Habitat Characteristics And Basic Food Source Differences Of Lateolabrax Maculatus In Subhabitats Of Salt Marshes In The Yangtze River Estuary

The salt marsh wetland in the Yangtze River Estuary has high primary productivity,changeable environmental conditions and high habitat heterogeneity.It provides a key place for many aquatic organisms to breed,feed and avoid enemies,and plays a key role in maintaining the diversity of biological resources in the estuary.In recent years,due to the influence of human activities such as beach reclamation,water pollution and overfishing,the salt marsh habitat in the Yangtze River Estuary has been destroyed,and the fish habitat characteristics have changed.Based on the net survey of salt marsh in the Yangtze River Estuary,niche analysis,population characteristics analysis and stable isotope techniques were used to systematically study the habitat characteristics of Lateolabrax maculatus in salt marsh in the Yangtze River Estuary.The main conclusions are as follows:1.Habitat characteristics of Chinese seabass in different sub habitats of the Yangtze River EstuaryThe results show that Chinese seabass is the dominant species in the Yangtze River Estuary.The spatial niche breadth of Chinese seabass decreases gradually in spring,summer and autumn,while the temporal niche width of Chinese seabass decreases in turn in tidal creek,Scirpus mariqueter vegetation area and mudflat.There is a significant temporal and spatial difference in the population distribution of Chinese seabass,with the highest in spring and the lowest in autumn.In terms of spatial,it is the most in tidal creek,followed by Scirpus mariqueter vegetation area,and mudflat the least in the population distribution of Chinese seabass.The majority of Chinese seabass entering the Yangtze River Estuary are juveniles,which occurrs mainly in spring.The small size individuals prefer to inhabit tidal creek,while the large size individuals prefer to inhabit mudflat and Scirpus mariqueter vegetation area.The average feeding level of Chinese seabass increases gradually from spring to winter in tidal creek,increases gradually from spring to autumn and decreases sharply in winter in mudflat,and reaches the maximum in summer and decreases gradually in autumn and winter in Scirpus mariqueter.In spring,summer and autumn,the average feeding order of Chinese seabass is Scirpus mariqueter>tidal creek>mudflat.In winter,the average feeding order of Chinese seabass is tidal creek>Scirpus mariqueter.>mudflat.It is speculated that the large-scale Chinese Lateolabrax japonic Chinese seabass enter the subhabitat of mudflat to pursue the prey of large individuals.2.Composition and relative contribution of basic food sources of Lateolabrax maculatus in three sub habitats of the Yangtze River EstuaryIn Jiuduansha salt marsh,carbon and nitrogen isotopes of Chinese seabass vary greatly in three subhabitats,and the feeding sources of Chinese seabass are complex.Theδ¹³C value increased gradually with month.Theδ¹⁵N increases gradually in May and June and continues to increase after a sharp decrease in July.Cluster analysising of the monthly averageδ¹³C andδ¹⁵N show that July has little similarity with other months.According to theδ¹³C andδ¹⁵N,Chinese seabass in Jiuduansha salt marsh could be divided into two groups:July and other months.The difference ofδ¹³C andδ¹⁵N in July from other months is related to the sharp increase of POM contribution and sharp decrease of algae contribution in July.It is speculated that the runoff in July may cause the change of POM content or composition,and then cause the obvious change of the feeding source of Chinese seabbass in July.The body length and body weight of Chinese seabass are positively correlated with the values ofδ¹³C andδ¹⁵N.Cluster analysising show that the body length of different groups could be divided into two groups:group I and group II.The body length of group I ranges from 28 to 128 mm,while that of group II ranges from 129 to 332 mm.Theδ¹³C andδ¹⁵N values of group I are significantly lower than those of group II（P<0.05）,and the stable isotopes of carbon and nitrogen of these two sizes of Chinese seabass have significant changes.The results of multi-source linear mixed model estimate the carbon contribution of major carbon sources to Chinese seabass show that the composition and contribution ratio of each basic food source are similar in the three subhabitats.POM and Spartina alterniflora are the major carbon sources in the three subhabitats,followed by algae,Scirpus mariqueter and Phragmites australis,which less contributed to Chinese seabass.The contribution rates of five carbon sources to different body length groups of Chinese seabass are different.Overall,the contribution of POM decreased with the increase of body length,while the contribution of Spartina alterniflora increased,while that of Scirpus mariqueter,Phragmites australis and algae is smaller.The contributions of POM and Spartina alterniflora to basal feeding sources increased with month.The results of cluster analysis show that Chinese seabass with different body lengths could be divided into two groups:group I（129～332 mm）and group II（29～332 mm）according to the difference of basal feed source composition and contribution rate.The basic feeding sources of Chinese seabass change from POM（>70%）to POM（50-66%）and Spartina alterniflora（32-47%）between group I（28～128 mm）and group II（129～332 mm）.