Detecting Petalura gigantea: Novel eDNA Method and Water Balance Modelling Insights Enable Improved Catchment Management and Conservation Outcomes

Abstract

Petalura gigantea, commonly known as the giant dragonfly, has long-lived fossorial larvae that are dependent on high water tables in peat swamps (mires) within its range in south-east Australia. It is an endangered species and is recognised as an appropriate umbrella species for the conservation of its upland swamp habitats. Detection of P. gigantea traditionally involves systematic exuviae surveys or line transect surveys for adults during the flying season from October to February. To address the limitations of these survey methods, we developed an environmental DNA (eDNA) assay to detect the species in swamp discharges. The eDNA quantitative polymerase chain reaction (qPCR) assay was successful in detecting a known population of P. gigantea and indicated the presence of larval populations in two swamps, one where traditional surveys had failed to detect the species. We used swamp water balance models, calibrated to three swamps, to inform the applicability of the eDNA detection method and to explore how catchment characteristics influence habitat suitability. Incorporating these hydrological considerations with basic climatic data enhances the reliability of eDNA detection. This approach, when combined with traditional survey techniques, supports improved conservation outcomes for this species and its endangered, groundwater-dependent, peat swamp communities. Developing eDNA assays for other peatland-dependent species globally could facilitate broader biodiversity assessments and bolster conservation of these sensitive habitats.