Analysis of the development and causes of formation of Eucampia zoodiacus red tide in Xiamen Harbor

The red tide event of 11-28,May in 1987 was caused by Eucampia zoodiacus,a coastal eurythermic phytoplankton.Results from the field monitoring indicated that during the red tide occurrence the optimal temperature and salinity for the multiplication of the red tide organism were 20-25℃ and 26-28.During the red tide event cell densities in two peak values both reached 3 000×10³ ind./dm³.Organism number in horizonal distribution increased from the harbour mouth to the inner harbour.Average number of the organism at the monitoring stations in the inner harbour was 2 930×10³ ind./dm³ which was 3.7 and 61 times higher than that at the two control monitoring stations.The organism number in vertical distribution apparently showed stepwise,day and night changes.Daily change of the phytoplankton number with spring and ebb tides exhibited a negative relativity.
Major reasons for this red tide event included species competition of red tide organisms,sudden increment in water temperature in short time,sharp decrement in salinity by rainfall,water eutrophication,high contents of stimulating materials such as Fe and Mn,poor water exchange condition and stable synoptic condition,etc.High content of dissolved oxygen and high pH value was resulted from the photosythesis of a great quantity of the red tide organisms.