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Invasive species are threatening India’s coastal biodiversity

A closer look at the spread of non-native species significantly altering ecological functions of marine ecosystems

India’s coastline, teeming with diverse marine life, faces an escalating threat from invasive species that have been steadily altering local ecosystems.

With the advent of the climate crisis and human intervention aggravating such alterations, invasive alien species (whose introduction threatens the biological diversity of a region) have become a silent threat to India’s coastal biodiversity, with far-reaching consequences for both marine and terrestrial ecosystems. Their rapid proliferation, coupled with the absence of natural predators, allows them to outcompete and disrupt native species, leading to both ecological and economic impacts.

This alarming situation is not isolated and is part of a larger narrative of invasive species affecting India’s coastal regions. Invasive species endanger the quality of life and local habitats across marine and estuarine environments including the Charru mussel, Red algae, and Snowflake coral among others.

According to a global assessment released last week by the Intergovernmental Platform on Biodiversity and Ecosystem Services (IPBES), more than 37,000 alien species have been introduced to regions and biomes around the world as a result of various human activities. This conservative estimate is currently increasing at previously unheard-of rates.

Recently, the spotlight also turned to the Caribbean false mussel (Mytilopsis sallei), which has wreaked havoc on Kerala’s native clams and oysters. Native to the Atlantic and Pacific coasts of South and Central America, this species has made significant inroads into Kerala’s coastal waters, extending its reach across estuaries from Thiruvananthapuram to Kasaragod. Its encroachment has now begun to impact mussel aquaculture farms owing to its rapid reproductive rate and remarkable tolerance, this invasive species has displayed the ability to survive even in freshwater environments.

The Zoological Survey of India (ZSI), under the Union environment ministry, however, clarified that the Caribbean false mussel was documented for the first time 40 years ago (around the 1980s) to have entered India along the Visakhapatnam coast. “The scale of proliferation now is such that it has spread drastically not only Kerala but across various regions along the Indian coastline with the movement of waves and ocean currents,” said C Raghunathan, additional director, ZSI.

Raghunathan said that ZSI, while not mandated to issue advisories to states, will be studying this species and its impact on local ecosystems across Kerala and other states.

The process of biological invasions

Biological invasions involve two issues: The human-mediated transport of a species to an area where it does not naturally occur, and the economic or environmental damage resulting from this, said Naveen Namboothri who heads the sustainable fisheries and education programmes at Dakshin Foundation.

Invasive species often hitch a ride on ships through various means, posing a significant threat to global biodiversity. They can attach themselves to ship hulls, using these vessels as a mode of transport to new regions. Ballast water, routinely taken on board and discharged by ships to maintain stability, can contain dormant invasive species that are later released into foreign waters. The ornamental fish trade introduced exotic species when aquarium organisms are released or escape into local ecosystems. Similarly, the seafood trade can inadvertently transport invasive species, especially through live seafood shipments. Furthermore, aquaculture facilities may inadvertently release invasive species, which escape or are released into surrounding waters, leading to ecological imbalances and often damaging native ecosystems.

India has 13 major ports and over 200 minor ports as maritime transport accounts for approximately 95% of India’s commerce volume and 70% of its value. Ships are regarded as the most important factor in the movement of alien species from one bioregion to another. “Make no mistake, invasive species are a human-generated problem, created by trade, transport and tourism. There needs to be a national plan and its effective implementation to offset these impacts,” Alok Bang, an ecologist and assistant professor, Azim Premji University.

The climate crisis is exacerbating these invasions

At the same time, the climate crisis is not just shifting weather patterns; it’s reshaping ecosystems in ways we are only beginning to understand. The interconnected dance of rising sea levels, ocean currents, and warming sea surface temperatures is providing invasive species with a global stage to perform their destructive acts.

“As sea levels creep higher, coastal habitats once considered impenetrable barriers are being breached, allowing invasive species to encroach upon new territories. Ocean currents act as nature’s highways, facilitating the travel of these invasive hitchhikers to distant shores, where they can establish a foothold. Meanwhile, the relentless rise in sea surface temperatures is altering the very conditions under which marine life thrives, often to the detriment of native species,” said Deepak Apte, marine biologist, conservation expert, former director of the Bombay Natural History Society.

In this intricate choreography of environmental change, invasive species are emerging as both the beneficiaries and the agents of disruption. The ZSI currently lists 99 marine species as invasive out of the tally of 157 invasive animal species in India. “The number is expected to be much more presently for marine species. We are actively monitoring the spread of such invasive species and documenting their impact,” added Raghunathan.

Here are five major invasions over the past decade across marine and estuarine environments:

1. Charru Mussel (Mytella strigata): Known as ‘Kerala’s Silent Invader’, this invasive bivalve mussel species established a formidable presence in the estuarine ecosystems and brackishwater lakes along the Kerala coast from 2017 onwards. Its rapid proliferation across the state, believed to have been triggered by the potent tropical cyclone Ockhi in 2017, is a matter of grave concern, said Dr A Bijukumar, department of aquatic biology and fisheries professor, University of Kerala.

