Linking the state of environmental DNA to its application for biomonitoring and stock assessment: Targeting mitochondrial/nuclear genes, and different DNA fragment lengths and particle sizes

Abstract

Environmental DNA (eDNA) analysis is a revolutionary tool for non-invasive, cost-effective, and highly sensitive monitoring of species distribution and abundance; however, there remain some uncertainties related to eDNA detection and quantification, as well as limitations in terms of its ecological interpretation. Although these may be elucidated by better understanding the characteristics and dynamics of eDNA, insight into such basic eDNA information has been limited in this decade, contrary to the advancements in eDNA applications targeting various taxa and environments. This review compiled previous findings regarding the characteristics and dynamics of macrobial eDNA and provides insights into how the basic knowledge of eDNA can contribute to the refinement and development of eDNA analysis for biomonitoring and stock assessment. A literature survey revealed that studies on the cellular and molecular state of eDNA were particularly lacking (18/728 papers from 2008 to 2020), resulting in a limited understanding regarding the process of eDNA transport and degradation. This review highlighted a number of studies targeting various types of eDNA beyond short mitochondrial DNA fragments (nuclear eDNA, longer eDNA fragments, and larger eDNA particles) to show how information on the state of eDNA improves the reliability of species detection and accuracy of abundance estimation, as well as provide more detailed information on individuals other than their presence and abundance. Linking the state of eDNA to its application will advance the analysis of eDNA and improve its application as a tool for monitoring biodiversity, ecosystem function, and fisheries resources.