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Invasion of Tristan da Cunha
The islands of Tristan da Cunha has a high significance of global biodiversity as the island is considered a natural World Heritage Site. This designation is largely due to the seabird population found on the archipelago. The biodiversity of the island is on the decline because of the introduction of invasive species. Due to Tristan da Cunha’s isolated archipelago ecology, and increase of tourism with cruise ships and research vessels, more invasive species are set to be introduced to Tristan da Cunha. The islands' vegetation and mammal species are not equipped to defend against or control introduced species, increasing island vulnerability, due to lack of defensive behavioral mechanisms, slow generational output rates. Efforts to decrease and eradicate invasive flora, fauna, and marine species are in the works and have yet to show any successful outcomes. The following described invasive species have been known to have harmful effects on the islands' vegetation and native species.

Weeds
The remote island of Tristan da Cunha acquired an estimated 137 non-native vascular plants that can be categorized into four species types; weeds (trees, shrubs, agricultural weeds), grassland species (grasses), garden escapes (vegetables), and other ruderal species. Vascular plants were accidentally introduced in a variety of ways including; impurities in flower or vegetable seeds, seeds or plant fragments from other imported plants and in soil, attached to containers, cars or people. The majority of invasive weed species that has been introduced to the island are spread by seed and cover 50% of arable land in widely distributed patches. These species include Prickly Sow-thistle (Sonchus asper), Smooth Sow-thistle (Sonchus poleraceus), Smooth Hawksbeard (Crepis capillaris), Scrambling Fumitory (Fumaria muralis), Green Field Speedwell (Veronica agrestis), Groundsel (Senecio vulgaris), and Nutgrass (Cyperus esculentus). Other invasive weed species that have a more localized distribution in plots include Prickly Sow-thistle (Sonchus asper), Smooth Sow-thistle (Sonchus oleraceus), Smooth Hawksbeard (Crepis capillaris), and Groundsel (Senecio vulgaris). Whether a species is distributed locally or widely depends on the seed’s dispersal mechanisms; larger seeds that have not adapted to wind dispersal will be distributed locally, while smaller seeds have adapted to wind dispersal will be widely distributed.

The invasive plants have had several negative impacts on native island plant species, including the competitive exclusion of many such species. The out-competition will and can alter the structure of plant communities and the quality of the islands' soil. Introduced vegetation has altered long-term carbon storage as well as the reduction of CO2 in the atmosphere. Native plants such as fern bushes, Phylica bushes, fern brakes, mires, and bogs, contain high organic content matter which functions as storage for carbon. With the introduction of harmful species, the islands will see a decrease in carbon storage of both the soil and vegetation. With multiple changes occurring within the soil due to invasive plant species, the nutrient cycle is bound to be negatively influenced. Invasive plants are also affecting the human population of Tristan da Cunha by being disease carriers and becoming agricultural pests in gardens and pastures.

The alien plants are able to survive and continue to grow and spread successfully on the islands because they have the ability to naturalize in temperate regions and have limited necessities needed to survive. The islands' isolation increases archipelago ecology uniqueness which increases susceptibility for foreign invaders. A small human population with minimal development encourages flora and fauna development within a limited food web which increases the invasive species abilities for self-defense.

Plants are being controlled by taking surveys of the invasive species, evaluating their impact on biodiversity, and evaluating the feasibility of their eradication. It would be nearly impossible to try and eradicate all invasive plant species so scientists are narrowing down particular species to control based on their impact and feasibility to eradicate. Mitigation plans that are taking place on Tristan are time-consuming and labor intensive that will take several years using mechanical and chemical procedures.

Land
A non-native species of house mice that have evolved to be 50% larger than the average house mice have adapted to Tristan da Cunha as they are thought to have been accidentally introduced by 19th century seal hunters who would dock on the islands. These mice have adapted by consuming Seaborg eggs and chicks (as they nest on the ground), killing an estimated 2 million chicks annually pushing the species to extinction. Gathering at night in groups of 9 or 10, the mice gather at the bird’s nest to feast. The invasive mice were introduced to the Gough Islands by sailors in the 19th century. With no natural predators, the invasive mice population is able to expand by producing new generations twice a year. With no natural predators and a high generational output rate, there is no way to control the growth of the invasive mice population. The native bird species has a slower generational output and exposure to the islands. Albatross, a specific native bird species, spends their first 10 years out at sea which extends the time it takes for behavioral mechanisms to react to the invasive mice. There are only about 2,000 Tristan Albatross birds left within the world and 99% of their population lives on the Tristan da Cunha islands. There are over twenty seabird species on the islands with a total breeding population estimated over 10 million breeding pairs; five of these species are threatened, while the Albatross seabird species is endangered.

Mitigation plans in order to eradicate or decrease the invasive rodent population on the islands was seriously discussed in March 2008 taking into consideration the islands' community. Discussion of aerial bait drop on Tristan brought up concerns of health and safety of the children, livestock and the security of the water supply. Because the proposed plans for mitigation were not fully agreed upon by the Tristan community, eradication methods were shelved until 2019.

In order to prevent the growth of the invasive mice population and extinction of the Albatross bird species, a 2019 Gough Island mouse eradication project was announced (Grundy, 2018). The RSPB and Tristan da Cunha Government have partnered to spread cereal pellets with rodenticide bait across the Gough Island's, in hopes to eradicate the invasive mice population. This solution plan may seem simple but can become complex when discussing dispersal methods, which is predicted to be by helicopter, because of the island’s remote location and harsh weather conditions. In areas that are hard to reach by helicopter, pellets will be scattered by hand. The goal of this operation is to restore Tristan da Cunha back to its natural state, ensuring it will still be one of the world’s most important seabird nesting sites. Other methods that may be more simple, such as reintroducing cats, would pose a greater threat to the fragile bird populations as they would likely to prey on the birds as well and cats have already been eradicated from the islands.

Marine
The biodiversity of marine life is limited given the islands isolation, making identifying the impacts of invasion difficult. While much of the marine life is unknown there has been an invasive species identified in the waters around the islands. This species includes the South American silver porgy (Diplodus argenteus argenteus) which is thought to have seek refuge in the area due to the wreck of an oil platform off the coast of Tristan in 2006. The silver porgy is omnivorous but is not linked to the consumption of the valued lobster populations that the islanders fish. The silver porgy is however suspected to be consuming components of the islands’ fragile kelp forest. The kelp forest is extremely limited in biodiversity and has a simple, short-chain food web. While this species is considered non-native and invasive, removal efforts are currently not prioritized. Continued monitoring is suggested and expedition research for all invasive marine species are ongoing.