One day in December 2012, a boy and his father made their way from Mylapore’s famous Kapaleeswarar temple to the temple tank across the road.

The temple is one of Chennai’s architectural highlights and, depending on who you believe, was built by the Pallavas in the 7th century CE or by the kings of Vijayanagar in the 16th century (after the original was destroyed by the Portuguese).

The man had grown up in Chennai when it was Madras and had accompanied his parents to the temple many times. Now, on a visit to Chennai in the only month of the year when the weather in the city is pleasant, he was making sure his son saw the temple. That wasn’t the only reason, though. The previous night, the man’s mother had mentioned that the temple tank was teeming with fish and the boy, like all boys his age (he was 10), wanted to see them.

The temple tank was fenced in—it was clean on account of that—and the boy and his father bought a packet of puffed rice (pori) to feed the fish near the gate. Like all temple tanks in south India, this one had steps leading down to it from all sides. They walked down the steps; the tank was full and the lower steps were underwater.

The man and his son stood a few steps above the water and sprinkled the puffed rice on it. A twisting, churning mass of fish appeared. Some were as long and thick as the man’s arm. They were eel-like, black and slimy. A few intrepid ones jumped up to a partially dry step to get at errant pieces of puffed rice and then wiggled their way back down into the water.

“African catfish," said the boy. “They have taken over."

The man told me this story.

I thought of him when I read about the piranha someone found in the Godavari.

Tale of a survivor

The African catfish (Clarias gariepinus), aka the African sharptooth catfish, is native to Africa and West Asia, where it is found pretty much everywhere—in lakes and rivers, swamps, agricultural canals, wells, even drains. Its numbers are so vast that the International Union for Conservation of Nature and Natural Resources (IUCN) hasn’t bothered to assess its conservation status.

Adults can grow up to 5ft in length and weigh up to 60kg. Bigger African catfish have been reported. They have wide mouths with four barbels—whisker-like protrusions on the side of the mouth—that give them a sinister look. They can swallow mid-sized water birds whole. And they are survivors.

Maybe because of the fish’s African origin, it can crawl on dry land, moving from one pool to another. It can also survive in shallow mud, dormant, waiting for the next rains, when it emerges.

These qualities and its size made it a popular choice for aquaculture in Africa in the 1970s. In the 1980s, it was introduced to other parts of the world. Scientists say it probably came to India via Bangladesh, probably courtesy the well-intentioned efforts of some development organization that was trying to help Bengali farmers.

In India, it was first seen in Andhra Pradesh, one of the hot spots of the Indian aquaculture boom of the 1990s. It has since colonized major rivers and water bodies, destroying native fish stock. It has invaded wetlands; recent studies show the African catfish preying on small terrestrial birds, aquatic birds and turtles in Keoladeo National Park, Bharatpur, and Periyar National Park on the Tamil Nadu-Kerala border.

Interestingly, a Red-bellied piranha made the headlines earlier this year when it was caught by a fisherman in the Godavari in Rajahmundry, Andhra Pradesh.

According to ichthyologist (fish scientist) A. Biju Kumar, “Carnivorous and voracious feeders such as the Bighead carp, African catfish and the infamous aquarium fish, the Red-bellied piranha, were imported into India illegally in the 1990s from different parts of the world."

Kumar sensed the threat quite early when he commented in a 2000 monograph that “if these exotic fishes establish themselves in natural water bodies, they may become a serious threat to the smaller indigenous fish species and invertebrates. Swarms of piranhas confined to small water bodies may attack large animals and even human beings".

Bollywood may have a field day with that, but the thought—of both piranhas attacking humans and a Bollywood horror film on piranhas—isn’t funny.

The alien invasion

The Himalayan tahr was introduced for sport in New Zealand. Favourable conditions led it to multiply and spread across the Southern Alps. The tahr was also introduced for sport in North America, Argentina and South Africa.

Photo: Ananda Banerjee/Mint

Six macaques were brought to Florida for the shooting of the 1939 hit film Tarzan Finds a Son! The monkeys, the commonest in north India, escaped from captivity and it is now estimated that their number has grown to more than 1,000.

