Effects Of Habitat Change Of Suaeda Salsa Saltmarsh On The Habitat Use And Diet Composition Of Two Numenius Curlews

Coastal wetlands'loss has become an important reason for the global decline of shorebirds population.The Suaeda salsa saltmarsh is a typical wetland along the upper coastal of the Yellow(Bohai)Sea,which serves as an important stopover habitat for migrant shorebirds distributed in East Asia-Australasia Flyway.However,the area of S.salsa saltmarsh has declined rapidly in recent decades.The Far Eastern Curlew Numenius madagascariensis and Eurasian Curlew N.arquata,two large congeneric migrant shorebird species,forage in the S.salsa saltmarsh along the northern Yellow(Bohai)Sea.However,the two curlews'migrant strategies are different,and their global populations show varied trends.By comparing the difference of habitat and foraging utilization among S.salsa saltmarsh and adjacent mudflat between two curlews,it can provide a guideline to understand the threated mechanism of endangered birds.Furthermore,it is also meaningful to protect and manage the endangered birds and habitats that they rely on.Moreover,different zones of tidal flat have dramatically diverse functions for shorebirds.As a typical component of coastal wetland distributed in supra-tidal zone and used by two curlews,investigating its temporal and spatial variation,which is extremely significant,will provide a better understanding of the driving factors affecting the population changes of two curlews.This study was carried out in Liaohekou estuarine wetland from 2017 to 2019.A survey on density and behavior and an observation on foraging behavior of two curlews between two habitats were conducted to examine the habitat and foraging utilization.We investigated the macro-benthic invertebrates of S.salsa saltmarsh and adjacent mudflat to compare the difference of prey composition between seasons and habitats.Based on Landsat imagery,spatial distribution and landscape pattern of S.salsa were studied from 1988 to 2018 in the coastal areas of China.Pearson correlation analysis was used to test the relationship between two curlews'populations and the change of area of S.salsa saltmarsh.The results show that:(1)Foraging is the main behavior of two curlews between S.salsa saltmarsh and mudflat during low tide periods(Far Eastern Curlew:68.14-90.91%;Eurasian Curlew:70.5-83.32%).The density of two curlews in S.salsa saltmarsh increased with the tide rising,besides,the percentage of foraging behavior decreased significantly,however,the percentage of resting behavior increased significantly.During high tide,the percentage of foraging behavior of Far Eastern Curlew is significantly higher than Eurasian Curlew in S.salsa saltmarsh in autumn(?²=50.651,P<0.001).(2)Carbs are the main diet composition of Far Eastern Curlew(74.12-86.27%)in both seasons and habitats.In contrast,the ragworms are the main prey of Eurasian Curlew in S.salsa saltmarsh in spring(74.4%),while the crabs are fed by Eurasian Curlew in other seasons and habitats(34.78-76.67%).The feeding rate on crabs of Far Eastern Curlew is higher in spring than autumn(z=2.30,P=0.02).There is no significantly habitat-specific difference of the feeding rate of Far Eastern Curlew.Besides,the feeding rate of Far Eastern Curlew is much higher than Eurasian Curlew on crabs(z=2.16,P=0.03).Furthermore,compared with other seasons,the feeding rate on ragworms of Eurasian Curlew is the highest in S.salsa saltmarsh in spring(z=7.194,P<0.001).Based on the investigation of macro-benthic invertebrates,the density of carbs burrow is higher in S.salsa saltmarsh in autumn than other seasons(t=3.56,df=15,P=0.003)but ragworms in spring(t=6.204,df=23,P<0.001).The density of carbs is higher in mudflat than S.salsa saltmarsh in spring(t₁₈=-2.211,P=0.04),and there is no significant difference of carbs'density in autumn between two habitats(t₃₀=1.959,P=0.059).Human disturbance dramatically decreased the foraging rate on crabs by Far Eastern Curlew,but not by Eurasian Curlew.(3)Based on the temporary and spatial analysis of S.salsa saltmarsh along northern Yellow(Bohai)Sea,S.salsa saltmarsh is mainly distributed in Liaodong Bay(Liaohekou-xiaolinghekou estuarine wetland),Yellow River Delta wetland and the Guangli-zhima estuarine wetland that located in northern Laizhou Bay and other estuarine wetlands with lower annual runoff.The S.salsa saltmarsh area of northern Yellow(Bohai)Sea decreased dramatically from 1988 to 2018(26,336-9,870 ha)and the loss rate was 62.52%.The effects of reclamation and degradation are two main reasons that decreased the area and distribution of S.salsa saltmarsh.(4)Laizhou Bay is the main decreasing region of S.salsa saltmarsh among Yellow River delta-Laizhou Bay from 1988 to 2018(13,675-6,521 ha).The population of two curlews in this region declined and then increased from 1998 to2018 and there is no significant correlation between the decrease of S.salsa saltmarsh area and the variation of two curlews'population(Far Eastern Curlew:r=-0.653,P=0.347;Eurasian Curlew:r=-0.291,P=0.709).The S.salsa saltmarsh area of Liaodong Bay still decreased dramatically from 1988 to 2018(11,216-2,585 ha).The population of Far Eastern Curlew in this region has been declining from 1998 to 2018but stable for Eurasian Curlew after declining since 2013.Furthermore,there is no significant relationship between the decrease of S.salsa saltmarsh area and the variation of two curlews'population in Liaodong Bay(Far Eastern Curlew:r=0.349,P=0.651;Eurasian Curlew:r=0.533,P=0.467).By conducting the comparative study on the habitat and foraging utilization of two Numenius curlews,our study revealed the important ecological function of S.salsa saltmarsh as a foraging and resting habitat during stopover period for two curlews,especially for Endangered Far Eastern Curlews.Although there is no obviously statistical correlation between the decrease of S.salsa saltmarsh area and distribution and the changes of two curlews'population,the decline in the available habitat area will inevitably impact on the curlews'population relying on this habitat.In order to maintain the stability and promote the population restoration of curlews,it is necessary to strengthen the protection,management and restoration of the S.salsa saltmarsh.