Background
The growth of citizen science data collection represents an underutilised resource for the early detection of marine species range extensions (i.e., expansion of species' distributions at the poleward edge). We present a framework for the systematic assessment of evidence for marine species range extensions around Australia from observations collected by different citizen science programmes.
Methods
Observations of 200 marine species on a preregistered target list from around Australia recorded from 2013–2022 were sourced from Redmap Australia, iNaturalist, and Reef Life Survey databases. We assessed the likelihood that each species underwent range extension using a decision-tree informed by citizen science observations and species traits.
Results
In total, 73 species (39%) were observed out-of-range, comprising 76 range extensions along different coastlines. Twenty-five range extensions were assessed as high confidence, five with medium confidence, and 46 with low confidence. Range extensions were concentrated in Australia's southwest (Western Australia) and southeast (New South Wales and Tasmania). The mean and maximum extent of range extensions were 318 km and 1250 km, respectively. Most (91%) range extensions identified were not previously described in the scientific literature from other data.
Conclusion
This assessment demonstrate that opportunistic citizen science monitoring can provide early detection of marine species range extensions at the continental scale. The results of this assessment are synthesised in two community engagement resources (state report cards and a national poster) and support an educational card game that utilises ‘species-on-the-move’ to communicate climate change impacts in marine systems.