Preliminary Ecological Studies On Phytoplankton In Shacheng Harbour, East China Sea

This thesis comes from"908 special Fujian—Gulf capacity survey and numerical simulation and environmental studies projects of Shacheng Harbour".This study bases on the ecology investigations on Shacheng Harbour in East China Sea in January and April,2006.The phytoplankton community composition, quantity distribution and diversity are elaborated in this paper.The community structure of phytoplankton is analyzed by the four ecology indexes of Shannon biodiversity index,Pielou evenness index,Margalef richness index and Simpson dominance index at first,then the multivariate statistical software PRIMER is further used to study phytoplankton community structure and its relations to environmental factors. In this paper it mainly refers to hierarchical cluster analysis(CLUSTER), non-metric multi-dimensional scaling analysis(MDS), principal component analysis(PCA), correlationtes test (RELATE) and biota-environment stepwise analysis (BIO-ENV ) in PRIMER software.At last it discusses the influences of various nutrients and irradiance upon the phytoplankton growth by in situ controlled incubation experiment.The main conclusions are as follows:●Species composition145 species of phytoplankton are identified in this research.They belong to 61 genera,the 4 phylum of Bacillariophyta,Pyrrophyta,Cyanophyta and Chrysoghyta. In January 109 species are identified and in April 115 species are identified.Skeletonema costatum, Coscinodiscus jonesianus and Melosira sulcata are the main dominant species,and their percentage of total cells and dominance in April are more higher than those of in January. Bacillariophyta is the main group of phytoplankton and Pyrrophyta secondly.●Quantitative distribution of phytoplanktonThe average abundance of water phytoplankon is respectively 1271.88 cells/L in January and 3113.24 cells/L in April,and the value of April is about 2.5 times than that of January.The multiples relations also exists in the result of net phytoplankton. Horizontal distribution characteristicsThe general variation of phytoplankton abundance is characteristic of the pattern of decreasing from the top to the mouth of the bay,which might be related to large aquaculture areas and rich nutrients brought by many rivers into the top bay.The level of phytoplankton abundance(1.48×103cells/L only) and nutrients concentrations of additional K station at the outer edge of the bay mouth is much lower than that of other stations in the bay,which might be the evidence of the above pattern. Vertical distribution characteristicsSurface phytoplankton abundance is higher than that of other investigated water layers,but we do not find obvious gradient abundance distribution among these layers.The limited water depth of bay and water disturbance caused by tides and so on may greatly influence the vertical distribution of phytoplankton in shallow sea. Nycterohemeral variationThe phytoplankton abundance in the day is generally higher that of in the night, but the difference is not significant (p>0.05). The difference in phytoplankton community structure between day and night is significant in April(p<0.05) but not in January(p>0.05) judging from Shannon diversity index and Pielou evenness index.In April phytoplankton abundance is higher in bottom water layer in the night, perhaps because batho-diatoms are easily impacted by tides and suspended in the night such as Pleurosigma sp. and Melosira sulcata.●Phytoplankton DiversityShannon-Wiener diversity index, Margalef richness index,Pielou evenness index and Simpson dominance index are respectively 2.609,2.923,0.845,0.231 in January and 2.390,2.650,0.726,0.306 in April.Judging from the above,phytoplankton community structure in January is more complex and stabler than that of in April. But the four indexes of Shannon index, Margalef index, Pielou index and Simpson index in surface layer in April are respectively 2.631,2.862,0.747 and 0.268, higher than those of other water layers in January and April,which indicates that surface phytoplankton community structure in April is more complicated. ●Phytoplankton community structure and invironmental factors analysisCluster analysis and MDS analysis indicate that phytoplankton community of Shacheng Harbour is divided into the two groups of inner bay group and outer bay group ,and the heterogeneity of the former is higher than that of the latter. PCA analysis of the environmental factors shows that the main variant factors in the two months are not the same:In January they are pH, suspended sediments and NH3,and in April they are DO,pH,NO3 and SiO4.RELATE analysis indicates that related standards between community structure and environment are significant,and the correlation coefficents are respectively 0.297(p=0.3 %) in January and 0.372(p=0.1 %) in April,so relevance in April is higher than that of in January. The best subsets of environmenal variables matched phytoplankton community structure are gained by BIO-ENV program,and they are (pH, DO,COD,NO2,NH3) and (pH,DO,COD,NO2,SiO4)in January, and (pH,NH3,SiO4) in April.●Effects of irradiance and nutrients on the growth of phytoplanktonIn situ incubation experiment is conducted to study growth variations of phytoplankton under nutrients enrichment, irradiance controlled and nutrients–irradiance coupling at the net cage aquaculture area near Shacheng Town in the baymouth of Shacheng Harbour in April,2006. The results indicate:Growth of phytoplankton is significantly inhibited under dark irradiance(1% natural irradiance and 50% natural irradiance);Picoeukphytoplankton is best grown under low irradiance(50% natural irradiance),and micro-nanophytoplankton is best grown under high irradiance(100% natural irradiance).During the incubation concentrations of chlorophyll-a display upward trend,and various nutrients show different changes:concentrations of nitrite and ammonium display downward trend,and concentrations of nitrate drop firstly and then ascend, and concentrations of phosphate in different gradients vary differently.Correlation analysis shows that micro-nanophytoplankton is significantly negatively correlated with nitrate,and its correlation coefficient and significant level are respectively -0.625 and 0.007; picophytoplankton is significantly positively correlated with phosphate,and its correlation coefficient and significant level are respectively 0.530 and 0.029.This incubation experiment is carried out under high nitrogen and low phosphorus condition in natural water,so potential phosphorus limitation exists(Redfield ratio >16:1).From the results we can find that phytoplankton of different size level have different nutrients absorption way,and picophytoplankton are more easily influenced by phosphorus limitation.●ProspectIn order to accelerate economic development of Fujian Province,the government focuses on coastal resources development ,and so new coast reclamation works is to be carried out in several important bays including Shacheng Harbour.The influences of coast reclamation works on surrounding ecosystem are long-term, potential and complicated,so it is of great significance to monitor, evaluate and forecast their ecological environment before and after the projects.This dissertation will provide the scientific basis for the development of biological resources and protection of ecological environment of Shacheng Harbour.