Island ecosystems are exceptionally fragile and easily disrupted by invasive species. These alien species have the ability to displace natives, change community structure, or alter ecological function. At Palmyra Atoll NWR, infiltrators have invaded refuge ecosystems and threaten the ecological integrity and biological diversity of the refuge.
Rats: Globally, rats have been implicated in 40 to 60 percent of recorded bird and reptile extinctions. At Palmyra, rats have had a pronounced negative impact to refuge habitats. Food abundance and favorable climate allow the rats to breed year round on Palmyra, producing a litter every month. The black rat (Rattus rattus) has proven to have a significant impact on the native flora and fauna of Palmyra. This introduced mammal is a predator to various species of nesting birds, land invertebrates, and plants, as well as a reservoir of disease and disperser of invasive plant seeds.
Plants: Over many years, humans have brought exotic and invasive plants to Palmyra Atoll. The known vascular flora of Palmyra Atoll NWR comprises 126 species. Only 25 are considered native, 48 are cultivated ornamentals or food plants, and the remaining 53 are not native and not fully established exotics.
Marine: Coral reefs face periodic stresses such as crown-of-thorns starfish (Acanthaster planci). This species preys on a variety of stony corals and infestation has reduced coral cover and diversity at Palmyra while also increasing reef erosion. More recently the outbreak of an invasive corallimorph (Rhodactis howesii) now threatens shallow reef habitats off the west side of the atoll and appears stimulated by dissolved iron from a nearby corroding Taiwanese longliner fishing vessel that ran aground near the ship channel in 1991.