Feeding Habit And Competitive Behavior Of The Chiromantes Dehaani In The Salt Marsh Of The Yangtze Estuary

Chiromantes dehaani,one of the dominant benthic animals in the high tidal flat of the Yangtze Estuary,has a large and widespread population.Their feeding habit and related behavior play an important role in the energy flow and material cycling of the salt marsh ecosystem.However,the feeding habit of C.dehaani in the different physical environments and the mechanisms by which environmental factors affect their competitive behavior are still need to be further studied at present.The north tidal flat of Chongming Island is distributed with typical salt marshes in the Yangtze Estuary,the great number of C.dehaani inhabiting there.In this study,three typical vegetation areas mentioned above were selected as experimental sampling zones,where Chiromantes dehaani,Spartina alterniflora,Phragmites australis,Assiminea violacea,Cerithidea sinensis and sediments were collected.The ¹³C and ¹⁵N stable isotope abundances of these samples were analyzed to obtain the feeding characteristics of C.dehaani in these vegetation areas.The indoor control experiments of the food competition behavior of C.dehaani with the different sexes and body sizes were under the different spatial and temperature conditions.Based on all the studies above,the following main conclusions were drawn:I.Feeding habit characteristics of C.dehaani1.Feeding preferences of C.dehaaniTrophic level calculations were carried out with stable isotope analysis of C.dehaani and food sources from the three sampling zones.The trophic level of the C.dehaani was found to be higher than that of the dominant plants and sediments in its habitat,with the trophic level of the C.dehaani being 0.9?1.31,0.77?1.16,and0.24?0.61 higher than that of the dominant plants(S.alterniflora and P.australis),sediments and dominant benthic snails(A.violacea and C.sinensis),respectively.The results indicated that C.dehaani mainly fed on the dominant plants in the habitat and organic matter in the sediment,while the dominant benthic snails also act as a certain food source for it.Meanwhile,the ¹³C isotope abundance analysis showed that the?¹³C values of the C.dehaani were 3.23?3.87‰higher than those of the dominant plants,1.43?1.73‰higher than those of the sediments,and-1.22?0.77‰higher than those of the dominant benthic snails.The preference for animal food in the different habitats was indicated by C.sinensis in the P.australis zone and A.violacea in the S.alterniflora zone.2.The effects of body size and food types on the feeding habits of C.dehaaniUsing carapace width as an indicator of body size,the?¹⁵N and?¹³C values of C.dehaani were correlated with carapace width in the three sampling zones,but there was no significant correlation between body size and carapace width(P>0.05).Analysis on the range of the?¹⁵N and?¹³C values of C.dehaani in the three sampling zones showed that of the?¹³C values was 4.30?9.88‰,indicating that the larger C.dehaani,the more diverse the diet it obtained.The?¹⁵N values ranged from 1.70 to 3.21‰,which was relatively lower,indicating that although the food intake of C.dehaani varied with the body size,the vegetation still appeared to be the main food source.Meanwhile,one-way ANOVA of the?¹³C and?¹⁵N of the individuals in the three sample zones showed that there was no significant difference among the?¹⁵N values of the C.dehaani from the three zones(P>0.05),although there was a significant difference between the?¹³C values of the Spartina alterniflora zone and Phragmites australis zone,Phragmites australis zone and S.alterniflora-P.australis zone(P<0.05).The difference in food types among the different sampling zones had some influence on the feeding habit of the C.dehaani.?.Factors influencing intraspecific feeding competition of C.dehaani1.The effects of temperature on intraspecific feeding competition of C.dehaaniThe effects of temperature on the feeding competition behavior of C.dehaani was investigated through controlled indoor experiments.The results showed that the competition intensity increased with increasing temperature,which had a highly significant correlation(P<0.01).The correlation coefficients of temperature with competition intensity of the male large-size individuals,male small-size individuals and female small-size individuals were 0.956,0.926,and 0.833,respectively.At the same temperature,the competition intensity of C.dehaani showed a positive correlation with the experimental duration.The competition intensity of some groups increased with increasing experimental duration was highly significant(P<0.01)or significantly(P<0.05).2.The effects of space size on intraspecific feeding competition of C.dehaaniThe effects of space size on the feeding competition behavior of C.dehaani was also investigated through controlled indoor experiments.The results showed that under the same experimental duration,the competition intensity of C.dehaani decreased with larger space.Most experimental groups showed a very significant negative correlation between competition intensity and space size(P<0.01).The correlation coefficient between the space size and competition intensity for the male large-size individuals was-0.860(P<0.01),for the male small-size individuals was-0.867(P<0.01),and for the female small-size individuals was-0.873(P<0.01).Under the same space size,the competition intensity of C.dehaani increased with the increasing of the experimental duration.Most groups showed a significant correlation(P<0.05)between competition intensity and experimental durations,and more than half of the groups showed a highly significant correlation(P<0.01).3.The effects of sex and body size on intraspecific feeding competition of C.dehaaniBased on the data from the experiments with the various temperatures and space sizes using C.dehaani of the different sexes and body sizes,it can be concluded that the competition intensity was higher in males than in females,and higher in large than in small individuals.Two-way ANOVA was conducted to measure the effects on the competition intensity by combining temperature and space size with body size and sex.There was a significant interaction effect between temperature and body size(P<0.05),while no significant interaction effect between the other three groups(P>0.05)was recorded.The effects of temperature and body size on intraspecific competition of the C.dehaani appeared to have more complicated mechanisms.In conclusion,the C.dehaani in the Yangtze Estuary had a certain feeding preference varied with habitat conditions and the dominant vegetation,and its food composition reflected its random omnivorous feeding habit.In addition,temperature,space size and body size had a great influence on intraspecific competition.The results can provide a basis for the further study on the intraspecific and interspecific relationships of the critical species in the salt marshes,the structure and function characteristics of the salt marsh ecosystem,and also for the conservation and management of the salt marshes.