2.2.6 eDNA surveying

Probably not relevant for Palau at this point.

There is an increasing demand for rapid biodiversity assessment tools that have a broad taxonomic coverage. The assessment of DNA obtained from environmental samples, or ‘‘environmental DNA’’ (eDNA), has shown great promise as a non-invasive method for monitoring terrestrial biodiversity. With only trace amounts of DNA needed to identify species, the data obtained can strengthen biodiversity assessments through improving the detection and monitoring of rare, cryptic, or protected species, increasing the taxonomic resolution of biodiversity surveys, allowing for increased sampling of inhospitable or challenging environments to survey, and aiding in the early detection of invasive species.

Within terrestrial systems careful consideration of the targeted substrate/s is essential (water and soil are the most commonly used substrates) because each type will likely sample different components of the biodiversity, depending on how the species are interacting with that specific substrate.

After DNA has been deposited in the environment, it starts degrading, but the rate at which this occurs differs between sample types and environmental conditions. The variability in DNA degradation rates influences the effectiveness of a sample type as a successful agent for eDNA biomonitoring. For these reasons, new eDNA substrates are continually being explored, and eDNA-based biomonitoring using water, soil, ingested or invertebrate-derived DNA (iDNA) are now common. Recently, the detection of species through airborne DNA has also been trialled to detect vertebrate taxa, using air samplers and spiders’ webs.60

To date, eDNA has been largely untested for detection of seabirds, especially those species in scattered and small populations, in remote locations. For example, it has been found that terrestrial birds and seabirds don’t tend to show up very reliably in the aquatic eDNA samples (for example), due to their minimal inputs of faecal matter and other DNA into fresh water sources.

However, one study in Australia’s subantarctic, on Macquarie Island, an island with known major seabird provenance, detected several uncommon species amongst the more common species. In that case, discarded feathers and faeces provided high quality DNA for species identification, assisting in detection of new species arrivals and new breeding sites.61