The beautiful gulmohar tree was introduced as an ornamental tree in Mumbai in around 1840 from Mauritius (where, in turn, it had been introduced from exotic Madagascar). In a few years, the red-flowering trees spread across the country.

The lanky, fast-growing eucalyptus is considered hazardous to nature for its thirst for water and damaging soil fertility. It was introduced into India in the 1970s for social forestry schemes and to provide pulpwood for the paper industry. Later, scientists found out that it is a host for cryptococcosis, a fungus that affects the human nervous system.

Examples of species outside their native range abound all over the planet. In science, these are known as biological invasions facilitated by humans.

The various species that have been introduced in lands away from their homeland have threatened or thrived at the cost of native biological diversity. These are known as invasive alien species. The broad consensus among scientists and conservationists is that these are a major threat to the biodiversity of the planet. However, not all non-native species are invasive; for instance, the ornamental palm trees that dot avenues in luxury hotels in India are harmless.

“We know little of the factors which lead to biological invasions, making it difficult to predict which species will become invasive and where invasion will occur," writes Alan Hamilton in the book Plant Invaders: The Threat to Natural Ecosystems. “It does, however, seem certain that the threat of invasions is growing, as more and more species of plants are moved around the world, planted in gardens or used in agriculture or forestry. Often, very little thought is given to the risks of plant invasion, for example by those promoting widespread use of fast-growing leguminous trees in agro-forestry schemes in the tropics."

Invasive species span the taxonomical spectrum—from microbes to plants to animals. According to the Convention for Biological Diversity, “The biological invasion of alien species is the second worst threat to biodiversity after habitat destruction."

The India Biodiversity Portal, managed by a consortium of institutions and non-governmental organizations (NGOs), is running a campaign to map the distribution of alien invasive species in India. And there are many.

Dead as the dodo

For millennia, humans have been introducing plants, animals and other organisms around the world. Historically, as humans colonized the world, they brought along species with them. Dogs, cats, horses, rats and mice were the most common, as were different species of edible plants. Many species got naturalized over time, such as India’s favourite vegetable, the potato. Its origins are in Peru and Bolivia in South America.

Ships have been integral to humanity for discovery, conquest, trade and travel between continents. Between the 15th and 18th centuries, when Europe was at the pinnacle of power, a succession of famous seafaring explorers such as Christopher Columbus, Vasco da Gama, Sir Francis Drake and Sir Walter Raleigh travelled far and wide to redraw the map of the world. This period was also known as the Age of Discoveries. The efforts of these explorers resulted in a new map of the world emerging, but it also led to several species travelling to far lands.

The results were shocking.

The last dodo, one of largest species of pigeons, vanished from the island of Mauritius in the 17th century because its habitat was destroyed by the introduction of animals brought by humans. “Since that time, 133 more bird species have become as dead as the dodo. Introduced mammals are responsible for 90% of all bird extinctions since 1500," states Don Stewart, director, Pacific region, Birdlife International, on the NGO’s website.

Today, Australia is trying to exterminate two million feral cats that threaten the continent’s small mammals and birds such as the Golden bandicoot and Greater bilby. The cost is estimated to be around A$6 million. Australia had previously exterminated the house crow.

New Zealand, like other island nations (their species are endemic and face greater threat from invaders) takes a dim and aggressive view of invasive species as detailed in a recent narrative in The New Yorker.

It’s not only the birds and the bees. Deadly viruses—invisible species—also travelled with European explorers to the ‘New World’. The most fatal was smallpox, which wiped out most of the indigenous people in America. Some other disease-spreading viruses included the influenza, measles and whooping cough viruses.

In the modern context, another source for growth of alien pathogens is the exotic pet trade. The number of people buying animals as pets and the number of different species being imported is increasing. These exotic pets are sometimes known to be the carriers of diseases such as West Nile Virus, swine flu, Human Immunodeficiency Virus and Ebola, which affect humans and domestic and wild animals.

