Optimising molecular strategies and sample types for marine biosecurity surveys

Once established, marine pests are difficult eradicate, therefore timely and accurate identification is key. Molecular tools such as environmental DNA (eDNA) are increasingly used in marine biosecurity surveillance, particularly in ports and harbours where visual surveys are difficult to conduct. However, challenges remain in ensuring these tools are cost-effective and accurate. This study aimed to optimise molecular strategies for marine pest surveys by: A) comparing the performance of different sample types (water, settlement plates, and plankton tows) in detecting taxa and B) assessing if pooling samples influences dections. Water samples detected the greatest number of unique taxa (319 − 1422), followed by settlement plates (126–208) and plankton tows (59–89). Surprisingly there was little overlap in the taxa detected across the different methods (0.7–4.6%). Five introduced species were detected. The pooling of settlement plate samples by homogenising before DNA extraction was inefficient with 50–72% fewer taxa detected compared to individual samples. However, when the settlement plate samples were pooled by soaking the plate and filtering the water, similar levels of richness were observed compared to individual plates (53 and 44, respectively). Freezing of settlement plates prior to soaking saw a significant increase in the number of taxa (88). This study demonstrates that different sample types detect distinct communities with water samples detecting the greatest number of taxa overall. Freezing settlement plates prior to soaking increased the diversity detected from these samples. Together, these findings provide guidance for designing more efficient molecular biosecurity surveys, supporting timely and accurate detections.