The Species And Distribution Of Litter Pollution In The Coral Reef Area Of The South China Sea And Its Physiological Effects On Hermatypic Corals

Marine litter pollution has become an important environmental issue affecting the health of coral worldwide.As a new type of pollutant,plastics have many types,large quantities,and wide distribution.Plastic particles are easily absorbed by organisms such as corals,affecting their food intake and limiting their normal physiological and metabolic activities.Therefore,the prevention and control of litter pollution in coral reef areas need to be urgently addressed.Based on the research background of hermatypic corals in the South China Sea,this paper uses a combination of on-site investigation and indoor simulation research to explore the comprehensive impact of macro litter pollution（size≥20mm）on coral.Through background investigation in the field,the types,abundance,and distribution of litter pollution are explored,and the impact of litter pollution on the health status of reef coral is analyzed based on the environmental behavior and biological effects of litter pollution,to determine whether litter pollution will cause varying degrees of damage to reef coral in the coastal waters of the South China Sea due to changes in environmental characteristics.Based on domestic and international research,the impact of different types of litter pollution on hermatypic corals and the differences in physical resistance of corals are clarified.Indoor simulation of the sustained stress of typical litter pollution（broken fishing nets）on the antler cup-shaped coral（Pocilopara damicornis）.Based on field investigations,stress experiments were conducted on key environmental factors（ammonia nitrogen enrichment,suspended solids accumulation）.The effects of fishing net coverage,elevated ammonia nitrogen,and suspended solids addition on the physiological status of reef coral were analyzed.Monitor the health status of corals and establish the impact mechanism of litter pollution on the physiological status of hermatypic corals in the South China Sea coral reef area.Through comprehensive analysis,the spatiotemporal variation characteristics of litter pollution in coral reef areas and its physiological impact mechanism on hermatypic corals were studied.The research results are as follows:1.The abundance of litter pollution in the coastal area of the South China Sea is18995.4 pieces·km^-2,ranging from 579.68 to 7964.25 pieces·km^-2,with an average of 3771.66 pieces·km^-2.The abundance of litter pollution in the northern reef area of Hainan Island is the highest,while the abundance of litter pollution in the Xisha reef area is the lowest.The abundance of litter pollution at a depth of 8m is 79.79±78.32～980.68±917.56 pieces·km^-2,with an average of 473.51±354.42pieces·km^-2;The abundance of litter pollution at 3m depth ranged from 36.14±30.14 to 612.17±550.85 pieces·km^-2,with an average of 296.31±223.04pieces·km^-2.The abundance of litter pollution at 8m depth was significantly higher than that at 3m depth（P≤0.05）.Among the litter pollutions found,fishing nets and fishing lines have the highest abundance,accounting for 51.59%and 26.31%of the total garbage;PP woven bags have the lowest abundance,accounting for 3.62%of the total.Human activities and environmental factors are the main reasons for the different distribution of litter pollution in various reef areas.Fishing,sea fishing,and other fishing activities can increase the accumulation of litter pollution.Environmental factors such as monsoon and ocean currents can affect the transportation of litter pollution.The coral coverage rate found in the survey ranges from 13.18 to 25.79%,with an average of 16.70%.The coral coverage rate in Xisha Reef Area is the highest（25.79%）,while the coral coverage rate in the northern reef area is the lowest（13.18%）;The amount of larval recruitment ranged from 2.14 to 6.83 ind·m^-2,with an average of 3.89 ind·m^-2.The juvenile recruitment amount in Xisha Reef Area is the highest(6.83 ind·m^-2),while the juvenile recruitment amount in the northern reef area is the lowest(2.14 ind·m^-2).Correlation analysis showed that there was a significant positive correlation between coral coverage and larval recruitment（r=0.5,P≤0.05）,and a significant positive correlation between fishing nets and fishing lines（r=0.54,P≤0.05）;There was a significant negative correlation between coral coverage and fishing nets（r=-0.49,P≤0.05）,and a significant negative correlation between juvenile recruitment and fishing nets（r=-0.52,P≤0.05）.Fishing nets and fishing lines can entangle the surface of coral,causing problems such as difficulty in predation,malnutrition,or infection with bacteria.This study recorded a total of12684 corals belonging to 10 families,19 genera,and 75 species.Among them,there are 9 families,15 genera,and 44 species of corals affected by litter pollution,totaling5689 pieces.The results showed that the branching and blocky growth forms of corals were most seriously affected by litter pollution,while other growth forms of corals were less affected by litter pollution.2.Fishing nets and multiple stresses cause physiological and metabolic abnormalities in Pocillopara damicornis,resulting in varying degrees of decline in coral photosynthesis performance（such as reduced Fv/Fm）,insect zooxanthellae density,chlorophyll a content,energy substances,and bone growth rate.Fishing net stress caused coral to secrete a large amount of mucus.At the end of the experiment,Fv/Fm decreased by 23.04%compared to the first day,and SOD enzyme activity increased by 66.63%compared to the control group.At the same time,energy consumption is maintained by reducing total sugar and lipid content.Compared to being stressed by fishing nets alone,corals in high ammonia nitrogen water bodies adhere to a large amount of algae,resulting in a 10.13%and 27.30%decrease in the density and chlorophyll a content of zooxanthellae,but they respond to environmental pressure changes by increasing protein content.The continuous accumulation of suspended solids affects the photosynthesis and respiration of corals.The total sugar,lipid,density of zooxanthellae,and chlorophyll a content of corals under ammonia nitrogen stress are 28.67%,50.79%,70.70%,and 61.70%lower than those of corals under ammonia nitrogen stress,respectively.Corals are significantly albino and exhibit significant negative growth.This result confirms that litter pollution has a negative impact on the physiological metabolism of coral,but when subjected to multiple stresses,the physiological changes of coral are more significant.In summary,the accumulation of litter pollution can hinder the survival of corals and limit their normal metabolic activities.Currently,the main research focus is on the impact of microplastic pollution and environmental factors on coral,while there are few studies on the impact of microplastic pollution on coral.Therefore,this study believes that the environmental characteristics of plastics should be analyzed in combination with the characteristics of litter pollution in coral reef areas,in order to improve the research level and pollution prevention capabilities of plastics in coral reef areas.