Travelling the world

Transoceanic travel has increased a billion times, constantly moving human, cargo and biota (both intentionally and accidentally) from one place to another.

“World trade has become the primary driver of one of the most dangerous and least visible forms of environmental decline: Thousands of foreign, invasive species are hitch-hiking the global trading network aboard ships, planes and railroad cars, while hundreds of others are travelling as commodities," wrote scientist Christopher Bright in his book Life Out of Bounds: Bio-invasion in a Borderless World. “The impact of these bio-invasions can now be seen on every landmass, in nearly all coastal waters (which comprise the most biologically productive parts of the oceans), and probably in most major rivers and lakes. This biological pollution is degrading ecosystems, threatening public health and costing billions of dollars annually. Confronting the problem may be now be as critical an environmental challenge as reducing global carbon emissions."

In the science journal Frontiers in Ecology and the Environment, Harold Mooney, a noted American ecologist, and Laura Meyerson, associate professor of habitat restoration ecology at the University of Rhode Island, wrote, “Through the years, the pace of this process has increased with modern trade, travel and technology, so that biological invasions have become a consequence of globalization."

The worst agent propagating the spread of alien species is maritime trade. As you read this, the global shipping industry is releasing thousands of species in alien waters. Oil tankers, container freight ships and submarines have ballast tanks. The water in these tanks, known as ballast water, stabilizes ships for a safe journey. However, the ballast water carries local aquatic species—exotic plants, animals, viruses and bacteria—that get discharged every time the ship reaches a new port in a different part of the world.

It is estimated that large ships carry more than 200,000 cubic metres of water, equivalent to the water in 2,000 Olympic-sized swimming pools. Every year, ballast tanks move 10 billion cubic metres of water from port to port.

“Every day some 3,000 to 10,000 different species are thought to be riding the ballast tanks," Bright wrote, adding, “This leads to a homogenization of estuary and bay life, through survival of the fittest come to dominate one coastline after another, slowly eroding the biological diversity of the planet’s coastal zones and jeopardizing their ecological stability."

Invasion biology

Throughout the 19th century, scientists made notes of introduced species in various places. Prominent among them were Swiss botanist Augustin de Candolle, his son Alphonse and English botanist Hewett C. Watson.

A century later, James Ritchie in Scotland and George M. Thomson in New Zealand wrote masterful, systematic tabulations of introduced species in The Influence of Man on Animal life in Scotland (1920) and The Naturalisation of Animals and Plants in New Zealand (1922), according to Daniel Simberloff, director, Institute for Biological Invasions, University of Tennessee, and author of Invasive Species: What Everyone Needs To Know.

In 1958, British ecologist Charles Elton produced an immensely popular work on alien species based on a series of BBC radio shows—The Ecology of Invasions by Animals and Plants. But it wasn’t until the 1980s that the study of invasive species became a discipline in its own right. Elton’s work addressed many of the ecological issues that we are facing today.

“In 1982, the Scientific Committee on Problems of the Environment (SCOPE), an arm of the International Council of Scientific Unions, recognized a growing number of reports of environmental problems caused by biological invasions and an absence of any sort of synthetic, scientific overview of the phenomenon. This led to the launch of modern invasion biology as a scientific field," comments Simberloff.

At present, it is estimated that the US has more than 6,000 introduced species and there are 12,122 species listed on the European invasive species gateway, known as Delivering Alien Invasive Species in Europe (DAISIE). According to the Global Invasive Species Database, here are the world’s 100 worst invasive species.

The Indian experience

India has its share of invasive species.

Major plant introductions in the country can be traced to the establishment of the East India Company’s botanical garden in 1786. In a short span of eight years, the company introduced around 300 plant species in the Calcutta botanical garden.

But there’s no consensus on the number of invasive species in the country.

In August 2004, during a workshop held at Banaras Hindu University’s botany department to discuss alien invasive species and biodiversity in India, scientists claimed that 40% of Indian plant species were alien and 25% invasive.

