Studies On The Phytoplankton Community And Molecular Identification Of Typical HAB Species In Daya Bay, South China Sea

The study of the phytoplankton community and environmental factors in Dapengao,Daya Bay was carried out from May 2007 to April 2008.Furthermore,several typical HAB species were analyzed after amplified by polymerase chain reaction(PCR),including Alexandrium, Prorocentrum and Akashiwo sanguinea.The purpose of this study is to understand the changes in phytoplankton community and environment conditions in typical maricultural areas,and to provide the basis data for the prevention of harmful algal blooms.A total of algal 175 taxa were identified during the survey.The total cell densities of phytoplankton ranged from 1.9×10~4cells/L to 1108.64×10~4cells/L.Diatom was the predominant group of phytoplankton,which contributed 76.18%of the total cell numbers,while dinoflagellate only held 8.21%.Diatoms were present throughout the whole year,and species such as Chaetoceros,Skeletonema costatum,Pseudo-nitzschia spp.,Thalassiostra rotula, dominated alternately.Dinoflagellates occurred more frequently and abundantly in spring and winter,and dominant species were Prorocentrum spp.,Scrippsiella spp.,Alexandrium spp.. Alexandrium spp.took up the absolute superiority in phytoplankton community in August 2007, with the cell density and proportion of 90.52×10~4cells/L and 4.00%,respectively.The high abundance and proportion of cyanobacteria were an important characteristic of phytoplankton stucture in surface microlayer at Daya Bay,which indicated the ongoing deterioration of water quality in the area.The averages of the density and percentage of cyanobacteria in surface microlayer were 7.63×10~4 cells/L and 42.14%.Microcystis spp.,Romeria simplex,Nostoc spp., Trichodesmium hidebrandtii peaked alternately between seasons.Average values of Shannon-weaver species diversity index(2.59)and evenness index(0.55) were within moderate level.The total cell numbers showed positive relationship with temperature and negative relationship with the DIN,but non-statistical significance correlation with other environmental parameters,which indicated that temperature and DIN were the key factors influencing the phytoplankton abundance.Furthermore,eight important HAB species of algae were amplified and analyzed.The sequences obtained were compared with typical sequences from GenBank,and phylogenetic trees were constructed by Neighbour-Joining methods.The results showed that ITS sequence had the higher variation speed,and was able to distinguish the inter-species genetic differences effectively.All of the four Alexandrium strains isolated from South China Sea and East Chian Sea,belonged to the genotype of "Temperate Asian".Two Prorocentrum strains form Daya Bay were P.triestinum and P.minimum,respectively,both of which had close relationship to the strain from South Korean.A strain of Akashiwo sanguinea from Daya Bay also closely related to the strain from South Korean,while Gyrodinium instriatum was close to the strain from China.