Field trials confirm that the presence and concentration of Crown of Thorns Starfish (CoTS) on any coral reef can be determined from environmental DNA (eDNA) extracted from a small sample of local seawater.
This is a very promising advance. Until now the only way to obtain early indication of the next mass outbreak has been by visual underwater monitoring (i.e. by diving on the reefs and counting individual CoTS – highly impractical and labour-intensive over an area the size of the GBR).
The research team was led by Dr Sven Uthicke (AIMS). The full report is available here. It acknowledges the support provided by the Lizard Island Research Station and two grants from The Ian Potter Foundation. See also AIMS media release.
The team developed a “digital droplet” PCR (ddPCR) method for detecting CoTS eDNA and estimating population density. These terms require brief explanation for the rest of us.
PCR stands for Polymerase Chain Reaction. It is a technique used to “amplify” (i.e. make multiple identical copies) of trace amounts of DNA located in or on almost any liquid or surface where DNA strands may be present.
eDNA is DNA taken from environmental samples, such as a 2 litre sample of sea water. In a marine context, it refers to microscopic (cellular) DNA that species have shed in their contact with the water. High throughput sequencing (HTS) technologies enable scientists to efficiently “read” such DNA to determine what species have been in contact with the sample and estimate their population densities. However, this is only possible if the distinctive characteristics of each species’ DNA is known and can be matched with that extracted from the sample. See Ichthyology, eDNA and barcoding.
Early detection is of course merely the starting point in the quest to contain future CoTS outbreaks. Advances in CoTS science and remaining knowledge gaps are detailed in Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016), a review undertaken by Professor Pratchett and other scientists. Five of the contributors received funding from The Ian Potter Foundation through LIRRF. See Closing CoTS knowledge gaps