The Asia-Pacific Forest Invasive Species Network (APFISN) reports that over the years, a number of forest invasive species (FIS) have been introduced in India without a consideration of the consequences. In time, many of the invasive species became naturalized in India and started being used for various purposes. APFISN identifies 111 FIS under the floral (weeds and plants), entomological (insects) and pathogenic (fungi) categories.

C. Sudhakar Reddy, at the forestry and ecology division of the National Remote Sensing Centre, Hyderabad, put the number of invasive alien flora species at 173 in his 2008 report Catalogue of Invasive Alien Flora of India.

A study titled The Management of Alien Species in India by zoologist Fatik Baran Mandal, published in the International Journal of Biodiversity and Conservation (2011), states that about 324 alien fish species had been introduced in India, including 291 ornamental fishes, 31 aquaculture fishes and two larvicidal fishes for killing mosquito larvae. Among these invasive specie are the brown trout, rainbow trout, African catfish, common carp, Mozambique tilapia and mosquito fish—all listed among the worst invasive fish species in the world.

The Mozambique tilapia is reportedly endangering native fish stocks in the Moyar river in Mudumalai Tiger Reserve, Periyar lake in Periyar Tiger Reserve, Thenmala river in Shenduruney Wildlife Sanctuary, Godavari river in Papikonda National Park and Coringa Wildlife Sanctuary.

A WWF-India report, The Terai Arc Landscape in India (2005), reveals that 18% of Indian plant species are alien. The Food and Agricultural Organization (FAO) of the United Nations estimated that out of about 45,000 species of plants recorded in India, nearly 1,800 are alien. Among arthropods (including insects), out of the known 54,430 species in India, nearly 1,100 are alien.

Intermixed growth

Whatever the number, according to the Wildlife Institute of India (WII), the problem of invasive species is yet to be tackled at the state or national level in a holistic manner.

Alien species affect forestry, agriculture, fisheries and aquaculture. According to the FAO, invasive species, especially weeds, are a serious problem for forestry and agriculture and have become an environmental issue. In flora (particularly weeds), it is also very difficult to distinguish between native and exotic species as they grow intermixed.

Among the invasive plants, the Lantana is regarded as one of the 10 worst invasive species in the world. The genus has more than 100 species, among which 25 have been recorded in India. “Lantana is one of the world’s worst weeds of South American origin that threatens native biodiversity of forest ecosystems across India," wrote Amit Love, Suresh Babu and C.R. Babu in their monograph Management of Lantana, An Invasive Alien Weed in Forest Ecosystems of India.

View Full Image A lantana plant. Photo: iStock

“It was introduced into India as a garden ornamental plant in 1807 and now has virtually invaded all the tropical and subtropical regions of India," they wrote. “Although attempts have been made to control Lantana by physical, chemical and biological methods, there is no success either in its control or the prevention of its spread. No effective management strategy is yet available for the containment of this alien weed."

Parthenium, another harmful exotic weed, is notorious for its rapid spread. It is native to the tropical and sub-tropical regions of Mexico, Central and South America and probably entered India in the beginning of the 20th century through contaminated grain, but went unrecorded for many decades. It was first recorded as a weed near Pune in 1951 and now has colonized river banks, and open and fallow fields, leading to loss of natural habitats, forage production and decline in biodiversity.

Once this species takes over an area, native grass and herbs cannot compete for light and nutrients. Parthenium was reported to cause a yield loss of up to 40% in several crops. It is known to be a menace to agriculture. The weed is also allergenic to human and animal health and causes respiratory problems such as asthma.

Another tropical American weed, Mikania micrantha, was introduced in India after World War II to camouflage airfields. Since then, the species has spread across the subcontinent. Mikania reduces the growth and productivity of several crops plants such as sugarcane, maize, rice, pineapple, cotton, tea and coffee. Infestation by the weed in natural forests in the north-east has caused large-scale habitat destruction.

