Information – Environmental Information System (ENVIS) Centre

Biological invasions constitute one of the severe environmental concerns of the present times because of their high ecological and economic costs. An alien species referred to as non-indigenous species are introduced by human being, unintentionally or deliberately, outside of their natural geographic range into an area where they are not naturally present. Larger parts of them are unable to endure in an unfamiliar environment without human involvement and eventually vanish. Nevertheless, some species manage to become accustomed to their new surroundings and in due course establish themselves in the wild, where they can cause considerable ecological and economic damage. Invasive alien species are plants, animals, pathogens and other organisms that are non-native to an ecosystem and which may cause economic or environmental harm or adversely affect human health (CBD, 2009). International Union for Conservation of Nature (IUCN) defines Alien Invasive Species as an alien species, which becomes established in natural or semi natural ecosystems or habitat, an agent of change, and threatens native biological diversity. Species that grow and reproduce quickly, and spread aggressively, with potential to cause harm, are given the label “invasive.”Invasive species are generally spread by human activities without any intention. Majority of the invasive species are alien but sometimes, indigenous species may also become invasive, usually under tainted environmental conditions such as grazing, cyclones, changes in nutrient regimes, colonisation by an invasive species, or other alterations.

The movement of people, trade, agriculture, tourism, as well as globalization facilitated the deliberate and unintentional movement of species around the world beyond their natural borders. On a global scale, the potential damage by invasive alien species to native species and ecosystems may be as severe as the impact due to habitat loss and degradation. Invasive alien species are considered as the second most common cause of recent and ongoing extinctions after habitat destruction and one of the main drivers of global biodiversity loss. They can also cause severe economic losses, risks to animal, plant and human health and create societal and cultural impacts. Invasive species cause harm to wildlife in many ways. When a new and aggressive species introduced into an ecosystem, it may not have any natural predators or controls. It can breed and spread quickly, taking over an area. Invasive species can also alter the abundance or diversity of species that are important habitat for native wildlife. Additionally, some invasive species are capable of changing the conditions in an ecosystem, such as changing soil chemistry or the intensity of wildfires. Invasive alien species cause species extinction, especially on islands and in freshwater habitats. In freshwater habitats, the introduction of alien species is the second leading cause of species extinction, and on islands it is the main cause of extinction over the years, along with habitat destruction.Invasive species are found in every type of habitat and are typically difficult to eradicate. Invasive species can cause harm by out-competing native species, or preying on them. They can sometimes increase fire risks or contribute to erosion.

Impact of Alien Invasive Species on Native Biodiversity

Alien Invasive species have been identified as the second greatest threat to biodiversity after habitat loss. A species is labeled ‘invasive’ when it can grow and reproduce rapidly, and spread aggressively, with the potential to cause harm.   Alien invasive species are either accidentally or deliberately introduced into an ecosystem that is remote to them. The species could be any living organism from bacteria and fungi to plants, insects, marine life, amphibians, mammals and so on.  The exotic species are introduced to a new location without any environmental checks and balances such as seasonal weather, diseases, or insect pests that kept them under control in their native range. This mechanism is used to support food security, recreation opportunities, and ecosystem rehabilitation.

The newly introduced plant species invade the natural areas and often threaten the local native communities and reduce the native species diversity by forming dense monocultures or altering ecosystem functioning (Daehler, 1998; Khuroo et al., 2007). In the case of native wildlife, the species may lack evolutionary defenses against the invading species, or be unable to compete with a species that has no existing predators. Invasive alien species can alter the habitat structure and disturbance regimes thus lowering the water tables, and increasing soil salinity levels.

Aquatic invasive plants affects the navigation and flood control, disrupt the recreational water usage, and drastically reduce dissolved oxygen levels leading to the extinction of aquatic animals and eventually become a breeding ground for mosquitoes. A case in point was the introduction of Cane toads in Australia to control the native cane beetles, which was harming sugar cane crops. The toads failed in controlling the cane beetles, but moreover reproduced rapidly and spread across Australia. The Cane toads produce toxic secretions that harm the native predators making it difficult to eradicate the toads.

