A long way from home: Biosecurity lessons learnt from the impact of La Niña on the transportation and establishment of tropical portunid species

Marine ecosystems can be modified and shaped by irregular interannual variations in oceanic current patterns and temperatures, such as El Nino and La Nina. These large scale oceanic events have also been shown to influence environmental stressors such as invasive marine species (IMS). Our study indicates that there is a causative link between these climatic events, and atypical detections of native and IMS. Significant La Nina events between 1970 and 2014 were associated with sightings of tropical crab species in temperate waters following a lag period of 18–24 months from the onset of the event. We identified a total of 72 records of six tropical portunid crabs species (from both Charybdis and Scylla) in temperate waters of south-western Australia following these La Nina events, based on reports in published scientific literature, grey literature and museum records, as well as citizen science networks such as FishWatch and PestWatch apps. We suggest that La Nina conditions facilitated transportation and temporary establishment of crab larvae from their native tropical habitat to temperate regions. As the strength of La Nina events is likely to increase into the future due to the escalating effects of climate change, it is likely that there will be a growth in associated atypical establishment events of IMS. Consequently, biosecurity managers will need to reprioritise resources in order to accommodate the potential impacts of these large scale oceanic events as part of their surveillance programmes.