Study On The Inhibitory Effect Of Porphyra Yezoensis Seedlings On Microscopic Propagule Of Ulva Prolifera

Green tide algae microscopic propagule is a collective term for spores,gametes,zygotes,and microscopic individuals of green tide algae.Studies have shown that they can quickly attach and germinate under the conditions of a suitable attachment substrate.The radial sand ridge of Jiangsu coast is an important Porphyra yezoensis aquaculture base in China,Porphyra yezoensis aquaculture area has expanded rapidly in recent years,and the density of aquaculture has been increasing.Porphyra yezoensis aquaculture raft are mainly composed of cables,bamboo shelf and net,raft structures provide a large amount of high-quality attachment substrates for the green tide algae to attach and grow,enabling them to grow and reproduce rapidly under the unique natural conditions of the northern Jiangsu shoal sea area.According to the Porphyra yezoensis aquaculture habits in Jiangsu,the aquaculture rafts are removed and recycled between March and April each year,and the green tide algae on it provide biomass for the early green tide floating.Therefore,mastering the distribution characteristics of green tide algae microscopic propagule and attached green algae in the source sea area and preventing the attachment and germination of green tide algae microscopic propagule on the aquaculture area are of great significance for the prevention and control of the green tide source.In this study,firstly,the distribution characteristics of green algae microscopic propagule in the early stage of the Yellow Sea green tide and the aquaculture raft area attached green algae were monitored and studied.Secondly,the interaction between Porphyra yezoensis seedlings and Ulva prolifera microscopic propagule was studied in the laboratory.Thirdly,the technology of restraining the green algae attachment was established in the sea area,which has achieved good restraining effect and provided the prevention and control of the source of green tide New methods and ideas are provided.Study on the distribution characteristics of Ulva microscopic propagule and aquaculture raft attached green algae in the early stage of green tide in the Yellow Sea.According to the survey of ship voyages in the South Yellow Sea in April-June 2018,it was found that the green tide algae microscopic propagule were widely distributed in the sea area during the survey,and showed different distribution characteristics between each months.A comprehensive comparison of the distribution of microscopic propagule in each month shows that the distribution of microscopic propagule is highly consistent with the area of the Porphyra yezoensis aquaculture rafting area,and moves north with floating green algae after the end of the aquaculture activity.The microscopic propagule showed a pattern of rising and then decreasing.In the identification of microscopic propagule species,the dominant species was Ulva flexuosa,followed by Ulva prolifera and Ulva linza.An investigation of attached algae in aquaculture raft racks found that the biomass of attached algae in aquaculture raft racks was significantly different,and the biomass of attached green algae in outer-sand aquaculture rafts was higher than that in the inner sands.The composition of green algae in the sand of Jiangjiasha is mainly dominated by Blidingia green algae,and Zhugensha,Dongsha,and Rudongneisha are dominant species of Ulva green algae.The Ulva compressa is the smallest,only detected in Dongsha,showing obvious geographical differences in the composition of the green algae biocommunity.During the survey,the temperature in the sea area increased and the salinity of the seawater decreased slightly,which is suitable for the germination and growth of green tide algae microscopic propagule.The establishment of the technology of restraining the green algae attachment by the attached seedling of Porphyra yezoensis.The interaction between Porphyra yezoensis seedlings and Ulva prolifera was studied.Through laboratory experiments on the effects of Porphyra yezoensis seedlings on the attachment and germination of green tide algae microscopic propagule,it was found that Porphyra yezoensis seedlings have a significant effect on the adhesion and germination of Ulva prolifera(P <0.01).The blank glass sheet has a large amount of Ulva prolifera attached and germinated.On the glass sheet with Porphyra yezoensis,only a small amount of Ulva prolifera propagules are attached and grown.The growth rate and Fv/Fm of Ulva prolifera seedlings were significantly decreased by cultivating Ulva prolifera seedlings alone and cultivating mixed with Porphyra yezoensis experiments,which indicates that Porphyra yezoensis has inhibitory effect on the growth of Ulva prolifera seedlings.Experiments in the aquaculture sea area found that the use of Porphyra yezoensis seedlings could reduce the biomass of green algae on rafts.Among the three methods of attaching seedlings used in the test,the direct cable seedling method can have a good effect of attaching seedlings,and has the highest feasibility.It can also increase the yield of 100 kg of Porphyra yezoensis per cable.The seedling rope winding method can also have a good effect if the winding density is controlled,but the increased production of Porphyra yezoensis is not easy to harvest.The method of raising seedlings by pouring spore water has not obtained good seedling effects under actual experimental conditions.But in theory there is a certain feasibility,and further attempts are needed.Through further continuous observation,it was found that the Porphyra yezoensis began to age and die around April 10 due to the rise of sea temperature,and its inhibition effect was greatly reduced.At this time,the raft frame should be take back in time.