Feeding Preferences And Effects To Typical Salt Marsh Plants Of The Dominant Crabs On The North Bank Of Hangzhou Bay

As the most typical macrobenthos in salt marsh,crabs are known as “ecosystem engineer”.Early studies have found that herbivorous behavior of geese,benthic insects and other animals can affect the growth and community composition of salt marsh vegetation.In recent years,some studies have shown that the herbivorous behavior of crabs can also cause top-down effects to the salt marsh vegetation.however,its internal mechanism still needs to be deeply understood.There existed competition growth of Spartina alterniflora and Phragmites in the tidal flat on the north bank of Hangzhou Bay.Previous investigation found that the crab species richness was high,which provided a good sample plot condition for studying the top-down effects of crabs.This study investigated the distribution of crabs,explored their feeding preference to different salt marsh plants and its effect on the growth of the plant,which can provide a basic reference for further revealing the control effect of crab on plant population growth and inter-specific competition.The study focus on the Fengxiang tidal flat on the North Bank of Hangzhou Bay as the mean research site.The research work was carried out from January 2018 to December 2018.The field sampling work synchronized laboratory experiment was mainly carried out in January,March,June and September.Seven sample plots were set up,including High intertidal zone of Spartina,Middle intertidal zone of Spartina,Low intertidal zone of Spartina,Mixed area,High intertidal zone of Phragmites,Middle intertidal zone of Phragmites and High intertidal zone of bare area.We selected the two dominant crabs,Helice tientsinensis and Sesarma plicata as the research objects.Combined with quarterly field sampling,indoor feeding experiment and crab control experiment to analyze the distribution of crabs during four seasons,the feeding preferences of two dominant crabs on typical salt marsh plants as well as the related factors.At the same time,investigated the inhibitory effect of crabherbivore on different growth stages of Spartina alterniflora.The main findings of this study can be summarized as follows:(1)The composition of crabs in Fengxian tidal flat on the North Bank of Hangzhou Bay and the spatial and temporal distribution characteristics of two dominant crabsThe composition of crabs in Fengxian tidal flat on the North Bank of Hangzhou Bay included 4 families and 5 species,namely Sesarma plicate,Chiromantes dehaani,Helice tientsinensis,Scylla serrata and Uca arcuata.Among them,Sesarma plicate and Helice tientsinensis are the two dominant species.The habitat selection of Helice tientsinensis and Sesarma plicate is inconsistent.The abundance of two crabs are different during four seasons.The abundance of Helice tientsinensis during autumn and winter is slightly higher than in spring and summer,while the abundance of Sesarma plicate during spring and summer is significantly higher than in autumn and winter.The characteristics of the distribution along the elevation are that Helice tientsinensis prefer active in the high tide zone while Sesarma plicate prefer the middle and low tide zones.The distribution characteristics of the two crabs in the vegetation area are that Helice tientsinensis prefer the Phragmites habitat,while Sesarma plicate prefer the Spartina alterniflora habitat.(2)Feeding preference of two crabs to different plants organsThe results of indoor feeding experiments showed that the feeding preference of two crabs were consistent with the fresh leaves of different plants.They showed significant preference to the leaves of Phragmites and Scirpus mariqueter,and the average food intake was about three times higher than Spartina alterniflora leaves.The results of feeding on different salinity leaves showed that both crabs have preference for high salinity leaves.During different seasons,the feeding results of crabs on different plant organs were different,but overall their feeding preference was:Leaves > Roots > Stalk.(3)The feeding effects of Helice tientsinensis on different growth period of Spartina alternifloraThe results of crab control experiments showed that the herbivory of Helice tientsinensis had different inhibitory effects on different growth period of Spartina alterniflora.At the seedling stage of Spartina,they were seriously fed and destroyed by crabs,resulting in a significant decrease on the height of the plants and the length of leaves.The higher density of crabs,the more significant destroy will be.Under high-density crab treatment,the feeding effect of Helice tientsinensis can cause 100%mortality of Spartina alterniflora seedlings.Under low-density crab treatment,the mortality rate of seedlings were 55.6%,the seedling height of seedlings were decreased by 56.6%,and the number of leaves was decreased by 75.00%.However,the feeding effect did not significantly inhibition to the growth of adult Spartina.Above all,this study Preliminary revealed the dominant species and the community distribution characteristics of the large benthic macrobenthos crabs in Fengxian tidal flat on the North Bank of Hangzhou Bay.Explored the feeding preference and consumption of Helice tientsinensis and Sesarma plicate to different plant materials.At the same time provided a reference basis for exploring the inhibition of the growth of the Spartina alterniflora through crab herbivory effects.