Key Impacts of Alien Invasive species on a Native Biodiversity

1. Habitat modification: Lantana has invaded most of India’s pasture lands (13.2 million hectares) besides forest and fallow areas, and the cost of controlling the situation is estimated to be US$ 70 per ha (Negi et al. 2019). At present, most of the natural forests in India are invaded by lantana resulting in the decline of the diversity and abundance of native species.

2. Predation: Guam, an island in the Pacific Ocean, is facing bird endangerment largely due to the brown tree snakes, an invasive species. The brown tree snake was introduced to the island and subsequently wiped out three-quarters of the native bird species and two of the eleven native lizard species. These snakes were also introduced to other Pacific islands and had similar impacts due to their preying on eggs, young and adult birds, and reptiles.

3. Competition for resources: Invasive species can compete with natives for food and space. Zebra mussels (Dreissena polymorpha) have spread throughout the Great Lakes region drastically since the 1980s. Mussels require the hard substrate to live on, and the foreign zebra mussels occupy space that is vital for the native mussels causing the latter to perish in the process.

4. Hybridization: North American mallards (Anas platyrhynchos) have been introduced in many places around the world where they mate with other ducks Endemic ducks in Florida, Hawaii, New Zealand, and Africa is in danger of extinction because of the hybridization by the North American mallard.

5. Pathogens: Invasive species are plausible pathogens. A popular example is the chestnut blight, a fungus that wiped out all the chestnut trees in the eastern US during1940s. Chestnut trees, which were dominant throughout the eastern US, were replaced by oak trees. The effect of this change in dominant species was not fully studied at the time, but scientists posit that several species of moths went extinct when the chestnut tree hosts perished.

Invasive alien species adversely impact the native biodiversity in several ways and various efforts have been made to control or eradicate them. These efforts include manual removal, pesticides, and biological controls. The eradication program that should be implemented depends on the strategy of particular invasive taxa.

References

• Daehler C.C. (1998). The taxonomic distribution of invasive angiosperm plants: Ecological insights and comparison to agricultural weeds. Biological Conservation, 84:167-180.
• Khuroo A.A., Rashid I.,Reshi Z., Dar G.H. and WafaiB.A. (2007). The alien flora of KashmirHimalaya. Biological Invasions, 9: 269-292.
• Negi, G.C.S., Sharma, S., Vishvakarma, S.C. et al. (2019) Ecology and Use of Lantana Camara in India, Bot. Rev. 85: 109–130.
• Threats to Biodiversity: Invasive Species

Invasion of Giant African Snail (Achatina fulica) and Its Management Strategies in Kerala

Invasive Alien Species

Species that introduced to a new environment other than its natural environment and if this species becomes problematic, it is termed an invasive alien species. It can be an animal or plant from another area of the world that do not belong in their new environment. The major pathways of introduction are by ship ballast water, accidental release, and most often, by people. Invasive species can lead to the extinction of native plants and animals, destroy biodiversity, and permanently alter habitats (NOAA, 2017). Invasive alien species are one of the greatest threats to global biodiversity, agriculture, livelihoods, human, animal health, and forestry (Pimentel, 2011). They can disturb not only the environment or ecology, but also the local economy (Simberloff, 2003). Hence, identifying the probable future distribution of invasive alien species is of paramount importance of early detection, prioritization of regions for conservation and effective management of invasive species (Bellard, 2013).

The Giant African Snail (Achatina fulica)

The largest mollusk of the terrestrial ecosystem, the giant African snail (Achatina fulica) is a Gastropod species. The adult snails grow up to 20cm in length and 250g in weight. It is a rapid-growing polyphagous plant pest that has been introduced from its native range in East Africa to many parts of the world as a commercial food source (for humans, fish and livestock) and as a novelty pet (Kotangale, 2011). It is capable of easily attaching itself to any mode of transport or machinery at any developmental stage, and is able to go into a state of aestivation in cooler conditions. Hence it is readily transportable over distances. Once this species escapes from its captivity, it is able to establish and reproduce prodigiously in tropical and temperate locations. As a result, A. fulica has been classified as one of the world’s top 100 invasive alien species by The World Conservation Union, IUCN (ISSG, 2003) and is also recognized as the second worst invasive alien species in the world by the global invasive species database (Lowe et al., 2000).

