The goal of this project is to monitor the spatial distributions of fish environmental DNA around artificial reefs quantitatively. By adding internal standard DNA, a standard curve (i.e., the relationship between the number of DNA copy and sequence read) will be drawn. Based on the standard curve, sequence reads of unknown DNA (non-standard DNA) will be converted to the number of DNA copy. The environmental DNA metabarcoding combined with internal standard DNA will enable quantitative monitoring of multispecies environmental DNA.