A Stable Isotope Analysis Based Study On Cannibalism Of Scylla Paramamosain Juvenile

Scylla paramamosain?mud crablet?is an important economic crablet and benthic predator in the coastal-estuary area of southern China.Sometines,cannibalism occurs in the natural population of crablet.The cannibal of crablet has the adaptive significance of stabilizing population size and age structure in natural environment,and it is easy to cause individual death in artificial cultivation.The difficulty in the study of cannibal of crablet is to find out the scale and regularity of death under artificial cultivation.Stable isotope analysis?SIA?was used in this study.With the idea of nutritional ecology,the carbon and nitrogen stable isotope ratios??15N and?13C?of crablet were determined to find out the cannibalism scale of laboratory animals under simulated artificial cultivation conditions,and to infer the cannibalism predation status under artificial cultivation conditions.The main results are as follows:1.The enrichment index of 815N formed by crablet:The results showed that the enrichment rate of nitrogen stable isotopes??15N?of crablet ranged from 0.48‰ to 1.89‰,and the half-life turnover required for ?15N was between 8.37 to 13.51 days.The time-based model is superior to the growth-based model in fitting the stable isotope enrichment process of experimental animals by non-linear regression.2.Changes of ?15N and ?13C caused by the molting of crablet:The ?15N and ?13C of experimental animals before and after molting?including from megalopa after molting for the first stage of crabletletlet and from the first stage of crabletletlet to the second stage of crabletlet?were detecteU.and the t-test of matched data of ?15N and?13C in residual cephalothoracic carapace of experimental animals showed that ?15N and ?13C were significantly increased?p = 0.014?and?p = 0.027?when megalopa after molting for the first stage of crabletletlet.And ?15N was no significant increased?p=0.082?,the ?13C was no significant reduced?p=0.209?.The ?15N of the residual cephalothorax was lower than that of the experimental animals before and after molting?p=0.0002?,and its ?13C was higher than that of the experimental animals before and after molting?p=0.0003?,indicating that the relationship of ?15N after molting was related to the exoskeleton with lower ?15N.The compound-specific isotope analysis?CSIA?of 15 specific amino acids showed that there were no significant changes in 6 amino acids before and after the megalopa after molting for the first stage of crabletletlet?p>0.05?,and 9 amino acids changed significantly?p<0.05?or very significantly?p<0.01?.3.Cannibal mortality rate of crablet:The mortality rates of monotrophic group and small group were recorded respectively.The results showed that the average daily mortality rate of monotrophic group was 2.16%,and the survival rate of experimental animals was 34.33%before the end of the experiment.The average daily disability mortality was 5.35%in the small group,and the survival rate of experimental animals was 6.74%before the end of the experiment,the cannibal mortality rate of crablet was 3.19%,accounting for 59.63%of the total mortality in the small group.4.Contribution rates of cannibalism to feeding of crablet:In a 7-week experiment,?15N and ?13C of monotrophic group,cannibalism group,small group and large group were measured respectively.It was found that the stable isotope enrichment rates of?15N and ?13C of experimental animals in monotrophic group were 1.63‰ and 1.33‰,respectively,and that of ?15N and ?13C of experimental animals in cannibalism group were 1.16‰ and 1.25‰?respectively.According to the Dual isotope,two-source mixing mode,cannibalism predation accounted for 7.53%of the small group and 9.88%of the large group,respectively.5.The relationship between cannibalism,molting and individual size of crablet:The correlation test between cannibal mortality and molting rate of crablet during the experiment period was made according to the weekly statistics,and found that there was a positive correlation between cannibalism and molting rate?p=0.004?,indicating that there were many cannibalism of crablet during molting.The correlation test showed that there was a positive correlation between the crablet size and its ?15N?p=0.014?,indicating that the asymmetry of the crablet size was also an important factor in the occurrence of cannibalism.There was no significant correlation between the molting rate and the ?¹⁵N and ?¹³C of crablet.