Study On The Relation Between Physicochemical Factors And Red Tide Algae Of Sandu Bay

Sandu Bay is an important component Fujian marine economy.With its unique environment,Sandu Bay has become nets breeding base for Large Yellow Croaker. It is not only the largest inner bay of Fujian province but of China.Also, it is the only spawning ground of Large Yellow Croaker in our country.Because of Sandu Bay's typical state of nearly closed,much attention is concentrating on environment of it.Since the 1990s,with the rapid development,the large yellow croaker aquaculture has become one of the pillar industries of Fujian Province.The surroundings of theinner bay is mostly influenced by the coastal area runoff and the sea tidal Though there were red tides outside of the bay frequently,we never monitored the endogenous red tide,also,the exogenous red tide has never affected the inner bay.However,with the economic development of East Fujian,people assembling into the coastal towns,more and more pollutant has been discharged into the sea,which contains quite a part of nutrient and makes inorganic nitrogen and active phosphate at a relatively high level in different extent.So if we pay little attention to the inner bay environment treatment and the nitrogen and phosphate extend to the bay- mouth,red tide algae will spread from the outer bay brine water to the Bay Top area in the dry year,and the red tide is unavoidable in the inner bay.Then the inner bay environment is more difficult to recover than that of the outside bay and severely encumber the further development of aquiculture.The present paper based on the investigation of environment in Sandu Bay area,studied water circumstance physical and chemical factors and red tide algae and discussed the relationship between them,the results were showed as follows:1.The content of N and P in Sandu Bay is higher than other waters,there is a trend for N content that in autumn is higher than that in summer, otherwise,the highest P content takes on autumn,then in spring,the summer is the lowest.The plane distribution show,both of the N and P content depressed from the bay-top to bay-mouth.2.The high N/P ratio present at No.Fjchch08 station and the lowest one present at No.Fjchch07.82.14%of the N/P values are lower than 16:1;it shows that there is short of N in Sandu Bay waters which suggests the N is the limitative factors for the developing and reproducing of red tide algae.3.The highest E value of nutrition status index presents at No.Fjchch07 station and next to No.Fjchch05 station,the lowest value presents at No.Fjchch06,the results indicate there is trending to eutrophication in bay-top area.4.A total of 62 species belonging to 34 genera of phytoplankton in Sandu Bay were indentified.Diatom was the majority of these phylums including 51 species belonging to 28 genera.Then was the dinoflagellate which including 11 species belonging to 6 genera.36 species of them were red tide algae and the major dominant species were Skeletonema costatum,Chaetoceros, Thalassiosira,Melosirasulcata,Gymnodini ummikimotoi,However the major dominant species were Skeletonema costatum during the whole monitoring period.5.The Regression Analysis results of the monitoring data showed that WT, pH,COD,DO,DO saturation,PO₄^--P,E,chlorophyll-a and N/P value significant correlated to the quantitative change of red tide algae seasonly.Study the combination of the characteristics and laws of red tide algae in east-Fujian and other relative researching works,we suggest that pH,COD,DO,DO saturation and chlorophyll-a have close relationship to red tide algae as inner Bay environmentally sensitive factors.It is tallies with the monitoring results of the outer Bay seas,as red tide algae developing,pH,COD,DO,DO saturation and chlorophyll-a are 8.66,19.76mg/L,13.50mg/L,189.9%and 82.38μg/L respectively.6.Regress analysis shows that the Salinity,Transparency,Vibrio,DIN, NO₂^--N,NO₃^--N and NH₃-N were uncorrelated or not significantly correlated to red tide.It is possibly owing to the impact of the coastal area runoffs and the seas tides,which make the monitoring data varies complicatedly.