Simulation Study On The Effects Of Sargassum Horneri Golden Tide On Harmful Algae And Zooplankton

In recent years,the Sargassum horneri golden tide had been intensified in coastal areas of China,which had a serious impact on the ecological environment and marine aquaculture industry.From the end of 2016 to the beginning of 2017,a large number of S.horneri invaded the north of Jiangsu Province.The Porphyra yezoensis aquaculture had been caused economic losses of more than 500 million yuan in the farming industry.And in the summer of 2017,gold tide,green tide and red tide appeared in the 35°N transect of the South Yellow Sea.In this paper,we studied how the decomposing liquid and culture medium of the golden tide causative species S.horneri affected the growth of green tide and red tide species,the survival of zooplankton,and the changes of pH,dissolved oxygen and nutrient concentration.The study was aimed to find out the effects of the golden tide process on the occurrence of green tide and red tide,as well as the impact of on the zooplankton and environment.As a result,we could provide a basis for evaluating the ecological effects of the golden tide.In the beginning of the research,we studied the effects of S.horneri decomposing liquid and culture medium to the growth of Ulva prolifera green tide and five red tide causitive species.We selected five red tide species,including Skeletonema costatum,Alexandrium catenella,Prorocentrum donghaiense,Karenia mikimotoi and Heterosigma akashiwo.The results showed that the high concentration of the S.horneri decomposing liquid(40g/L)and culture medium(10 g/L)could inhibit the attachment and germination process of microscopic propagules and seedling growth of U.prolifera.The inhibition rate of the decomposing liquid(40g/L)on the attachment germination process of microscopic propagules was 45.8 % on the 12 th day,and the rate of seedling growth was 25 % on the 15 th day.The inhibition rate of the culture medium(10 g/L)on the attachment germination process of microscopic propagules was 29.6 % on the 12 th day,and the rate of seedling growth was 22.8 % on the 15 th day.In addition,lower concentrations of decomposing liquid(20g/L and 10g/L)and culture medium(5g/L)could promote the growth of seedling.The S.horneri decomposing liquid and culture medium could affect the growth of red tide causative species.The growth of K.mikimotoi was most significantly inhibited.The inhibition rate of decomposing liquid(40 g/L)and culture medium(10 g/L)were 90.4% and 92.9% on the 12 th day.The inhibition rate of decomposing liquid(40 g/L)on the growth of P.donghaiense was 65.9 % on the 12 th day.The inhibition rate of culture medium(10 g/L)on the growth of S.costatum was 27.7 % on the 12 th day.While the growth inhibition of H.akashiwo and A.catenella were not significant.Above all,the results indicated that the S.horneri decomposing liquid(20g/L and 10g/L)and culture medium(5g/L)could inhibit the attachment and germination of microscopic propagules and promote the growth of U.prolifera seedling.However,high concentration of decomposing liquid(40 g/L)and culture medium(10 g/L)could inhibit the attachment and germination of microscopic propagules and the growth of seedling,and also significantly inhibit the growth of K.mikimotoi.The high concentration of decomposing liquid(40 g/L)could significantly inhibit the growth of P.donghaiense.The high concentration of culture medium(10 g/L)could significantly inhibit the growth of S.costatum.It could be seen that the decline and outbreak stage of the golden tide would affect the occurrence of the green tide and red tide.Then we further explored the effects of S.horneri decomposing liquid and culture medium on the survival of zooplankton.We selected Artemia salina,Brachionus plicatilis and Neomysis awatschensis as the tested organisms.The results showed that the A.salina larva in the experimental group of the S.horneri decomposing liquid(40 g/L)died within 96 h,and the survival rate in the culture medium(50 g/L)was 21%,the impact was extremely significant.The S.horneri decomposing liquid could also affect the survival of N.awatschensis.The N.awatschensis in the decomposing liquid-treated group(40 g/L)died within 96 h,and all concentrations of the culture medium had no significant effect.The survival of the B.plicatilis was not affected by the decomposing liquid and culture medium.Therefore,the gold tide would threaten the survival of some zooplankton during the decline and outbreak stage,and may even had an impact on the zooplankton community structure in severe cases.In addition,when the S.horneri body was decomposed in light and dark conditions at 10?,15?,20? and 25?,it was found that the decomposition of S.horneri would cause the change of seawater pH and the decrease of dissolved oxygen content.The experimental results under light and dark treatments are not much different,but they increased significantly with increasing temperature.At 25°C,the pH of the experimental group(50 g/L)increased from 6.15 to 7.39,and the dissolved oxygen content decreased from 7.03mg/L to 1.54mg/L.Anymore,the S.horneri body could also release large amount of ammonium nitrogen and phosphate during the decomposition.At 20°C,the phosphate content of the high concentration group(50 g/L)of the decomposing liquid was 356 ?mol/L on the 10 th day,and the ammonium nitrogen content reached 2120 ?mol/L on the 15 th day.At 25°C,the phosphate content of the same concentration of decomposing liquid on the 10 th day could reach 268 ?mol/L,and the ammonium nitrogen content reached 2105 ?mol/L on the 5th day.The results showed that the S.horneri would significantly affect the pH,dissolved oxygen content and nutrient concentration of the water in the process of decomposition.Therefore,the golden tide would cause serious environmental and ecological effects in the process of decline.Through the above experiments,it was proved that the S.horneri gold tide could not only affect the occurrence of the green tide and red tide,but also cause serious impact on zooplankton and ecological environment during the decline and outbreak stage.The ecological effects caused by the golden tide should be payed enough attention.