Effects Of Fisheries Habitat Restoration On Fish Community Structure And Basic Food Source In The Yangtze River Estuary

The habitat of the Yangtze River Estuary is unique and complex,with extensive tidal flats wetlands.With high primary productivity,large habitat heterogeneity,rich food resources and biological communities,tidal flats wetlands have become important habitats for fish and other aquatic animals,playing spawning grounds,nursery grounds,baiting grounds,migratory channels and other fisheries ecological support functions,and are of great importance in the maintenance of biodiversity and sustainable production of fisheries resources.However,in recent years,with the impact of human activities such as water-related construction and beach reclamation,the area of the mudflat wetlands in the Yangtze River Estuary has been drastically reduced,and the fish habitat has been seriously threatened,resulting in a declining trend of fish populations.Restoration and protection of tidal flats wetland habitats in the Yangtze River Estuary have become important.In response to the slow recovery of damaged tidal wetlands in the tidal flats of the Yangtze River Estuary,restoration is carried out by planting Scirpus triqueter on the high beach and setting up a three-dimensional floating beds planted with Phragmites australis on the low beach.In this study,we investigated the habitat restoration effect of"planting Scirpus triqueter+three-dimensional floating beds planted with Phragmites australis"restoration technology.1 Effects of wetland habitat restoration on fish community structure in the tidal flats of the Yangtze River EstuaryIn order to identify the effects of tidal flats habitat restoration on fish community structure in the Yangtze River Estuary,fish samples were collected in June 2021（spring）,November 2021（autumn）,January 2022（winter）,and July 2022（summer）in the south branch of the Yangtze River Estuary.The study was conducted by fixed plug net in the habitats restoration areas and the control areas.The number of fish species,individuals,biomass and diversity indices were compared between the restoration and control areas.Total of 27 fish species belonging to 21 genera in 8 orders and 9 families were collected during the study period,of which 22 species were collected in the restoration areas and 21 species in the control areas.The results showed that the total Margalef richness index（D）was 6.8,the total Shannon-Wiener diversity index（H′）was 4.92,the total Simpson simplicity index（C）was2.47,and the total Pielou evenness index（J’）was 2.99,and the overall biodiversity index was17.18 in the restoration areas,which was significantly higher than that of the control areas（15.82）.The frequency of fish larvae collected restoration areas（67%）was significantly higher than that in the control areas（44%）in the spring,indicating a strong preference of juvenile fish for the restoration areas.The results showed that the habitat restoration in the tidal flats of the Yangtze River Estuary provided nursery sites for juvenile fish to a certain extent and increased fish diversity.2 Effects of tidal flats habitat restoration on fish food webs and trophic levels in the Yangtze estuaryIn order to understand the effects of tidal flats habitat restoration on fish food webs and trophic levels,fish,benthic organisms,SOM,POM,and plant samples were collected from the restored and control areas of the tidal flats wetlands in winter（January 2022）and summer（September 2022）based on stable isotope techniques using fixed plug nets,geo-cage nets,and three-layer composite gill nets.Theδ¹³C andδ¹⁵N values and trophic levels of primary producers,shrimps and crabs,and fish in the restoration and control areas were compared and analyzed.The results showed that the range ofδ¹³C values of fish in the restored area was larger than that in the control area in terms of carbon isotope ratios,indicating that the fish in the restored area had a wider range of food sources.Theδ¹³C andδ¹⁵N coordinates of fish in winter and summer showed that the fish species located at the apex of the polygon in the restoration area in winter included Pelteobaggrus nitidu,Odontamblyopus lacepedii,Hemiculter bleekeri,Liza haematocheila,Saurogobio dumerili and Cynoglossus purpureomaculatus,while the fish located at the apex in the control areas included Coilia nasus,Hemibarbus maculatus,Xenocypris argentea,Mugil cephalus,Larimichthys polyactis and Acanthogobius ommaturus.The fish species located at the apex of the polygon in the restoration area in summer were Pelteobaggrus nitidus,Odontamblyopus lacepedii,Hyporhamphus intermedius,Xenocypris macrolepis,Xenocypris argentea,Liza carinata,Boleophthalmus pectinirostris,Eleutheronema rhadinum and Cynoglossus purpureomaculatus,and the fish located at the apex in the control area included Cynoglossus gracilis,Coilia nasus,Hyporhamphus intermedius,Parabramis pekinensis,Xenocypris macrolepis,Boleophthalmus pectinirostris and Repomucenus olidus.The trophic structure of the restoration area was more complex than that of the control area,and the fish species located at the apex of the polygon were more diverse and more complete in the restoration area than in the control area,indicating that the restoration technique of"planting Scirpus triqueter+three-dimensional floating beds planted with Phragmites australis"may have the ecological function of improving the trophic structure of fish in the tidal flats of the Yangtze River Estuary.The mean trophic levels of fish in the restoration area and the control area in winter were 3.16 and 3.19,respectively,with no significant differences;the mean trophic levels of fish in the restoration area and the control area in summer were 2.20 and 5.09,respectively,with significant differences（P<0.05）.It is possible that the anthropogenic activities during the ecological restoration affected the exchange of materials and energy between the restored waters and the main river channel,which influenced the structure and trophic level of the fish food web in the restored area.In summary,the restoration technique of"planting Scirpus triqueter+three-dimensional floating beds planted with Phragmites australis"can effectively increase the species,number and biomass of fish,optimize the fish population structure,enhance the fish biodiversity in the restoration area,and provide a good habitat for fish to grow,develop,nurture and shelter.The restoration technology can,to a certain extent,expand the food sources and improve the nutrient structure of fish in the tidal flats,so that the ecological functions of the tidal flats can be restored and play an important role in the restoration and reconstruction of fish habitats.