Toxic Effects Of Gonyaulax Polygramma On Saccharina Japonica And Its Identification Method

In recent years,with the rapid development of social economy in coastal areas and the gradual appearance of climate change effect,The offshore ecosystem has obvious changes and the frequent occurrence of harmful algal blooms(HABs),which poses a serious threat to the social and economic development of coastal areas and the health of residents.It is urgent to improve the monitoring method of red tide and prevent and control the harmful effect caused by harmful algal blooms.Gonyaulax polygramma is a common species of red tide in offshore China.It belongs to Dinophyceae,Gonyaulacales,Gonyaulacaceae,Gonyaulax.The red tide formed by Gonyaulax Polygramma can kill fish and shellfish,which has a serious impact on the mariculture industry.At the end of2021,a large-scale red tide of Gonyaulax polygramma appeared in the Saccharina japonica culture region of the coast of Rongcheng,Shandong Province.The affected area of Saccharina japonica culture industry exceeded 9300 hm2,causing an economic loss of2 billion(RMB).This thesis plans to take Gonyaulax polygramma as the main target algae species and try to explore the harm effect and mechanism of the red tide of Gonyaulax polygramma on cultured Saccharina japonica,develop the target algae species identification method based on FlowCytometer and Microscope(FlowCAM)and artificial intelligence algorithm(YOLOv3 model).The main research results are as follows:A strain of Gonyaulax polygramma was cultured in the red tide area and its toxic effect and mechanism on Saccharina japonica were discussed.The effects of different types of nutrients on the growth of Gonyaulax polygramma were preliminarily analyzed through laboratory simulation experiments.The results showed that Gonyaulax polygramma mainly uses nitrate as nitrogen source and its growth is not sensitive to changes in N/P ratios.In the laboratory,the co-culture experiments of Saccharina japonica(sporophyte)seedlings with Gonyaulax polygramma,Akashiwo sanguinea and Skeletonema sp.were conducted,the results showed that Gonyaulax polygramma(5×10~5cells/m L)and Akashiwo sanguinea(2×10~5cells/m L)had inhibitory effects on the growth and photosynthetic activity of Saccharina japonica seedlings under experimental density,while Skeletonema sp.(6.9×10~7cells/m L)had a slight stimulant effect.From good to bad,the growth status of Saccharina japonica in each treatment group was in order as follows:Skeletonema sp.group,blank group,Akashiwo sanguinea group and Gonyaulax polygramma group.During the experiment,the maximum light energy conversion efficiency(Fv/Fm)of sporophyte tip of Saccharina japonica continued to decrease,and the leaf bleaching began to appear on the 12th day and gradually spread to the base.At the end of the experiment,the lengths of Saccharina japonica in each group were 17.86cm,16.94 cm,9.86 cm and 8.81 cm,and the widths were 6.24 cm,5.13 cm,3.77 cm and3.6 cm,respectively,the length and width of the leaves of the Akashiwo sanguinea and Gonyaulax polygramma groups were significantly lower than Skeletonema sp.and blank groups(p<0.05).The high-throughput sequencing analysis of the microbial community during the experiment showed that there were significant differences in the microbial community composition among the experimental groups,and no bacterial groups were found to be significantly related to the bleaching and decay of kelp.The results show that the red tide is an important cause of the damage of the cultured Saccharina japonica,but its mechanism remains to be further explored.The image data of algae species were obtained by FlowCAM and the identification method was developed by YOLOv3 model.Gonyaulax polygramma,Prorocentrum lima and Alexandrium catenella with similar morphology and size were selected as target species respectively,the image data of target algae species were collected by FlowCAM,the target algae species recognition algorithm was established by YOLOv3 model,and the influence of morphological changes and similar algae species on model recognition was evaluated.The results showed that the morphology of algae species had an important effect on the recognition results of the model.The morphological characteristics of the front and side sides of Prorocentrum lima were significantly different,and the recognition ability of the model(mAP)decreased by 40%when the front side was divided to recognize algae species;both Gonyaulax polygramma and Alexandrium catenella are spherical,and the morphology of algae species is similar from different angles.It will lead to the deterioration of the identification performance of target algae species by YOLOv3 model,and there is a phenomenon that Alexandrium catenella is misjudged as Gonyaulax polygramma.However,most of the algal cells of the two microalgae could still be distinguished,and the mAP value could reach 0.949.The identification experiments were carried out under different conditions,such as single species,mixed,Unshelled and fixed.The results showed that the YOLOv3 model had good applicability for the identification of the algae.The optimal mAP values under single species,mixed,Unshelled and fixed conditions were 0.882,0.846,0.902 and 0.878,respectively.In conclusion,the effects of different algae species on the growth and physiological state of cultured Saccharina japonica seedlings were studied through the laboratory co-culture experiment.The results showed that the red tide of Gonyaulax polygramma was an important reason for the damage of cultured Saccharina japonica.This thesis attempts to construct an algae species identification method based on FlowCAM and YOLOv3 models,analyzes and evaluates the identification effects of algae species under different conditions.Through the research,the identification method of Gonyaulax polygramma was developed,which improved the scientific understanding of the harm effect of Gonyaulax polygramma,and provided means support and scientific basis for the prevention and control of red tide of Gonyaulax polygramma.