The Field And Experimental Research Of Detrimental Effects Of HABs In The East China Sea

Large-scale blooms of dinoflagellates, such as the non-toxic species Prorocentrum donghaiense and the toxic species Karenia mikimotoi(hemolytic toxin producer), have occurred frequently in the East China Sea(ECS) in recent decades. In this thesis, several cruises were conducted during P. donghaiense blooms in the ECS in 2013, during which we illustrated the effects of different phases of the P. donghaiense bloom on zooplankton community structure, and measured the adverse effects of P. donghaiense blooms on the copepod C. sinicus. To test the observed detrimental effects in the field, we also investigated the effects of the dinoflagellate on the population dynamics of the copepod Calanus sinicus and the rotifer Brachionus plicatilis. For the toxic dinoflagellate K.mikimotoi responsible for the massive mortalities of abalones, we also studied the mechanisms of K.mikimotoi affecting the abalone Haliotis discus hannai. The results will help us identify the potential threats to the marine ecosystem posed by dinoflagellate HABs.During a spring P. donghaiense bloom(April–May 2013) along the northern coast of Fujian Province(120°–121°30 "E, 26°30" –28°N), we found that the bloom decreased the abundance of copepods and had no significant effect on chaetognaths and small jellyfish. However, the abundance of small jellyfish increased over the course of the study. The zooplankton community changed from being copepod and small jellyfish- to small jellyfish-dominated during the bloom. In the bloom areas, the copepod Calanus sinicus showed higher mortality and lower egg production rates(EPR) than those in the non-bloom areas. The results suggested that P. donghaiense blooms had detrimental effects on the structure of zooplankton community and the recruitments of C. Sinicus.Under laboratory conditions, we also found the detrimental effects of the dinoflagellate on the population dynamics of the copepod C. sinicus and the rotifer Brachionus plicatilis.The dinoflagellate may have detrimental effects on the survival of C. sinicus individuals at different stages and on reproduction of this copepod. Compared to the control treatment(Skeletonema costatum), the presence of P. donghaiense decreased the survival rates of adults and nauplii during the 16 d experiment. Survival of nauplii decreased to 49%, relative to the nearly 80% survival of adults. Among the six stages of nauplii, individuals at NII and NIII were more susceptible to P. donghaiense. Lower egg production rates and hatching success were also observed when copepods were exposed to P. donghaiense. Moreover, exposure to the dinoflagellate in the field density also caused lower lifetime egg production, shortened life span, lower net reproductive rate, finite rate of increase and intrinsic rate of population increase. Results suggest that P. donghaiense had detrimental consequences for the reproduction and population recruiments of C. sinicus and B. plicatilis.For the toxic dinoflagellate K. mikimotoi responsible for massive mortalities of abalones, we investigated the effects of K. mikimotoi on the survival of the abalone Haliotis discus hannai at different environmental conditions. At the aeration condition(the suitable conditions of DO, p H, and total ammonia at the same time), the mortality rates reached 33.3% in 48 h, and reached 100% in 96 h when exposed to K. mikimotoi at the cells amounts of 3×104 /m L, which indicated that the rapid mortalities of abalones were caused by the detrimental effects of K. mikimotoi. At the non-aeration condition, DO was in the range of 7.1-1.8 mg/L, the mortality rates reached 100% in 16 h when exposed to K. mikimotoi at the cells amounts of 3×104 /m L. The results showed that the low oxygen condition made the toxic effects stronger. Exposure to a low density of K. mikimotoi(not exceeding 104cells/m L) could not cause a high mortality rates of the abalone, however, which caused physiological and physiological changes of abalone. We found that exposure to K. mikimotoi caused the shrink and deformation of afferent and efferent branchial vessel in the gill, and also induced the disruption of the gill lamella. The major protein enzyme in the gill, including Na+-K+-ATP, Ca2+-Mg2+-ATP, also showed inhibited activities. Immune status of the abalone was also assessed, using ?ow-cytometric hemocyte analyses for hematological characteristics and hemocyte functions. The most pronounced effects were increases in dead hemocytes and declines in the phagocytic abilities. Changes in hemocyte function attendant with shifts in hyalinocyte/granulocyte ratiowere observed aswell. We also investigated the effects of K. mikimotoi on the antioxidant enzymes of the abalone, including superoxide dismutase(SOD), catalase(CAT), and glutathione peroxidase(GSH-Px). The results showed that K. mikimotoi declined the activity of the enzyme SOD and CAT in the abalone gills, and SOD, GSH-Px in the hepatopancreas. In addition, we compared the toxic effects of two strains of K. mikimotoi on the abalones. The results indicated that K. mikimotoi strain from Fu Jian, showed severe toxicity effects on abalones, but weak in another strain from South China Sea. However, the concentration of hemolytic toxin was similar in both strains. The total concentration was about 0.6 μg/m L during exponential phase. Moreover, the methanol crude extracts of the toxin showed non-lethal effects on abalones. Therefore, we inferred that the toxic effects of K. mikimotoi on abalones originated from some more active substances.The non-toxic P. donghaiense bloom led to significant changes in the zooplankton community, which changed from being copepod and jellyfish dominated to being small jellyfish dominated during the bloom. P. donghaiense blooms also had detrimental consequences for the recruitments of C. sinicus. And the toxic K. mikimotoi blooms caused adverse effectes on the histological features in the gill, hematological and the antioxidant characteristics, which posed significant threat to the aquature of abalne. In recent decades, large-scale P. donghaiense and K. mikimotoi blooms have taken place in the ECS every year, affecting areas as large as 104 km2. In the long term, the bloom with such large spatial and temporal scales, may lead to the accumulation of the observed detrimental effects. In this situation, the marine ecosystem in the ECS will hardly restore, ultimately, which may result in the marine desertification.