Invasive Pomacea snails: actual and potential environmental impacts and their underlying mechanisms.
Apple snails are large freshwater snails belonging to the family Ampullariidae that inhabit tropical to temperate areas. The South American apple snails Pomacea canaliculata and Pomacea maculata have been introduced to other continents where they have successfully established and spread. Our review aims to analyse the mechanisms of the impacts that these invasive Pomacea provoke or may provoke. Nine basic mechanisms were identified: grazing/herbivory/browsing, competition, predation, disease transmission, hybridisation with native species, poisoning/toxicity, interaction with other invasive species, promotion of collateral damage of control methods on non-target; species and when acting as prey. The most important impacts are those related to their grazing on aquatic macrophytes, algae and rice and their competition and predation on other aquatic animals, mostly macroinvertebrates, including other apple snails. Invasive Pomacea are also responsible for outbreaks of an emergent parasitic disease (human eosinophilic meningitis). Their great abundance in invaded areas, their bioaccumulation of pollutants and their natural toxicity may impact on their predators and on trophic webs through apparent competition, trophic cascades and biomagnification. The biota from man-managed and natural wetlands may be unintentionally affected by mechanical, chemical and biological control against invasive Pomacea. Their capacity to hybridize may affect the distinctiveness and ecological traits of native Pomacea in invaded regions of America. Established populations of these invaders may either facilitate or resist the establishment of other exotic species. Field surveys and more realistic experimental approaches with multiple interacting species are needed to better understand the environmental impacts of invasive Pomacea and their underlying mechanisms.