Impacts of Alien Land Arthropods and Mollusks on Native Plants and Animals in Hawaii

Over 2,000 alien arthropod species and about 30 alien non-marine mollusks are established in the wild in Hawai'i, While the data are too meager to assess fully the impacts of any of these organisms on the native biota, the documentation suggests several areas of critical concern. Alien species feed directly on native plants or their products, thus competing with native herbivores and affecting host plants. Alien predators and parasites critically reduce the populations of many native species and seriously deplete the food resources of native predators. Some immigrant species spread diseases that infect elements of the native biota. Others are toxic to native predators. There is also competition for other resources, such as nesting and resting sites. Even apparently innocuous introduced species may provide food for alien predators, thus keeping predator populations high with an attendant greater impact on native prey. Control measures targeted at alien pests may be hazardous to natives. Mitigative measures must be based on sound research and firmer understanding of the complex interactions and dynamics of functioning ecosystems. Strict quarantine procedures are cost effective in preventing or delaying the establishment of potential pests. Strict control or fumigation is needed for nonessential importations (such as cow chips, Christmas trees, and flowers in bulk). Improved review of introductions for biological control is required in order to prevent repeating past mistakes. Biocontrol introductions must be used only for bona fide pests and used in native ecosystems only in special circumstances. Sufficient funds must be committed at the time of any intentional introduction for long-term monitoring of its efficacy and environmental impacts. Mitigation of other novel perturbations (e.g. land clearing, grazing, rooting by feral pigs (Sus scrofa), and invading weeds) that favor alien invertebrates will also lessen their impacts.