Effects Of Spartina Alterniflora Invasion On Habitat Utilization And Diet Selection Of Red-crowned Cranes In The Yellow River Delta,China

Smooth Cord-grass(Spartina alterniflora)is an invasive plant species distributed in low tidal flats of coastal wetlands in China.Due to its strong adaptability and reproductive ability,it rapidly propagates and expands in the eastern coastal wetlands of China after invasion.The wetlands along the eastern coast of China are an important component of the East Asian-Australasian Flyway,with multiple national level nature reserves and internationally important wetlands distributed.Shandong Yellow River Delta National Nature Reserve is one of them.It is an important stopover and wintering place for red-crowned cranes(Grus japonensis).According to the synchronous survey results of the number of red-crowned cranes in recent years,the population of wintering red-crowned cranes in China has shown a continuous downward trend,mainly due to habitat destruction and loss.The invasion of Smooth Cord-grass led to the destruction of the original wetland,and the suitable habitat of the red-crowned crane,Suaeda salsa,was greatly reduced in mudflat.However,in Yellow River Delta,the research on the habitat utilization and feeding selection of red-crowned cranes on Smooth Cord-grass mudflat has not been studied in detail.By studying the difference of red-crowned cranes’habitat utilization and diet selection of Smooth Cord-grass mudflat and Saline Seepweed(Suaeda salsa)mudflat,we can understand the threat of Smooth Cord-grass invasion to red-crowned cranes and the enlightenment of Smooth Cord-grass governance and management.This study was carried out in the Yellow River Delta National Nature Reserve in Shandong Province from 2021-2022.Through investigating the population number of migrating and wintering red-crowned cranes,analyzing the use of Smooth Cord-grass and Saline Seepweed mudflat,according to the analysis of Smooth Cord-grass wetland area changes in the Yellow River Delta,we understand the impact of Smooth Cord-grass invasion on the habitat utilization of red-crowned cranes,and through the investigation of crabs and other benthic animals,Evaluate the impact of Smooth Cord-grass invasion on the diet selection of the red-crowned cranes by analyzing food residues in fecal samples.The main research results are as follows:(1)Red-crowned cranes will used Smooth Cord-grass mudflat in Yellow River Delta as their habitat during migration and wintering,but there is a certain period difference in utilization intensity.They prefer to use Saline Seepweed mudflat during migration(F=8.400,P=0.008,P<0.01),and have a higher selectivity to Smooth Cord-grass beach during wintering(F=14.452,P=0.001,P<0.01).(2)Remote sensing interpretation shows that the area of Smooth Cord-grass mudflat in Yellow River Delta will expand from 37.62 km2 to 58.33 km2 in 2016-2021,with an area of 20.71 km~2.The mudflat area of Saline Seepweed decreased from289.43km~2 in 2016 to 233.25km~2 in 2021,with a net decrease of 56.18km~2.The changes of Smooth Cord-grass(F=5.284,P=0.163)and Saline Seepweed mudflat area(F=9.280,P=0.099)were not significantly related to the number of red-crowned cranes.(3)By analyzing the composition of food residues in fecal samples of red-crowned cranes in two habitats in Yellow River Delta,we found that:○1 The red-crowned cranes mainly feed on crabs during migration and overwintering,in addition to some shellfish,snails and fish;○2 By analyzing the proportion of crab residues in red-crowned cranes feces samples,it was found that there was no period difference in the proportion of crabs in red-crowned cranes feces samples collected in Smooth Cord-grass mudflat(F=0.34,P=0.855),but there was a significant difference in the proportion of crabs in Saline Seepweed mudflat(F=129313,P=0,P<0.01),and the proportion of crabs eaten in the migration period was higher than that in Smooth Cord-grass mudflat;○3 The red-crowned cranes mainly feed on Helice tientsinensis and less on Macrophthalmus japonicus,and has a preference for female Helice tientsinensis.(4)Analysis of crab species and density in two habitats showed significant differences in the number of female Helice tientsinensis(F=2.34,P=0.017)and female Macrophthalmus japonicus(F=5.13,P=0.044),while there was no significant difference in the number of male Helice tientsinensis(F=3.02,P=0.123)and male Macrophthalmus japonicus(F=3.71,P=0.073).The density of female crabs in Smooth Cord-grass mudflat is lower than that in Saline Seepweed mudflat.There was no significant habitat difference in the density of crab caves in autumn(F=2.175,P=0.102).In the study area,there was no significant difference in crab cave density between Smooth Cord-grass habitats and Saline Seepweed.The survey of large benthos also found that the recorded Smooth Cord-grass includes the Potamocorbula laevis,Iridona iridescens,Hediste japonica,Perinereis aibuhitensis and Nassarius festivus.The distribution of these benthic animals provides more feeding options for the red-crowned cranes.By studying the influence of red-crowned cranes on the habitat utilization and diet selection of Smooth Cord-grass and Saline Seepweed mudflat wetlands,this study concluded that Smooth Cord-grass can be used as the habitat for red-crowned cranes to migrate and overwinting.There is no significant statistical correlation between the increase of Smooth Cord-grass mudflat area and the changes of red-crowned cranes’overwintering population.However,during the migration period,the red-crowned cranes can more easily obtain high-quality female Helice tientsinensis in the mudflat of Saline Seepweed.The expansion of Smooth Cord-grass will have some impact on the red-crowned cranes that depends on the habitat of Saline Seepweed.In order to maintain the stability of the red-crowned cranes population and promote the population recovery,it is also necessary to strengthen the management of Smooth Cord-grass and the restoration of Saline Seepweed mudflat wetlands.