The giant African snail (up to 17 cm shell length) is a pest that has an extensive negative impact on agriculture and can serve as vector for several parasites, including Angiostrongylus cantonensis, a nematode parasite that causes (human) eosinophilic meningitis, an emergent disease (Prociv, 2000). Apart from economic loss and human health issues, A. fulica, is also a general nuisance to people.

Giant African Snail in Kerala

The giant African snail was introduced into India in 1847 at Calcutta, from Mauritius  by W.H. Benson, a malacologist (Srivastava,1992). Later on several incidents of introduction occurred in different areas by the way of trade and transport, intentionally and unintentionally, as pets, for commercial use, research purpose, and as a part of fantasy (Robinson, 1999). This snail was introduced to Kerala, in 1955 for research purposes.

An infestation of snails in the state was initially reported from Palakkad in the 1970s. From 2014 onwards, heavy infestation of Giant African snail was reported from various parts of  Kerala during the Monsoon season. The recent studies stated that it has invaded all districts in the state, except Idukki (KSDMA, 2016). The presence of fewer predators, hermaphroditic nature, high reproductive rate, skill for hibernation, and generalist feeding nature makes them an invasive species (Thiengo et al, 2008) in Kerala. Giant African snail is known to attack more than 500 plant species, including vegetables, coconut, cocoa, papaya, banana, areca nut, coffee, and even rubber plants. The two key negative impacts caused by A.fulica in Kerala are the agricultural damage and the subsequent cost of controlling the snails.

Management of Achatina fulica

The management options are usually seen as mechanical, chemical, and biological control, in addition to ecosystem management. Physical control is dependent on the collection and demolition of snail and their eggs from the infested sites (Raut and Barker, 2002).

Chemical management of the snails includes the application of different chemicals to terminate the organism. Application of sodium chloride, arsenate-metaldehyde bait, Snail Kill (metaldehyde), and cypermethrin, copper sulphate was effective against A. fulica (Rao and Singh, 2002). The usage of plant-derived molluscicides like Cedrus deodara oil, Allium sativum bulb powder, and Nerium Indicum bark in snail control prove to be very effective (Rao and Singh, 2002). In addition, Tobacco Decoction – Copper Sulphate mixture (TDCS) is an effective removal method against A. fulica.

Biological control of A.fulica using its natural predators will affect the endemic snail population, and thus this method was not suitable in Kerala. Besides its natural predators Sus scrofa, Rattus rattus, Bandicota indica, Herpestes edwardsii, and Suncus murinus are the main local predators that help us to eradicate giant African snail.

References

• Cowie RH, Robinson DG. Pathways of Introduction of Non indigenous Land and Freshwater Snails and Slugs. Washington, DC: Island Press; 2003.
• Davis MA. Invasion Biology. 2009. Oxford University Press. Oxford.
• Kerala State Disaster Management Authority. Kerala State Disaster Management Plan 2016.
• Kotangale JP. Giant African snail (Achatina fulica Bowdich). JEnviron Sci Eng 2011;53:6.
• Lowe S, Browne SM, Boudjrlas S, De Poorter M. 100 of the world’s worst invasive alien species: A selection from the global invasive species database. The Invasive Species Specialists Group of the Species Survival Commission of the World Conservation Union. First published in Aliens 12, December 2000. Reprinted November 2004. Auckland: Hollands Printing, 2000.
• Pimentel D, Lach L, Zungia R, Morrison D. Environmental and economic costs associated with alien invasive species in the United States. In: Pimentel D, editor. Biological invasions: Economic and environmental costs of alien plant, animal, and microbe species. Florida: CRC Press, 2011.
• Prociv P, Spratt DM, Carlisle MS. (2000) Neuro-angiostrongyliasis: unresolved issues. Int J Parasitol.2000; 30: 1295–1303
• Simberloff D, Martin JL, Genovesi P, Maris V, Wardle DA, Aronson J, et al. Impacts of biological invasions:what’s what and the way forward. Trends Ecol Evol. 2003; 28: 58–66.
• Thiengo SC, Fernandez MA, Torres EJ, et al. First record of anematode Metastrongyloidea (Aelurostrongylus abstrusus larvae) in Achatina (Lissachatina) fulica (Mollusca, Achatinidae) in Brazil. J Invertebr Pathol 2008; 98:6.
• What is an Invasive Species?