Infestation by invasive aquatic weed is another major cause of concern in India. Kariba weed (Salvinia molesta) and water hyacinth (Eichornia crassipes) are known to choke freshwater bodies and wetlands across India, putting farmers and paddy cultivation in jeopardy. Salvinia made its entry in India before 1900, while the water hyacinth was introduced as an ornamental pond plant from the Amazon basin in the 1890s. In recent years, a group of scientist has put water hyacinth to good use—to treat polluted water.

View Full Image Water hyacinth. Photo: Ananda Banerjee/Mint

Foraging for food

A recent WII report, Human-Wildlife Interactions and Invasive Alien Species in India (2015), says the reduction in native food plants due to an increase in the range of invasive species is one of the reasons for the straying of wild herbivores in search of food.

Take the case of rhinos straying out of the Pobitora Wildlife Sanctuary in Assam. Invasive alien species such as Desmodium triflorum (Creeping Tick-trefoil), Cardiospermum halicacabum (balloon plant), Ipomea carnea (pink morning glory) and Argemone mexicana (Mexican poppy) in Pobitora Wildlife Sanctuary are rapidly increasing in cover and competing with native fodder species, leading to an increase in crop-raiding incidents by rhinos. Similarly, the increase in Lantana cover has resulted in decreased habitat use by elephants in the dry deciduous forest of Mudumalai Tiger Reserve.

View Full Image Elephant completely dwarfed by Lantana. The front has been cleared for wildlife viewing. Photo: Ramki Sreenivasan/Conservation

The WII study compiles a list of important alien invasive species that pose threat to different ecosystems. They are:

Terrestrial Ecosystem: Lantana camara, Mikania micrantha (bitter vine), Parthenium hysterophorus, Prosopis juliflora, Leucaena leucocephala, Chromolaena, Ageratum, Cassia tora, Xanthium strumarium and Achatina fulica.

Islands Ecosystem (Andaman and Nicobar): Axis axis (spotted deer) and Hoplobatrachus tigerinus (Indian bullfrog).

Freshwater Ecosystem: Eichhornia crassipes (water hyacinth), Ipomea carnea (pink morning glory), Mozambique tilapia and Clarias gariepinus (African catfish).

Marine Ecosystem: Kappaphycus alvarezii (a species of seaweed).

But history can’t be blamed for the spread of all invasive species. In the past 25 years, at least five species of insect and mite pests have invaded India, affecting agricultural, horticultural and forest production. The study Invasive Alien Insects and Their Impact on Agro Ecosystem by Y.H. Sujay, H.N. Sattagi and R.K. Patil, department of agricultural entomology, University of Agricultural Sciences, Dharwad, Karnataka, lists these following invasive insects in India: Woolly apple aphid (1889), San Jose scale (1911), Lantana bug (1915), cottony cushion scale (1921), potato tuber moth (1937), diamond-back moth (1941), Pine woolly aphid (1970), Subabul psyllid (1988), serpentine leaf miner (1990), coffee berry borer (1990), spiraling whitefly (1994), silverleaf whitefly (1999) and blue gum chalcid (2006).

In 2009, a group of scientists flagged the potential of agricultural crops to turn into invasive species. Coffee, one of the most widely cultivated plants and dealt in worldwide, could be one of them.

“The conservation impact of invasive plant species on tropical biodiversity is widely recognized, but little is known of the potential for cultivated crops turning invasive in tropical forest regions," according to the paper Brewing Trouble: Coffee invasion in relation to edges and forest structure in tropical rainforest fragments of the Western Ghats, India by Atul Arvind Joshi of Forest Research Institute, Dehradun, and Divya Mudappa and T.R. Shankar Raman of the Nature Conservation Foundation, Mysuru. “In this context, coffee needs urgent attention, as it is the most traded global agricultural commodity, cultivated in over 11 million hectares mainly in tropical countries around the world. The occurrence and spread of coffee in tropical rainforests that are globally recognized repositories of biodiversity is a matter of conservation concern."

“Our study shows how coffee is very much an invasive weed in the Western Ghats tropical rainforests," the authors wrote.

A fast-changing planet

Island ecosystems are particularly at peril from invasive species.

