Distribution Of Invasive Crayfish Procambarus Clarkii In Yuanyang Terrace Revealed By EDNA

Yuanyang is famous for its rice terrace, which is a World Cultural Heritage. The occurrence of invasive crayfish Procambarus clarkii, however, caused great damage to the rice terraces, by digging holes in terrace walls. So it is critical to monitor the current distribution and spread dynamics of P. Clarkii. The conventional monitoring is mainly performed by trapping cage, which is labor- and time-consuming. Particularly, the monitoring data become less reliable when the population density decrease. Aquatic species can release environmental DNA (eDNA) into water via secretions and faeces. The environmental DNA could be used to monitor the presence of target species. The aim of this study is to test the effectiveness of eDNA in monitoring the distribution of crayfish in the terraces in Yuanyang.In this study, the eDNA of crayfish were analyzed for water samples from Yuanyang to survey the distribution of crayfish using fluorescence quantitative PCR (qPCR). First, DNA from crayfish tissue were used to test the threshold of eDNA concentration in qualitative and quantitative detection by qPCR. Second, the living crayfish were raised in controlled experiment, from which the water samples were diluted and analyzed using qPCR, providing a reference correlation between the eDNA concentration and population density. Finally, a total of 58 water samples were collected from the terraces in Yuanyang and the concentration of eDNA were determined, which were used to infer the distribution and population density of crayfish. We also monitored the crayfish distribution in the 58 sampling sites using conventional trapping cage. The results based on eDNA were compared with those based on trapping cage, using the observation data by local farmers as independent evidence.The major results are as follows:1) The lower threshold of eDNA concentration for qualitative and quantitative detection in qPCR was 10-4 ng/μL (i.e. LOQ) and 10-8 ng/μL (i.e. LOD), respectively;2) The eDNA method was more effective than the conventional method based on trapping cage especially in case of low population density. Specifically, in the total 58 samples, the local farmer identified 37 samples to be invaded by crayfish. For these positive samples, the eDNA method retrieved 22 samples (59.4%) while the trapping cage method only retrieved 2 samples (5.40%).3) For the remained 21 samples that were identified as negative ones by local farmers, both eDNA and trapping cage gave similar negative results, i.e. absence of crayfish. These data suggested that the eDNA seems not prone to false positive results.4) The current distribution map of P. Clarkii in Yuanyang was inferred based on the above results.Taken together, these data suggested that the eDNA method were effective and efficient for species detection of P. Clarkii in aquatic habitat. These data are useful for better management of this invasive species in Yuanyang and are informative for rapid detection of other aquatic species.