| Salt marsh is one of the most productive ecosystems in the world,mainly distributed in subtropical and tropical estuarine and coastal areas.Crabs are important large benthic animal groups in salt marsh,they participate in and influence a variety of ecosystem processes,and play an important role in the whole ecosystem.Chiromantes dehaani is one of the benthic animals in high tide flat in the Yangtze River estuary,it has a large population and it's widely distributed,its feeding behavior also has a great influence on food web structure and energy flow of the ecosystem,what's more,its feeding behavior has a great influence on the primary producers and consumers,and the salt marsh plant's engraftment and growth,it also plays a key role in the salt marsh sediments environment.Therefore,searching into the crab's feeding ecological characteristics is of great significance in understanding its effect on the ecological process of salt marsh,such as litter return,the distribution of organic matter and the succession of the salt marsh plants.In this paper,we take the typical salt marsh wetland in the Yangtze River estuary as the research area,focus on Chiromantes dehaani.Based on present researches,combined with domestic and foreign researches,we proposed the sampling scheme and experimental methods,and choose five kinds of typical vegetation distribution area in Chongming Island,set sample plots.We collect and analysis crabs,plants and sediment samples seasonally.Through the stomach content analysis and stable isotope determination,we get the temporal and spatial differentiation characteristics of Chiromantes dehaani's diet.Through the laboratory feeding experiment and the analysis of related attributes of the plants,properties of the crab and interspecific competition,the feeding preference characteristics and related factors were obtained.Combined with the results of field work and the laboratory feeding experiments,we concluded the characteristics and related factors of Chiromantes dehaani's feeding preference.The main results can be summarized as the following aspects:During the most of the crab's life history,the plant leaves are the main food source,it also takes in sediment and benthic animals,so it can be considered an omnivore.Chiromantes dehaani's feeding preference has obvious spatial and temporal variation characteristics.Its feeding rate,stomach contains are different in different habitats and seasons.Chiromantes dehaani in reed sample plot mainly take in reed leaves and sediment,it also takes in Assiminea violacea and Obelisk Vertagus in the habitat;the result of stable isotope showed that the Chiromantes dehaani's food source in reed and Spartina alterniflora mixed sample plot includes fresh reed leaves Assiminea violacea and sediment;crabs in Spartina alterniflora sample plot mainly eat fresh leaves and sediment,also take in Assiminea violacea;sediment and fresh leaves are main food source in reeds and Phacelurus latifolius mixed sample plot,Assiminea violacea also accounts for a definite proportion;main food source of crabs in Taxodium distichum and herbal sample plot is reed leaves,sediment,and Assiminea violacea.The feeding intensity is larger in spring and summer,and weaker during the fall;sediment takes more percentage in the stomach contains in spring than in other seasons,plant debris takes more proportion in the stomach contains in autumn than in other seasons.Additionally there are differences between different habitats,especially habitats between south and north branch in the Yangtze River.The feeding experiment results show that C.dehaani does have certain feeding preference for different kinds of food,it prefers snail meat.There are different types of leaf traits,such as the size,state,toughness,content of nutrients and some chemical components,which will affect the taste of the leaves,and leads to the feeding preference for different food.There also exist certain differences in feeding preferences to different foods between crabs in different habitats,we could consider that inhabits niche will affect the crab's feeding behavior,it is related to the abundance and availability of different food in the habitat.At the same time,in different seasons the feeding preference of C.dehaani is also changing.The feeding preference characteristics show that: in spring,crabs from Spartina alterniflora habitat prefer eating Solidago canadensis when compared with other types of plants,but it's not significant,crabs from the other four habitats take in leaves of Spartina alterniflora a bit more.In autumn,crabs from all habitats except those from Taxodium distichum and herbal sample plot prefer leaves of Spartina alterniflora,crabs from Taxodium distichum and herbal sample plot take in more Solidago canadensis leaves,crabs from reed and Phacelurus latifolius mixed sample plot prefer eating reed leaves.So we think that the feeding preference of Chiromantes dehaani should be determined by the specific conditions,not only considering the seasons that change the feeding preference,but also considering the domestication of their habitats.After researching on related factors,we found that Chiromantes dehaani's feeding preference is influenced by many factors,not only by the factors of crab itself(shell width,chela wide),but also by the factors of food(the toughness and water content of the plants),at the same time,to a certain extent,their diets are affected by interspecific competition.There are many factors affecting feeding characteristics,however,this study could not include every factor,for example,the plant carbon nitrogen ratio,the influence of the secondary chemical material and so on,how to put these indexes together and give them different weights to judge the synthesis of these factors on Chiromantes dehaani's feeding behavior,needs further study.In a word,we can think that Chiromantes dehaani is an omnivorous animal with plants being its main food source.Its feeding habits have significant spatial-temporal changes,and it also has certain feeding preferences.The results of this paper can provide a scientific basis for further study of the structure and function of the salt marsh wetland ecological system and using biological means to manage and protect the salt marsh wetland. |
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