Environmental DNA (eDNA) for early warning of crown-of-thorns outbreaks: Genetic detection of larvae and post-settlement individuals at extremely low densities

Innovative early warning tools are required for timely intervention of current crown-of-thorns seastar (COTS) outbreak spread and future outbreaks. We have developed environmental DNA (eDNA) methods that allow us to a) quantify COTS larvae in plankton samples and, b) detect post-settlement COTS on reefs with sensitivity greatly surpassing traditional surveys.

COTS larval eDNA work has been supported by tourism operators and COTS Control Vessels with > 7000 samples collected since 2014. This dataset can now be employed to i) elucidate spawning times and patterns, ii) investigate larvae distribution and connectivity, iii) examine relationship between COTS larvae and water quality (e.g. ‘nutrient hypothesis of outbreaks’). In a monitoring context, detection of COTS larvae constitutes the earliest possible indicator for population build-up.

COTS post-settled eDNA work aims at identifying trace amounts of COTS eDNA in a small volume of seawater. We have demonstrated that COTS densities below those classified as ‘outbreaks’ can be detected and deviations from baseline (=population build-up) can be employed for early warning. In addition, we can detect exceedance of threshold levels with easy-to-use and fast methods.

We propose to integrate larval and post-settlement eDNA monitoring into a large-scale COTS monitoring program for early warning detection and to assist efficient COTS control.