What is Environmental DNA
Environmental DNA, or eDNA, is genetic material left behind by living organisms in their surroundings. When fish, whales, or other sea creatures move through water, they shed tiny pieces of DNA through their skin, scales, mucus, and waste. This DNA floats in the water and can be collected by scientists using special filters. Unlike catching and studying actual animals, eDNA sampling is non-invasive and does not harm wildlife.
How eDNA Persists in Seawater
eDNA does not just float alone in seawater. Instead, it quickly binds to particles like sediment grains, plankton, and organic matter. These particles act like protective shields, keeping the DNA safe from ultraviolet light from the sun and from bacteria that would otherwise break it down. The salt in seawater also plays a role, as it helps stabilize the DNA molecules and slows degradation compared to freshwater environments.
How Long eDNA Lasts
In typical ocean conditions, eDNA remains detectable for about 7 to 21 days. However, this timeframe varies based on several factors. Warmer water temperatures cause faster bacterial growth, which degrades eDNA more quickly. Colder ocean regions may preserve eDNA longer. Water depth, salinity, and the presence of enzymes that break down DNA also influence how long eDNA survives in a specific location.
Scientific Applications
Marine scientists use eDNA sampling to monitor which fish species live in specific ocean areas without needing to catch or harm them. By filtering seawater and analyzing the DNA found in it, researchers can create a detailed picture of underwater biodiversity. This technique is especially valuable for tracking endangered species, monitoring invasive species, and studying fish populations in remote or deep-sea locations where traditional surveying methods are difficult or impossible.
Factors Affecting eDNA Persistence
Multiple environmental conditions determine how long eDNA stays intact in seawater. Temperature is the most significant factor, with warm water shortening persistence time. Light exposure, oxygen levels, and the activity of microorganisms all contribute to eDNA breakdown. Additionally, the type of organism matters, as DNA from some species may degrade faster than others. Understanding these factors helps scientists plan their sampling strategies and interpret their results accurately. 
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