Estimating transport and detectability of <i>Chironex fleckeri</i> environmental DNA in an open coastal bay

Environmental DNA (eDNA) has emerged as a powerful tool for species detection and monitoring; however, understanding its dispersion and transport dynamics and how this influences detectability is essential to enhance the accuracy of eDNA use. A biophysical model was used to investigate the spatiotemporal dispersion of Chironex fleckeri eDNA in an open coastal bay in northern Australia. The model revealed that local hydrodynamics, geomorphology and meteorological conditions shaped 'detection shadows', with eDNA detectability constrained from hundreds of metres to kilometres from seeding locations. These dispersion estimates are closely aligned with empirical detections of C. fleckeri medusae and polyps, demonstrating the utility of biophysical models for estimating eDNA transport and dispersal dynamics. The findings highlight the influence of eDNA decay and dilution on detectability and provide valuable insights for interpreting detections of targeted taxa. Here, we demonstrate the broader potential of combining biophysical modelling with eDNA sampling.