The Changes Of Phytoplankton Community Structure And The Analysis Of Its Impact Factors In Qinzhou Bay

The present study investigated the community structure of phytoplankton and its adaption to the environment in Qinzhou Bay based on four cruises including 2013-11,2014-04,2014-08 and 2014-12 using the software PRIMER 6.The results were as follows:Total of 187 species,including forma and varietas,were identified during four cruises.Amongst,one hundred and twenty-six species were identified as Bacillariophyta,and 54 species were identified as Pyrrophyta,accounting for 67.38% and 28.88% of the total species number,respectively.It also contained two species of Chrysophyta and one species belonging respectively to Xanthophyta,Cyanophyta,Haptophyta,Euglenophyta and Cryptophyta.One hundred and thirty four species,which belonged to 6 phyla and 54 genera,were identified from net-phytoplankton.One hundred and forty eight species were identified from water phytoplankton which belonged to 8 phyla and 71 genera.The dominant species showed obvious seasonal succession during the investigation.Excepted that Phaeocystis globosa was considered a dominant species due to the algal bloom in the cruise of 2014-12,the dominant species in other three cruises belonged to eurythemal diatoms.The cell densities of phytoplankton significantly varied in different seasons,and the horizontal distribution and seasonal changes of net-and water-phytoplankton did not identically match.The cell density of net-phytoplankton in August 2014 was the highest and the lowest cell density was found in November 2013.For water phytoplankton,the highest cell density was found in the cruise of December 2014 due to the bloom of P.globosa.Apart from the cruise of 2014-12,phytoplankton community in other three cruises showed high community diversity index and evenness index,which suggested that the community structure of phytoplankton in these seasons remained comparatively stable.The outbreak of P.globosa affected on the stability of phytoplankton and ecosystem in Qinzhou Bay.With respect to nutrient concentration in water,the dissolved inorganic nitrogen(DIN)contents were low in spring and summer and gradually increased from the south to the north of Qinzhou bay.The dissolved inorganic phosphorus(DIP)content distributed more regularly.The high value was found near the shore in three cruises(2013-11,2014-08,2014-12),but the high value area moved offshore in the cruise of 2014-04.The analysis of CA and MDS was employed to reveal the differences of phytoplankton community during four cruises using the software PRIMER 6.The results showed that the community structure of phytoplankton differed among four cruises.The results of ANOSIM test showed that the differences tested by CLUSTER and MDS were significant with the significance level of 0.01%.These results proved the markedly seasonal variations in Qingzhou Bay during our investigation.We further compared the monthly changes of four cruises using pair-test,and found the monthly differences of phytoplankton community were also significant.Besides,we found the different species in four cruises revealed by SIMPER analysis were eurythermal and euryhalinous species or nearshore species in warm temperate waters.These species adapted well to the water environment in Qinzhou Bay.The above differences of species were basically similar in both net-phytoplankton and water phytoplankton.Principal component analysis(PCA)was conducted to determine the influences of environment factors on the community structure of phytoplankton.The results showed the coefficients of environment factors in different months were varying and indicated that the contribution of environment factors to the community structure of phytoplankton varied with the month.Meanwhile,the results of BIOENV analysis showed that the correlation coefficients between the cell abundance of phytoplankton and environment factors were high in most months,which suggested a good correlation between the cell abundance and environment factors during our survey.Among different environment factors,the nitrogen contents in water showed relatively better correlation with the growth of phytoplankton,especially in the cruises of 2013-11 and 2014-12.The DIP content showed better correlation to the phytoplankton abundance in the cruise of 2014-04,while the temperature and salinity factor was only correlated well to the phytoplankton abundance in the summer cruise of 2014-08.