Imagine being able to detect the presence of an animal, plant, bacteria, or just about any organism of interest in the air, water, or on land just because the organism left behind trace amounts of its nuclear or mitochondrial DNA in its mucus, excrement, tissue, or when it dies. This discarded genetic material in an organism’s surroundings is called environmental DNA (eDNA). The term also refers to the molecular biology tool.

eDNA has many synonyms. It is considered a similar molecular identification tool as DNA barcoding, which uses 650 base pair sequence of the mitochondria DNA cytochrome c oxidase subunit I (mtDNA COI). The main difference is that eDNA fragments are even smaller, about 100 base pairs or less. These similarities are why eDNA detection is also known as minibarcode detection. DNA barcoding is for detecting a single species whereas metabarcoding allows for the detection of all species in a community. eDNA was also known as microbial DNA, used back in the 1980s to detect bacterial communities in marine sediments. Whatever the name, its growing popularity across many fields of study is a testament to its usefulness.

Since our eDNA training platform is on the Rusty crayfish (freshwater) and our collaborator from Universiti Malaysia Terengganu (UMT) studies the Crocea clam (marine), we pay attention to the degree that eDNA persists in these two different ecosystems and amend our protocol accordingly. eDNA in freshwater systems is typically distributed homogenously whereas in marine systems, eDNA is diluted and dispersed due to the immense volume of the sea, tides, and currents. Warmer temperatures and increased UV radiation at sea level are known to degrade DNA, factors to be considered when sampling in tropical marine waters.

All things considered, eDNA is a tool that is reliable and can be done non-invasively, which is great if the organism you are after is shy, hard to find, dangerous, rare, endangered, or all of that. In some cases, eDNA has also detected the extinct wooly mammoth in ancient soil! Hence, our excitement with this tool as it lends itself to frequent monitoring and involvement of citizen scientists.