Factors affecting biphasic degradation of eDNA released by Japanese jack mackerel (Trachurus japonicus)

Understanding environmental DNA (eDNA) persistence and degradation processes is necessary for the precise assessment of species distribution and abundance in marine environments via eDNA. Given the various particle sizes and persistence states of eDNA in water, biphasic degradation of eDNA, composed of its initial rapid and subsequent slower decay, may describe the fate of eDNA more precisely than monophasic degradation. However, it remains unclear which environmental factors influence eDNA decay rates at each decay phase. Here, the factors characterizing the biphasic degradation of eDNA were assessed by re-analyzing the dataset of a previous study, which estimated Japanese jack mackerel (Trachurus japonicus) eDNA decay rates using a monophasic decay model. A biphasic decay model was newly applied to the dataset, and the fitness was compared between decay models. Biphasic models were better fitted to the time-series decreases in Trachurus japonicus eDNA concentrations for all treatment levels. Moreover, eDNA decay rates significantly varied depending on temperature, fish biomass density, and genetic region, though only at the initial rapid phase. These results indicate the importance of microbial and enzymatic degradation of eDNA particles at the initial rapid phase. None of the variables significantly affected eDNA decay rates at the subsequent slower phase, which implies that microbial and enzymatic effect on eDNA degradation may be weakened during the decay phase. Further elucidating the effects of other environmental parameters (e.g., pH, dissolved oxygen, and UV level) on the biphasic eDNA degradation process would be helpful for a more precise understanding of the fate of eDNA considering its various states in water.