Alien invasion of a different kind: How exotic pets are threatening Kerala’s biodiversity

Exotic pet trade has been listed as one of the primary causes of the spread of invasive species, recognised as the second most important reason for biodiversity loss, next to habitat destruction. More than 100 such alien species have been reported in Kerala, many of them introduced as part of the pet industry

Updated - November 11, 2022 06:12 pm IST

Published - November 10, 2022 07:53 pm IST - THRISSUR: 

The Avalappandi Canal, near Perambra, in Kozhikode has turned pink due to massive flowering of the invasive alien species Red Cabomba. It chokes the waterbodies ecologically and economically, affecting the growth of native aquatic plants and freshwater fish. Red Cabomba has been found in seven rivers and two lakes in the southern Western Ghats alone. Native to Central and South America, it is a popular aquarium plant.

The Avalappandi Canal, near Perambra, in Kozhikode has turned pink due to massive flowering of the invasive alien species Red Cabomba. It chokes the waterbodies ecologically and economically, affecting the growth of native aquatic plants and freshwater fish. Red Cabomba has been found in seven rivers and two lakes in the southern Western Ghats alone. Native to Central and South America, it is a popular aquarium plant. | Photo Credit: The Hindu

In February last year, 12-year-old Adityan D. Thampi of Thrissur got a cute red-eared turtle while fishing in a canal near his house at Kalathodu, a couple of km from the city centre. Little did he know about his catch. But scientists at the Kerala Forest Research Institute (KFRI) who noticed the Facebook post of the boy sensed the danger. 

It was a Trachemys scripta elegans, a red-eared slider turtle, considered one of the world’s worst invasive species. It is a favourite among pet lovers, especially children. Children fall for them due to their low price, colour, and cute size, which can fit into a match box. 

“But the fascination fades away when the turtle grows fast, consuming lot of food. As it grows larger in size it no longer fits into small tanks. When it becomes difficult to maintain them, people dump them in lakes and ponds without knowing that the turtle can threaten biodiversity. Their population grows fast in the wild since they are away from their native predators,” says T.V. Sajeev, Senior Principal Scientist, KFRI, Peechi.

Pistia stratiotes (Water lettuce) is one of the most noxious aquatic weeds in the world. It is a popular aquarium, garden plant.

Pistia stratiotes (Water lettuce) is one of the most noxious aquatic weeds in the world. It is a popular aquarium, garden plant. | Photo Credit: The Hindu

They pose a huge threat to native turtle species as they mature fast, grow bigger and are aggressive, he says.

Originated from areas around the Mississippi river and the Gulf of Mexico, this turtle was transported across the globe through the trade of exotic pets. Its population has been established in almost every continent, except Antarctica, and reported from at least 73 countries. 

Pet trade

The red-eared slider turtle is an example of how the pet industry unwittingly opens the doors for biological invasions that are harmful to the native ecosystem.  The annual trade in exotic pets is a multi-billion dollar global business. Recent research has put the Indian pet care market size at ₹74,000 crore in 2022, which is predicted to be around ₹210,000 crore by 2032. 

Exotic pet trade is listed as one of the primary causes of the spread of invasive species according to a recent academic review published in the journal Frontiers in Ecology and Environment

The International Union for Conservation of Nature (IUCN) defines an alien species as one introduced outside of its natural range; if this species negatively impacts native biodiversity, it is termed an invasive alien species. 

People often purchase exotic pets without knowing what they are getting themselves into, says Maneesh Ammattil, who is doing research on red-eared slider turtles at the KFRI. 

“Red-eared sliders can transmit parasites and diseases against which our native turtles have no immunity. Studies confirm that red-eared sliders carry various bacterial diseases where they can act as vectors. Some studies indicate that they are found to carry a number of pathogens, including Salmonella Pomona, Cryptosporidium parvum, Shigella, and Klebsiella,” says Mr. Maneesh.

Finding the turtle in the water body in Thrissur brought forth its presence in the wild in Kerala. It is reported from many States, including Maharashtra, temples ponds of Bengaluru, Himayat Sagar of Hyderabad, Dhanas and Sukhna lakes of Chandigarh, Rajarhat, Kolkata, Fateh Sagar Lake, Udaipur, Goa, Gujarat, and Tamil Nadu apart from Kerala. 

Red-eared slider turtles can transmit parasites and diseases against which native turtles have no immunity. It is a favourite among pet lovers, especially children, who fall for their low price, colour, and cute size.

