insignificantly with season.Salinity in winter is highest as 20. Nutrient was higher in spring and autumn,while lower in winter.Nitzschia(16.9%) and Navicula(8.4%) were dominant in diatom assemblage, Nanodiatom such as Cycloetlla,Thalassiosira and Skeletonema occurred in mostly surveys.Prorocentrum was dominant in dinoflagellate assemblages,which Cell density in Nov.2003 and Jan.2004 were up to 10~7～10~8 cells/L,and percentage of that in phytoplankton was 23%and 42.3%,respectively.Nanodiatom such as Cyclotella caspia increased significantly and its cell density was up to 6.36×10~8 cells/L,while density of other species was 10~2～10~4 cells/L only,and less species number.The percentage of dominant species such as Cylindrotheca closterium,Cyclotella caspia,Amphora angusta and Nitzschia in phytoplankton was up to 34.8%.4.Nitzschia(13 species) and Pleurosigma(11 species) were dominant in cage culture area of Tongan bay during Apr.2004 to Feb.2005,the percentage of that in total species number were12.9%and 5.9%,respectively.The species number of Chaetoceros and Coscinodiscus were up to 6 or 7.Cylindrotheca closterium,Lithodesmium undulatum,Nitzschia,Amphora and Navicula occurred frequentl.Chaetoceros were dominant,in term of species number or cell density.Skeletonema bloomed in Aug.and Dec.to 1.9×10~5 cells/L,while its cell density in other month is low.Diatoms with relatively larger cell size such as Nitzschia fasciculata and Nitzschia hybria were dominant in spring and summer,while nanodiatom such as Nitzschia panduriformis var.minor and Cocconeis scutellum var. parva were dominant in winter.5.Rhizosolenia were dominant,in term of cell density in aquaculture area of Sangou bay,while Thalassiosira(9 species,13.9%),Coscinodiscus(6 species,9.2%) and Chaetoceros(5 species,7.7%) were dominant,in term of species number.The sub-dominant species Rhizosolenia,Licmophora,Thalassiosira,Pseudo-nitzschia pungens,Melosira sulcata and Eucampia zodiacus occurred in laminaria culture area, scallop culture area and oyster culture area.Cell density and species number of phytoplankton in laminaria culture were more than that in other aquaculture areas.31 species of nanodiatom(53.9%of total species number) were identified in aquaculture area of Sangou bay.The most species-rich genera was Thalassiosira(25.7 %),while Skeletonema were dominant(5.5×10~4 cells/L),in term of cell density.6.Red-tide causative microalgae usually bloomed in Jiaozhou bay with narrow estuary,high nutrition content.Pseudo-nitzschia pungens bloomed in shellfish culture area of Jiaozhou bay during Mar.2005,and cell density were up to 2.7×10~7cells/L. The species number and cell densitiy of diatom except Pseudonitzschia pungens during redtide was low,while cell density of dinoflagellate cyst was up to 4.7×10~3cells/L.7.Redtide caused by dinoflagellates and diatoms occurred frequently in Daya bay with long aquaculture history and eutrophication.Rhizosolenia alata bloomed in aquaculture area in Daya bay during Feb.2004 and cell density of Rhizosolenia alata were up to 3.2×10~5cells/L.Besides Rhizosolenia alata,nanodiatom were sub-dominant species,such as Thalassiosira.8.The dominant species of diatom assemblages in different aquaculture area varied. Amphora angusta(32.8%),Cyclotella caspia(30.4%),Cylindrotheca closterium (23.7%),Navicula(11.3%) were dominant in prawn culture ceils,while Cocconeis scutellum(38.6%),Nitzschia panduriformis(13.3%),Navicula ramosissima(7.3%),Chaetoceros lorenziana(5.4%),Coscinodiscus asteromphalus(5.2%) were dominant in cage culture area,Chaetoceros debilis(69.6%) was dominant in scallop culture area,Rhozolenia alata var.Indiana(19.2%),Rhizosolenia hebetate f. semispina(20.5%),Pseudonitzschia pungens(15.4%) were dominant in laminaria culture area,respectively.9.In general,cell density of diatom assemblage in aquaculture area varied significantly with season.Cell density of diatom in aquaculture area was highest in spring,followed by autumn,summer and winter.Being influenced by different environment in different aquaculture,phytoplankton usually bloomed under eutrophication,making evenness index of community lower and community destabilized.10.Species composition of nanodiatoms in marine aquaculture waters and the percentage contribution of nanodiatoms(＜20μm) to micro-diatom(20-200μm) were studied.The species number and cell density of nanodiatoms in marine aquaculture are were dominant.Species number in Laminaria culture area is highest,while that is lowest in scallop culture area.Cell density of nanodiatoms in scallop culture area is similar to that in laminaria culture area.Average cell density of planktonic nanodiatoms such as Skeletonema coastatum and C.caspia were highest in prawn culture area.Benthic nanodiatoms such as Navicula,Nitzschia and Cocconeis were dominant in cage culture area.Nanodiatoms occurred in all sampled sites and season.Mostly,nanodiatoms were dominant in summer and winter.11.The morphological characteristics,accurrence season and distribution of six representative diatom species in marine aquaculture waters of China were described in detailed.Falcula M.Voigt from samples in prawn culture area of Quanzhou bay was first described in China in terms of taxonomy,and a detail description of taxonomic characteristics,ecological habit and distribution of Falcula hyalina Takano a species attached to marine copepod,was described as a newly recorded species in China..