Recent advances in environmental DNA‐based biodiversity assessment and conservation

Knowledge of species distribution across space and time is critical to ecological conservation and environmental management at the local, regional and global scales (Albert et al., 2021). Traditional morphologybased surveys on either singlecelled protists or larger animals and plants are timeconsuming and largely expertdependent (Baird & Hajibabaei, 2012; Liu et al., 2017; Yang et al., 2017). Recently, there has been considerable interest in the detection of environmental DNA (eDNA) fragments to allow species identification and monitoring within different environments, including soil, sediment, water, snow or air (Abdullah et al., 2021; Rees et al., 2014; Xie et al., 2018). The eDNA analysis can be used to detect common, endangered, invasive or rare species (Liu et al., 2019; Sepulveda et al., 2020), and provide a potent tool for elucidating mechanistic insights into ecological and evolutionary processes (Baird & Hajibabaei, 2012; Bohmann et al., 2014; Pawlowski et al., 2021). In past decades, eDNA metabarcoding has been increasingly used to study the present and past biodiversity from population to community levels, and eDNAbased surveys have revolutionized studies in ecology and biodiversity sciences, particularly in aquatic ecosystems (Euclide et al., 2021; Valentini et al., 2016). The significance of various human activities has resulted in multiple interacting environmental stressors in all types of ecosystems (Pukk et al., 2021; Yang et al., 2022). Such stressors, including global climate change, invasive species, chemical pollution and habitat loss, have led to biodiversity crises and threatened the human sustainability and ecosystem health (Osathanunkul & Minamoto, 2021; Yang et al., 2017). Comprehensive biodiversity assessment and conservation management are prerequisites for addressing these significant challenges in the Anthropocene (Mace et al., 2012; Sepulveda et al., 2020). Indeed, effective biodiversity assessment and conservation management require a deep understanding of organisms’ geographical distributions and their respective roles in ecosystem processes and services (Mo et al., 2021; West et al., 2021). However, researchers and conservation managers have encountered numerous obstacles in answering these fundamental and applied research questions at the local, regional and global scales. The aim of this special issue— Environmental DNAbased biodiversity assessment and conservation— was to provide a selection of studies that highlight the utility and diversity of eDNAbased research for biodiversity assessment and conservation management within marine and freshwater ecosystems. This special issue includes 12 articles that advance our knowledge of eDNA. Together, these studies deliver compelling evidence for successful applications of eDNAbased surveys in aquatic ecosystems in the Anthropocene.

tion and monitoring within different environments, including soil, sediment, water, snow or air (Abdullah et al., 2021;Rees et al., 2014;Xie et al., 2018). The eDNA analysis can be used to detect common, endangered, invasive or rare species (Liu et al., 2019;Sepulveda et al., 2020), and provide a potent tool for elucidating mechanistic insights into ecological and evolutionary processes (Baird & Hajibabaei, 2012;Bohmann et al., 2014;Pawlowski et al., 2021). In past decades, eDNA metabarcoding has been increasingly used to study the present and past biodiversity from population to community levels, and eDNA-based surveys have revolutionized studies in ecology and biodiversity sciences, particularly in aquatic ecosystems (Euclide et al., 2021;Valentini et al., 2016).
The significance of various human activities has resulted in multiple interacting environmental stressors in all types of ecosystems (Pukk et al., 2021;Yang et al., 2022). Such stressors, including global climate change, invasive species, chemical pollution and habitat loss, have led to biodiversity crises and threatened the human sustainability and ecosystem health (Osathanunkul & Minamoto, 2021;Yang et al., 2017). Comprehensive biodiversity assessment and conservation management are prerequisites for addressing these significant challenges in the Anthropocene (Mace et al., 2012;Sepulveda et al., 2020). Indeed, effective biodiversity assessment and conservation management require a deep understanding of organisms' geographical distributions and their respective roles in ecosystem processes and services West et al., 2021). However, researchers and conservation managers have encountered numerous obstacles in answering these fundamental and applied research questions at the local, regional and global scales.
The aim of this special issue-Environmental DNA-based biodiversity assessment and conservation-was to provide a selection of studies that highlight the utility and diversity of eDNA-based research for biodiversity assessment and conservation management within marine and freshwater ecosystems. This special issue includes 12 articles that advance our knowledge of eDNA. Together, these studies deliver compelling evidence for successful applications of eDNA-based surveys in aquatic ecosystems in the Anthropocene.

| Biodiversity and distributions
Six papers in this issue are focused on the biodiversity assessment and conservation management. Environmental DNA metabarcoding provides a valuable and complementary survey technique in conservation and management (Sepulveda et al., 2020). One study indicated that a simple eDNA metabarcoding assessment using a high number of low-volume (50-ml) samples, centrifugation and a single gene (mitochondrial 12S gene) can describe the coarse fish community structure of freshwater lakes and rivers (Euclide et al., 2021).
The authors also suggested that additional conventional sampling and environmental DNA sampling may be necessary for a complete diversity census. Osathanunkul and Minamoto (2021) used eDNA-based approaches to qualitatively and quantitatively track the crocodile newt in Thailand. They found Tylototriton uyenoi is severely declining due to anthropogenic factors, thereby suggesting that eDNA-based methods could help in designing an effective conservation plan. In north-western Australia, West et al. (2021) applied metabarcoding of the mitochondrial 16S rRNA and CO1 genes to detect bony fish, elasmobranchs and aquatic reptiles from 71 mid-shelf, inshore, coastal and nearshore estuarine sites. Their eDNA metabarcoding was a highly sensitive detection tool that was able to discern fine-scale patterns of marine fishes across the largescale oceanic region. Therefore, by no means will this special issue provide a full picture of environmental DNA (eDNA)-based studies; rather, it can serve as a window to showcase the recent and global developments in environmental DNA-based biodiversity assessment and conservation management. We believe further substantial advance is foreseeable in the fields of eDNA-based studies because they are entering an exciting and rapidly accelerating era. Over the past several decades, a key scientist in the study of urban ecology and sustainable development has been Prof. Jingzhu Zhao (1958-2021)-sadly, he died of cancer on 4 August 2021, and we dedicate this paper to him.