Abstract:
The world is becoming increasingly connected as human populations grow and international commerce changes. The movements of marine vessels create a complex global maritime network that is now the most significant pathway for the introduction and spread of invasive aquatic species (IAS) to coastal ecosystems around the world. Preventing establishment of marine IAS in new locations requires spatially explicit tools that can identify areas where incursions are likely to inform targeted surveillance and response strategies.
Focusing on the New Zealand seascape, we used network analysis to quantify the potential for the post-incursion dispersal of a new IAS through commercial and recreational vessel pathways. Networks were constructed using vessel movements from automated identification system signals, along with recreational boater surveys, and life history characteristics of the recently detected invasive green algae from the genus Caulerpa (C. brachypus and C. parvifolia). Using network and spatial modelling we (i) quantified the strength of vessel-mediated links from known established populations in New Zealand to the Northland region's coastline, (ii) Identified coastal sites in Northland where anchoring events of potentially infested vessels had occurred, highlighting likely points of introduction and (iii) integrated these into a priority list allowing management agencies to effectively allocate resources to limit further spread.
We found that over a one-year period more than 4,000 anchoring events originating from incursion sites occurred in the Northland region. From these anchoring data, we identified 13 sites that showed a high relative likelihood of incursion, with the outer Bay of Islands area experiencing the highest relative introduction pressure. In addition, our work suggests that invasive Caulerpa had frequent opportunities to be transferred long distances beyond Northland, and that individuals could potentially be transported in a viable state across the entire country.
Synthesis and applications: This study presents a transferable framework for prioritising surveillance and early detection efforts for IAS. By integrating spatial data on vessel movements with species traits, managers can identify sites with a high relative incursion likelihood and increase detection speed. The approach supports timely, cost-effective decision-making and can be adapted to biosecurity planning in diverse coastal regions worldwide.
