Spatio-temporal Distribution Of Green Macroalgal Micro-propagules In The Coastal Waters Of Qinhuangdao

Since 2015,green tides disasters have occurred annually in the coastal waters of Qinhuangdao,causing serious losses to the local tourism and aquaculture and threatening the safety of Beidaihe tourism area.Micro-propagules play an important role in the early stage of formation and development of green tides.Clarifying the tempo-spatial characteristics of micro-propagules and its role in Qinhuangdao green tide is helpful to reveal the occurrence mechanism of green tide.Therefore,a yearround survey was conducted on Jinmeng Bay(39°53.500? 39°52.750?N,119°32.900?~119°33.000?E)of Qinhuangdao from May 2020 to April 2021.The tempo-spatial characteristics,species composition and main influencing factors of micro-propagules in water and sediments were analyzed,and distribution characteristics of various substrates of green algal micro-propagules in sediments of Jinmeng bay were studied.The attachment process of micro-propagules and the preference of substrates was investigated through laboratory experiment,and the role of micro-propagules in the formation of green tide in Qinhuangdao was comprehensively analyzed.The main results are as follows:1.Tempo-spatial characteristics of macroalgal micro-propagules in the coastal waters of Qinhuangdao: macroalgal micro-propagules was abundant in outbreak area and adjacent waters and sediments.In terms of time,the number of propagules in the water reached 17 inds/L before the peak of green tide from March to April.During the peak period,the number of propagules was only 3 11 inds/L from May to September.From November to January of the next year,no green algal seedlings were observed in the water.The number of propagules in sediments was the highest in June 2020,reaching to 148 inds/g,followed by May,42 inds/g.No green algal seedlings were observed in July,October 2020 and January 2021,and ranged from 0 to21 inds/g in other months.Spatially,both water and sediment showed the distinct distribution characteristics that the abundance of micro-propagules in the affected area of green tides was higher than that in the non-affected area.The abundance of stations near the coast of Jinmeng Bay showed the highest(142 inds/g)in the sediment,while there were few green algal seedlings in the three stations outside Lianhua island.From the vertical distribution of sediments,the abundance of micro-propagules in the surface sediments(0 2 cm)of Jinmeng Bay was high,up to 132 inds/g.When the sediment depth exceeds 5 cm,the abundance of green algae micro-propagules decreaseed greatly.2.The distribution of macroalgal micro-propagules affected by many factors:the abundance of micro-propagules in water and sediments in the coastal waters of Qinhuangdao was mainly affected by suspended algae and attached algae.The number of propagules was significantly positively correlated with the biomass of suspended algae and attached algae in the outbreak area.From May to September,the number of propagules was high during the outbreak period of green tide in Jinmeng Bay.In June,the biomass of suspended algae reached up to 800 g/m3.In addition,the abundance of green algal micro-propagules was closely related to environmental factors,and had a significant positive correlation with nitrogen and phosphate.And it had a negative correlation with temperature and salinity.3.Differences in the attachment of U.prolifera to different substrates: U.prolifera can attach and germinate on shells,spiral shells,habitat tubes of polychaeta,sand,stones and plastics,but there were differences in germination rates.The number of U.prolifera micro-propagules germinated on the plastic was the highest,and the seedling was the longest on the habitat tubes of polychaeta.On the shell and spiral shell,the number and the length of the seedling both performed well,which made them the suitable substrate for the micro-propagules to attach.The substrates were widely distributed in the sediments of Jinmeng Bay,Qinhuangdao,which not only provided sufficient substrate for the attachment of algal micro-propagules,but also provided necessary conditions for their germination and growth.4.Analysis of the role of algal micro-propagules in the outbreak of green tide:Algal micro-propagules existed in the water and sediments of Jinmeng Bay,and in the sediments of Jinmeng Bay,a large number of suitable substrates such as shells and spiral shells provided rich substrates for the attachment and germination of micropropagules.When the environmental conditions were suitable,the micro-propagules could germinate and grow on the attachment base,which is an important source of attached macroalgae in seaweed farm and contributed to the outbreaks of green tide in Qinhuangdao.This study will provide scientific data for revealing the occurrence mechanism of green tide in Qinhuangdao and provide support for the early prevention and control of green tide in Qinhuangdao.