India, in the grip of invasive alien species
A recent Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), report has warned that human activities are leading to the introduction of more than 37,000 invasive alien species to marine, aquatic and terrestrial ecosystems globally. More than 3,500 of these are harmful, threatening the survival of ecosystems and affecting human health and livelihoods. India too is experiencing a rise in invasive alien species threatening freshwater, terrestrial and marine ecosystems [1].
What are invasive species
Invasive Alien Species (IAS) include any plant or animal that is introduced into an environment where it does not naturally belong. The plant or animal survives and gradually establishes itself in the new environment and multiplies rapidly, replacing the original/ native species leading to biotic homogenisation, replacement of native species and reduction in biodiversity of the region. This leads to gradual deterioration of ecosystems affecting food and water security, health and livelihoods [1].
Invasive species are characterised by their fast growth rate; ability to reproduce in adverse environmental conditions such as extreme heat, pollution; fast reproduction rate and dispersal rates; ability to survive on wide range of food items and their ability to associate with humans. Invasive alien species can be introduced accidentally or intentionally, and can cause considerable harm to natural ecosystems, biodiversity, livelihoods, water and food security and human health and economy [1].
For example, invasive mosquito species like Aedes albopictus that originated in southeast Asia and has now spread to all continents except Antarctica have led to the spread of infectious diseases such as dengue fever, chikungunya, zika and yellow fever [2]. Invasive alien plants such as common ragweed is known to affect human health through pollen causing hay fever, asthma, and allergic dermatitis. Plants like water hyacinth are extremely aggressive and are able to double their growth in 1 to 2·5 weeks, and can affect freshwater biodiversity by decreasing oxygen levels and thus harming native fish populations and lead to deterioration in the water quality of aquatic ecosystems [2].
Read this article to know how.
How do invasive species enter natural environments
Human migration, demand for food resources often lead to introduction of commercially important exotic agriculture and aquaculture species into the environment. Some of these species can accidently escape into the wild and then evolve as an invasive [3].
Ornamental trade, unscientific aquaculture practices, sport fishing, mosquito control, natural disasters and ballast water can also lead to the introduction of invasive alien species into water bodies. A number of exotic ornamental fish, aquatic plants and other small pet animals are sold in states such as Andhra Pradesh, Chandigarh, Gujarat, Karnataka, Kerala, Maharashtra, New Delhi, Tamil Nadu and West Bengal and these have been found to evolve as invasive [3]. For example, mosquito fish, tilapia, giant gaurami, guppies, platyfish are now being found in the Chalakudy river in the Western Ghats, a biodiversity hotspot [3].
Studies show that construction of dams and river linking and beautification projects are also leading to the introduction of invasive species in freshwater bodies in India [3].
Other examples of IAS include carrot grass that gained entry into India through imported wheat from the USA in the 1950s, the entry of invasive river tamarind that got into India through the social afforestation programmes undertaken by the Government of India, and the proliferation of Mozambique tilapia, a fast-growing fish introduced as a source of income for disadvantaged fishing communities, but which is now replacing the native fish communities in Indian water bodies threatening livelihoods [4].
Coastal ecosystems are also under threat due to introduction of invasive alien species. Coastal ecosystems support unique habitats such as estuaries, lagoons, mangroves, backwaters, salt marshes, mud flats, rocky shores and sandy stretches that house a number of endemic and IUCN threat category species [5]. They also support three Gulfs (Gulf of Mannar (East coast), Gulf of Kachchh and Gulf of Khambat (West coast), and three major reefs atoll, fringing and barrier which support rich coral and fish diversity and several endemic and endangered species [5].
The entry of invasive alien species through ballast water discharge can have the most deleterious impacts on marine diversity. Shipping transfers over 80 percent of the world’s cargo and about 12 billion tonnes of ballast water throughout the global oceans each year. Ballast is defined as any solid or liquid that is brought on board ship to increase the draft and regulate the stability or to maintain stress loads [5].
The marine/ocean water loaded for ballast purposes contains a variety of organisms starting from microorganisms to smaller chordate and aquatic plants. Many of the aquatic species die before they reach their destination because of the stressful ballasting and de-ballasting processes and the environmental conditions prevailing inside ballast tanks that are unfriendly for the survival of the species [5].
However, some of the individuals/ species are able to survive and slowly establish themselves in these new habitats and evolve as an invasive species in due course of time and often outcompete native species and disturb the ecological balance of the native habitats thus threatening the livelihoods of the coastal communities. Natural disasters such as floods, tsunamis and cyclones also play an important role in introducing invasive species in marine habitats [5]. However, there is very little information available on modes of entry of invasive species into marine waters besides aquaculture.
Economic burden of invasive alien species
While invasive species are known to affect aquatic and terrestrial ecosystems, livelihoods and health, very little information is available in the country on the economic burden caused due to IAS. A recent study by Bang, A et al. (2022) titled 'Massive economic costs of biological invasions despite widespread knowledge gaps: a dual setback for India' finds that:
The total economic costs incurred by IAS to the Indian economy amount to US$ 182.6 billion, and US$ 127.3 billion over the period 1960–2020. West India incurs the highest costs at US$ 616 million, South India at $ 64.2 million and North at US$ 23.9 million.
Of the five nations incurring maximum IAS costs, i.e., the USA, Australia, Brazil and China, India is second to the USA in per unit area costs, followed by Australia, Brazil and China while it stands fourth in per capita costs, ahead of China, and below Australia, the USA and Brazil.
Most of the costs have been found to be due to six invasive insects and four invasive plant species. Invasions by semi-aquatic and aquatic plants and animals put a greater monetary burden to the economy. The semi-aquatic costs are solely due to the health care costs caused due to yellow fever mosquito.
As high as 93 percent of losses borne due to AIS can be attributed to ‘diverse/unspecified’ category for India, making it challenging to address invasion borne costs.
More than 99 percent of economic losses affect multiple sectors and are classified as “mixed costs”. For example, costs resulting from the yellow fever mosquito are borne by the health sector, but they also burden authorities and stakeholders. Eichhornia and many other exotic weeds have affected the fisheries sector, but have also caused a steady decline in the tourism sector that relies on water bodies.
The economic burden/ costs due to IAS have increased five times over the last six decades in India due to an increasing numbers and spread of IAS in India, and due to inadequate legal and policy frameworks to prevent them.
The costs are feared to rise further with increase in trade, transport and climate change globally as it can can provide more opportunities for introducing IAS.
The reported economic costs grossly underestimate the actual costs, considering India’s population size, gross domestic product and high numbers of IAS.
There is an urgent need to make citizens aware of the impact of invasive alien species on aquatic ecosystems and focus on preventing alien species from entering water bodies. Policymakers need to urgently address socio-ecological issues related to introduction and spread of IAS in India and launch a national biological invasion research programme to deal with the situation, argues this study.