Non-native gastropods in high elevation horticultural facilities in Hawaii: a threat to native biodiversity

To preserve native floras and faunas of tropical oceanic islands, it is critical to limit the establishment of terrestrial non-native gastropods (i.e. snails, including slugs), particularly those from temperate regions, as they can become abundant in high elevation areas, often the last refuges of native species. In Hawaii, the horticultural trade has been associated with many introductions, but threats posed by nurseries at high elevations have not been assessed. To examine these potential threats, we surveyed gastropods in 21 high elevation (>500m) horticultural/agricultural facilities on three Hawaiian Islands (Oahu, Maui and Hawaii) and compared these surveys to 31 previous low elevation nursery surveys (<500m) on the same islands. High elevation nurseries harbored distinct non-native gastropod assemblages, which were composed primarily of species from temperate regions. Gastropods from temperate regions had larger elevation ranges in nurseries than those from tropical areas. Our results highlight that nurseries, particularly those at higher elevations, represent key sources for establishment of temperate gastropods, a critical threat to the remaining Hawaiian biodiversity. We also found that high elevation nurseries on Maui and Hawaii supported non-native species not found in Oahu nurseries, indicating that Oahu may not be the only source of introductions into high elevation nurseries. We hope these results will spur active control of non-native gastropods in nurseries, particularly those at higher elevations, to potentially prevent further ecological damage to the already imperiled Hawaiian flora and fauna.