Moreover, the frequent movement of fishing vessels from inshore waters to estuaries has likely accelerated its spread. “The rapidly increasing biomass of M. strigata has decimated populations of the green mussel (Perna viridis) and supplanted dominant clam species such as the short-neck clam (Marcia recens) and backwater oysters like Magallana bilineata and Saccostrea cuccullata. These native species not only support the livelihoods of hundreds of local fishers but also play a crucial role in the area’s aquaculture systems,” said Dr Bijukumar. As M. strigata continues to thrive across various zones of the Indian coastline with varying salinity gradients, ranging from the estuary mouth to the river discharge zone, it poses long-term threats to the biodiversity and ecosystem services of the lake, underscoring the urgent need for mitigation measures.

2. Red algae (Kappaphycus alvarezii): The invasive red algae, K. alvarezii, originally from the Philippines, has become a significant ecological concern. Introduced to India in the 1990s by the CSIR-Central Salt and Marine Chemicals Research Institute, Gujarat, it was subsequently introduced to the Palk Bay at the southern tip of the country. Initially intended for cultivation within the Gulf of Mannar Biosphere Reserve, this seaweed escaped cultivation sites and established colonies in neighbouring areas, ultimately invading the coral reef ecosystem of Kurusadai Island in the Gulf of Mannar.

“Extensive investigations revealed that K. alvarezii not only overgrew native corals but also led to the degradation of seagrass, sea beds, and associated fisheries. Attempts at manual removal in 2008 and early 2009 were largely unsuccessful, as the species displayed a counterproductive regrowth mechanism, perpetuating its dominance in the habitat,” said Dr S Bijoy Nandan, dean, faculty of marine sciences, Cochin University of Science and Technology.

3. Snowflake coral (Carijoa riisei): The snowflake coral (C. riisei), originally native to the tropical Western Atlantic and Caribbean regions, has emerged as a potential threat to India’s coastal diversity. Reports have documented the presence of C. riisei on native coral species in various parts of the Indian coastal system, including Goa, the Gulf of Mannar, and the Andaman and Nicobar Islands. Notably, this coral species demonstrates a remarkable ability to establish colonies on diverse substrates, ranging from metal and concrete to plastic, ropes, and shipwrecks, in addition to native corals.

The invasion of C. riisei was first officially reported on May 10, 2009, in the Kundol region of the Nicobar Islands by the ZSI. “This invasive coral attaches itself to various surfaces in the sea, usurping space and vital nutrients from other marine species, including corals, sponges, algae, and ascidians. Such encroachment results in a reduction of marine biodiversity, making it a pressing concern for coastal ecosystems,” said Raghnuthan.

4. Green Crab (Carcinus maenas): Also known as the European green crab, this species has established itself in various parts of India’s coastline, including Goa and Odisha. These aggressive predators pose a dual threat – they prey on local shellfish and destroy mangroves, which are vital breeding and nursery areas for many marine species. Their unchecked presence continues to jeopardise coastal biodiversity. “We term this species as a menace to mangroves as it has spread to many places now across the east and the west coast. It impacts other smaller inhabitants of the mangrove system including bivalves, snails, barnacles, bryozoans, tunicates, mollusks, sponges etc., and it wants to be the dominant species in the habitat,” said E Vivekandan, emeritus scientist, ICAR – Central Marine Fisheries Research Institute.

5. Tilapia (several fish species belonging to the family Cichlidae, native to Africa and the Middle East): The invasive Tilapia species has left a considerable mark on India’s marine and estuarine habitats, raising concerns about its impact on the local ecosystem. Originally introduced for aquaculture, Tilapia’s rapid proliferation has turned it into a formidable invader.

“These aggressive fish not only outcompete native species for resources but also alter the habitat itself. Tilapia’s ability to thrive in a wide range of salinity levels allows it to penetrate both marine and estuarine environments, displacing native fauna and flora alike. Such disruptions lead to imbalances in the delicate web of life in these habitats. This has been observed across almost all southern states in India,” said Namboothri. Moreover, Tilapia’s feeding habits often cause sediment resuspension and contribute to the degradation of water quality.

Invasive species are a global problem, and their management requires coordinated efforts at the local, national, and international levels. Dr S Bijoy Nandan highlighted that India cannot look at these invasions in isolation and needed a Bioinvasion Policy that factored in a national action, state based strategies and detailed research committees, and factored in antimicrobial resistance. “By addressing the issue of invasive species threatening India’s coastal biodiversity, we can protect these vital ecosystems for future generations. It’s time to act decisively to safeguard our coastal treasures,” he said.

The authorities are taking a nuanced approach to this sensitive issue. “The government’s action plan to stop invasive species from spreading includes improving quarantine facilities at airports and seaports, following international guidelines for ballast water disposal, assessing the impact of exotic species, regulating the introduction of exotic species for business purposes, and conducting surveys on introduced and invasive species. We don’t issue licences for cultivating invasive alien species, and the National Biodiversity Authority has been mandated to assess this issue with support from expert members and the ZSI,” said a senior official from the Ministry of Environment, Forests and Climate Change.

Badri Chatterjee is head, Communications (Climate & Energy) at Asar Social Impact Advisors, a research and communications organisation that works on social and environmental issues.

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