Optimising the detection of invasive marine species using environmental DNA

Increased travel and trade have facilitated movement of non-indigenous species around the world. Environmental DNA (eDNA) is a rapid and sensitive approach for detecting the presence of invasive species, however, sampling needs to be optimised to increase detection probability. The aim of the study was to determine the optimum eDNA filtering parameters for the detection of two marine invasive species by determining: i) the size fraction the eDNA signal is most strongly associated with; ii) whether the optimal particle size for eDNA detection varies between a marine plant and marine animal; and iii) whether eDNA particle size distribution changes over time. Water samples from laboratory-controlled experiments and from established populations of two taxonomically distinct invasive species (Asterias amurensis and Undaria pinnatifida), were sequentially filtered through a series of descending filter pore sizes. Subsamples were taken over four time points (0, 24, 48 and 72 hours after specimen removal) to assess how eDNA particle size changed over time. DNA was quantified using species-specific quantitative polymerase chain reaction (qPCR) to determine the concentration of DNA captured in each size fraction. The strongest DNA signal was consistently captured on the 8 ?m and 1.2 ?m filters for both species and across all time points. These findings suggest eDNA particles shed by these species predominantly take the form of cellular debris (> 8 ?m) and individual mitochondria captured by the 1.2 ?m filter. Targeting A. amurensis and U. pinnatifida using these pore sizes will capture the majority of the eDNA as well as increase the volume of water that can be sampled, thus increasing sensitivity and the probability of detection.<p></p>