Invasion Pathways for Invasive Aquatic Species: Case Studies from Florida

Florida’s tropical climate provides a hospitable environment to tourists and exotic species alike because air temperatures rarely dip below freezing for extended periods of time. Bodies of water in Florida are among the most highly invaded aquatic systems in the world owing to their ability to serve as incubators for a wide range of introduced aquatic species. An important issue that is rarely explored is how these invaders reach Florida in the first place. Vectors or introduction pathways for exotic aquatic species are many and diverse; although some non-native species are introduced via natural phenomena such as extreme weather events or movement of fauna, many invaders arrive as a result of anthropogenic actions. To compound the situation, isolated introductions can quickly expand to widespread invasions because the majority of waters in Florida are interconnected. In this paper, I will outline the events that led to the introduction to Florida of several historically problematic aquatic species, including waterhyacinth (Eichhornia crassipes) and hydrilla (Hydrilla verticillata). I will also discuss the likely introduction pathways responsible for a number of new invaders, including feathered mosquitofern (Azolla pinnata), giant salvinia or kariba-weed (Salvinia molesta), rotala (Rotala rotundifolia), redroot floater (Phyllanthus fluitans), crested floatingheart (Nymphoides cristata) and tropical American watergrass (Luziola subintegra). A number of these exotic species are federally listed noxious weeds, which in theory should virtually eliminate their movement and introduction, at least by anthropogenic means. In practice, new invaders are routinely discovered in Florida; despite existing legislative prohibitions of their importation and distribution, their presence is often attributed to intentional or accidental introduction by water garden, aquarium or fish pond owners. It is therefore clear that the most effective strategy to reduce the introduction and spread of invasive aquatic species is through diligent monitoring of waters and increased public awareness of the environmental damage caused by non-native aquatic invasive species.