Water sampling and eDNA preservation
In the field, seawater was collected in sterile 2 L plastic bottles based on volumes used in previous studies in our lab and other studies on the detection of rare and invasive species (Robson et al.2016; Simpfendorfer et al. 2016; Uthicke et al. 2018). For all field experiments, prior to sampling, all equipment was soaked in 10% bleach for 2 hr and then rinsed with reagent-grade water (x3) to eliminate the risk of contaminants. Equipment controls, where 500 mL of sterilised water was passed through the water pump and filters before placed into Longmire’s solution, were taken before sampling at each of the sites to detect for possible cross contamination of equipment.
Environmental DNA was extracted from sea water samples using a workflow process (Preserve, Precipitate, Lyse, Precipitate, Purify (PPLPP)), Edmunds and Burrows, (unpublished) (Appendix S3, Supporting information). Once precipitated through the PPLPP process, DNA was purified using the Zymo One Step PCR Inhibitor Removal Kit (Irvine, California, USA).