Invasive species are one of the biggest dangers to island environments because they can quickly upset the natural balance. Many islands have plants and animals that exist nowhere else in the world, and these native species often don’t have a natural defense against new predators, pests, or diseases. When invasive species arrive, they can spread rapidly, crowding out or even wiping out native species, damaging coral reefs, forests, and coastlines, and putting the entire ecosystem at risk.
These threats don’t just affect nature—they also impact people. Invasive species can harm farming, fishing, and tourism, which are vital to island communities. They can also threaten cultural traditions and the natural resources that local people depend on. Protecting islands from invasive species means working together as a community to prevent new introductions, act quickly when new species are found, and take care of the land and sea that sustain both wildlife and people.
The USVI has a long history of human-mediated species introductions, dating back to the arrival of the first human colonizers who brought plants and animals up the Antillean island chain from South America. These introductions have increased with the intensification of travel and trade. The pathways of introduction vary depending on the species; many species are intentionally imported for agriculture, domestic use, or for horticulture, posing the risk of potential release or escape (Lovell et al. 2006, Daley et al. 2012, Platenberg 2016). Many important agriculture species fall into this category, such as Papaya (Carica papaya) and Genip (Meliccoccus bijugatus), as well as deer, donkeys, goats, and pigs. Houseplants and ornamentals can be culprits, such as the Snake Plant (Sanseveria spp.). Significant threats to wildlife populations are posed by escaped housepets that become feral, such as cats, dogs, and more recently Boa constrictors on St. Croix. Some species are accidentally introduced as hitchhikers through the importation of materials, e.g., rats (Rattus spp.), the Pacific Lionfish (Pterois spp.), Cuban Treefrogs (Osteopilus septentrionalis), and Puerto Rican Coquis (Eleutherodactylus coqui). Others are introduced intentionally as biocontrol for species that were unintentionally introduced, thereby compounding the problem. Two key examples in the USVI of these are the Small Indian Mongoose (Herpestes auropunctatus) that was deliberately introduced to control rats, and Cane Toads (Rhinella marina) that were released as a biocontrol for white grub (beetle larvae) agricultural pests.
Virtually all of the habitats in the U.S. Virgin Islands are affected either directly, or indirectly by invasive species. Non-native plants can alter habitat and prevent recruitment of native forest species. Problematic species include Mother-in-law Tongue (Sanseveria trifasciata), Tan-tan (Leucaena leucocephala), Chinaberry (Melia azedarach), and Sweetlime (Triphasia trifolia). Water Hyacinth (Eichhornia crassipes) is a problem in wetlands and waterways where it chokes up the water surface and consumes nutrient resources. Feral cats, rats, mongoose, and to a lesser extent stray dogs, have a tremendous negative impact on native species through direct predation. Nesting success of seabirds and sea turtles can be severely reduced by rats in seabird colonies and mongoose on turtle nesting beaches. Cats are well known for their strong prey response and will capture and kill anything they encounter, including birds and the endangered VI Tree Boa.
Other problematic terrestrial vertebrates include White-tailed Deer (Odocoileus virginianus), goats (Capra hircus), hogs (Sus scrofa), and donkeys (Equus asinus) that destroy native vegetation through eating, trampling, or excavating, thus changing habitat structure. Feral chickens (Gallus gallus domesticus) can change forest structure by removing seeds and seedlings. Cane Toads (Rhinella marina) and the Common Ground lizard (Ameiva exsul; native to STT/STJ, but introduced to STX) consume native species of frogs, lizards and invertebrates (Treglia et al. 2013). Less understood are the invertebrate pests, many of which arrive with landscaping or horticulture material. Fire ants (Solenopsis spp) are a significant threat to ground nesting birds and small terrestrial reptiles, as these can quickly overwhelm and consume pipping eggs, chicks, and lizards. The Agave Weevil produced near complete mortality of one of the endemic Century Plants (Agave missionum), and Tiger Mosquitos (Aedes aegypti) are responsible for transmitting viral diseases to humans, such as dengue fever, chikungunya, and zika. The marine environment is similarly affected by invasive species. The invasive seagrass, Halophila stipulacea, has rapidly altered seagrass bed structure thus limiting shelter and forage for seagrass inhabitants, including Nassau Grouper and Green Sea Turtles. The Indo-Pacific Lionfish (Pterois spp) poses a great threat to fish stocks in the USVI due to its ability to consume large portions of food relative to its body weight and reproduce rapidly and in great numbers.
The ‘Invasive Species Virgin Islands’ site (http://invasives.vi.gov) is an ongoing inter-agency program documenting and managing alien species in the territory. It provides the species inventory, management protocols, and reporting frameworks that feed directly into our SWAP’s invasive species action plans. By linking to it, we align SWAP actions with established local management efforts.