Red-eared slider turtles can transmit parasites and diseases against which native turtles have no immunity. It is a favourite among pet lovers, especially children, who fall for their low price, colour, and cute size. | Photo Credit: The Hindu

Countries across the world have spent a great amount of money for the eradication of red-eared slider. For example, the cost of the ongoing eradication programme in Queensland, Australia, is one million Australian dollars until now.

The KFRI has issued a public notice to pet owners not to release these turtles to the wild and has collected more than 250 turtles from across the State and protecting them at its centres. 

Biodiversity loss 

Invasive alien species are recognised as the second most important reason for biodiversity loss, next to habitat destruction. They can be plants, animals, and microorganisms. More than 100 such alien species have been reported in Kerala. And research shows that many of them have been introduced as part of the pet industry. 

A recent study by a group of scientists in Kerala on ‘Distribution of alien invasive species in aquatic ecosystem of the southern Western Ghats’ (Aquatic Ecosystem Health and Management Society) recorded 32 alien species, including four plant species (macrophytes) and 28 fish species. Of the 28 fish species, seven have been identified as invasive. 

The study reveals that of the 32 alien species, 15 were introduced into the natural water bodies of the southern Western Ghats through the aquarium hobby and trade. While six species were introduced solely for promoting aquaculture, three were introduced for mosquito control, and three for either aquarium keeping or promotion of aquaculture. 

Of the 32 alien species, 11 were native to Southeast Asia, ten to South America, seven to Central or North America, and four to Africa. 

Exotic aquarium fishes

Many species of exotic fish are known to exist in the inland waters of Kerala, posing threat to the native biodiversity. They include popular aquarium fish such as Pterygoplichthys multiradiatus (algae sucker/sucker cat), Poecilia reticulata (guppy), Trichogaster trichopterus (three-spot gourami), and Xiphophorus maculatus (platy). 

Among invasive and alien fish, the most widely distributed species is the Mozambique Tilapia (O. mossambicus), occurring in all 44 rivers, 18 reservoirs, and two lakes.  Common Carp (C. carpio) is the second most common invasive species, recorded from 17 rivers, 29 reservoirs, and one lake. On the other hand, guppy is distributed in 14 rivers and 22 reservoirs. 

Impact of floods 

Many alien species, especially those commonly traded for the aquarium hobby, escaped to natural waters after the catastrophic floods in 2018 and 2019.  These floods also resulted in the release or escape of large-sized predatory species such as Arapaima gigas and Atractosteus spatula into the natural water bodies, say researchers. 

Large populations of guppy and platy observed continually over the last few years in the Chalakudy river confirm their widespread invasion in this riverine hotspot. 

Another major risk factor is the rearing of exotic aquarium fish in open systems such as granite quarries and homestead ponds. Quarry farming of ornamental fish is an emerging activity in Kerala. A vast majority of such quarries are not protected with fencing/netting. During monsoon, these fish may escape into the adjoining natural ecosystems. 

Invasive plants

Three invasive plants S. molesta (giant salvinia), Pistia stratiotes (water cabbage), and E. crassipes (water hyacinth) were introduced to the region as garden plants or for research purposes, and their entry into natural systems is believed to be accidental. 

In the recent past, an entire water body near Perambra in Kozhikode turned pink due to massive flowering of an invasive alien species Red Cabomba (Cabomba furcata). Pink bloom turned Avalappandi Canal an instant tourist spot. But scientists and environmentalists are concerned. 

The hasty growing cabomba is a visual delight but becomes a potential outspread in the water bodies by active stem propagation, hindering penetration of light into water. It chokes the water bodies ecologically and economically, affecting the growth of native aquatic plants and freshwater fish. It requires a large quantity of oxygen, which results in decline of biodiversity and water quality, says Karthika M. Nair, research scholar with the KFRI. 

A recent survey found Red Cabomba in seven rivers and two lakes in the southern Western Ghats alone. Native to Central and South America, cabomba is a popular aquarium plant. 

“Prevention of invasion through biosecurity regulations should be the main focus to manage biological invasion. Constant surveillance is needed to detect the species before it spreads into the wild. Restoration of invading sites is crucial to avoid re-invasion,” says Dr. Sajeev, who coordinates activities of the Nodal Centre for Biological invasions at the KFRI. He insists that engagement with stakeholders at all stages is important.

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