Invasive Species
Invasives are plants and animals that have been introduced from elsewhere and negatively impact the indigenous ecosystems and species of their new home. One of the reasons why the Phoenix Islands supports such outstanding flora and fauna is due to its isolation.
Upon human arrival, several invasive plants and animals were introduced, including Pacific and Asian rats, rabbits, cats, ants, pigs, dogs and lantana. Some of the negative impacts these invasives bring include the elimination of native seabirds and plants, particularly through the destruction of the eggs and young, and introduced plants taking over other plant life, modifying the natural island ecosystem.
There are current plans to eradicate mammalian pests on Rawaki, Birnie and McKean by 2008, which will subsequently enable populations of native seabirds to be secured or recolonized.Invasive Plants and Animals
A key reason why the Phoenix Islands support such outstanding flora and fauna values is that the islands have been isolated for millennia. This has enabled the seabirds and other fauna to live and nest safely in the absence of invasive pests and exploit the food rich seas around the islands. Invasives are plants and animals that have been introduced from elsewhere and which proliferate and impact on the indigenous ecosystems and species of their new home. Many invasive plants and animals have been introduced to the Phoenix Islands with varied and often catastrophic results. Impacts can be direct (e.g. predation) or indirect, e.g. subtle changes in habitat and loss of potential source of food (e.g. frigatebirds relying on other birds for food source). Some of the more serious invasive species currently present include:
- Pacific rats which have eliminated the more sensitive small seabirds over time, and reduced the populations of lizards and invertebrates.
- Asian rats which have recently arrived on McKean Island and devastated the local fauna (see “A recent disaster” to the right).
- Rabbits which are damaging the Rawaki ecosystem and compete for shade with seabirds and destroy their eggs and young.
- Cats which have eliminated many seabird species from the large islands.
- Pigs and dogs which are sometimes introduced to some of the large islands where they destroy seabird colonies.
- Lantana and other weeds, particularly on Abariringa. Even the dense coconut plantations of Manra, Orona and Nikumaroro are a recent introduction during periods of temporary human resettlement and they are currently colonizing Enderbury.
Photo Caption: Enderbury with seabird colonies and scattered coconut trees
Many invasive species of plants and animals threaten the integrity of the Phoenix Islands. Some of these are not yet recorded in the group, but they could easily reach the islands in the future. Key species and groups of invasives are summarised below.
Pacific rat – Rattus exulans Location: most islands
Impacts: – eat eggs and chicks of small seabirds, eat lizards and modify ecosystem
Biosecurity needs: eradicate Pacific rats from key islands including initially the small Birnie Island to allow recolonisation by many seabird species from neighbouring Rawaki; improve biosecurity, e.g. ensure rats are not shifted from island to island.
Photos courtesy Ray Pierce and Mike Thorsen
Location: Recently arrived on McKean Island; this and related species are likely to be present on many fishing vessels in region
Impacts: – kill most seabirds and their eggs and chicks, kill lizards and modify ecosystem
Biosecurity needs: urgently eradicate McKean rats; improve biosecurity, e.g. impose need for the removal rats from all authorized vessels in PIPA and bait stations to be maintained on them; no illegal landings.
European rabbit – Oryctolagus cuniculus Location: Rawaki – released 19th Century
Impacts: – loss of plant species and increased erosion, loss of eggs and chicks of seabirds, especially burrowing petrels, storm-petrels and shearwaters, including serious threat to the continued survival of Phoenix petrel.
Biosecurity needs: eradicate rabbits from Rawaki. There is no chance of recolonisation.
Photos courtesy Ray Pierce and Mike Thorsen
Feral house cat – Felis catus Location: Orona, Manra, Abariringa; recently died out at Enderbury and possibly Nikumaroro
Impacts: – complete loss of all petrels, storm-petrels, shearwaters, blue noddies from islands on which cats occur and declines in most other seabird species including tropicbirds, boobies and frigatebirds, and possible decline in lizard populations
Biosecurity needs: eradicate cats from Orona and other islands. Ensure cats are not brought to islands.
Location: not known from the Phoenix Islands, but yellow crazy ants, red fire ants and others are present at an increasing number of ports in the Pacific Region and easily transported by boat
Impacts: – potentially devastating impacts to fauna and flora and ecology of the Phoenix Islands. Invasive ants can kill not only other ants, but also larger invertebrates, lizards and seabirds, including the threatened species present.
Biosecurity needs: increase biosecurity levels e.g., ant surveillance (and control if needed) at embarkation ports for regular sailings to the islands, surveillance on boats, and surveillance at likely invasion points (Abariringa, landing points and camps on the other islands) and act on any detection of invasive ants.
Invasive plants Location: many plant species have been introduced to the Group over hundreds of years. Abariringa is the island that is most heavily infested with invasive or potentially invasive species.
Impacts: some species, e.g. coconuts can completely modify the island ecosystems. Locally on Abariringa and potentially on other islands, lantana can be invasive, supplanting other plant species.
Biosecurity needs: increase biosecurity levels e.g., restricted species entry, seed surveillance in transported goods and surveillance at likely invasion points (Abariringa, landing points and camps on the other islands) and act on any detection of invasive plants (as per invasive ants).