# Beyond Exponential Decay: How Biphasic and Delayed Decay Dynamics Shape Marine eDNA Dispersal

## TL;DR

This study shows that marine eDNA dispersal is better understood using biphasic or delayed decay models instead of the commonly assumed exponential decay, which can lead to inaccurate estimates.

## Contribution

The paper introduces a multiprong approach combining literature review, experiments, and modeling to demonstrate the impact of biphasic and delayed eDNA decay dynamics on dispersal.

## Key findings

- Biphasic or delayed decay patterns were observed in over half of the reviewed studies and in experiments at 13°C and 20°C.
- Alternative decay dynamics increased eDNA concentrations by two to four times after 24 hours compared to exponential decay.
- Using exponential decay models can lead to under- or overestimation of eDNA release depending on local hydrodynamics.

## Abstract

Accurate interpretation of marine environmental DNA (eDNA) monitoring surveys depends on understanding how eDNA concentrations change once released by organisms into the surrounding environment. Despite growing evidence for multiple eDNA decay patterns, such as biphasic and delayed decay, many studies assume by default a single‐phase exponential decay model. Here, we took a multiprong approach with a literature review of eDNA decay experiments, an experimental study of empirical decay patterns, and high‐resolution Lagrangian particle tracking to quantify how different decay patterns drive eDNA dispersal at two contrasted locations in the Bay of Biscay, Northeast Atlantic. Biphasic or delayed eDNA dynamic patterns were found in over half of the reviewed empirical studies and at 13°C and 20°C in our experiment, with the first 12 h being key to detecting biphasic or delayed decay dynamics. Compared to single‐phase exponential decay, the alternative decay dynamics increased eDNA concentrations by about a factor of two to four after 24 h, depending on the decay pattern. Assuming an exponential decay may lead to under‐ or overestimation of the amount of eDNA released when the decay dynamics are actually biphasic or delayed, depending on local hydrodynamics. In conclusion, considering the appropriate eDNA decay type is critical for marine eDNA transport models and eDNA monitoring data interpretation.

We used a multiprong approach with a literature review of eDNA decay experiments, an experimental study of empirical decay patterns, and high‐resolution Lagrangian particle tracking to quantify how different decay patterns drive eDNA dispersal at two contrasted locations in the Bay of Biscay, Northeast Atlantic. Assuming an exponential decay may lead to under‐ or overestimation of the amount of eDNA released when the decay dynamics are actually biphasic or delayed, depending on local hydrodynamics.