Environmental DNA, or eDNA, refers to all the tiny traces of genetic material that is left behind as living things pass through water or soil.

In your backyard, local stream or boggy field lurks a secret web of co-conspirators. Largely unseen, they slink and swoosh, creep and crawl, helping each other to survive. Sometimes there are many, sometimes there are few. How do we know this? They leave their DNA behind.

From kērēru to kōwhai, and the leaves in the wind, all living things shed genetic information into their local environment. This is called environmental DNA, or eDNA.

For example, a bird flies over a lake and drops a feather. Under the surface, a fish swims around and, if it is unlucky, gets gobbled up by bigger fish. Likewise, an insect may fall into the lake, and leaves fall from trees. These plants and animals leave behind ‘genetic breadcrumbs’ (such as skin cells and faeces) in the environments they live in.

 

"In one drop of water are found all the secrets of the ocean." 

Poet and philosopher, Kahlil Gibran 

We get a picture of plants and animals

By collecting up discarded DNA and sequencing it, we can get a picture of the plants and animals in a local area.

Once it is shed into the water, eDNA sticks around for a few hours to a few days. The time depends on whether it is in freshwater, marine water, stagnant water, and so on. Other material that’s in the environment can also break eDNA down.

We can survey the environment quickly

Environmental DNA is a new and powerful tool, and can be a way to scan environments quickly to detect change.

In some applications, eDNA may eventually replace some current survey methods, such as visual counts, netting, and electrofishing. It has the advantages of being non-destructive and doesn’t require animal capture.

There can be limitations

Environmental DNA can’t tell you how big a fish is, or the size of a population. A single water sample may pick up a large piece of skin or scale that contains a lot of DNA, leading you to believe there is a large population nearby, when really all of that DNA just came from one individual.