Xiamen Yundang Lake Red Tide Occurrence In Ecological Studies

Red tide, or Harmful Algal Blooms (HAB), is now considered to be a marinedisaster all around the world. This article researched the red tides occurred inYundang Lagoon Where the water body was hypertrophic, and present severalmethods to prevent the outbreak of red tides. The main contents of this research canbe summarized as the following:The results indicated 40 species of red tide organisms among 103 species ofphytoplankton identified. Species composition was dominant by eurytopic species andwarm water species. Skeletonema costatum. Thalassiosira rotula. Chaetocerostorttaimus. Peridinium quinquecorne. Chlorella sp. and Euglena sanguinea causedred tide in Yundang Lagoon, in 2001.All these phytoplanktons caused red tide in Yundang Lagoon are not toxic algae.Except for Peridinium quinquecorne, the number of any species of dinoflagcllate wasless than 104cell/dm3. Three species of toxic algae were identified in the samples of2001. They were Alexandrtum tamarense. Gymnodinium sp. and Niuschia pungens.Because the numbers of all species of toxic algae were less than 104 cell/dm3, probablythere was no toxic algae which can cause red tide in Yundang Lagoon.Species diversity aPparently changed with (cold and wann) seasons. Thcre were alow diversity in cold season, 12 species in January and a high diversity in warmseason, 69 species in May. In July, when the water temperature was highest in 2001,red tide broke out and the ecosystem was destroyed, so the diversity of this month waslower than that of May. It was also founded that predominant species ofphytoplankton changed very frequently in Yundang Lagoon. Average annual numberof phytoplankton reached 2.20 × 107cell/dm3 Which was 96.4 times more than that incontrol monitoring station. Clear patterns of diumal vertical migration of three species,Skeletonema costatum. Thalassiosl'ra rotula and Chlorella sp. were observed.Average annual concentration of reactive phosphate in water body of YundangLagoon reached 0.19mg/dm3. The distribution is characterized by higher in winder,lower in summer. In sununer, organic and inorganic phosphorus in sediment mayIVAbstractdissolve into he water body in the fOrm of reactive phosphate to meet the demand ofred tide biota.The concentration of ZN, NO3---N, NO2---N and NO.+-N were sepaxately3.730, 0.438, 0. l01 and 3. l9lmg/dm'. According to the ratio of NO#+-N/Z N(85.5%),species of Pyrrophyta could not be the predominant species of Yundang Lagoon.Minus correlation between the number of phytoplankton and the concentration ofinorganic nitrogen was observed.COD is the main factor which impact the distriblltion of species of phytoplankton.In the water body where the value of COD was high, the nuxnber of diatom was lowBecause low temperatuxe of the water limited the rate of propagation of red tideorganisms, red tide could break out only in the seasons When the temperature washigh.Avoiding eutrophication of water body is the radical way to prevent the outbreakof red tide.