Go with the flow: integrating hydraulic models with eDNA based species detection

Biodiversity estimates of fish communities for environmental monitoring and research have traditionally been obtained with survey methods, which are invasive, selective, expensive, and may be highly affected by weather and hydrodynamic constraints. Recent advances in molecular methods now provide the opportunity to generate biodiversity data on an unprecedented scale through DNA-barcoding organisms from environmental (water/sediment) samples (eDNA). eDNA sampling is a non-selective approach that enables reconstruction of entire biological communities in a cost-effective, non-invasive manner. Evidence from recent independent studies now shows that eDNA based methods provide higher probabilities for detecting fish species than traditional methods, and under certain circumstance indicate the relative abundance of species within a community. Such methods are already used by DEFRA to monitor lake fish communities, based on research developed at the University of Hull.

Aquatic eDNA degrades rapidly, with a half-life of 12-24 hours, and therefore in the absence of strong currents there is limited dispersal. Hence there is a relatively straightforward relationship between eDNA and fish distribution in lentic environments, such as lakes, ponds or reservoirs. However, in hydrologically dynamic environments such as rivers, estuaries and marine habitats the spatial interpretation of eDNA is complicated by advection by the flow, which also may change depending on location within the water column. Thus environmental flows may limit the spatial resolution of eDNA surveys and currently preclude quantitative reconstruction of local fish communities. Although the nature of eDNA is not fully understood it is believed that it is largely bound to sediment particles and organic matter. Therefore, a step change in environmental monitoring capability will be achieved by coupling hydraulic sediment transport models with probabilistic models of eDNA decay.