Vertical Distribution Patterns Of Mangrove Arboreal Mollusks And Its Influencing Factors

As an important fauna in mangrove ecosystem,the arboreal mollusks inhabit different positions of mangrove forest and play a crucial role in the material circulation of mangrove ecosystem.The special geographical location,climatic conditions,environmental factors and biocoenosis of the intertidal mangrove area have created unique climbing behavior and vertical distribution patterns.There are two means about the vertical distribution patterns of intertidal arboreal mollusks normally,distribution pattern along the intertidal zone and climbing height interval.Arboreal mollusks' vertical distribution patterns and habitats have higher heterogeneity due to their moderate mobility which could be affected by some physical factors like tidal dipping,flooding frequency,salinity,temperature,humidity,and biological factors such as predators,mangrove species and interspecific competition.Among multitudinous environmental and biological,tidal dipping and mangroves are essential for the vertical distribution and climbing interval of arboreal mollusks along the intertidal zone.How to quantify the specific effects of tidal flooding in intertidal mangroves on vertical distribution of arboreal mollusks and describe the role of perched plants in the diversity of arboreal mollusks climbing locations are two problems that need to be solved when describing the vertical distribution of arboreal mollusks under the background of sea level rise.The surface elevation is an important parameter to quantify the influence of environmental factors such as tidal dipping in the intertidal zone,which is widely used in the research of intertidal mangrove forestation and restoration.This study draws on the experience in studying plant community and selects Beilun estuary,Guangxi,as experimental location.Different sites with gradients in surface elevation were set at the six mangrove areas within estuary based on the Yellow Sea datum in order to quantify the influence in the vertical distribution patterns along intertidal zone and climbing interval of tidal dipping,and study the diversity of vertical distribution patterns of different arboreal mollusk species at sites of different surface elevation.The influence of four mangrove species on climbing positions of arboreal mollusks and other environmental factors which could have possibility to affect the spatial distribution of arboreal mollusks were also explored.The main conclusions are as follows:1.A total of 33 species of 12 families of arboreal mollusks were investigated in two seasons,the most common families is Littorinidae and Ellobiidae.Dominant species is Littoraria melanostoma,Littoraria ardouiniana and Littoraria scabra.Arboreal mollusks' total average density is 16.54 ind./m2,total average biomass is 7.5 g/m2.2.There are significant differences in density of arboreal mollusks in different sites of different surface elevation along the intertidal zone.Average density of arboreal mollusks from huge to small is followed 25 cm>50 cm>75 cm>150 cm>125 cm>100 cm>190 cm.The diversity index is lower in the middle and higher in both ends.Different arboreal mollusk species have different suitable distribution elevation.As widely distributed species,Littoraria melanostoma and Littoraria ardouinian be found on each sites o different surface elevation.Littoraria scabra is richly concentrated in those sites which surface elevation below 100 cm.Littoraria pallescens,Enigmonia aenigmatica and Nerita yoldi distributed in the lower surface elevation,and all have the elevation expectation which less than 70 cm.The distributed elevation of Terebralia sulcate and Neritina violacea is higher,which mostly concentrated between 75 cm and 150 cm.Cerithidea ornate and Cassidula nucleus are considered to be narrow in vertical distribution interval,both have the elevation expectation which higher than 150 cm.The distribution of arboreal mollusks' density and biomass along different intertidal sites is mainly affected by surface elevation and plant density.Distance from shore,seawall and crown density all has significant impact to vertical distribution of abrboreal mollusks along intertidal zone.3.The climbing height of arboreal mollusks showed a decreasing trend along the surface elevation.The climbing height of Littoraria melanostoma,Littoraria ardouiniana and Littoraria scabra is negatively correlated with the surface elevation.The climbing height relative to the zero tidal level of Huang Ocean of those three species is positively correlated with the surface elevation.For Littoraria ardouiniana,the average vertical height relative to the zero tidal level of Huang Ocean has same interval in every sites of different surface elevation.For Littoraria scabra and Littoraria melanostoma,the average vertical height relative to the zero tidal level of Huang Ocean is distributied below the mean higher-high-water mark of spring tides.There is large difference in the distribution height interval of different arboreal mollusk species relative to the zero tidal level of Huang Ocean,but most of them are distributed below the mean high-water mark of spring tides.In addition to the surface elevation,the climbing height of different species of arboreal mollusks is also affected by other environmental factors such as distance from shore,seawall and plant density.4.There are obvious preferences for the distribution of different arboreal mollusks on mangrove species.Littoraria melanostoma,Littoraria ardouinian and Littoraria pallescens is mainly distributed on the leaves of mangroves.Littoraria scabra allways be found on branchs of mangroves.Terebralia sulcate,Cerithidea ornate and Neritina violacea more inhabit the trunks of mangroves.The distribution intervals and distribution positions of mollusks vary between different mangrove plants.On Kandelia obovata,the suitable vertical range of mollusks is the largest,it is the smallest on Bruguiera gymnorrhiza.The proportion of mollusks on the leaves of Avicennia marina is the largest.More quantity mollusks inhabit the branches on Kandelia obovate,Aegiceras corniculatum and Bruguiera gymnorrhiza.