Dynamic Distribution Of Ulva Spp. Micro-propagules In The South Yellow Sea

Green tide is a phenomenon in which large-scale marine green algae multiply in the intertidal zone or shallow sea area,causing a surge in biomass,which caused ecological anomalies.It occurs in many coastal countries around the world.The green tide disaster in China had been continuously erupting for 13 years in the Yellow Sea,and it has become one of the major marine disasters.Remote sensing satellite images showed that the green tide was initially formed in the southern Yellow Sea,and gradually migrated to the northern part of the Yellow Sea during the outbreak.This article focused on green algae micro-propagules as the research object,explored the existence and distribution characteristics of micro-propagules in water bodies and sediments during the early,middle and late periods of green tide outbreaks,and investigated the changed characteristics of green algae micro-propagules on the time scale of Qingdao sea.And obtained sterile micro-propagules of Ulva prolifera under laboratory conditions,set the temperature gradient experiment to explore the optimal temperature for the growth and development of Ulva prolifera.The following results were obtained:1.In the early stage of green tide outbreak,the abundance of micro-propagules in the offshore waters of Jiangsu ranged from 100 and 400 ind./L,with an average value of 304 ind./L.The stations with high values ??were located in the laver raft area,and the overall distribution trend was closer to the shore than to the far shore.There are mainly four main types of green algae micro-propagules,namely Ulva prolifera,Ulva mediterranea,Ulva compressa,and Ulva linza.The proportion of Ulva prolifera was the smallest,at 0.6%,which was far lower than the dominant species,Ulva mediterranea,which was 96.6%.2.During the green tide outbreak period,the abundance of micro-propagules in the Yellow Sea was between 0 and 163 ind./L,with an average value of 10 ind./L.The overall distribution showed the characteristic of more north and less south.Thereare mainly three types of green algae micro-propagules,namely Ulva prolifera,Ulva mediterranea and Ulva compressa.The proportion of Ulva prolifera was the highest,at 91.8%,which was the main dominant species.The proportion of Ulva mediterranea had dropped significantly to 6.4%.The number of micro-propagules in the sediments ranged from 0 to 85 ind./L,with an average value of 4 ind./L.The distribution showed the characteristics of more north and less south.The main types of green algae micro-propagules were Ulva prolifera and Ulva mediterranea,the proportions are 53.1% and 46.9% respectively.3.At the end of the green tide outbreak,the number of micro-propagules in the northern Yellow Sea ranged from 0 and 16 ind./L,with an average value of 2 ind./L.The distribution was scattered and mainly concentrated near the shore.The types of green algae micro-propagules mainly included four species,namely Ulva prolifera,Ulva mediterranea,Ulva compressa and Blidingia sp.The ratio of Ulva prolifera was low,at 2.9%,and the ratio of Ulva mediterranea rapidly increased to 91.3%.The number of micro-propagules in the sediments ranged from 0 to 20 ind./L,with an average value of 2 ind./L,were distributed near the shore.There were two types of micro-propagules,namely Ulva prolifera and Ulva mediterranea,with the proportions of 76 % and 24 %,respectively.4.The abundance of micro-propagules in surface water and sediments in Qingdao sea has obvious seasonal changes,showing a bimodal change characteristic.The main peak appears in spring,the secondary peak appears in autumn,and the abundance of micro-propagules was lowest in winter.A statistical analysis of the occurrence rate of Ulva prolifera in each month showed that the highest occurrence rate of Ulva prolifera in summer was 3.5%,and then began to decline in autumn and winter,and the lowest proportion in winter.5.The experiment of marine bacteria inducing the growth of Ulva prolifera micro-propagules at different temperatures showed that the induction of marine bacteria on the growth and development of Ulva prolifera at 18? was better than that at 12? and 24?.This study clearly describes the distribution characteristics of green algae micro-propagules in the coastal waters of the Yellow Sea and the annual variation characteristics of green algae micro-propagules in the coastal areas of Qingdao.The reaults showed that the distribution of green algae micro-propagules in the early stage of green tide was mainly composed of Ulva mediterranea,in the middle period wasmainly composed of Ulva prolifera,and in the later period was mainly composed of Ulva mediterranea,indicating that the occurrence of green tide was related to the mass reproduction and migration of micro-propagules.At the same time,it also proved that the micro-propagules of Ulva prolifera were not the local seed bank of the green tide in Qingdao.It was a provenance in the region after successive outbreak of green tide for many years,which provides the basis for further revealing the outbreak mechanism of green tide in the Yellow Sea.Finally,temperature gradient experiments in the laboratory showed that at 18?,marine bacteria had a better induction of the growth and development of sterile Ulva prolifera micro-propagules,to lay a foundation for further study on the mechanism of algae interaction.