The Andaman and Nicobar Islands are a case in point.

Conservationists estimate that at least 556 species of plants, three snails, four insects, 19 birds, 12 mammals, 13 marine fishes and one virus as invasive alien species, if not more, exist in the Andamans. In 1950, elephants were brought to these islands for logging and forestry work. The timber company responsible for the upkeep of the pachyderms soon went bankrupt.

Around 40-50 elephants were set loose in the forest and, over time, the population increased and turned feral. “Elephants along with Axis deer, another introduced species for sport by the British, led to the disappearance of a few local species and are likely to affect species richness over large parts of the island chain, if not controlled. Satellite images indicate degradation of vegetation where these species occur," says Rauf Ali, a conservation biologist.

Among the 19 introduced bird species, only six—common myna, house sparrow, blue rock pigeon, grey francolin, house crow and Indian peafowl—now survive in the islands. The common myna and house sparrow are the most successful colonizers in the Andaman and Nicobar Islands. The myna is even in the ignominious list of IUCN’s 100 worst invasive species.

Not everyone is training their guns on invasive species. Ecologists such as Mark Davis, DeWitt Wallace professor of biology at Macalester College, St Paul, Minnesota, US, have appealed for patience.

“Don’t judge species on their origins, instead assess organisms on environmental impact rather than on the fact that they are natives or non-natives," wrote Davis. “It is time for scientists, land managers and policymakers to ditch this preoccupation with the native-alien dichotomy and embrace more dynamic and pragmatic approaches to the conservation and management of species—approaches better suited to our fast-changing planet."

Well-known British nature writer and author Mark Cocker has written compassionately for the Chinese water deer, which is an introduced species in the UK and considered a part of the country’s natural landscape. According to Cocker, the species is much better off in the UK than in its native home range.

Another well-known nature writer, David Quammen, evokes a future in which the earth is a “planet of weeds". He predicts that because of introductions and extinctions, in the future, the earth as a whole will have fewer species—“the global weed, both plants and animals".

At a click of the mouse

The digital economy is helping the spread of invasive species.

Science Daily reports that trade in invasive plants is increasingly shifting to the Internet and being conducted on auction platforms like eBay. As a result, one click is all it takes to spread potentially invasive plants from continent to continent—and unintentionally encourage biological invasions.

A new paper by Franziska Humair, Luc Humair, Fabian Kuhn and Christoph Kueffer at Eidgenössische Technische Hochschule, Zurich, highlights this. The authors monitored online trade of about two-thirds of the world’s flora on eBay and nine other online trading platforms.

Over the 50 days of the monitoring phase, the researchers found 2,625 different plant species offered for sale on eBay. That corresponds to about 1.4% of the seed plants they were looking for. Of all the plants for sale, 510 are known to be invasive in at least one region somewhere in the world. And out of that group, 35 are on the IUCN’s list of the 100 worst invasive species.

“To put it briefly, the vast majority of invasive species can be easily obtained with just a click of the mouse," says Franziska Humair.

That may well be how the piranha ended up in the Godavari. “Our preliminary enquiry in the field revealed that this species is now available in most of the aquarium shops and is occasionally found in the fisherman’s catch at Dhawaleshwarm barrage in Rajahmundry. The fish is being cultured around the Godavari river mainly in inland water and canals," wrote scientists J.A. Johnson, R. Paromita and K. Sivakumar from WII in a report published in January 2014.

Today, global aquarium fisheries and trade is said to be a multimillion dollar industry, with more than 1 billion ornamental fish comprising more than 4,000 freshwater and 1,400 marine species traded annually.

A.K. Singh, director, Directorate of Coldwater Fisheries Research, Indian Council of Agricultural Research, wrote in a 2014 paper titled Emerging Alien Species in Indian Aquaculture: Prospects and Threats that “generating information on aquarium species is extremely difficult as the trade is secretive in nature".

Indeed, piranha are available at most shops selling aquarium fish in New Delhi. And no one will tell you how they got there.

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