Hydrodynamics of passive environmental DNA (eDNA) detection

Passive detection of environmental DNA (eDNA) in aquatic environments is a promising, low-cost alternative biomonitoring tool for studies of species abundance and distribution in the ocean. The effectiveness of passive detection depends on the interplay between the fluid transport (advection and diffusion), the state (particulate vs. dissolved) and fate (shedding, decay, and settling rates) of the eDNA molecules, and the sampling protocol (filter type, position, submergence times, etc.). A simplified numerical model of the passive detection process was developed to simulate the time-dependent eDNA concentration at the surface of porous membrane filters of varying geometry, orientation, and translational speed in the water. The predictions of the numerical model were tested in controlled laboratory experiments using known concentrations of eDNA collected from 2 different invertebrates and 1 vertebrate. In addition to studying purely diffusive detection of eDNA by stationary samplers, the effect of flow advection was studied with a combination of translating samplers in quiescent flow and stationary samplers exposed to uniform flow. Understanding the mechanisms that control the transport and retention of eDNA on passive samplers will be critical for designing future sampling protocols and subsequently relating detected eDNA to species presence in space and time.