🧬 eDNA
Every organism — from a blue whale to a bacterium — sheds biological material into its environment continuously: skin cells, faeces, mucus, urine, hair, pollen, and decomposing remains, all containing DNA. Environmental DNA (eDNA) — the detection and analysis of this shed genetic material from environmental samples — is transforming biodiversity monitoring in ways that would have been inconceivable two decades ago. By collecting a sample of water, soil, or air and sequencing the DNA it contains, ecologists can now detect the presence of species that passed through an area hours or days ago, identify entire communities of organisms from a single sample, and monitor biodiversity continuously at remote or inaccessible locations.
of water sufficient for eDNA species detection
persistence of fish eDNA in river water
species identified from single eDNA sample
detection accuracy for target species eDNA
eDNA methods were first applied systematically in aquatic systems, where they have proven especially powerful. The detection of Asian carp eDNA in the Great Lakes — before any individual fish had been physically caught — demonstrated that eDNA could provide early warning of invasive species presence, potentially allowing prevention of establishment before it occurred. The technique has since been applied to detecting endangered species: great crested newts in UK ponds, European sturgeon in rivers, freshwater mussels in upland streams, and whale sharks in open ocean. In most cases, eDNA detection is more sensitive than conventional surveys — detecting species presence at lower densities and from fewer sample visits — while also being less invasive (no capture, handling, or disturbance of target animals).
The most recent frontier in eDNA research is airborne eDNA — biological particles suspended in the air that can be collected and sequenced to identify organisms present in terrestrial environments. Studies conducted in zoos have demonstrated that airborne eDNA sampled from the vicinity of animal enclosures can accurately identify the species present, even species housed in nearby but separated enclosures. Field applications are expanding rapidly: a study in Denmark used airborne eDNA to detect species from the surrounding forest and agricultural landscape, identifying dozens of vertebrate and invertebrate species from air samples collected at a single location. The prospect of monitoring terrestrial biodiversity from airborne eDNA samples — potentially collected by drones over remote habitats — is generating enormous scientific excitement.
The application of environmental DNA (eDNA) analysis to freshwater systems has been particularly transformative, enabling the detection of fish, amphibian, invertebrate, and plant species from water samples collected without any direct observation of the organisms. In rivers, eDNA from upstream organisms is transported downstream in a detectably degrading signal, allowing surveys of entire river catchments from sampling points at the downstream end. Applications range from the early detection of invasive species (American signal crayfish eDNA was detected in UK rivers weeks before visual surveys confirmed their presence), to non-invasive monitoring of critically endangered species (great crested newt eDNA surveys are now standard practice in UK planning assessments), to the detection of rare species in remote locations where conventional survey effort would be prohibitive. The technique's sensitivity is remarkable — great white shark DNA has been detected in seawater at concentrations equivalent to one shark per 250,000 litres of water — and ongoing developments in longer-read sequencing and droplet digital PCR are further increasing the precision of species detection and abundance estimation from environmental samples.
The standardisation of eDNA methods — including agreed protocols for sample collection, filtration, extraction, and amplification that minimise contamination and maximise comparability between surveys — is an ongoing collaborative effort involving taxonomists, molecular biologists, statisticians, and field ecologists whose combined expertise is essential for translating a technically impressive methodology into a robust, repeatable monitoring tool with well-characterised error rates and detection probabilities.
Environmental DNA (eDNA) metabarcoding — the amplification and sequencing of DNA fragments from environmental samples (water, soil, air) to detect the species that contributed them — has transformed biodiversity assessment over the past decade. A single litre of river water, filtered to collect DNA fragments shed by the organisms that live in or pass through the water, can be analysed to detect hundreds of species of fish, amphibians, invertebrates, plants, fungi, and bacteria — providing a comprehensive biodiversity inventory that would take months of traditional survey effort to compile. The technique has been applied to marine waters to track whale migration routes from the DNA they leave in the water column; to soil samples to characterise the extraordinary diversity of soil invertebrate communities; to cave waters to detect the presence of cryptic species that rarely surface; and to sediment cores to reconstruct the historical composition of plant and animal communities stretching back centuries or millennia. The sensitivity of eDNA methods continues to improve, with some studies detecting species from single individuals in large water bodies — a capability that has transformed early warning systems for aquatic invasive species detection.
Conservation science methods delivered to your inbox.
✅ Subscribed!
Dr. Al-Rashid has conducted field research across the Arabian Peninsula, East Africa, and Southeast Asia for 13 years. Her expertise spans biodiversity survey methods, camera trap ecology, and the use of remote sensing in conservation biology.