| In the past few decades, harmful algal blooms (HAB) have increased in frequency, intensity and geographic distribution all over the world. These occurrences of HAI3 represent a significant and expanding threat to human health and fishes resources, especially for the marine aquaculture. In China, with the quickly developing of marine aquaculture industry, the severe eutrophication in the aquaculture area is becoming the main causes for the HAB. As HAB are characterized with rapid occurrence and disappearance, it is very difficult to catch the integrated dynamic course. Nevertheless, acquiring the variation data of environmental factor in the course of HAB is still the basis for exploring the mechanism of flAB outbreaking and forecasting its occurrence. Focusing on the problems above, this paper reviews data collected by authors from the major project funded by NSFC (The dynamics and countermeasures of harmful algal blooms in typical aquaculture area along the Chinese coast) in the past few years. Based on the data, the eutrophication degree of aquaculture water in northeast region of Jiaozhou Bay was assessed. The dynamic courses of two HAB events, which occurred in July of 1998 and June of 1999 respectively, are analyzed. By using the in-situ seawater of Jiaozhou Bay, the simulation culture experiments were designed to study the main influencing factors to HAB. In the past several years, red tides often occurred during summer in the northeast aquaculture region of Jiazhou Bay. The concentrations of ammonia, nitrate, nitrite, phosphate and silicate in this region were monitored in I 998 and 1999. Based on the concept of potential eutrophication, the Nutrient Quality Index (NQI) was used to assess the nutritional condition of seawater. The results showed that the average concentration of dissolved inorganic nitrogen(DIN), dissolved inorganic phosphate (DIP) and silicate in this 3 Abstract region were significantly higher than that of other places of Jiaozhou Bay. The relatively high concentration of DIN and phosphate was mainly resulted from increasing input of industrial wastewater and sewage, among them, wastewater discharge from shrimp pond exerted important influence on the eutrophication. The loading of silicate mainly came from the runoffs in rainy days. In summer the sea area was in the stage of phosphorus- limited potential eutrophication and the algal proliferation was restricted, but the condition was easily changed by external complement. In the northeast aquaculture region of Jiaozhou Bay, a Skeletonema costatum red tide and a Eucampio zoodiacus red tide occurred respectively on July 1998 and June 1999. Variations of environmental factors and their influence on red tide organisms were determined. With the increasing of biomass, the contents of pH~ DO increased while the nutrients(DIN, TIP, Si) concentration decreased. The concentration of nutrients and biomass were relatively high before red tide in this region, and the strong rain brought more nutrients and other nutriment to seawater. After rain, warm, low-salinity and eutrophic water resulted in the rapid proliferation of phytoplankton. On the nutrient structure, compared to TIN (total inorganic nitrogen), the concentration of silicate and phosphate were relatively deficient. The correlation analysis was used to determine the controlling factors of red tide, and the resul... |
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