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1. eDNA-based methods represent non-invasive and cost-effective approaches for species monitoring and their application as a conservation tool has rapidly increased within the last decade. Currently, they are primarily used to determine the presence/absence of invasive, endangered or commercially important species, but they also hold potential to contribute to an improved understanding of the ecological interactions that drive species distribution. However, this next step of eDNA-based applications requires a thorough method development.2. We developed an eDNA assay for the white-clawed crayfish (Austropotamobius pallipes), a flagship species of conservation in the UK. Multiple subsequent in-situ and ex-situ validation tests aimed at improving method performance allowed us to apply eDNA-based surveys to evaluate interactions between white-clawed crayfish, crayfish plague and invasive signal crayfish.3. The assay performed well in terms of specificity (no detection of non-target DNA) and sensitivity, which was higher than more established traditional species survey methods. Quantification of species biomass was, however, less reliable. 4. Comparison of eDNA sampling methods (precipitation vs. various filtration approaches) revealed that optimal sampling method differed across environments and might depend on inhibitor concentrations. 5. Finally, we applied our methodology together with established assays for crayfish plague and the invasive signal crayfish and demonstrated their significant interactions in a UK river system. 6. Our analysis highlights the importance of thorough methodological development of eDNA-based assays. Only a critical evaluation of methodological strengths and weaknesses will allow us to capitalise on the full potential of eDNA-based methods and use them as decision support tools in environmental monitoring and conservation practices..

In response to the global decline of the White‐clawed crayfish Austropotamobius pallipes, key conservation strategies have been developed in the United Kingdom and Ireland, including the supplementation of existing populations and establishment of new populations, using captive‐breeding methods and/or translocations. The South West Crayfish Partnership (SWCP), a group of UK‐based conservation organizations, oversees population‐enhancement programmes in south‐west England. Since 2006 the SWCP has established 16 ark sites (safe refuges) and conducted one river supplementation. In total, 17 sites have been stocked with over 5000 translocated and captive‐hatched A. pallipes, increasing the number of discrete in situ populations in the region by at least 75%. A similar programme in southern Wales, led by Natural Resources Wales, has restocked three river catchments and one English still‐water site with a total of over 4700 captive‐reared juvenile A. pallipes. Although many of these ark sites are newly established, preliminary monitoring results are encouraging; at least 75% of ark sites in south‐west England are currently viable and the three Welsh sites that have been monitored so far suggest continued presence of White‐clawed crayfish.

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Time-of-flight spectra of the nascent H atoms, and laser induced fluorescence excitation spectra of the nascent NH 2 radicals, are leading to a very complete knowledge of the energy disposal following photodissociation of NH 3 through its A 1 A 2 excited state. Both the dissociation rates and the product distributions are sensitive to the values of the vibrational and rotational quantum numbers of the quasi-bound levels of the parent molecule. The most populated fragment states involve the a-axis rotational, and bending vibrational, motions of the NH2 with modest excitation of further rotational degrees of freedom at low internal energy. For most NH 2 internal states the accompanying H atoms recoil close to the initial plane of NH 3 excitation, but for a specific subset of product states the H atoms recoil perpendicular to this plane. These measurements and their interpretation give a detailed insight into the intramolecular motion of the dissociating NH3 molecule, which is dynamically controlled but yet involves most of the internal degrees of freedom.